Yuanbo Zhang

When electrons are confined in two-dimensional materials, quantum-mechanically enhanced transport phenomena such as the quantum Hall effect can be observed. Graphene, consisting of an isolated single atomic layer of graphite, is an ideal realization of such a two-dimensional system. However, its behaviour is expected to differ markedly from the well-studied case of quantum wells in conventional semiconductor interfaces. This difference arises from the unique electronic properties of graphene, which exhibits electron-hole degeneracy and vanishing carrier mass near the point of charge neutrality. Indeed, a distinctive half-integer quantum Hall effect has been predicted theoretically, as has the existence of a non-zero Berry's phase (a geometric quantum phase) of the electron wavefunction--a consequence of the exceptional topology of the graphene band structure. Recent advances in micromechanical extraction and fabrication techniques for graphite structures now permit such exotic two-dimensional electron systems to be probed experimentally. Here we report an experimental investigation of magneto-transport in a high-mobility single layer of graphene. Adjusting the chemical potential with the use of the electric field effect, we observe an unusual half-integer quantum Hall effect for both electron and hole carriers in graphene. The relevance of Berry's phase to these experiments is confirmed by magneto-oscillations. In addition to their purely scientific interest, these unusual quantum transport phenomena may lead to new applications in carbon-based electronic and magneto-electronic devices.

Novel physical phenomena can emerge in low-dimensional nanomaterials. Bulk MoS2, a prototypical metal dichalcogenide, is an indirect bandgap semiconductor with negligible photoluminescence. When the MoS2 crystal is thinned to monolayer, however, a strong photoluminescence emerges, indicating an indirect to direct bandgap transition in this d-electron system. This observation shows that quantum confinement in layered d-electron materials like MoS2 provides new opportunities for engineering the electronic structure of matter at the nanoscale.

Two-dimensional crystals have emerged as a class of materials that may impact future electronic technologies. Experimentally identifying and characterizing new functional two-dimensional materials is challenging, but also potentially rewarding. Here, we fabricate field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometres. Reliable transistor performance is achieved at room temperature in samples thinner than 7.5 nm, with drain current modulation on the order of 10(5) and well-developed current saturation in the I-V characteristics. The charge-carrier mobility is found to be thickness-dependent, with the highest values up to ∼ 1,000 cm(2) V(-1) s(-1) obtained for a thickness of ∼ 10 nm. Our results demonstrate the potential of black phosphorus thin crystals as a new two-dimensional material for applications in nanoelectronic devices.

We investigate electronic transport in lithographically patterned graphene ribbon structures where the lateral confinement of charge carriers creates an energy gap near the charge neutrality point. Individual graphene layers are contacted with metal electrodes and patterned into ribbons of varying widths and different crystallographic orientations. The temperature dependent conductance measurements show larger energy gaps opening for narrower ribbons. The sizes of these energy gaps are investigated by measuring the conductance in the nonlinear response regime at low temperatures. We find that the energy gap scales inversely with the ribbon width, thus demonstrating the ability to engineer the band gap of graphene nanostructures by lithographic processes.

The electronic bandgap is an intrinsic property of semiconductors and insulators that largely determines their transport and optical properties. As such, it has a central role in modern device physics and technology and governs the operation of semiconductor devices such as p-n junctions, transistors, photodiodes and lasers. A tunable bandgap would be highly desirable because it would allow great flexibility in design and optimization of such devices, in particular if it could be tuned by applying a variable external electric field. However, in conventional materials, the bandgap is fixed by their crystalline structure, preventing such bandgap control. Here we demonstrate the realization of a widely tunable electronic bandgap in electrically gated bilayer graphene. Using a dual-gate bilayer graphene field-effect transistor (FET) and infrared microspectroscopy, we demonstrate a gate-controlled, continuously tunable bandgap of up to 250 meV. Our technique avoids uncontrolled chemical doping and provides direct evidence of a widely tunable bandgap-spanning a spectral range from zero to mid-infrared-that has eluded previous attempts. Combined with the remarkable electrical transport properties of such systems, this electrostatic bandgap control suggests novel nanoelectronic and nanophotonic device applications based on graphene.

Materials research has driven the development of modern nano-electronic devices. In particular, research in magnetic thin films has revolutionized the development of spintronic devices1,2 because identifying new magnetic materials is key to better device performance and design. Van der Waals crystals retain their chemical stability and structural integrity down to the monolayer and, being atomically thin, are readily tuned by various kinds of gate modulation3,4. Recent experiments have demonstrated that it is possible to obtain two-dimensional ferromagnetic order in insulating Cr2Ge2Te6 (ref. 5) and CrI3 (ref. 6) at low temperatures. Here we develop a device fabrication technique and isolate monolayers from the layered metallic magnet Fe3GeTe2 to study magnetotransport. We find that the itinerant ferromagnetism persists in Fe3GeTe2 down to the monolayer with an out-of-plane magnetocrystalline anisotropy. The ferromagnetic transition temperature, Tc, is suppressed relative to the bulk Tc of 205 kelvin in pristine Fe3GeTe2 thin flakes. An ionic gate, however, raises Tc to room temperature, much higher than the bulk Tc. The gate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2 opens up opportunities for potential voltage-controlled magnetoelectronics7–11 based on atomically thin van der Waals crystals. Monolayers of Fe3GeTe2 exhibit itinerant ferromagnetism with an out-of-plane magnetocrystalline anisotropy; ionic gating raises the ferromagnetic transition temperature of few-layer Fe3GeTe2 to room temperature.

Two-dimensional graphene monolayers and bilayers exhibit fascinating electrical transport behaviors. Using infrared spectroscopy, we find that they also have strong interband transitions and that their optical transitions can be substantially modified through electrical gating, much like electrical transport in field-effect transistors. This gate dependence of interband transitions adds a valuable dimension for optically probing graphene band structure. For a graphene monolayer, it yields directly the linear band dispersion of Dirac fermions, whereas in a bilayer, it reveals a dominating van Hove singularity arising from interlayer coupling. The strong and layer-dependent optical transitions of graphene and the tunability by simple electrical gating hold promise for new applications in infrared optics and optoelectronics.

Gate-modulated low-temperature Raman spectra reveal that the electric field effect (EFE), pervasive in contemporary electronics, has marked impacts on long-wavelength optical phonons of graphene. The EFE in this two-dimensional honeycomb lattice of carbon atoms creates large density modulations of carriers with linear dispersion (known as Dirac fermions). Our EFE Raman spectra display the interactions of lattice vibrations with these unusual carriers. The changes of phonon frequency and linewidth demonstrate optically the particle-hole symmetry about the charge-neutral Dirac point. The linear dependence of the phonon frequency on the EFE-modulated Fermi energy is explained as the electron-phonon coupling of massless Dirac fermions.

In a magnetic topological insulator, nontrivial band topology conspires with magnetic order to produce exotic states of matter that are best exemplified by quantum anomalous Hall (QAH) insulators and axion insulators. Up till now, such magnetic topological insulators are obtained by doping topological insulators with magnetic atoms. The random magnetic dopants, however, inevitably introduce disorders that hinder further exploration of quantum effects in the material. Here, we resolve this dilemma by probing quantum transport in MnBi$_2$Te$_4$ thin flake - a topological insulator with intrinsic magnetic order. In this layered van der Waals crystal, the ferromagnetic layers couple anti-parallel to each other, so MnBi$_2$Te$_4$ is an antiferromagnet. A magnetic field, however, aligns all the layers and induces an interlayer ferromagnetic order; we show that a quantized anomalous Hall response emerges in atomically thin MnBi$_2$Te$_4$ under a moderate magnetic field. MnBi$_2$Te$_4$ therefore becomes the first intrinsic magnetic topological insulator exhibiting quantized anomalous Hall effect. The result establishes MnBi$_2$Te$_4$ as an ideal arena for further exploring various topological phenomena.

In an ideal graphene sheet charge carriers behave as two-dimensional (2D) Dirac fermions governed by the quantum mechanics of massless relativistic particles. This has been confirmed by the discovery of a half-integer quantum Hall effect in graphene flakes placed on a SiO2 substrate. The Dirac fermions in graphene, however, are subject to microscopic perturbations that include topographic corrugations and electron density inhomogeneities (i.e. charge puddles). Such perturbations profoundly alter Dirac fermion behavior, with implications for their fundamental physics as well as for future graphene device applications. Here we report a new technique of Dirac point mapping that we have used to determine the origin of charge inhomogeneities in graphene. We find that fluctuations in graphene charge density are not caused by topographical corrugations, but rather by charge-donating impurities below the graphene. These impurities induce unexpected standing wave patterns due to supposedly forbidden back-scattering of Dirac fermions. Such wave patterns can be continuously modulated by electric gating. Our observations provide new insight into impurity scattering of Dirac fermions and the microscopic mechanisms limiting electronic mobility in graphene.

Phosphorene, a single atomic layer of black phosphorus, has recently emerged as a new two-dimensional (2D) material that holds promise for electronic and photonic technologies. Here we experimentally demonstrate that the electronic structure of few-layer phosphorene varies significantly with the number of layers, in good agreement with theoretical predictions. The interband optical transitions cover a wide, technologically important spectral range from the visible to the mid-infrared. In addition, we observe strong photoluminescence in few-layer phosphorene at energies that closely match the absorption edge, indicating that they are direct bandgap semiconductors. The strongly layer-dependent electronic structure of phosphorene, in combination with its high electrical mobility, gives it distinct advantages over other 2D materials in electronic and opto-electronic applications.

The ability to tune material properties using gating by electric fields is at the heart of modern electronic technology. It is also a driving force behind recent advances in two-dimensional systems, such as the observation of gate electric-field-induced superconductivity and metal-insulator transitions. Here, we describe an ionic field-effect transistor (termed an iFET), in which gate-controlled Li ion intercalation modulates the material properties of layered crystals of 1T-TaS2. The strong charge doping induced by the tunable ion intercalation alters the energetics of various charge-ordered states in 1T-TaS2 and produces a series of phase transitions in thin-flake samples with reduced dimensionality. We find that the charge-density wave states in 1T-TaS2 collapse in the two-dimensional limit at critical thicknesses. Meanwhile, at low temperatures, the ionic gating induces multiple phase transitions from Mott-insulator to metal in 1T-TaS2 thin flakes, with five orders of magnitude modulation in resistance, and superconductivity emerges in a textured charge-density wave state induced by ionic gating. Our method of gate-controlled intercalation opens up possibilities in searching for novel states of matter in the extreme charge-carrier-concentration limit.

Understanding the mechanism of high-transition-temperature (high-Tc) superconductivity is a central problem in condensed matter physics. It is often speculated that high-Tc superconductivity arises in a doped Mott insulator1 as described by the Hubbard model2–4. An exact solution of the Hubbard model, however, is extremely challenging owing to the strong electron–electron correlation in Mott insulators. Therefore, it is highly desirable to study a tunable Hubbard system, in which systematic investigations of the unconventional superconductivity and its evolution with the Hubbard parameters can deepen our understanding of the Hubbard model. Here we report signatures of tunable superconductivity in an ABC-trilayer graphene (TLG) and hexagonal boron nitride (hBN) moiré superlattice. Unlike in ‘magic angle’ twisted bilayer graphene, theoretical calculations show that under a vertical displacement field, the ABC-TLG/hBN heterostructure features an isolated flat valence miniband associated with a Hubbard model on a triangular superlattice5,6 where the bandwidth can be tuned continuously with the vertical displacement field. Upon applying such a displacement field we find experimentally that the ABC-TLG/hBN superlattice displays Mott insulating states below 20 kelvin at one-quarter and one-half fillings of the states, corresponding to one and two holes per unit cell, respectively. Upon further cooling, signatures of superconductivity (‘domes’) emerge below 1 kelvin for the electron- and hole-doped sides of the one-quarter-filling Mott state. The electronic behaviour in the ABC-TLG/hBN superlattice is expected to depend sensitively on the interplay between the electron–electron interaction and the miniband bandwidth. By varying the vertical displacement field, we demonstrate transitions from the candidate superconductor to Mott insulator and metallic phases. Our study shows that ABC-TLG/hBN heterostructures offer attractive model systems in which to explore rich correlated behaviour emerging in the tunable triangular Hubbard model. By varying the vertical displacement field in a trilayer graphene and hexagonal boron nitride moiré superlattice, transitions can be observed from the superconducting phase to Mott insulator and metallic phases.

Electrons moving in graphene behave as massless Dirac fermions, and they exhibit fascinating low-frequency electrical transport phenomena. Their dynamic response, however, is little known at frequencies above one terahertz (THz). Such knowledge is important not only for a deeper understanding of the Dirac electron quantum transport, but also for graphene applications in ultrahigh speed THz electronics and IR optoelectronics. In this paper, we report the first measurement of high-frequency conductivity of graphene from THz to mid-IR at different carrier concentrations. The conductivity exhibits Drude-like frequency dependence and increases dramatically at THz frequencies, but its absolute strength is substantially lower than theoretical predictions. This anomalous reduction of free electron oscillator strength is corroborated by corresponding changes in graphene interband transitions, as required by the sum rule. Our surprising observation indicates that many-body effects and Dirac fermion-impurity interactions beyond current transport theories are important for Dirac fermion electrical response in graphene.

The Mott insulator is a central concept in strongly correlated physics and manifests when the repulsive Coulomb interaction between electrons dominates over their kinetic energy1,2. Doping additional carriers into a Mott insulator can give rise to other correlated phenomena such as unusual magnetism and even high-temperature superconductivity2,3. A tunable Mott insulator, where the competition between the Coulomb interaction and the kinetic energy can be varied in situ, can provide an invaluable model system for the study of Mott physics. Here we report the possible realization of such a tunable Mott insulator in a trilayer graphene heterostructure with a moiré superlattice. The combination of the cubic energy dispersion in ABC-stacked trilayer graphene4–8 and the narrow electronic minibands induced by the moiré potential9–15 leads to the observation of insulating states at the predicted band fillings for the Mott insulator. Moreover, the insulating states in the heterostructure can be tuned: the bandgap can be modulated by a vertical electrical field, and at the same time the electron doping can be modified by a gate to fill the band from one insulating state to another. This opens up exciting opportunities to explore strongly correlated phenomena in two-dimensional moiré superlattice heterostructures. Report of the likely observation of a Mott insulator in trilayer graphene with a moiré potential. The Mott state can be tuned between different filling fractions via gating, which will enable the careful study of this paradigmatic many-body state.

Studies of two-dimensional electron systems in a strong magnetic field revealed the quantum Hall effect1, a topological state of matter featuring a finite Chern number C and chiral edge states2,3. Haldane4 later theorized that Chern insulators with integer quantum Hall effects could appear in lattice models with complex hopping parameters even at zero magnetic field. The ABC-trilayer graphene/hexagonal boron nitride (ABC-TLG/hBN) moiré superlattice provides an attractive platform with which to explore Chern insulators because it features nearly flat moiré minibands with a valley-dependent, electrically tunable Chern number5,6. Here we report the experimental observation of a correlated Chern insulator in an ABC-TLG/hBN moiré superlattice. We show that reversing the direction of the applied vertical electric field switches the moiré minibands of ABC-TLG/hBN between zero and finite Chern numbers, as revealed by large changes in magneto-transport behaviour. For topological hole minibands tuned to have a finite Chern number, we focus on quarter filling, corresponding to one hole per moiré unit cell. The Hall resistance is well quantized at h/2e2 (where h is Planck’s constant and e is the charge on the electron), which implies C = 2, for a magnetic field exceeding 0.4 tesla. The correlated Chern insulator is ferromagnetic, exhibiting substantial magnetic hysteresis and a large anomalous Hall signal at zero magnetic field. Our discovery of a C = 2 Chern insulator at zero magnetic field should open up opportunities for discovering correlated topological states, possibly with topological excitations7, in nearly flat and topologically nontrivial moiré minibands. A topological Chern insulating state is reported to emerge from strong correlations in flat moiré bands in a graphene superlattice and by applying a vertical electric field the Chern number is switched.

We have developed a unique micromechanical method to extract extremely thin graphite samples. Graphite crystallites with thicknesses ranging from 10 - 100 nm and lateral size $\sim$ 2 $\mu$m are extracted from bulk. Mesoscopic graphite devices are fabricated from these samples for electric field dependent conductance measurements. Strong conductance modulation as a function of gate voltage is observed in the thinner crystallite devices. The temperature dependent resistivity measurements show more boundary scattering contribution in the thinner graphite samples.

Scanning tunnelling spectra of a graphene field-effect transistor reveal an unexpected tenfold increase in conductance as a result of phonon-mediated inelastic tunnelling. The honeycomb lattice of graphene is a unique two-dimensional system where the quantum mechanics of electrons is equivalent to that of relativistic Dirac fermions1,2. Novel nanometre-scale behaviour in this material, including electronic scattering3,4, spin-based phenomena5 and collective excitations6, is predicted to be sensitive to charge-carrier density. To probe local, carrier-density-dependent properties in graphene, we have carried out atomically resolved scanning tunnelling spectroscopy measurements on mechanically cleaved graphene flake devices equipped with tunable back-gate electrodes. We observe an unexpected gap-like feature in the graphene tunnelling spectrum that remains pinned to the Fermi level (EF) regardless of graphene electron density. This gap is found to arise from a suppression of electronic tunnelling to graphene states near EF and a simultaneous giant enhancement of electronic tunnelling at higher energies due to a phonon-mediated inelastic channel. Phonons thus act as a ‘floodgate’ that controls the flow of tunnelling electrons in graphene. This work reveals important new tunnelling processes in gate-tunable graphitic layers.

Electric field effect devices based on mesoscopic graphite are fabricated for galvanomagnetic measurements. Strong modulation of magnetoresistance and Hall resistance as a function of the gate voltage is observed as the sample thickness approaches the screening length. Electric field dependent Landau level formation is detected from Shubnikov--de Haas oscillations. The effective mass of electron and hole carriers has been measured from the temperature dependent behavior of these oscillations.

Development of new, high quality functional materials has been at the forefront of condensed matter research. The recent advent of two-dimensional black phosphorus has greatly enriched the material base of two-dimensional electron systems. Significant progress has been made to achieve high mobility black phosphorus two-dimensional electron gas (2DEG) since the development of the first black phosphorus field-effect transistors (FETs)$^{1-4}$. Here, we reach a milestone in developing high quality black phosphorus 2DEG - the observation of integer quantum Hall (QH) effect. We achieve high quality by embedding the black phosphorus 2DEG in a van der Waals heterostructure close to a graphite back gate; the graphite gate screens the impurity potential in the 2DEG, and brings the carrier Hall mobility up to 6000 $cm^{2}V^{-1}s^{-1}$. The exceptional mobility enabled us, for the first time, to observe QH effect, and to gain important information on the energetics of the spin-split Landau levels in black phosphorus. Our results set the stage for further study on quantum transport and device application in the ultrahigh mobility regime.

Valley pseudospin, the quantum degree of freedom characterizing the degenerate valleys in energy bands, is a distinct feature of two-dimensional Dirac materials. Similar to spin, the valley pseudospin is spanned by a time reversal pair of states, though the two valley pseudospin states transform to each other under spatial inversion. The breaking of inversion symmetry induces various valley-contrasted physical properties; for instance, valley-dependent topological transport is of both scientific and technological interests. Bilayer graphene (BLG) is a unique system whose intrinsic inversion symmetry can be controllably broken by a perpendicular electric field, offering a rare possibility for continuously tunable valley-topological transport. Here, we used a perpendicular gate electric field to break the inversion symmetry in BLG, and a giant nonlocal response was observed as a result of the topological transport of the valley pseudospin. We further showed that the valley transport is fully tunable by external gates, and that the nonlocal signal persists up to room temperature and over long distances. These observations challenge contemporary understanding of topological transport in a gapped system, and the robust topological transport may lead to future valleytronic applications.

Although copper oxide high-temperature superconductors constitute a complex and diverse material family, they all share a layered lattice structure. This curious fact prompts the question of whether high-temperature superconductivity can exist in an isolated monolayer of copper oxide, and if so, whether the two-dimensional superconductivity and various related phenomena differ from those of their three-dimensional counterparts. The answers may provide insights into the role of dimensionality in high-temperature superconductivity. Here we develop a fabrication process that obtains intrinsic monolayer crystals of the high-temperature superconductor Bi2Sr2CaCu2O8+δ (Bi-2212; here, a monolayer refers to a half unit cell that contains two CuO2 planes). The highest superconducting transition temperature of the monolayer is as high as that of optimally doped bulk. The lack of dimensionality effect on the transition temperature defies expectations from the Mermin–Wagner theorem, in contrast to the much-reduced transition temperature in conventional two-dimensional superconductors such as NbSe2. The properties of monolayer Bi-2212 become extremely tunable; our survey of superconductivity, the pseudogap, charge order and the Mott state at various doping concentrations reveals that the phases are indistinguishable from those in the bulk. Monolayer Bi-2212 therefore displays all the fundamental physics of high-temperature superconductivity. Our results establish monolayer copper oxides as a platform for studying high-temperature superconductivity and other strongly correlated phenomena in two dimensions. Transport and scanning tunnelling microscopy studies of freestanding monolayers of an unconventional layered copper oxide establish that the superconducting properties of copper oxides are not changed in the 2D limit.

Metasurfaces in metal/insulator/metal configuration have recently been widely used in photonics research, with applications ranging from perfect absorption to phase modulation, but why and when such structures can realize what kind of functionalities are not yet fully understood. Here, based on a coupled-mode theory analysis, we establish a complete phase diagram in which the optical properties of such systems are fully controlled by two simple parameters (i.e., the intrinsic and radiation losses), which are in turn dictated by the geometrical/material parameters of the underlying structures. Such a phase diagram can greatly facilitate the design of appropriate metasurfaces with tailored functionalities (e.g., perfect absorption, phase modulator, electric/magnetic reflector, etc.), demonstrated by our experiments and simulations in the Terahertz regime. In particular, our experiments show that, through appropriate structural/material tuning, the device can be switched across the functionality phase boundaries yielding dramatic changes in optical responses. Our discoveries lay a solid basis for realizing functional and tunable photonic devices with such structures.

Modulating the phase of electromagnetic waves has many applications in photonic research. A new mechanism allows a thin graphene metasurface to reliably achieve an extremely large phase modulation in THz radiation.

Spectroscopic studies of electronic phenomena in graphene are reviewed. A variety of methods and techniques are surveyed, from quasiparticle spectroscopies (tunneling, photoemission) to methods probing density and current response (infrared optics, Raman) to scanning probe nanoscopy and ultrafast pump-probe experiments. Vast complimentary information derived from these investigations is shown to highlight unusual properties of Dirac quasiparticles and many-body interaction effects in the physics of graphene.

Electron-electron and electron-phonon interactions are two major driving forces that stabilize various charge-ordered phases of matter. The intricate interplay between the two give rises to a peculiar charge density wave (CDW) state, which is also known as a Mott insulator, as the ground state of layered compound 1T-TaS2. The delicate balance also makes it possible to use external perturbations to create and manipulate novel phases in this material. Here, we study a mosaic CDW phase induced by voltage pulses from the tip of a scanning tunneling microscope (STM), and find that the new phase exhibit electronic structures that are entirely different from the Mott ground state of 1T-TaS2 at low temperatures. The mosaic phase consists of nanometer-sized domains characterized by well-defined phase shifts of the CDW order parameter in the topmost layer, and by altered stacking relative to the layer underneath. We discover that the nature of the new phases is dictated by the stacking order, and our results shed fresh light on the origin of the Mott phase in this layered compound.

Images of the second-generation Dirac cones that form when graphene is placed on hexagonal boron nitride show the potential of using superlattices to engineer the electronic band structure of van der Waals heterostructures. Graphene/hexagonal boron nitride (h-BN) has emerged as a model van der Waals heterostructure1 as the superlattice potential, which is induced by lattice mismatch and crystal orientation, gives rise to various novel quantum phenomena, such as the self-similar Hofstadter butterfly states2,3,4,5. Although the newly generated second-generation Dirac cones (SDCs) are believed to be crucial for understanding such intriguing phenomena, fundamental knowledge of SDCs, such as locations and dispersion, and the effect of inversion symmetry breaking on the gap opening, still remains highly debated due to the lack of direct experimental results. Here we report direct experimental results on the dispersion of SDCs in 0°-aligned graphene/h-BN heterostructures using angle-resolved photoemission spectroscopy. Our data unambiguously reveal SDCs at the corners of the superlattice Brillouin zone, and at only one of the two superlattice valleys. Moreover, gaps of approximately 100 meV and approximately 160 meV are observed at the SDCs and the original graphene Dirac cone, respectively. Our work highlights the important role of a strong inversion-symmetry-breaking perturbation potential in the physics of graphene/h-BN, and fills critical knowledge gaps in the band structure engineering of Dirac fermions by a superlattice potential.

Electric arc furnace (EAF) dust is an important secondary resource which contains multiple metallic elements, such as zinc, lead, iron, chromium and cadmium. Recycling of EAF dust is not only favorable to increasing economic potential of the dust by recovering these valuable metals, but also of benefit to solving disposal and environmental problems caused by the heavy metals (e.g., lead, chromium and cadmium) entrained in the dust. Among the existing processes and those under development, pyrometallurgical routes are considered the primary choice for processing of EAF dust because of its high potential metal recovery, easy treatment of residue and relatively short flow sheet. In this paper, the authors reviewed the chemical and physical properties of EAF dust and its thermodynamic characteristics in pyrometallurgical processing, followed by an in-depth discussion of a variety of the pyrometallurgical processes for recycling of the dust, including Waelz kiln process, rotary hearth furnace (RHF) process, PRIMUS process, OXYCUP process, coke-packed bed process, Ausmelt process, electric smelting reduction furnace (ESRF) process, Plasamadust process, plasma-arc process, Elkem multi-purpose furnace (EMPF) process, submerged plasma process, pig iron zinc oxide (PIZO) process, flame reactor process, thermal plasma reduction process, microwave processing, solar thermal reduction process, iron bath smelting process, calcification process and halogenation process. Particular attention is devoted to specific technical challenges emerging in the pyrometallurgical processing of EAF dust and to the corresponding potential measures for improving the dust recycling by promoting the processing efficiency with elimination of secondary hazardous pollutants.

In this Letter, we report the observation of thermally induced rotation of graphene on hexagonal boron nitride (h-BN). After the rotation, two thermally stable configurations of graphene on h-BN with a relative lattice twisting angle of 0° (most stable) and 30° (metastable), respectively, were found. Graphene on h-BN with a twisting angle below (above) a critical angle of ∼12±2° tends to rotate towards 0° (30°) at a temperature of >100 °C, which is in line with our theoretical simulations. In addition, by manipulating the annealing temperature and the flake sizes of graphene, moiré superlattices with large spatial periods of graphene on h-BN are achieved. Our studies provide a detailed understanding of the thermodynamic properties of graphene on h-BN and a feasible approach to obtaining van der Waals heterostructures with aligned lattices.Received 30 November 2015DOI:https://doi.org/10.1103/PhysRevLett.116.126101© 2016 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasThermal propertiesPhysical SystemsGrapheneTechniquesAnnealingAtomic force microscopyCondensed Matter, Materials & Applied Physics

We investigate the electronic structure of the flat bands induced by moiré superlattices and electric fields in nearly aligned ABC trilayer graphene (TLG) boron-nitride (BN) interfaces where Coulomb effects can lead to correlated gapped phases. Our calculations indicate that valley-spin resolved isolated superlattice flat bands that carry a finite Chern number C=3 proportional to the layer number can appear near charge neutrality for appropriate perpendicular electric fields and twist angles. When the degeneracy of the bands is lifted by Coulomb interactions, these topological bands can lead to anomalous quantum Hall phases that embody orbital and spin magnetism. Narrow bandwidths of ∼10 meV achievable for a continuous range of twist angles θ≲0.6° with moderate interlayer potential differences of ∼50 meV make the TLG-BN systems a promising platform for the study of electric-field tunable Coulomb-interaction-driven spontaneous Hall phases.

Plastic combustion has adverse impacts on air quality and human health. In this work, a novel non-aromatic Si, P, N-containing hyperbranched flame retardant (HPNSi) was synthesized and proposed to epoxy resin. The modified epoxy exhibits not only reduced fire hazards and less smoke production in favor of eco-friendly, but also remarkable mechanical properties and lower curing temperature for facile processability. With 6 wt% incorporation, the peak heat release and total smoke production were reduced by 29.6% and 20.7%, respectively, and the time to ignition (TTI) increased as well as the fire growth rate (FIGRA) dropped off, which is of vital significance for saving lives in a fire. Meanwhile, the impact strength and flexural strength greatly enhanced by 72.9% and 22.0%, while its curing temperature was lower than that of controlled EP system. Interestingly, we also found that the solid carbon particles on the char surface apparently reduced from SEM image. The blending of its unique non-aromatic hyperbranched structure containing Si, P, N with epoxy architecture was responsible for the desirable integrated enhancement. The broad possibilities in the field of flame-retardant plastic with reduced fire hazards and excellent integrated performance enable the novel hyperbranched flame retardant a bright future for application.

Abstract Dynamical controls on terahertz (THz) wavefronts are crucial for many applications, but available mechanism requests tunable elements with sub-micrometer sizes that are difficult to find in the THz regime. Here, different from the local-tuning mechanism, we propose an alternative approach to construct wavefront-control meta-devices combining specifically designed metasurfaces and globally tuned graphene layers. Coupled-mode-theory (CMT) analyses reveal that graphene serves as a tunable loss to drive the whole meta-device to transit from one functional phase to another passing through an intermediate regime, exhibiting distinct far-field (FF) reflection wavefronts. As a proof of concept, we design/fabricate a graphene meta-device and experimentally demonstrate that it can reflect normally incident THz wave to pre-designed directions with different polarizations under appropriate gating voltages. We finally design a graphene meta-device and numerically demonstrate that it can generate vectorial THz beams with continuously varying polarization distributions upon gating. These findings pave the road to realizing a wide range of THz applications, such as sensing, imaging, and wireless communications.

High-performance electronic packaging materials with favorable processability are highly desirable to satisfy the booming of new generation communication technology. Herein, the bisphenol A cyanate ester (BADCy) resins containing Si-O-C hyperbranched polysiloxane were fabricated with facile curing process to achieve the application of electronic packaging. The fabricated BADCy resins exhibited not only significantly reduced curing temperature in favor of facile processability, but also dramatically enhanced toughness for prolonging the service life of packaging materials. The curing peak temperature was miraculously decreased by 93.5 °C. Meanwhile, the impact strength was significantly enhanced by 105.3%. Notably, the BADCy resins presented lower dielectric constant (ε of 2.59) and dielectric loss tangent values (tan δ of 0.0062) at 10 GHz. The results suggest that HSiEP possesses promising potential applications in the field of electronic packaging.

The design of high transparent epoxy resins (EPs) with excellent flame retardancy and mechanical strength is still intractable, while the current use of phosphorus-based flame retardant usually destroys the transparency and color of EPs. This work reports a phosphorus-free hyperbranched polyborate (HBPB) as a multifunctional flame retardant additive for EPs. The HBPB was synthesized via a facile, one-pot, solvent- and catalyst-free polycondensation with branched aliphatic backbone and borate group, which features good compatibility within resin matrix and does not affect its curing processability. Compared to neat EP, the as-constructed EP composite with 9% addition of HBPB displays the high fire resistance (30.2% LOI value and UL-94 V0 rating), and the fire hazards such as smoke, heat and toxic gases release are significantly reduced without introducing phosphorus group. Surprisingly, the EP material can well maintain its high transparency and color with ultra-high toughness (21.38–40.50 kJ m−2) and flexural strength (137.03–197.08 MPa) achieved, especially the glass-transition temperature can be improved from 150 °C to 170 °C, making it superior to previously described counterparts. Highlighting the compelling results, this work provides a promising candidate on seeking the halogen-free solutions to alleviate the high price of phosphorus-based FRs, and paves a useful strategy toward designing high transparent, high-performance polymeric materials.

Microalgae biotechnology is a promising pathway to cope with CO2 emission and energy crisis due to high CO2 fixation rate and lipids productivity. However, bottlenecks of high energy cost, low photosynthetic efficiency and poor economic feasibility severely hinder its commercialization. Understanding process mechanisms of microalgae photosynthetic CO2 fixation and lipids production, and thus seeking possible regulations to enhance weak links are potential process regulation strategy for augmented competitiveness. Firstly, mass transfer and conversion processes of microalgae photosynthesis involving CO2 and light were comprehensively illuminated in this review. In detail, mechanisms of CO2 and light transfer in microalgae suspension, bioavailable carbon and photon assimilation by microalgae cells, as well as intracellular mass conversion were illustrated. Besides, synergistic effects of light and CO2 on microalgae photosynthesis were depicted from perspective of electrons and protons supply-demand relationships between photosynthetic photo-reaction and dark-reaction steps in chlorophyll. Possible weak links in these processes were emphasized to provide guideline for regulation. Secondly, available regulation strategies for CO2 and light mass transfer, cellular assimilation and intracellular conversion were summarized. Subsequently, economic and environmental impacts of process regulation on microalgae CO2 fixation and biodiesel output were evaluated to lit up large-scale applicability. Finally, challenges and future directions of microalgae biotechnology were described to inspire in-depth research and engineering practice. This review may provide a novel process regulation standpoint for operating microalgae-based CO2 fixation and biodiesel production in the most efficient manner, further facilitating the applicability of microalgae biotechnology towards carbon neutrality and biodiesel production.

Bioconversion of nutrients and energy from landfill leachate (LL) to biohydrogen and volatile fatty acids (VFAs) using dark fermentation (DF) is a promising technique for developing a sustainable ecosystem. However, poor performance of DF caused by vulnerable fermentative bacteria vitality and strong LL toxicity significantly hinder its commercialization. Herein, an integrated technique linking microalgae photosynthesis and DF was proposed, in which mixed microalgae were applied to robustly reclaim nutrients and chemical oxygen demand (COD) from LL. Then, microalgae biomass was fermented into biohydrogen and VFAs using the DF process. Underlying synergistic mechanisms of the interaction of Scenedesmus obliquus and Chlorella vulgaris resulting from the functioning of extracellular polymeric substances (EPS) were discussed in detail. For better absorption of nutrients from LL, the mixed microalgae secreted obviously more EPS than pure microalgae, which played vital roles in the assimilation of cellular nutrients by forming more negative zeta potential and secreting more tyrosine-/tryptophan-family proteins in EPS. Besides, mixed microalgae produced more intracellular proteins and carbohydrates than the pure microalgae, thereby providing more feedstock for DF and achieving higher energy yield of 10.80 kJ/L than 6.64 kJ/L that was obtained when pure microalgae were used. Moreover, the energy conversion efficiency of 7.75% was higher for mixed microalgae than 4.77% that was obtained for pure microalgae. This work may inspire efficient disposal of LL and production of bioenergy, together with filling the knowledge gaps of synergistic mechanisms of dual microalgal interactions.

Abstract Single‐layered MoS 2 is a promising anode material for lithium‐ion batteries (LIBs), sodium‐ion batteries (SIBs), and potassium‐ion batteries (PIBs) due to its high capacity and isotropic ion transport paths. However, the low intrinsic conductivity and easy‐agglomerated feature hamper its applications. Here, a charge‐driven interlayer expansion strategy that Co 2+ replaces Mo 4+ in the doping form to endow MoS 2 layers with negative charges, thus inducing electrostatic repulsion, together with the insertion of gaseous groups, to drive interlayer expansion which once breaks the confinement of interlayer van der Waals force, single‐layered MoS 2 is obtained and uniformly dispersed into carbon matrix arising from the transformation of carbonaceous gaseous groups under high vapor pressure, is proposed. Co atom doping helps enhance the intrinsic conductivity of single‐layered MoS 2 . Carbon matrix effectively prevents agglomeration of single‐layered MoS 2 . The doped Co atoms can be fully transformed into ultrasmall Co nanoparticles during conversion reaction, which enables strong spin‐polarized surface capacitance and thus significantly boosts ion transport and storage. Consequently, the prepared material delivers superb Li/Na/K‐ion storage performances, which are best in the reported MoS 2 ‐based anodes. The proposed charge‐driven interlayer expansion strategy provides a novel perspective for preparing single‐layered MoS 2, which shows huge potential for energy storage.

Soil cadmium (Cd) contamination can reduce wheat yield and quality, thus threatening food security and human health. Herein, morphological physiology, Cd accumulation and distribution, proteomic and metabolomic analyses were performed (using wheat cultivars 'Luomai23' (LM, Cd-sensitive) and 'Zhongyu10' (ZY, Cd-tolerant) at the seedling stage with sand culture) to reveal Cd tolerance mechanism. Cd inhibited wheat growth, caused oxidative stress, hindered carbon and nitrogen metabolism, and altered the quantity and composition of root exudates. The root Cd concentration was lower in ZY than in LM by about 35% under 15 μM Cd treatments. ZY reduced Cd uptake through root exudation of amino acids and alkaloids. ZY also reduced Cd accumulation through specific up-regulation (twice) of major facilitator superfamily (MFS) proteins. Furthermore, ZY enhanced Cd cell wall fixation and vacuolar compartmentalization by increasing pectin contents, hemicellulose1 contents, and adenosine triphosphate binding cassette subfamily C member 1 (ABCC1) transporter expression, thus reducing the Cd organelle fraction of ZY by about 12% and 44% in root and shoot, respectively, compared with LM. Additionally, ZY had enhanced resilience to Cd due to increased antioxidant capacity, plasma membrane stability, nitrogen metabolism, and endoplasmic reticulum homeostasis, indicating that the increased Cd tolerance could be because of multi-level coordination. These findings provide a reference for exploring the molecular mechanism of Cd tolerance and accumulation, providing a basis for safe utilization of Cd-contaminated soil by breeding Cd-tolerant and low Cd-accumulating wheat varieties.

The authors present a scanning tunneling spectroscopy (STS) study of the local electronic structure of single and bilayer graphene grown epitaxially on a SiC(0001) surface. Low voltage topographic images reveal fine, atomic-scale carbon networks, whereas higher bias images are dominated by emergent spatially inhomogeneous large-scale structure similar to a carbon-rich reconstruction of SiC(0001). STS spectroscopy shows an ∼100meV gaplike feature around zero bias for both monolayer and bilayer graphene/SiC, as well as significant spatial inhomogeneity in electronic structure above the gap edge. Nanoscale structure at the SiC/graphene interface is seen to correlate with observed electronic spatial inhomogeneity. These results are relevant for potential devices involving electronic transport or tunneling in graphene/SiC.

In this paper, the reduction roasting of laterite ore in the absence or presence of sodium sulfate was carried out for nickel beneficiation by wet magnetic separation. Sodium sulfate is found to be capable of enhancing the reduction of laterite ore through liberating iron and nickel from Ni/Fe substituted-lizardite, as well as increasing the size of ferronickel particles considerably. When the laterite pellets were reduced at 1100 °C for 60 min, the average particle size of ferronickel grains was approximately 50 μm in the presence of sodium sulfate, which far exceeded the size of 5–10 μm in the absence of sodium sulfate. Compared with those reduced without sodium sulfate, the Ni grade of ferronickel concentrate increased from 2.33% to 9.48%, and the magnetic separation recovery of Ni increased from 56.97% to 83.01% with the addition of 20 wt.% sodium sulfate. Experimental evidence showed that troilite (FeS) serves as an activating agent to accelerate melt phase formation via a low melting point (985 °C) Fe–FeS eutectic. This markedly facilitated the aggregation of ferronickel particles during reduction, along with the selective enrichment of Ni by suppressing the complete metallization of Fe.

Interference between different possible paths lies at the heart of quantum physics. Such interference between coupled discrete and continuum states of a system can profoundly change its interaction with light as seen in Fano resonance. Here we present a unique many-body Fano system composed of a discrete phonon vibration and continuous electron-hole pair transitions in bilayer graphene. Mediated by the electron-phonon interactions, the excited state is described by new quanta of elementary excitations of hybrid phonon-exciton nature. Infrared absorption of the hybrid states exhibit characteristic Fano lineshapes with parameters renormalized by many-body interactions. Remarkably, the Fano resonance in bilayer graphene is continuously tunable through electrical gating. Further control of the phonon-exciton coupling may be achieved with an optical field exploiting the excited state infrared activity. This tunable phonon-exciton system also offers the intriguing possibility of a 'phonon laser' with stimulated phonon amplification generated by population inversion of band-edge electrons.

The feasibility of an integrated technological route for comprehensive utilization of red mud was verified in this study. Valuable components in the mud, including Fe2O3, Al2O3 and SiO2 were stepwise extracted by magnetic separation and sulfuric acid leaching from reduced red mud, and meanwhile TiO2 was enriched in the leaching residue. Sodium salts were proved to be favorable for the magnetic separation of metallic iron and the subsequent acid leaching of Al and Si, through facilitating the reduction of iron oxides and the growth of metallic iron grains, together with enhancing the activation of Al and Si components during the roasting process. After reductive roasting in the presence of 6% Na2CO3 and 6% Na2SO4, a magnetic concentrate containing 90.2% iron with iron recovery of 95.0% was achieved from the red mud by magnetic separation. Subsequently, 94.7% Fe, 98.6% Al and 95.9% Si were extracted by dilute sulfuric acid leaching from the upper-stream non-magnetic material, yielding a TiO2-rich material with 37.8% TiO2. Furthermore, value-added products of silica gel and Al(OH)3 were prepared from the leachate by ripening and neutralizing.

Energy bandgap largely determines the optical and electronic properties of a semiconductor. Variable bandgap therefore makes versatile functionality possible in a single material. In layered material black phosphorus, the bandgap can be modulated by the number of layers; as a result, few-layer black phosphorus has discrete bandgap values that are relevant for optoelectronic applications in the spectral range from red, in monolayer, to mid-infrared in the bulk limit. Here, we further demonstrate continuous bandgap modulation by mechanical strain applied through flexible substrates. The strain-modulated bandgap significantly alters the density of thermally activated carriers; we for the first time observe a large piezo-resistive effect in black phosphorus field-effect transistors (FETs) at room temperature. The effect opens up opportunities for future development of electromechanical transducers based on black phosphorus, and we demonstrate an ultrasensitive strain gauge constructed from black phosphorus thin crystals.

We find the scanning tunneling spectra of backgated graphene monolayers to be significantly altered by many-body excitations. Experimental features in the spectra arising from electron-plasmon interactions show carrier density dependence, distinguishing them from density-independent electron-phonon features. Using a straightforward model, we are able to calculate theoretical tunneling spectra that agree well with our data, providing insight into the effects of many-body interactions on the lifetime of graphene quasiparticles.

Effects of sodium salts on reduction roasting and Fe–P separation of high-phosphorus oolitic hematite ore were studied in the process of coal-based direct reduction followed by wet magnetic separation. Various parameters, including reducing temperature and time, type and dosage of sodium salts, grinding fineness of magnetic separation feed and magnetic field intensity were investigated. The results of reduction and Fe–P magnetic separation are significantly improved by the addition of sodium sulfate and borax, in comparison with those in the absence of additives. A magnetic concentrate with total iron grade of 92.7% and phosphorus content of 0.09% was obtained from an oolitic hematite ore containing 48.96% iron and 1.61% phosphorus when reduced in the presence of 7.5% sodium sulfate and 1.5% borax and wet magnetic separated under the proper conditions. The results of optical microscopy and X-ray diffraction (XRD) analyses of reduced pellet reveal that metallic iron grains exist in sizes of 10–20 μm and are associated with gangue minerals closely when reduced in the absence of sodium salts. By contrast, the oolitic structure is destroyed and metallic iron grains grow markedly to the mean size of 50 μm when reduced in the presence of sodium sulfate and borax. Sodium salts are capable of destroying the oolitic structure via reacting with gangues, enhancing the reduction of iron oxide and promoting the growth of metallic iron grains during reduction, which is beneficial for Fe–P separation of the oolitic hematite ore.

There are abundant ferruginous manganese ores (abbr. Fe-Mn ores) in many parts of the world. For example, almost half of the manganese ore resources in India are ferruginous and more than 73% of the manganese ores in China belong to Fe-Mn ores with a low Mn/Fe mass ratio (<3). With the depletion of high grade manganese ore resources, the Fe-Mn ores are becoming important substitution resources for extracting manganese. In general, the production of Mn alloy from manganese ores requires that the Mn grade is more than 30% and the Mn/Fe mass ratio is greater than 5. During the production of electrolytic manganese or manganese chemical products, the issue of co-leaching of Mn and Fe complicates the purification procedure for the MnSO4 solution if Fe-Mn ores are used as raw materials. Numerous approaches are reported to realize the selective extraction and separation of Mn and Fe from the Fe-Mn ores. The extraction and separation technologies cover physical beneficiation, chemical beneficiation (hydrometallurgy and pyrometallurgy) and physico-chemical combined processes. This present work reviews the technical principles, parameters and recovery efficiencies of diverse processes on the aspect of selective extraction and separation of Mn and Fe from Fe-Mn ores. This review can provide guidance for selecting appropriate methods to exploit Fe-Mn ores or other secondary resources containing Fe and Mn oxides. The authors also put forward a new route to produce manganese ferrite materials using Fe-Mn ores as the raw materials.

In recent years, the comprehensive utilization of low-grade manganese oxide ores has received much attention due to the shortage of high-grade manganese ore resources. In this study, low-grade manganese oxide ores were treated by reduction roasting using chemically pure sulfur as a reductant. Then, the roasted samples were subjected to sulfuric acid leaching to extract manganese (Mn). The effects of roasting temperature, roasting time, S/Mn mole ratio, sulfuric acid concentration, leaching temperature, stirring rate, leaching time and liquid-to-solid ratio on the Mn and Fe leaching were discussed. The leaching efficiencies of 95.6% for Mn and 14.5% for Fe were obtained under the following optimized conditions: 550 °C of roasting temperature, 10 min of roasting time, 0.50 of S/Mn, 1.0 mol/L of sulfuric acid concentration, 25 °C of leaching temperature, 200 r/min of stirring rate, 5 min of leaching time and 5:1 of liquid-to-solid ratio.

Graphene-based electric power generation that converts mechanical energy of flow of ionic droplets over the device surface into electricity has emerged as a promising candidate for blue-energy network. Yet the lack of a microscopic understanding of the underlying mechanism has prevented ability to optimize and control the performance of such devices. This requires information on interfacial structure and charging behavior at the molecular level. Here, we use sum-frequency vibrational spectroscopy to study the roles of solvated ions, graphene, surface moiety on substrate and water molecules at the aqueous solution/graphene/polymer interface. We discover that the surface dipole layer of the neutral polymer is responsible for ion attraction toward and adsorption at the graphene surface that leads to electricity generation in graphene. Graphene itself does not attract ions and only acts as a conducting sheet for the induced carrier transport. Replacing the polymer by an organic ferroelectric substrate could allow switching of the electricity generation with long durability. Our microscopic understanding of the electricity generation process paves the way for the rational design of scalable and more efficient droplet-motion-based energy transducer devices.

Two-dimensional (2D) materials may offer the ultimate scaling beyond the 5 nm gate length. The difficulty of reliably opening a band gap in graphene has led to the search for alternative, semiconducting 2D materials. Emerging classes of elemental 2D materials stand out for their compatibility with existing technologies and/or for their diverse, tunable electronic structures. Among this group, black phosphorene has recently shown superior semiconductor performances. Silicene and germanene feature Dirac-type band dispersions, much like graphene. Calculations show that most group IV and group V elements have one or more stable 2D allotropes, with properties potentially suitable for electronic and optoelectronic applications. Here, we review the advances in these fascinating elemental 2D materials and discuss progress and challenges in their applications in future opto- and nano-electronic devices.

Acid leaching-solvent extraction is an effective process to extract scandium from scandium-bearing resources. This study was aimed to investigate the extraction behavior of metal ions, including Sc3+, Fe3+, Al3+and Ca2+, in phosphoric acid medium using P204. More than 95% of scandium was selectively extracted under the conditions of pH value of 1.5–1.8, aqueous-organic ratio of 3 and oscillation for 15 min. The impurity elements like Fe3+, Al3+ and Ca2+, were separated via the solvent extraction process using P204 (e.g., separation coefficient of scandium to iron is 298). In stripping process, the majority of co-extracted metal ions can be removed from the organic phase with hydrochloric acid solution. The scandium-bearing organic phase was stripped with 4 mol/L NaOH, wherein the recovery of scandium attained about 95% while that of the co-extracted iron and aluminum were only 3.1% and 1.2%, respectively. It was also confirmed that both P204 and H3PO4 played roles in extraction reaction, and the desirable extraction of scandium in P204 was attributed to the ion exchange between hydrogen ion of PO(OH) and Sc3+ on acidic condition (pH = 0.4–1.5). Impurity elements (Fe3+ and Al3+) also reacted with phosphate anion to form hydrophilic ions, and in turn result in selective extraction of scandium in phosphoric acid leachate using P204.

We construct a continuum model for the Moir\'e superlattice of twisted bilayer MnBi$_2$Te$_4$, and study the band structure of the bilayer in both ferromagnetic (FM) and antiferromagnetic (AFM) phases. We find the system exhibits highly tunable Chern bands with Chern number up to $3$. We show that a twist angle of $1^\circ$ turns the highest valence band into a flat band with Chern number $\pm1$ that is isolated from all other bands in both FM and AFM phases. This result provides a promising platform for realizing time-reversal breaking correlated topological phases, such as fractional Chern insulator and $p+ip$ topological superconductor. In addition, our calculation indicates that the twisted stacking facilitates the emergence of quantum anomalous Hall effect in MnBi$_2$Te$_4$.

NdFeB permanent magnet scrap is regarded as an important secondary resource which contains rare earth elements (REEs) such as Nd, Pr and Dy. Recovering these valuable REEs from the NdFeB permanent magnet scrap not only increases economic potential, but it also helps to reduce problems relating to disposal and the environment. Hydrometallurgical routes are considered to be the primary choice for recovering the REEs because of higher REEs recovery and its application to all types of magnet compositions. In this paper, the authors firstly reviewed the chemical and physical properties of NdFeB permanent magnet scrap, and then carried out an in-depth discussion on a variety of hydrometallurgical processes for recovering REEs from the NdFeB permanent magnet scrap. The methods mainly included selective leaching or complete leaching processes followed by precipitation, solvent extraction or ionic liquids extraction processes. Particular attention is devoted to the specific technical challenge that emerges in the hydrometallurgical recovery of REEs from NdFeB permanent magnet scrap and to the corresponding potential measures for improving REEs recovery by promoting the processing efficiency. This summarized review will be useful for researchers who are developing processes for recovering REEs from NdFeB permanent magnet scrap.

In order to explore the effect of oxygen concentration on the exothermic characteristics of coal spontaneous combustion (CSC), the coal exothermic reaction process under different oxygen concentrations was analyzed with the aid of synchronous thermal analyzer. Moreover, the Gaussian function was adopted to perform the multimodal fitting for the oxidation exothermic stage of CSC, and the kinetic calculation of the fitting results was carried out. The following research results were obtained. Oxygen-depleted conditions can reduce the heat release of coal, delay the occurrence of the characteristic temperature point and prolong the reaction time. The coal oxidation exothermic process results from the superposition of three reaction mechanisms, namely oxidative decomposition, gas-phase combustion and solid-phase combustion, which are all inhibited under oxygen-depleted conditions. Besides, oxidative decomposition and gas-phase combustion tend to convert to solid-phase combustion under oxygen-depleted conditions. The apparent activation energy and the pre-exponential factor of coal are reduced as the oxygen concentration decreases. The CSC reaction intensity declines under oxygen-depleted conditions, so CSC can be suppressed by reducing the oxygen concentration. Nevertheless, under oxygen-depleted conditions, CSC lasts longer and is more difficult to extinguish. In addition, coal that is hard to spontaneously combust is also difficult to be extinguished. This research conduces to the study on CSC mechanism and the prevention and control of CSC hazards under oxygen-depleted conditions.

We report XLINK, a multi-path QUIC video transport solution with experiments in Taobao short videos. XLINK is designed to meet two operational challenges at the same time: (1) Optimized user-perceived quality of experience (QoE) in terms of robustness, smoothness, responsiveness, and mobility and (2) Minimized cost overhead for service providers (typically CDNs). The core of XLINK is to take the opportunity of QUIC as a user-space protocol and directly capture user-perceived video QoE intent to control multi-path scheduling and management. We overcome major hurdles such as multi-path head-of-line blocking, network heterogeneity, and rapid link variations and balance cost and performance.

Chromium-bearing slags produced during the stainless-steel smelting (SSS) are important recyclable secondary resources. Recovery of chromium from these slags is not only beneficial to increase the slag’s economic potential but also favorable to solve the environmental problems induced by the chromium (VI) in the slags. This study aims to review the technologies for recovering chromium from the chromium-containing SSS slags. To begin with, chromium resources and consumption around the world were analyzed. Then, the physicochemical characteristics of the SSS slags were provided, followed by a deep discussion on varieties of the normal and lately developed methods for recovering chromium from the slags, including physical separation, smelting reduction, thermal plasma, alkaline roasting-water leaching, alkaline leaching, and bioleaching processes. Specific attention was paid to the technical challenge appearing in the recovery of chromium from the SSS slags and to the possible measures for enhancing the chromium recovery by promoting the processing efficiency.

The co-spontaneous combustion of coal and gangue widely exists in the world and threatens the safety of coal mines. In this paper, the microstructure of coal and gangue were tested and the thermal behavior during the co-spontaneous combustion process of coal and gangue with different mass ratios were investigated by using synchronous thermal analyzer, and the combustion characteristic indices and kinetic parameters were calculated. The results indicated the carbon content of gangue is much lower than that of coal, but the content of oxygen-containing functional groups and sulfides in gangue are far higher than that in coal. Moreover, gangue possesses more developed pores and specific surface area. With the increase of coal mass fraction, the combustion index of ignition of mixed samples increases linearly, while the combustion index of burnout and synthetical combustion grows exponentially. The mixtures of coal and gangue follows the interfacial reaction at the oxygen adsorption stage and the order reaction at the moisture evaporation and combustion stages. The practical apparent activation energy at the moisture evaporation and combustion stages is higher than the theoretical value. However, it shows the opposite result at the oxygen adsorption stage. Coal and gangue inhibit each other at the moisture evaporation and later combustion stages, but promote each other at the oxygen adsorption and earlier combustion stages. On the whole, the co-spontaneous combustion process of coal and gangue is dominated by promotion. As a result, the practical values of mass loss and heat release in the whole reaction process are greater than the theoretical ones. Therefore, the danger of spontaneous combustion is higher when coal and gangue coexist.

In order to accurately determine the ignition temperature (Ti) of coal, Coal spontaneous combustion (CSC) process was tested by a simultaneous thermal analyzer. Next, the abrupt change point of the differential derivative thermogravimetric curve (DDTG) of coal after the high adsorption temperature was taken as the Ti of CSC. Besides, variations of kinetics and thermodynamics during the CSC before and after the Ti were calculated. It was found that the mass loss, heat releases and gaseous products of coal changed slowly before the Ti and surged sharply after the Ti. The coal at ignition temperature was in thermodynamic equilibrium with low activity. However, when the temperature was greater than Ti, the aromatic hydrocarbons in coal begin to decompose, resulting in the increased of active sites and the release of volatiles, and the coal enters an irreversible combustion stage. At this time, upward trends were obtained for the apparent activation energy, pre-exponential factor, enthalpy change, and entropy change, while a gradual decrease was observed for the Gibbs free energy change. Moreover, reaction intensity between oxygen and coal would be increased due to increased of active sites in the coal and enhanced of volatiles release under a slower heating rate.

This study is aimed at exploring the relationship between the variations of micro-groups and the thermal effect during the heating process of coal spontaneous combustion (CSC). To this end, the thermal effect and microstructure variation characteristics of CSC were analyzed by means of differential scanning calorimetry and in-situ infrared spectroscopy. The results reveal that the exothermic reaction of CSC falls into five stages: water evaporation, desorption-induced heat absorption, slow heat release, benzene ring pyrolysis and combustion. Aliphatic hydrocarbons in coal oxidize into carbonyl which further oxidizes into carboxyl. The dynamic variations of key groups during the different stages of CSC were determined through grey correlation analysis. In addition, structural contribution, a new parameter to characterize the contribution of microstructure to thermal effect of CSC, was defined. The results disclose that the correlations between the thermal effect and the microstructure variation in different stages differ, but the key groups follow the change process of hydroxyl → aliphatic hydrocarbons → oxygen-containing functional groups → aromatic hydrocarbons on the whole. The change of key groups is related to the thermal effect and microstructure reaction characteristics of CSC. The contribution of a microstructure to the thermal effect of CSC is determined by the comprehensive product of its initial content, variations in different stages and correlation. Different microstructures correspond to varying contributions in different stages of CSC. The key to preventing CSC is to hinder the oxidative consumption of –OH(f) and the oxidation of aliphatic hydrocarbons with the highest contents into -C = O and –COOH.

Under the complicated driving conditions, the sharp acceleration and deceleration actions would cause the high-rate charge and discharge current of electric driving system in hybrid electric vehicle (HEV), which brings about a serious impact on the battery lifetime. The hybrid energy storage system (HESS) combined with battery and ultracapacitor (UC), would be a possible solution to this problem. For HEV with HESS, in addition to improving fuel economy, realizing the protection of battery is also an important objective. However, improving one aspect performance may sacrifice another aspect performance. The tradeoff between multiple optimization objectives remains a challenge for energy management design. Aiming at this problem, a multi-objective optimization energy management strategy based on velocity prediction for a dual-mode power split HEV with HESS is proposed in this paper. Firstly, to get the precise predictive input sequence, generalized regression neural network (GRNN) is used to predict future velocity. Secondly, the power distribution of dual-mode power spilt HEV with HESS is described as a rolling optimization problem in the prediction horizon of model predictive control (MPC). A new cost function considering the fuel consumption and the protection of the battery is brought forward, and the optimization problem is solved using Pontryagin's minimum principle (PMP). Moreover, the Powell-Modified algorithm is introduced to execute the solving process of PMP. Finally, the proposed strategy is verified by comparing it with four other strategies under four different driving cycles. Compared to the rule-based strategy, the proposed strategy reduces root mean square (RMS) of battery current and fuel consumption by up to 18.5 % and 18.9 %, respectively.

Removal of antimony from wastewater is essential because of its potential harm to the environment and human health. Nano–silica and biogenic iron (oxyhydr)oxides composites (BS–Fe) were prepared by iron oxidizing bacteria (IOB) mediation and the batch adsorption experiments were applied to investigate antimonite (Sb(III)) and antimonate (Sb(V)) removal behaviors. By contrast, the synthetic BS–Fe calcined at 400 ℃ (BS–Fe–400) exhibited a large specific surface area (157.353 m2/g). The maximum adsorption capacities of BS–Fe–400 were 102.10 and 337.31 mg/g for Sb(III) and Sb(V), respectively, and experimental data fit well to the Langmuir isotherm and Temkin models, and followed the pseudo–second order kinetic model. Additionally, increasing pH promoted Sb(III) adsorption, while inhibited the adsorption of Sb(V), indicating that electrostatic attraction made a contribution to Sb(V) adsorption. Moreover, different co–existing ions showed different effects on adsorption. Characterization techniques of FTIR and XPS indicated that the main functional groups involved in the adsorption were –OH, C–O, CO, C–C, etc. and Sb(III) and Sb(V) may bind to iron (oxyhydr)oxides via the formation of inner–sphere complexes. The present work revealed that the synthetic BS–Fe–400 by nano–silica and biogenic iron (oxyhydr)oxides held great application potential in antimony removal from wastewater.

Root radial transport is important for cadmium (Cd) absorption and root-shoot translocation. However, the relationship between root structural characteristics and radial transport of Cd in wheat is still unclear. Six wheat cultivars with different Cd tolerance and accumulation characteristics were used to investigate the roles of root phenotype, microstructure, and apoplastic and symplastic pathways in Cd uptake and root-shoot transport in pot culture. Longer root length, smaller root diameter, and more numerous root tips were more conducive to Cd absorption, while thicker roots were able to retain more Cd, thus reducing root-shoot transport and improving Cd tolerance of shoots. Cd stress can induce the deposition of apoplastic barriers in wheat roots, and the deposition of the apoplastic barrier increases under greater stress. The formation of apoplastic barriers can reduce Cd absorption and transfer to the shoot, and the presence of passage cells can weaken this effect. The cell wall thickening induced by Cd stress enhanced Cd adsorption capacity in wheat roots, but there was no significant correlation between Cd content and polysaccharide content in the cell wall. The up-regulated expression of TaHMA3 and TaVP1, which encode proteins related to Cd compartmentalization, was associated with increased Cd tolerance in wheat and decreased Cd translocation to aboveground parts. The morphology and anatomy of roots appear to play critical roles in Cd tolerance, uptake, and translocation in wheat. The present study provides useful information for the selection of wheat cultivars with low Cd accumulation.

Despite many efforts are being undertaken to design high tribo-performance epoxy nanocomposite, it still remains a great challenge to comprehensively address the interface issue and poor mechanical strengths for real engineering requirements. This work reports a facile yet efficient strategy (synergism of soft and hard materials) to coordinate the interface-property relationship. Herein, we composited graphene with molybdenum disulfide to fabricate rGO-MoS2 interlayered nanostructure as hard solid lubricant, as the hyperbranched polysiloxane with unique flexible SiOC backbone was synthesized via facile polymerization as soft component within epoxy network. These two nanomaterials can be well used to construct EP composite for easy processing, and their merits regarding lubricity and toughening are well exerted, especially the interface could be improved without surface treatment. The optimized material with superior impact strength (23.5 ∼ 37.4 kJ·m−2), low friction coefficient (0.42 ∼ 0.16) and volume wear rate (70.6 % reduction) was obtained with respect to previous counterparts. Interestingly, TEM of ultra-thin resin slice found that hyperbranched polysiloxane could affect the distribution and nanostructured interface of graphene/MoS2, encouraging a facile and low-cost approach towards surface engineering of high-performance polymer composite. Besides, the tribo-mechanism and nano-reinforced mechanism were investigated and discussed in detail. In light of the compelling effects, this work paves an effective way toward the designs of high-performance polymer tribo-materials for real engineering uses.

Secondary aluminum dross (SAD) containing high levels of AlN and fluorine/chlorine salt is a typical hazardous waste generated from aluminum electrolytic and recycling processes. Numerous studies have reported the denitrification of SAD by pyrometallurgical or hydrometallurgical techniques. However, these methods were always inefficient due to strict restrictions on raw materials or the risk of secondary pollution. In this study, a new idea of deep denitrification of SAD by self-driven hydrolysis of AlN and the enhancement of mechanical ball milling was proposed. Thermodynamic analysis suggested that Al(OH)3, Si and SiO2 can be dissolved in the alkaline environment generated by the hydrolysis of AlN alone under low liquid–solid ratio (L/S) conditions. The results of the kinetic fit indicated that the denitrification reaction was controlled by the chemical reaction at the early stage, then shifted to the mixing control as the reaction progressed. The experimental results confirmed that Al(OH)3, Si and SiO2 entered the solution as Al(OH)4- and H3SiO4- during the hydrolysis of SAD, then formed aluminosilicate precipitation (feldspar). This reaction promoted the dissolution of Al and Si, which in turn enhanced the removal of nitrogen. Under the optimal process conditions (L/S = 1.5, T = 80 °C, t = 300 min, ball mill speed = 200 rpm), the residual amount of nitrogen in SAD was reduced to 0.39 wt%, and the denitrification rate reached 93.05%.

Cadmium (Cd) is a persistent heavy metal that poses environmental and public health concerns. This study aimed to identify the potential biomarkers responsible for Cd tolerance and accumulation by investigating the response of the content of essential metal elements, transporter gene expression, and root exudates to Cd stress in broomcorn millet (Panicum miliaceum). A hydroponics experiment was conducted using two broomcorn millet cultivars with distinct Cd tolerance levels and accumulation phenotypes (Cd-tolerant and Cd-sensitive cultivars). Cd stress inhibited lateral root growth, especially in the Cd-sensitive cultivar. Furthermore, Cd accumulation was significantly greater in the Cd-tolerant cultivar than in the Cd-sensitive cultivar. Cd stress significantly inhibited the absorption of essential metal elements and significantly increased the calcium concentration. Differentially expressed genes involved in metal ion transport were identified via transcriptome analysis. Cd stress altered the composition of root exudates, thus increasing lipid species and decreasing alkaloid, lignan, sugar, and alcohol species. Moreover, Cd stress significantly reduced most alkaloid, organic acid, and phenolic acid exudates in the Cd-tolerant cultivar, while it increased most lipid and phenolic acid exudates in the Cd-sensitive cultivar. Some significantly changed root exudates (ferulic acid, O-coumaric acid, and spermine) are involved in the phenylalanine biosynthesis, and arginine and proline metabolic pathways, thus, may be potential biomarkers of Cd stress response. Overall, metal ion absorption and root exudates are critical for Cd tolerance and accumulation in broomcorn millet. These findings provide valuable insights into improving Cd phytoremediation by applying mineral elements or metabolites.

In the hope of exploring the effect of coal gangue left in goaf on coal spontaneous combustion, the variations of thermal effects and free radical parameters during coexisting spontaneous combustion of coal and coal gangue were tested, and kinetic at different heating stages were calculated. The following beneficial findings were obtained. For the mixed samples, the heat flow curve, ignition temperature, and free radical concentration all decline with the increase of coal gangue content, and the free radical parameters exhibit periodic changes with increasing temperature. Both the experimental value of thermal effect and free radical concentration with coal and coal gangue mixture during the spontaneous combustion process are higher than the calculated value. The calculation results of kinetic show that at the endothermic stage, the activation energies of the mixed samples decline with the increase of coal gangue, and the experimental value of activation energy is greater than the calculate value; at the exothermic stage, the case is exactly the opposite. Furthermore, due to the higher reactivity of coal gangue groups and stronger thermal conductivity, the coexistence of coal and coal gangue spontaneous combustion reaction is promoted. Resultantly, coal spontaneous combustion is normally more threatening in gangue-containing goafs.

Type-II superlattice (T2SL) detectors represent a promising advancement in long-wavelength infrared (LWIR) photodetector with significant potential across various applications. This study aims to explore the effect of different InAs layer thicknesses on the properties of InAs/GaSb LWIR SLs, which are fabricated by molecular beam epitaxy (MBE). By employing a comprehensive multi-technique analysis, including Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Energy-Dispersive X-ray Spectroscopy (EDXS), X-ray Photoelectron Spectroscopy (XPS), and Photoluminescence (PL). We substantiate the outstanding surface morphology, high-quality strain-balanced characterization, actual growth thickness assessment, and elemental content analysis using advanced spectroscopy techniques. These results demonstrate comprehensive insights into the 14/7 ML InAs/GaSb SLs elemental composition and distribution, enhancing understanding of superlattice properties for LWIR applications.

Electrons in graphene have a pseudospin, but controlling this degree of freedom is challenging. Evidence now suggests that the moiré superlattices arising in two-dimensional heterostructures can be used to electrically manipulate pseudospins. Electrons in graphene are described by relativistic Dirac–Weyl spinors with a two-component pseudospin1,2,3,4,5,6,7,8,9,10,11,12. The unique pseudospin structure of Dirac electrons leads to emerging phenomena such as the massless Dirac cone2, anomalous quantum Hall effect2,3, and Klein tunnelling4,5 in graphene. The capability to manipulate electron pseudospin is highly desirable for novel graphene electronics, and it requires precise control to differentiate the two graphene sublattices at the atomic level. Graphene/boron nitride moiré superlattices, where a fast sublattice oscillation due to boron and nitrogen atoms is superimposed on the slow moiré period, provides an attractive approach to engineer the electron pseudospin in graphene13,14,15,16,17,18. This unusual moiré superlattice leads to a spinor potential with unusual hybridization of electron pseudospins, which can be probed directly through infrared spectroscopy because optical transitions are very sensitive to excited state wavefunctions. Here, we perform micro-infrared spectroscopy on a graphene/boron nitride heterostructure and demonstrate that the moiré superlattice potential is dominated by a pseudospin-mixing component analogous to a spatially varying pseudomagnetic field. In addition, we show that the spinor potential depends sensitively on the gate-induced carrier concentration in graphene, indicating a strong renormalization of the spinor potential from electron–electron interactions.

Humic acid (HA) was the predominant component of the MHA (modified humic acid) binder invented by the authors. This work aims to study the effect of the solution pH value on the HA adsorption onto natural magnetite/hematite/quartz particles and the strength of green pellets with the MHA binder. The SEM images for HA indicated that HA had distinct morphology at different pH values. The adsorption density of HA on the three oxide minerals was significantly pH-dependent and decreased with increasing pH value. The zeta potential values of the magnetite, hematite and quartz particles coated by HA became negative and the isoelectric point of the three natural oxide minerals disappeared in the tested pH value range. The electrostatic interaction and the ligand exchange were the two leading interactions for the HA sorption onto the magnetite/hematite particles, while the small adsorption amount of HA onto the quartz was attributed to the hydrogen-bond interaction. The pH value of the MHA binder solution affects markedly the strength of green pellets from magnetite and hematite concentrates. At pH ~ 7.0, the HA molecule was expanded and dispersed well and the relatively strong bonding bridges were formed among the iron ore particles. The optimal pH value was founded to be around 7.0 for preparing high-quality iron ore green pellets.

A novel type of organic binder, modified humic acid (MHA), has been developed and patented in China. Humic acid (HA) is one of the main active fractions in the MHA binder. In this study, adsorption of HA onto natural magnetite, hematite and quartz surfaces as a function of initial HA concentration was comparatively investigated. It was found that the initial HA concentration has a positive effect on the adsorbance of HA onto magnetite and hematite surfaces but HA was hardly adsorbed by quartz particles even if the initial HA concentration was very high. When increasing the initial HA concentration, the zeta potential of magnetite/hematite particles became more negative because the negatively charged HA molecules entered into the electric double layer of the iron ore particles, while there was nearly no change in the zeta potential of quartz particles. There was less change in the zeta potential of magnetite compared to that of hematite. DRIFTS studies showed that there was a stronger chemisorption between the HA molecules and the iron ore surfaces under alkaline conditions. ESEM images further confirmed that magnetite particles coated by HA easily clustered to form agglomerates via chemisorption and physisorption, and the aggregates bonded together with HA by chemisorption were more resistant to breakage, which would be beneficial for the strength of green pellets.

The present study aims to provide a preliminary guide for microwave processing of low-rank coals by investigating the dielectric characteristics of an Indonesian low-rank coal based on determination of its permittivity from 21 °C to approximately 1000 °C at 915 and 2450 MHz in argon. The results show that the relative dielectric constant of the coal gradually decreases with increasing temperature below 200 °C due to dewatering. It then has a considerable increase up to 750 °C because of devolatilization and carbonization, preceded by a slight decrease due to physical-chemical and chemical processes connected with the mobility of macromolecular chains of the coal. Thereafter, it increases with a declined rate ascribed to the coal's continuous structure transformations. The dielectric loss factor shows a similar variation, except the presence of the “dielectric loss peak” at about 600 °C, associated with rise of microwave loss. The microwave penetration depth of the coal presents a depth peak at approximately 400 °C, indicating potential application of variable frequency microwave heating to large-scale processing. The reflection loss (RL) patterns reveal the strong coal slab thickness dependences of magnitude and location of absorption peaks in the range 0.02–0.20 m, with minimum RL values of − 42.39 dB and − 47.92 dB obtained at thicknesses of 0.16 and 0.06 m at 915 and 2450 MHz, respectively. This dissimilarity is primarily attributed to the different dielectric parameters and wavelengths at these frequencies. Microwave heating functions sufficiently in a narrow temperature range from about 500 to 700 °C, in which target temperature can be selected for efficient coal processing.

To realize a fast and smooth operating mode transition process from electric driving mode to engine-on driving mode, this paper presents a novel robust hierarchical mode transition control method for a plug-in hybrid electric bus (PHEB) with pre-transmission parallel hybrid powertrain. Firstly, the mode transition process is divided into five stages to clearly describe the powertrain dynamics. Based on the dynamics models of powertrain and clutch actuating mechanism, a hierarchical control structure including two robust H∞ controllers in both upper layer and lower layer is proposed. In upper layer, the demand clutch torque can be calculated by a robust H∞controller considering the clutch engaging time and the vehicle jerk. While in lower layer a robust tracking controller with L2-gain is designed to perform the accurate position tracking control, especially when the parameters uncertainties and external disturbance occur in the clutch actuating mechanism. Simulation and hardware-in-the-loop (HIL) test are carried out in a traditional driving condition of PHEB. Results show that the proposed hierarchical control approach can obtain the good control performance: mode transition time is greatly reduced with the acceptable jerk. Meanwhile, the designed control system shows the obvious robustness with the uncertain parameters and disturbance. Therefore, the proposed approach may offer a theoretical reference for the actual vehicle controller.

The problems of worldwide energy shortage and environment pollution are becoming more and more serious, thus lots of attention has been paid to renewable and sustainable energy. The development of photovoltaic technology was rapid in recent years as one of the promising renewable energy, the worldwide total amount of photovoltaic power plants had reached nearly 100 GW in 2012, and about 90% of the worldwide solar cells are crystalline silicon solar cells. But there is still a large gap between the electricity costs of photovoltaic and traditional fossil energy, lots of methods have been tried to decrease the costs. The efficiency of the cell could be increased by concentration, and parts of the solar cells are replaced by cheaper optical elements in concentration photovoltaic, thus the costs of photovoltaic could be decreased by concentration. The traditional solar cells used for concentration were III–V multi-junction solar cells, their costs were high although they had high efficiency, thus people tried to use cheaper silicon solar cells for concentration to decrease the costs further. In this work, six kinds of silicon solar cells with different structures used for concentration were summarized; the device structures, manufacturing processes and efficiencies of the cells were compared. The prospects of concentrator silicon solar cells were predicted, the Si HIT cell using back contact structure, the multi-junction cell containing Si back contact cell and the Si VMJ cell used with Ge and GaP VMJ cells were considered to have good potential in low, middle, high and very high concentration photovoltaic.

Manganese oxide ore is one of the most important resources. Owing to the depletion of high-grade ores, attention has turned to low-grade ones containing multiple elements such as iron, silicon, and aluminum. Conventional processes for extracting manganese are characterized by high production costs, intensive energy consumption, heavy environmental issues, or high co-leaching of impurities. In this study, selective sulfation roasting–water leaching is proposed for recovering manganese from iron rich low-grade manganese oxide ores using SO2 as reductant. Thermodynamic analysis indicated that manganese dioxide is readily transformed to sulfate. However, the sulfation of ferric oxide only occurs in the presence of both SO2 and O2. The thermodynamic stability region for MnSO4 and Fe2O3 demonstrated selective sulfation of manganese dioxide is feasible. The experimental validation for sulfation roasting and water leaching revealed that 90.6% of manganese and only 3.5% of iron were extracted when sulfation roasting was conducted at 500 °C for 60 min with SO2 partial pressure (SO2 / (SO2 + N2)) of 0.5%–1.0% (Vol.), and the leaching process was performed at 50 °C for 15 min with liquid-to-solid ratio of 5. This process is able to recover manganese from various low-grade manganese oxide ores.

Magnetic reduction roasting followed by magnetic separation process is reported as a simple route to realize separation of Mn and Fe from ferruginous manganese ores (Fe-Mn ores). However, the separation and recovery of Mn and Fe oxides are not very effective. This work clarified the underlying reason for the poor separation and also proposed some suggestions for the magnetic reduction process. In this work, the effect of temperature on the magnetic reduction roasting – magnetic separation of Fe-Mn ore was investigated firstly. Then the reduction behaviors of MnO2-Fe2O3 system and MnO2-Fe2O3-10 wt.%SiO2 system under 10 vol.% CO-90 vol.% CO2 at 600–1000 °C were investigated by XRD, XPS, SEM-EDS, VSM, DSC and thermodynamics analyses. Reduction and separation tests showed that higher reduction temperature was beneficial to the recovery of iron while it's not in favor of the recovery of manganese when the temperature was over 800 °C. The formation of composite oxide MnxFe3−xO4 with strong magnetism between the interface of the MnO2 and Fe2O3 particles leaded to the poor separation of iron and manganese. In addition, the formation mechanism of MnxFe3−xO4 from MnO2 and Fe2O3 as well as the interface reaction reduced under 10 vol.% CO was discussed in this study. Finally, some suggestions were recommended for the magnetic reduction roasting for utilizing the Fe-Mn ores effectively.

Lead (Pb) ions are chronically detected in soil, underground and natural water, there is a need for low-cost in situ remediation techniques. A novel mineral based magnetic adsorbent, consisting of natural vanadium, titanium-bearing magnetite particles coated by humic acid (abbr. VTM-HA), was developed for removing Pb(II) from wastewater. In this study, adsorption-desorption characteristics and mechanisms of Pb (II) on the VTM-HA adsorbent were investigated. The regeneration and reuse feasibility of the VTM-HA adsorbent were also conducted. The adsorption tests further verified that Pb(II) was removed rapidly and efficiently by the VTM-HA adsorbent. Moreover, Pb (II) adsorbed on the VTM-HA adsorbent could be easily eluted using a small amount of acidic eluent, and the desorption of Pb (II) could reach 99.3 wt% in 0.1 M HNO3 (pH = 1). After five adsorption-desorption regeneration cycles, the magnetism and Pb(II) adsorption capacity of the regenerated VTM-HA adsorbent almost kept unchanged. The results indicated that the VTM-HA adsorbent had excellent adsorption capacity and regenerative ability, which could be used as ideal adsorbents for removing Pb (II) from acid wastewater in commercial application. The mechanisms of Pb (II) adsorption and desorption were explored by FTIR, XPS analysis and DFT calculation.

The advent of black phosphorus field-effect transistors (FETs) has brought new possibilities in the study of two-dimensional (2D) electron systems. In a black phosphorus FET, the gate induces highly anisotropic 2D electron and hole gases. Although the 2D hole gas in black phosphorus has reached high carrier mobilities that led to the observation of the integer quantum Hall effect, the improvement in the sample quality of the 2D electron gas (2DEG) has however been only moderate; quantum Hall effect remained elusive. Here, we obtain high quality black phosphorus 2DEG by defining the 2DEG region with a prepatterned graphite local gate. The graphite local gate screens the impurity potential in the 2DEG. More importantly, it electrostatically defines the edge of the 2DEG, which facilitates the formation of well-defined edge channels in the quantum Hall regime. The improvements enable us to observe precisely quantized Hall plateaus in electron-doped black phosphorus FET. Magneto-transport measurements under high magnetic fields further revealed a large effective mass and an enhanced Landé g-factor, which points to strong electron–electron interaction in black phosphorus 2DEG. Such strong interaction may lead to exotic many-body quantum states in the fractional quantum Hall regime.

Taking the complex but regular characteristics of bus routines into account, the stochastic dynamic programming (SDP) might be a method with more potential to optimize the energy management of a plug-in hybrid electric bus (PHEB). However, the discrete transmission system and the continuous power system make it a complicated multidimensional optimal problem, particularly for PHEB with automated mechanical transmission (AMT), and the optimal decisions, which are obtained based on historical data, might not always well satisfy the driver's expectation to vehicle maneuverability under various driving conditions. To solve these problems, an adaptive approach based on the SDP is proposed in this paper. Exhaustively, the SDP is propelled into the input of the transmission to only optimize the torque split under the special gearshift logic, which reduces the dimensions of optimization and obtains more applicable optimal sequences. Then, an adaptive factor, which trades off the vehicle fuel economy and drivability in real time by dynamically adjusting the gearshift points and the torque split, is developed for the variation of the complicated bus driving cycles. The simulation results demonstrate that the proposed method could well respond to the variations of the driving conditions (e.g., road grade and vehicle load). Furthermore, the performance of the proposed method is discussed in detail by comparisons with different control strategies. More importantly, the proposed approach has great potential to be applied in practice.

The Chinese economy is in a critical period of continuous transformation of new and old kinetic energy and economic transformation and upgrading. Copper, the second largest strategic raw material, is still central to China’s economic development. As the major producer and consumer of electrical and electronic equipment (EEE), China’s production and consumption of refined copper is the largest in the world. Thus, it is necessary to forecast the supply and demand of China’s future copper. There is a huge gap between copper production and consumption in China, the current identified copper resources cannot meet copper consumption in the next five years, thus the import of copper will be more crucial for China’s future copper industry. Due to trade frictions, restriction on imports and other reasons, the import of copper from other countries will exist a lot of uncertainties. Hence, the domestic copper waste and scraps could be the suitable secondary resource for recycling copper in China. According to the grade and value of copper scraps, establishing quality standards and optimizing the disassembly process of the domestic Cu-bearing waste & scraps, and using the suitable method are the key to recycling the domestic copper scraps.

Abstract Moiré superlattices of van der Waals heterostructures provide a powerful way to engineer electronic structures of two-dimensional materials. Many novel quantum phenomena have emerged in graphene and transition metal dichalcogenide moiré systems. Twisted phosphorene offers another attractive system to explore moiré physics because phosphorene features an anisotropic rectangular lattice, different from isotropic hexagonal lattices previously reported. Here we report emerging anisotropic moiré optical transitions in twisted monolayer/bilayer phosphorenes. The optical resonances in phosphorene moiré superlattice depend sensitively on twist angle and are completely different from those in the constitute monolayer and bilayer phosphorene even for a twist angle as large as 19°. Our calculations reveal that the Γ-point direct bandgap and the rectangular lattice of phosphorene give rise to the remarkably strong moiré physics in large-twist-angle phosphorene heterostructures. This work highlights fresh opportunities to explore moiré physics in phosphorene and other van der Waals heterostructures with different lattice configurations.

To explore the thermal behavior and hazard during the spontaneous combustion fires (SCFs) of coal and coal gangue (CG), the characteristics of heat release and thermal transfer during the SCFs of coal and CG were tested. The results indicate that coal contains more combustibles and aromatic hydrocarbons, while CG possesses higher contents of ash and inorganic silicate. Coal has a stronger heat release capacity, while CG owns a smaller specific heat capacity, a larger thermal diffusivity and a greater thermal conductivity. Thus, CG performs better with respect to heat transfer. The apparent activation energy of coal is larger in the endothermic stage, whereas that of CG is more notable in the exothermic stage. Based on heat release and heat transfer performance, hazardous zones during the SCFs of coal and CG were identified, and the combustion growth index was established to quantify the hazard of SCF disasters. The results show that the hazard is determined by both heat release and thermal transfer capacities. Coal or CG with a combustible component of 31.3 %, which not only releases massive heat but also transfers heat quickly, corresponds to the most considerable hazard of SCF disasters.

The flat bands resulting from moiré superlattices exhibit fascinating correlated electron phenomena such as correlated insulators, ( Nature 2018, 556 (7699), 80-84), ( Nature Physics 2019, 15 (3), 237) superconductivity, ( Nature 2018, 556 (7699), 43-50), ( Nature 2019, 572 (7768), 215-219) and orbital magnetism. ( Science 2019, 365 (6453), 605-608), ( Nature 2020, 579 (7797), 56-61), ( Science 2020, 367 (6480), 900-903) Such magnetism has been observed only at particular integer multiples of n0, the density corresponding to one electron per moiré superlattice unit cell. Here, we report the experimental observation of ferromagnetism at noninteger filling (NIF) of a flat Chern band in a ABC-TLG/hBN moiré superlattice. This state exhibits prominent ferromagnetic hysteresis behavior with large anomalous Hall resistivity in a broad region of densities centered in the valence miniband at n = -2.3n0. We observe that, not only the magnitude of the anomalous Hall signal, but also the sign of the hysteretic ferromagnetic response can be modulated by tuning the carrier density and displacement field. Rotating the sample in a fixed magnetic field demonstrates that the ferromagnetism is highly anisotropic and likely purely orbital in character.

Common prosperity is the essential requirement of socialism and an important feature of Chinese-style modernization. Data from 284 cities in China from 2011 to 2020 were collected to construct an evaluation system of the digital economy and common prosperity and establish relevant econometric models to explore their impact, spatial spillover, and mechanism. It is found that: (1) the digital economy has an obvious role in promoting common prosperity, this promotion role is dynamic and nonlinear, and the digital economy’s promotion is more obvious in low-level digital economy regions; (2) the digital economy has obvious externalities, and there is a spatial spillover effect in the process of promoting common prosperity; (3) resource allocation efficiency plays a mediating role in the process of promoting common prosperity development in the digital economy. Finally, countermeasures and suggestions are proposed in four aspects: strengthening the development of the digital economy, increasing investment in digital infrastructure, enhancing the digital governance capacity of the government, and building a digital economy demonstration zone. The research results deepen the understanding of the digital economy and common prosperity and provide some insights for the ultimate realization of common prosperity.

Silicon/carbon (Si/C) anodes have been successfully used in commercial lithium-ion batteries because of their high capacity and excellent safety. Nevertheless, their cycling stability and fast-charging capability are still unsatisfactory due to large volume expansion and slow charge transport capability under industrial electrode conditions. Here, we fabricate a Si/C anode via homogeneously depositing amorphous SiC nanolayers on graphite armored with N-doped porous flexible vertical graphene sheets (VGSs) (named as Si-C/VGSs/graphite). SiC nanolayers consist of homogeneously dispersed sub-nanometer Si particles in 3D carbon skeleton, which effectively alleviate the volume change of Si, and hugely accelerate electron and Li-ion transport. The N-doped VGSs possess porous structure, good flexibility, numerous exposed edges, and directional ion transport channels, which provide rational space for accommodating volume change of Si, buffer the stress caused by the volume change, increase the electrical contact points between Si-C/VGSs/graphite, and accelerate Li-ion transport, respectively. Consequently, Si-C/VGSs/graphite delivers superior rate capacity and long cycle life under industrial electrode conditions. When matched with the cathode of Li[Ni0.8Co0.1Mn0.1]O2, the full cell demonstrates a predominant fast-charging capability (180.8 Wh kg−1, charging for 8.2 min, 5C) accompanied by long cycle life.

Ludwigite ore has not yet been utilized on an industrial scale due to its complex mineralogy and fine mineral dissemination in China. Boron–iron separation and dissolution activity of boron-bearing minerals in alkaline liquor are the two key issues in the utilization of ludwigite ore, governing the boron recovery as well as operating cost. This paper proposes an innovative process for extraction of boron and iron from ludwigite ore based on coal-based direct reduction process with sodium carbonate (Na2CO3). The novel process involves reduction roasting, combined leaching and grinding of reduced ludwigite ore, followed by magnetic separation of leach residue, and experimental validation for each of the processing steps is demonstrated. Alkali-activation of boron and metallization of iron were synchronously achieved during carbothermic reduction of ludwigite ore in the presence of Na2CO3. Consequently, boron was readily extracted in the form of sodium metaborate (NaBO2) with water at room temperature during ball mill grinding, and metallic iron powder was recovered from the leaching-filtering residue by magnetic separation. Boron extraction of 72.1% and iron recovery of 95.7% with corresponding iron grade of 95.7% in the magnetic concentrate were achieved when ludwigite ore was reduced with 20% sodium carbonate at 1050 °C for 60 min.

Phase transformation of MnO2 and Fe2O3 roasted in air atmosphere at temperatures of 500–1400 °C for synthesizing manganese ferrite (MnxFe3 − xO4) has been reported. In current work, the morphologies and properties of the MnxFe3 − xO4 products with various x values during the synthesis process were characterized by XRD, XPS, SEM-EDS, AFM, VSM and Vickers-type microhardness analyses to further understand the formation mechanism of MnxFe3 − xO4 from MnO2 and Fe2O3 by solid-state reaction. Results showed that the x value in the MnxFe3 − xO4 gradually increased to 1 with the extension of roasting time from 30 min to 120 min at 1300 °C. Morphology measurements indicated the MnxFe3 − xO4 particles presented polyhedron structure and the shape of polyhedron particles gradually became regular with the increasing of x value. In addition, it's interesting to find that the polyhedron particles had multi-layer stacking structure and the thickness of each layer was about 5 nm. The saturation magnetization of the MnxFe3 − xO4 samples increased with the rising of x value. A polyhedral MnFe2O4 (x = 1) product with saturation magnetization of 78.5 emu/g was obtained when the MnO2 and Fe2O3 briquettes with molar ratio of 1:1 were roasted at 1300 °C for 120 min. Moreover, the Hv hardness of the MnxFe3 − xO4 increased from 154.8 kg/mm2 to 339.4 kg/mm2 with elevating the temperature from 1000 °C to 1300 °C.

Sodium salts were used in the reduction roasting and magnetic separation process to separate and recover iron and manganese from the high-iron manganese oxide ores to utilize the complex ores. Results showed that Na2S2O3 was the most effective salt. A magnetic concentrate with 86.39 wt% TFe and 96.21 wt% Fe recovery as well as a nonmagnetic product with 54.84 wt% TMn and 85.96 wt% Mn recovery was obtained when the ore sample was reduced at 1100°C for 100 min in the presence of 7 wt% Na2S2O3. In addition, the effects of roasting and separation parameters on the recovery of manganese and iron and the function mechanism of Na2S2O3 were investigated.

Atmospheric leaching of nickel from limonitic laterite ores is regarded as a promising approach for nickel production, despite its low nickel recovery and slower leaching rate than high pressure acid leaching. Sulfur dioxide can enhance the sulfuric acid leaching of laterite, but its behavior for enhancing atmospheric sulfuric acid leaching was uncertain due to SO2 losses and emission. In this study, sodium sulfite was used as a substitute for SO2 gas in the leaching and the sulfuric acid leaching characteristics of Ni and Fe from a limonitic laterite in the presence of sodium sulfite were investigated. A linear correlation exists between the extraction of Ni and Fe, indicating the difficulty in selective leaching of Ni over Fe. Most nickel is isomorphically substituted within the goethite and it is difficult to dissolve in a high oxidation–reduction potential solution environment, resulting in a low nickel recovery. SO2(aq) generated from the reaction of sodium sulfite in sulfuric acid solution, lowers the potential for the reducing reaction of FeOOH to give Fe2+, accelerating the iron extraction and nickel liberation from goethite.

Chromium was selectively recovered from ferronickel slag by roasting the slag with addition of Na2O2, followed by water leaching. The thermodynamic analysis revealed that in the presence of Na2O2 at appropriate temperatures, the Cr2O3 in the ferronickel slag can be converted to NaCrO2, instead of Na2CrO4, which prevents the formation of highly toxic Cr (VI). The experimental results confirmed that under the optimal alkaline roasting and water leaching conditions of the mass ratio of ferronickel slag to Na2O2 of 1, roasting temperature of 600 °C, roasting time of 1 h, leaching temperature of 50 °C, leaching time of 1 h, and liquid-to-solid ratio of 10 mL/g, 92.33% of Cr was leached with 64.28% of Na and 11.16% of Si and only 0.06 wt % Cr was left in the leaching residue. The high leaching percentage of Cr was a result of the transformation of Cr2O3 in the ferronickel slag to NaCrO2 with a loose structure during alkaline roasting that was beneficial to water dissolution. Compared to the traditional alkaline roasting process, the proposed more environmentally friendly method did not produce toxic Cr (VI) during recovery of chromium and the resulting residue has potential to be used as a good construction material.

The feasibility of a facile technological route to preparation of refractory materials from a ferronickel slag with the addition of sintered magnesia was verified in this study based on the thermodynamics analysis and the experimental exploration of the effect of the sintered magnesia addition on the phase transformation of ferronickel slag during the sintering process. For the first time, the results of thermodynamics calculation, X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analyses revealed that the original phase of the slag can be transformed to high melting point phases by addition of MgO during the sintering process at high temperatures (e.g., 1350 °C). Specifically, the olivine in ferronickel slag decomposed initially, generating a low-iron olivine phase and an enstatite phase. With increasing addition of sintered magnesia, the enstatite phase changed to forsterite, and the iron, aluminum, and chromium components in the ferronickel slag converted to high melting point spinel phases, including magnesium aluminate spinel and magnesium chromate spinel via a low-magnesium transient phase. The experimental results showed that a good refractory material with refractoriness of 1660 °C, bulk density of 2.92 g/cm3, apparent porosity of 1.82%, and compressive strength of 100.61 MPa could be obtained when the slag was sintered with addition of 20 wt % sintered magnesia at 1350 °C for 3 h. Due to the low production cost and property superiority of the prepared refractory material over commercial counterparts, the method proposed in this study is expected to have widespread applications in recycling of ferronickel slag.

The present study proposes a novel strategy for preparation of refractory materials from potentially hazardous ferronickel slag by microwave sintering of the slag with addition of sintered magnesia in which a series of chemical reactions were involved. This strategy was developed based on examination of the phase transformations and microstructural changes of the slag during microwave sintering through X-ray diffraction (XRD) analysis and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analysis, which determined the properties of refractory materials derived from the slag. It was shown that under microwave irradiation there existed rapid transformation of the olivine phase in the slag to high-melting point phases, including forsterite and spinels (e.g., magnesium iron chromate spinel, magnesium chromate spinel, and magnesium iron aluminate spinel). As a result, a high-quality refractory material with refractoriness of 1730 °C, bulk density of 2.80 g/cm3, apparent porosity of 1.6%, and compressive strength of 206.62 MPa was obtained by microwave sintering of the slag at 1350 °C for only 20 min with addition of 25 wt % sintered magnesia. Because the microwave sintering strategy not only elevated the refractoriness by 70 °C, but also reduced the heating duration required by the conventional approach by 6 times, it demonstrated apparent technological superiority and wide application prospect in preparing superior-quality refractory materials from ferronickel slag and relevant industrial waste, which contributed to conservation of resources and energy as well as environmental protection.

To ensure the strength of limonitic laterite sinters, more fuel needs to be added to the sintering process. Higher content of FeO, which was found to be an important factor affecting the sintering mineralization, would be produced inevitably at higher fuel dosage, while it has received less attention in the sintering process of limonitic laterite. In this study, the mineralization mechanism of the limonitic laterite sinters with different FeO content was explored by controlling fuel dosage in the sintering process. The results indicated that the increase of FeO contributed to improving the yield and quality index and had little adverse influence on the metallurgical properties of the sinters. Increasing the FeO content in the sinter was helpful to the formation of high-iron and needle-like SFCA-I (composite calcium ferrite composed of SiO2, Fe2O3, FeO, CaO, and Al2O3), which had lower formation temperature and could enhance the strength of the sinter.

Much chromite ore processing residue (COPR), which is defined as hazardous solid waste due to virulent Cr (Ⅵ), is produced from chromium salt industry. C-bearing dust from steel industry is a kind of typically solid waste with poor surface activity. The iron ore sintering process has the potential on large-scale harmless utilization of COPR and C-bearing dust. This study proposes a new approach of co-utilizing COPR and C-bearing dust during limonitic laterite sintering process. The negative influence of COPR and C-bearing dust on permeability was offset by the fuel attribute of extra C from C-bearing dust. The results indicate that, while 6% COPR and 8% C-bearing dust were added, the tumble index and yield of the sinters were basically equal to those of the blank samples. The toxic Cr (Ⅵ) was reduced to Cr (Ⅲ) which was concentrated in high alumina spinel phases during the sintering process. The obtained sinters were identified as nontoxic, and no secondary waste was generated throughout the clean utilization process.