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In this study, we proposed that homo superalkali NM4 clusters with high tetrahedral geometry, can be applied to develop high-performance hydrogen storage materials. Moreover, their special bonding structures and chemical stability make them ideal units for decoration of different kinds of pristine monolayers. We made a trial to decorate the NLi4 clusters onto the 1D graphene nanoribbon, and employed density functional theory (DFT) computational studies to solve its electronic structure, and further evaluate its applicability in hydrogen storage. We found that the electronic charges on Li atoms were successfully transferred to the pristine monolayer, thus a partial electronic field around each Li atom was formed. This subsequently leads to the polarization of the adsorbed hydrogen molecules, and further enhances the electrostatic interactions between the Li atoms and hydrogen. Each NLi4 cluster can adsorb at most 16 hydrogen molecules. For this novel material, its total capacity of hydrogen storage can reach to 11.2 wt %, surpassing the target value of 5.5 wt %, set by the U.S department of energy (DOE) [1], making itself an ideal unit for advanced energy materials design.

Density functional theory (DFT) computational studies were conducted to explore the hydrogen storage performance of a monolayer material that is built on the base of carbon nitride (g-C3N4, heptazine structure) with decoration by magnesium (Mg). We found that a 2 × 2 supercell can bind with four Mg atoms. The electronic charges of Mg atoms were transferred to the g-C3N4 monolayer, and thus a partial electropositivity on each adsorbed Mg atom was formed, indicating a potential improvement in conductivity. This subsequently causes the hydrogen molecules’ polarization, so that these hydrogen molecules can be efficiently adsorbed via both van der Waals and electrostatic interactions. To note, the configurations of the adsorbed hydrogen molecules were also elucidated, and we found that most adsorbed hydrogen molecules tend to be vertical to the sheet plane. Such a phenomenon is due to the electronic potential distribution. In average, each adsorbed Mg atom can adsorb 1–9 hydrogen molecules with adsorption energies that are ranged from −0.25 eV to −0.1 eV. Moreover, we realised that the nitrogen atom can also serve as an active site for hydrogen adsorption. The hydrogen storage capacity of this Mg-decorated g-C3N4 is close to 7.96 wt %, which is much higher than the target value of 5.5 wt % proposed by the U.S. department of energy (DOE) in 2020 [1]. The finding in this study indicates a promising carbon-based material for energy storage, and in the future, we hope to develop more advanced materials along this direction.

Rechargeable aqueous Zn ion batteries (ZIBs) have recently attracted immense interest for large-scale energy storage systems stemming from their high natural abundance, environmental benignity, and high safety. However, the frustrating structural degradation in the cathode and the inherent Zn dendrite growth on the anode severely hinder the progress for future application. Herein, we report a zinc/sodium manganese oxides (denoted as Zn/NMO) battery with pre-inserted Na+ ions and crystal water in the cathode interlayer, which greatly facilitates cations diffusion without serious structural distortion. More importantly, Na2SO4 additive in ZnSO4-based electrolyte can eliminate Zn dendrites by modifying the deposited pattern of Zn2+ ions. Consequently, the Zn/NMO battery exhibits a high capacity (367.5 mAh g−1 at 0.65 C) and super long-term cyclic stability (only 0.007% capacity fading after 10000 cycles at 6.5 C). Besides, operando and ex situ electrochemical characterizations demonstrate that the formation of byproducts in the cathode surface leads to improved capacity and low Coulombic efficiency during the electrochemical activation process. Density functional theory (DFT) calculation further reveals the interface reaction mechanism, in which the solvation energy of electrolyte ions is responsible for the H+/Zn2+ insertion/extraction in the cathode material.

Zinc sulfide (ZnS) exhibits promise in sodium-ion batteries (SIBs) because of its low operation voltage and high theoretical specific capacity. However, pristine ZnS is not adequate in realizing rapid and robust sodium storage owing to its low reversibility, poor structure stability, and sluggish kinetics. To date, most efforts focus on utilizing carbonaceous incorporation to improve its electrochemical performances. Nevertheless, it remains an arduous challenge for realizing superior rate capability while obtaining stable cycling. Herein, inspired by the crystal structure of hexagonal ZnIn2S4, which possesses an intrinsic layered feature with larger unit-cell volume versus that of ZnS, indium incorporation is thus deployed as an immediate remedy. In/ex situ investigations combined with density functional theory calculations are conducted to reveal the superior kinetics, high reversibility, and good structure stability of ZnIn2S4. Notably, the formed indium-based derivatives during cycling manifest a Na+ (de)intercalation process, thereby exciting a synergetic mechanism to stabilize electrochemical cycling. As a result, the electrochemical performances of Zn-based sulfide are significantly improved via the indium incorporation. Furthermore, a full cell based on the ZnIn2S4 anode with the superior electrochemical performance is developed. This work provides an effective tactic of heteroatom incorporation for optimizing structure as well as exciting a complementary reaction process toward developing superior anodes for high-performance alkali-ion batteries.

Quantum dots (QDs) light-emitting diodes (QLEDs) are considered the most promising candidate for application in displays. While the efficiency of QLEDs has been greatly developed in recent years and is comparable to that of organic light-emitting diodes (OLEDs), it still remains challenging to realize both high efficiency and long lifetimes. In this work, we report efficient and stable red QLEDs with the maximum current efficiency of 13.48 cd A-1, external quantum efficiency of 18.65%, and low efficiency roll-off at high luminance with a long lifetime exceeding ∼2.9 × 105 h, representing a 3-fold increase in stability. Tailoring the composition of QDs suppresses nonradiative Forster resonant energy transfer and Auger recombination and provides favorable valence band alignment to boost the hole injection. Our work suggests that tailoring the nanostructures of QDs offers an effective means to simultaneously achieve high efficiency and high stability, accelerating QLED technology for practical applications in displays and lighting.

Seawater desalination is the most promising solution to a sustainable water future. However, state-of-the-art desalination technologies suffer from energy intensiveness and high capital expenditure. To address these issues, we have developed a novel, membrane-less desalination battery comprising negatively charged redox-active electrodes. A two-dimensional (2D) Ni and Co bimetallic metal–organic framework anchored on a black phosphorus nanosheet (NiCo MOF@BP) composite with fast sodium ion transport kinetics and favourable redox potentials for sodiation/desodiation when coupled with reduced graphene oxide supported silver nanoparticles (Ag@rGO) is applied. The incorporation of black phosphorus stabilizes the NiCo MOF and improves the overall electrical conductivity. Ultrastable cycling (46.5 mA h g−1 after over 1000 cycles in 2 M NaCl solution and 33.4 mA h g−1 after over 500 cycles in synthetic seawater at 0.3 A g−1) and rate performance (25.7 mA h g−1 at 2.5 A g−1) are realised. Besides, a high coulombic efficiency of 96.9% and superb energy recovery of 70.7% are achieved. As such, a low energy consumption of 0.034 W h g−1 with a salt removal capacity of 103.1 mg g−1 is obtained using synthetic seawater as the electrolyte, which is among the lowest in energy consumption when compared with other similar desalination technologies. The exploration of this novel cathode material paves the way for future material selection for desalination batteries.

Hybrid perovskites are favoured over other numerous optoelectronic materials, thanks to their rapidly enhanced power conversion efficiency (PCE) and facile processing. At present, future developments are seriously hampered by the high toxicity of heavy metals and poor stability. Inorganic lead-free perovskites, CsSn1−xGexI3−yBry, are herein explored for superior optical performance by first-principles calculations based on density functional theory (DFT). It is unveiled that the valence band maximum (VBM) is mainly occupied by the p-orbit of halide ions, while the conduction band minimum (CBM) is composed of the p-orbit of the metal ion. Moreover, Bader charge analysis shows that CsSn0.5Ge0.5I3 corresponds to the most obvious charge transfer compared to the others. The defect formation energy indicates that perovskite compounds CsSn1−xGexI3−yBry, are more easily synthesized than the series CsSn1−xGexI3, and the physically accessible area is also determined in the coordinate system defined by the chemical potential change of the host atoms, ΔμSn and ΔμI. Additionally, the absorption spectra show that among the doped compounds of the form CsSn0.5Ge0.5I3−yBry, perovskite CsSn0.5Ge0.5I2Br is superior in terms of optical response in the visible-light range. The results shed a new light on the study of highly efficient and stable lead-free perovskite-based solar cells (PSCs).

Precise and selective separation of ions using two-dimensional (2D) laminar membranes is a budding research field with potential applications in water treatment, desalination, sensing, biomimicry and energy storage. However, most experiments are designed around pressure or concentration–driven processes without leveraging on the charged nature of ionic species. By applying an electric field across a 2D graphene oxide-based (GO-based) membrane, we demonstrate how ionic selectivity can be enhanced by changing the polarity or increasing the strength of the field. As opposed to traditional permeation experiments, the effects of selectivity are not limited to the membrane itself and can be dynamically tuned during ion removal by changing the strength of the applied electric field. Two types of membranes were investigated in a series of experiments using binary solutions of monovalent and divalent salts. The first is a classical, unmodified GO membrane and the second is a GO membrane with d-spacing restricted by functionalization with ethylenediamine (EDA). Monovalent ion selectivity was detected for both membranes with the EDA–GO membrane achieving a monovalent ion selectivity between 1.5–5 as compared to 1.3–3.5 for the GO membrane. Using density functional theory (DFT) calculations, we determined that the presence of EDA enhanced the formation of K+ and Na+ complexes which would cause distortions in local interlayer distances.

The combination of piezoelectricity with other unique properties (like the topological insulating phase and intrinsic ferromagnetism) in two-dimensional (2D) materials is worthy of much intensive study. In this work, the piezoelectric properties of 2D topological insulators InXO (X = Se and Te), derived from monolayer InX (X = Se and Te) by double-side oxygen functionalization, are studied by density functional theory (DFT). Large piezoelectric strain coefficients (e.g. d11 = −13.02 pm V−1 for InSeO and d11 = −9.64 pm V−1 for InTeO) are predicted, which are comparable and even higher than those of many other familiar 2D materials. Moreover, we propose two strategies to enhance the piezoelectric response of monolayer InXO (X = Se and Te). Firstly, biaxial strain (0.94–1.06) is applied, and the d11 (absolute value) is increased by 53%/56% for monolayer InSeO/InTeO at 1.06 strain, which is due to the increased e11 (absolute value) and reduced C11–C12. In the considered strain range, the InXO (X = Se and Te) monolayers are always 2D topological insulators, which confirms the coexistence of piezoelectricity and nontrivial band topology. Secondly, a Janus monolayer In2SeTeO2 is designed by replacing the top Se/Te atomic layer in monolayer InSeO/InTeO with Te/Se atoms, and is dynamically and mechanically stable. More excitingly, Janus monolayer In2SeTeO2 is also a 2D topological insulator with sizeable bulk gap of up to 0.158 eV, confirming the coexistence of intrinsic piezoelectricity and its topological nature. The calculated d11 is −9.9 pm V−1, which is in the middle of those of InSeO and InTeO monolayers. Finally, the carrier mobilities of monolayer InXO (X = Se and Te) are obtained, which show a rather pronounced anisotropy between electrons and holes, and are almost isotropic between the armchair and zigzag directions. Our work implies that it is possible to use the piezotronic effect to control the quantum transport process, ultimately leading to the novel device applications of monolayer InXO (X = Se and Te), and can stimulate further experimental work.

Transition metal doped ZnO (TM-ZnO) nanoparticles with 3% dopant content are successfully prepared via a simple solvothermal route. This work highlights Mn, Fe, Co, Ni or Cu ions as the dopant transition metals. The as-prepared samples are wurtzite phase ZnO crystals, and the average sizes of undoped ZnO and TM-ZnO nanoparticles range from 200 nm to 400 nm. XPS studies confirm that the transition metal ions are successfully doped into the crystal lattice of ZnO. The band gaps of the undoped ZnO and TM-ZnO crystals are calculated by using UV-DRS spectroscopic measurements. The visible light response of ZnO nanomaterials is improved by doping transition metal ions. For investigating the influence of transition metal doping on the photocatalytic performance of ZnO, the photodegradation rate of methylene blue (MB) is investigated under simulated sunlight irradiation. The photocatalytic properties of ZnO doped with transition metals are improved at different degrees, among which Cu-doped ZnO exhibits the best photocatalytic performance. Based on density functional theory (DFT) calculation result, a possible photocatalytic mechanism is proposed. Furthermore, the antibacterial performance of Cu-doped ZnO is investigated by selecting E. coli, under simulated sunlight irradiation and remarkable sterilization of E. coli is achieved.

Based on hybrid density functional calculations, the geometrical and electronic structures of a two-dimensional (2D) CdO/CdS heterostructure (HT) formed by a CdO monolayer (ML) and a CdS ML are investigated. The formation of the CdO/CdS HT is exothermic, and the CdO/CdS HT shows excellent ability for visible light absorption. The CdO/CdS HT with a rotation angle of 0° possesses the characteristics of type-II band alignment and strong built-in electric field across the interface, which boost the photogenerated carrier separation. Besides, the band edge positions of the CdO/CdS HT of 0° are energetically favorable for overall water-splitting processes with the pH scope of 0-3.6. Therefore, the CdO/CdS HT is a promising photocatalyst to split water.

The $\gamma $ -ray total dose radiation effects on ferroelectric Al-doped HfO2 (HfAlO) thin films with an n-type Si substrate were studied. The $I$ - $V$ , $P$ - $V$ , $C$ - $V$ and fatigue characteristics of the HfAlO-based Metal-Ferroelectric-Insulator-Semiconductor (MFIS) structure were analyzed with the increasing total dose from 0 to 1 Mrad (Si). The remnant polarization ( $P_{\mathrm {r}}$ ) values, the capacitance ( $C$ ) values and the switching voltage ( $V_{\mathrm {c}}$ ) of this MFIS gate structure decreased with the increasing total dose. A TCAD model of Metal/HfAlO/SiO2/Si (MFIS) was proposed to explain the degradation mechanism of ferroelectric properties of the MFIS structure. We find that the new interface defects caused by radiation can reduce the electric field strength with the increasing total dose, which can significantly influence the irradiation properties of the HfAlO/SiO2/n-Si gate structure. These results provide the basis to applications for the HfO2-based devices in radiation working environment.

The construction of a heterostructure (HS) is an effective strategy to modulate the desired properties of two-dimensional (2D) materials and to extend their applications. In this paper, based on the density functional theory, we predict a metal-free type-II HS formed by h-BN and C2N single layers. The h-BN/C2N HS possesses a smaller bandgap than individual h-BN and C2N single layers, and it exhibits excellent visible light absorption. Importantly, its band edge positions satisfy the requirements for spontaneous water-splitting. With the assistance of the built-in electric field across the HS and the band offset, the photoinduced carriers can be readily spatially separated. Free energy calculations indicate the high catalytic activity for water oxidation and reduction reactions. The performance can be further enhanced by strain, which modulates the bandgap and the band edge positions of the HS. The band alignment may undergo a transition from type-I to type-II under strain, offering an effective switch for the reaction. The appropriate bandgap, suitable band edge positions, and effective carrier separation make the h-BN/C2N HS a promising candidate for use as a photocatalyst in water-splitting.

The metallic tortuous hollow ring array in the metallic film is proposed to enhance the modulation efficiency of the graphene based terahertz (THz) amplitude modulation. In the tortuous ring configuration, multimode resonant is excited to enhance the interaction between the THz wave and the graphene. With the change of the chemical potential of the graphene layer, the resonant frequencies are shift and the transmission peaks are tuned. It is enhanced more than 9 times for the amplitude modulation depth of the THz transmission and a maximum modulation efficiency of 74 dB/eV is obtained in the tortuous ring array based modulator. The enhancement of the modulation efficiency will decrease of the applied modulation voltage and will help to the energy saving and device lifetime prolonging.

In this work, we investigate the effect of cavity size on the change of the physical fields of diamond synthetic cavity and the mechanism of large cavity to improve the growth rate of the large single crystal diamond under high pressure and high temperature (HPHT) conditions. Finite element method (FEM) is used to simulate the temperature and convection field of the Φ15 and Φ10 cavity assemblies. Temperature simulation results indicate that the increase of cavity size leads to the increase of axial and radial temperature difference of catalyst. Convection simulation results show that the convection velocity and strength of the catalyst increases significantly with the increase of the cavity size. The increase of temperature difference and convection velocity and strength lead to the acceleration of crystal growth. The simulation results were perfectly validated by the synthetic experiments. This work not only elucidates the mechanism of large cavity to improve the growth rate, but also provides a theoretical reference for the application of the large-size cavity in the diamond synthetic industry.

We have studied the adsorption and decomposition of several poisonous gases (H2S, HCN and NH3) on metal (Li, Mg, Al, Ni and Pt) absorbed phosphorene by means of density functional theory. The results indicate Pt-decorated phosphorene has the strongest adsorption capacity for H2S due to the maximum adsorption energy of −1.101 eV in all possible structures of H2S on metal-decorated phosphorene. HCN and NH3 could be effectively captured by Al and Ni-decorated phosphorene with large adsorption energies of −2.166 and −1.284 eV, respectively. Considering the low price and more friendly environment of Al light metal, the strong adsorption ability of HCN shows that Al-decorated phosphorene is very promising to remove toxic gases. The energy barrier of the first dehydrogenation for poisonous gases on metal decorated phosphorene is relatively low, which shows the dissociation process is favorable, while the second dehydrogenation has a higher energy barrier, suggesting the decomposition process is difficult to occur.

We have calculated and discussed the electronic and optical properties of two-dimensional (2D) CdS/g-C6N6 heterostructures by using hybrid density functional of HSE06. The CdS and g-C6N6 can form CdS/g-C6N6 heterostructures through weak van der Waals (vdW) interactions. The CdS/g-C6N6 composites are indirect bandgap semiconductors and type-II heterostructures. The visible light absorbtion of CdS/g-C6N6 composites is obviously improved, and the band alignment is beneficial for spontaneous water redox reactions. Furthermore, the electrons migrating from CdS layer to g-C6N6 leads to the built-in electric field formation, which promotes the effective separation of photogenerated carriers. These factors imply CdS/g-C6N6 composites are promising visible light water-splitting photocatalysts.

Sodium ion batteries (SIBs) have achieved much attention and actively developed. Among possible anode materials of SIBs, nanosized metallic antimony is one of the most promising ones. However, the large volume changes of Sb and insufficient cyclability still remain a huge challenge for the large-scale applications. Herein, the effect of different Sb contents (named as C@Sb, C@Sb-L and C@Sb-H) on electrode performance, morphology, stability, and sodium storage mechanism has been systematically evaluated for the first time by a feasible electrospinning technique. As a result, the as-prepared C@Sb nanofibers exhibit excellent sodium storage performance with high-rate performance of 272.1 mAh g−1 at 20 A g−1, large reversible discharge capacity of 437.6 mAh g−1 after 300 cycles at 1 A g−1 and ultralong cycling life of 4000 cycles at 5 A g−1, such a cycling performance and high-rate capability for the C@Sb anode has rarely been reported. The significantly enhanced performance is ascribed to the synergetic effects between the well-dispersed ultrafine Sb nanoparticles and the N-rich 3D conductive carbon network structure. This homogeneously dispersed structure of ultrafine Sb nanoparticles encapsulated in the carbon network can dramatically improve the volume change and particle aggregation of Sb during ultralong charge/discharge process, thus solving the major problems of pulverization, loss of electrical contact and low utilization rate facing Sb anode. In addition, the full cell of Na3V2(PO4)3@C//C@Sb shows a high output potential of about 2.75 V and a discharge capacity of 264.3 mAh g−1 after 500 cycles at 1 A g−1. Those promising results should provide the basis for the potential large-scale application of Sb-based materials as high-performance anode for SIBs.

Using hybrid density functionals, we study the interfacial interactions and electronic properties of ZnO/AlN composites with the consideration of rotation angles and biaxial strains in order to enhance the photocatalytic performance for water-splitting. The different rotated composites, and -2% strained, original, and 2% strained ZnO/AlN composites can be easily prepared owing to the negative interface formation energies. The bandgaps and band alignments of ZnO/AlN composites can be significantly tuned by biaxial strains. Particularly, the appropriate bandgap for visible light absorption, proper band alignment for spontaneous water-splitting, and the formed electric field promoting photoinduced carrier separation make the 2% strained ZnO/AlN composite a potential candidate for photocatalytic water-splitting. This work shines some light on designing two dimensional heterostructured photocatalysts.

A computational study with the B3LYP density functional is carried out to explore the effects of additives (HOTf vs. HOTs) on the Cu(OTf)2-catalyzed synthesis of 4-quinolones. The optimal reaction path includes intermolecular nucleophilic addition (Step I), a H+-transfer process (Step II), intramolecular nucleophilic cyclization (Step III) and the elimination/formation process of MeOH (Step IV). The usage of Cu(OTf)2 as the catalyst significantly promotes Step I and Step III. More importantly, the additive HOTf can not only play the role of the proton-transfer shuttle to assist H+-shift by the stepwise proton-transport process in Step II and Step IV, but also can act as the hydrogen-bond donor to facilitate the intramolecular cyclization between C1 and C5 in Step III. Due to the assistance of HOTf, the rate-determining free energy barrier of the Cu(II)-catalyzed reaction is greatly reduced from 167.8 to 135.0 kJ mol−1, which explains the experimental phenomena well (0% vs. 89% in yield). Interestingly, the hydrogen-bond donor/proton-donor ability of the additives (HOTf vs. HOTs) is found to be the primary factor that critically affects the catalytic activity of the additives in the present Cu(II)-catalyzed reactions. For the additives of sulfonic acid type HO3S-R (R: –CF3vs. –PhCH3), the use of a strong electron-withdrawing group –CF3 is advantageous for the additive-assisted reactions. In a word, the present study is expected to help one understand the influence of additives on transition metal-catalyzed reactions including the ring-closed process and the proton-transfer process.

A computational study with the M06-2X/B3LYP density functional is carried out to explore the effects of NH4OAc on the Cu(I)-catalyzed heterocyclization of α-acyl-α-alkynyl ketene dithioacetals to form 3-cyanofurans. The calculations suggest the following. (a) The use of CuBr as the catalyst decreases significantly the free energy barriers of intramolecular cyclization and intermolecular addition. (b) NH4OAc can be decomposed into NH3 and HOAc. NH3 as the proton shuttle is critical in the stepwise H+-transport process because it can greatly reduce the rate-determining free energy barrier of whole Cu(I)-catalyzed reactions (from 251.1 to 130.1 kJ mol−1). (c) HOAc also plays a role similar to that of NH3 in the H+-transport reactions. These studies are expected to improve our understanding of transition-metal-catalyzed reactions and provide guidance for the future design of new catalysts and new reactions.

As outstanding light harvesters, solution-processable organic–inorganic hybrid perovskites (OIHPs) have been drawing considerable attention thanks to their higher power conversion efficiency (PCE) and cost-effective synthesis relative to other photovoltaic materials. Nevertheless, their further development is severely hindered by the drawbacks of poor stability and rapid degradation in particular. First-principles calculations based on density functional theory (DFT) are hence performed towards the perovskite compounds MA1−αFAαPbI3−βXβ (X = Cl, Br), with the aim of exploring more efficient and stable OIHPs. In addition to that, a hybrid density functional is adopted for exact electronic properties, and their band structures indicate that the doped series are all direct band-gap semiconductors. Moreover, the defect formation energies indicate that the stability of perovskite compounds can be significantly enhanced via ion doping. Meanwhile, it is unveiled that the optical performance of the doped perovskite series is also effectively improved through ion doping. Therefore, the investigated perovskite compounds MA1−αFAαPbI3−βXβ (X = Cl, Br) are promising candidates for enhancing solar-energy conversion efficiency. Our results pave a way in deeper understanding of the inherent characteristics of OIHPs, which is useful for designing new-type perovskite-based photovoltaic devices.

The electronic structures of two dimensional (2D) CdS/ZnO heterostructure (CdZnHT) consisting of CdS singlelayer (SL) and ZnO SL are explored based on hybrid density functional calculation. The negative interface formation energies suggest the formation of CdZnHT is exothermic. The bandgap of CdZnHT is favorable for absorbing visible light, and the decent band edge position makes it thermodynamically feasible for spontaneous generation of oxygen and hydrogen. The formed electric field across the interface induced by charge transfer will reduce photogenerated carrier recombination and promote carrier migration. Particularly, CdZnHT is a type-II heterostructure. Oxygen generation takes place at ZnO layer and hydrogen production occurs at CdS layer, which will also promote the effective separation and migration of phogogenerated carriers and enhance photocatalytic performance. These findings suggest that 2D CdZnHTs are possible candidates as water-splitting photocatalysts.

First principles calculation based on density functional theory has been applied to systematically study the electronic structure, especially band gap of recently synthesized periodic porous structure, graphene nanomesh, as well as its analogous system BN nanomesh. These porous structures possess various band gaps due to two parameters: neck length and width. The modulation of these parameters can be achieved through different etching templates in experiments. Two mechanisms, plane and nanoribbon, are proposed to understand the band gap variation with respect to neck length and width, qualitatively. We also examine electronic frontier states around Fermi level. Especially, armchair necked BN nanomesh has separated highest occupied and lowest unoccupied states in real space, which also makes it be reactive at different site. The hydrogen storage potentials based on transition metal atoms such as Sc trapped in anionic decorated pores are also been explored. No clustering problem is found and one Sc can adsorb four H 2 molecules with binding energy per H 2 of 0.13 eV.

It still remains a great challenge to develop a high-performance anode for sodium ion batteries. In this work, carbon-coated CoP3(CoP3@C) nanocomposites have been obtained by a high energy mechanical milling and used as an anode of sodium ion battery for the first time, showing a larger discharge capacity, longer cycling life and better rate capability as compared to plain CoP3. The superior performance is not only originated from significantly enhanced diffusion kinetics associating with the improvement of electron conductivity and volume change based on the presence of carbon layer, but also attributed to the partially pseudocapacitive behaviors of the redox reaction to construct a rapid electron transport pathway. In addition, the XRD and TEM analysis reveal that the Na-storage mechanism of the CoP3@C anode involves a conversion reaction from CoP3 to Na3P and metallic Co at the initial discharge and charge state. This study also provides a significant strategy to design special hybrid materials with excellent sodium storage capability for meeting the demand of large-scale energy storage systems.

Two-dimensional (2D) gallium sulfide (GaS), hexagonal boron nitride (h-BN) and graphitic carbon nitride (g-C3N4) have been fabricated and expected to be promising photocatalysts under ultraviolet irradiation. Here, we employ hybrid density functional calculations to explore the potential of the 2D GaS-based heterojunctions GaS/h-BN (g-C3N4) for the design of efficient water redox photocatalysts. Both heterostructures can be formed via van der Waals (vdW) interaction and are direct bandgap semiconductors, whose bandgaps are reduced comparing with isolated GaS, h-BN or g-C3N4 monolayers and whose bandedges straddle water redox potentials. Furthermore, the optical absorption of GaS/h-BN (g-C3N4) heterostructures is observably enhanced in the ultraviolet–visible (UV–vis) light range. The electron–hole pairs in GaS/h-BN (g-C3N4) heterostructures are completely separated from different layers. In addition, the in-plane biaxial strain can effectively modulate the electronic properties of GaS/h-BN (g-C3N4) heterostructures. Thus the GaS/h-BN (g-C3N4) heterostructures are anticipated to be promising candidates for photocatalytic water splitting to produce hydrogen.

Hybrid density functional has been adopted to investigate the structural, electronic, and optical properties of ZnO/MoS2 and ZnO/MoSe2 composites as compared with the results of ZnO, MoS2, and MoSe2 monolayers. The results indicate that MoS2 and MoSe2 monolayers could contact with monolayer ZnO to form ZnO/MoS2 and ZnO/MoSe2 heterostructures through van der Waals (vdW) interactions. The calculated bandgap of ZnO/MoS2 (ZnO/MoSe2) is narrower than that of ZnO or MoS2 (MoSe2) monolayers, facilitating the shift of light absorption edges of the composites towards visible light in comparison with bare ZnO and MoX2 monolayers. Through the application of strain, the ZnO/MoS2 and ZnO/MoSe2 composites which own suitable bandgaps, band edge positions, efficient charge separation, and good visible light absorption will be promising for visible light photocatalytic water splitting. These results provide a route for design and development of efficient ZnO/MoS2 and ZnO/MoSe2 photocatalysts for water splitting.

The monolayer InSe has drawn extensive attention since it was firstly fabricated by exfoliation and encapsulation in 2017. In the paper the g-C6N6/InSe heterostructure is designed to achieve high-performance photocatalytic application, and it is unveiled that the g-C6N6/InSe is a typical type-II heterstructure. There is significant charge transferred from the g-C6N6 to the InSe in the heterostructure, which is demonstrated by charge density difference and Bader charge analysis. Moreover, the built-in electric field exists between the InSe layer and the g-C6N6 layer, which is favorable for the effective separation of photogenerated electron-hole pairs. In the meanwhile the binding energy shows that the g-C6N6/InSe is a van der Waals heterostructure, and the band gap for that can be effectively tuned by interfacial strain. In addition, it is manifested that absorption coefficient for the g-C6N6/InSe heterostructure in the visible-light range is enhanced remarkably as compared with individual InSe layer, which implies that constructing heterostructure is an effective way to improve optical performance. Furthermore, elementary reactions are also discussed in detail to evaluate photocatalytic activity. These results pave a path to deepen the understanding of the InSe-based heterostructure, which is useful to design and synthesize new water-splitting photocatalysts applied in the visible-light range.

Constructing tubular graphitic carbon nitride homojunctions is an attractive endeavor to accelerate the dissociation of its Frenkel excitons and charge transfer dynamics, but the realization of this strategy remains a major challenge. Herein, carbon nitride homojunction with open tubular interior, porosity and interconnected feature has been developed via one-step pyrolyzing urea and l -cysteine. The experimental results and DFT calculations indicate that such unique tubular S-scheme homojunctions not only apparently boost in-plane exciton dissolution and suppress the inversive charge recombination via built-in electric field, but also decrease Gibbs free energy of intermediate hydrogen absorption. Thus, the tubular carbon nitride homojunctions display an excellent hydrogen production (4548.4 μmol/g/h), which is 35-fold improvement than that of pristine carbon nitride, outperforming the most reported donor-acceptor-based carbon nitride homojunctions and tubular carbon nitride. This work provides useful guidance to rational fabrication of S-scheme carbon nitride homojunction with positive exciton splitting and interfacial charge transfer for energy and environmental applications.

Using first-principles calculations, the hydrogen storage capacity of bimetal alloy nanostructures has been carried out. We select two stable structures, Al 10 Li 8 and Al 13 Li 20 , as paradigms, where Li atoms are exposed and unsaturated on the surfaces of Al clusters. The advantages of these structures are: (1) Li atoms do not cluster on the surfaces of Al nanoclusters. (2) Al 10 and Al 13 are much lighter than previous studied systems C 60 and C 48 B 12 . (3) Both Al 10 Li 8 and Al 13 are very stable magic clusters. We show that in these two systems each exposed Li atom is able to bind one H 2 molecule. The average binding energies are 0.10 and 0.13 eV/H 2 , with gravimetric densities of 4.1 wt% and 7.5 wt%, respectively, nearly meet and exceed the requirement of 5.5 wt% set by DOE.

The graphene-like ZnO (g-ZnO) nanosheets were synthesized and shown to exhibit highly photocatalytic activity for the degradation of RhB under ultraviolet irradiation. In this work, we utilize cationic–anionic passivated codoping to explore the potential of the g-ZnO nanosheet for the design of efficient water redox photocatalysts by employing density functional theory calculations with the hybrid HSE06 functional. Our calculations show that anion–cation passivated codoped systems not only are more favorable than the corresponding monodoping in the g-ZnO nanosheet due to the Coulomb interactions but also effectively reduce the band gap without introducing unoccupied states which accelerate the electron–hole recombination. The charge-compensated P–Sc and C–Zr codoped g-ZnO nanosheets are energetically favorable for hydrogen evolution but not insufficient to produce oxygen, indicating that they could serve as Z-scheme photocatalysts. The C–Ti, N–Y, and P–Y codoped systems may be potential potocatalysts for ...

Using first-principles calculations, we have explored the magnetic properties of zigzag edge graphene nanoribbons (ZGNR) with planar tetrahedral coordinated carbon (ptC) or silicon (ptSi). It is observed that the ptC can convert antiferromagnetic-coupled ZGNR into ferromagnetic one, while the ptSi cannot. These contrast results can attribute to the differences between magnetic ptC and non-magnetic ptSi atoms. Moreover, both ZGNR-ptC and ZGNR-ptSi structures are metallic and stable. Thus, the unique magnetic properties and high stabilities of these systems strongly suggest the feasibility of designing novel ferromagnetic devices.

Density functional theory is employed to investigate the adsorption and dissociation of several acidic gases (CO 2 , NO 2 and SO 2 ) on metal (Li, Al, Ni and Pt) decorated phosphorene. The results show that light metal (Li, Al) decorated phosphorene exhibits a strong adsorption of acidic gases, i.e., the adsorption energy of CO 2 on Li decorated phosphorene is 0.376 eV which is the largest in all adsorption of CO 2 on metal decorated phosphorene and Al decorated phosphorene is most effective for capture of NO 2 and SO 2 due to large adsorption energies of 3.951 and 3.608 eV, respectively. Moreover, Li and Al light metals have stronger economic effectiveness and more friendly environment compared with the transition metals, the strong adsorption ability of acidic gases and low price suggest that Li, Al decorated phosphorene may be useful and promising for collection and filtration of exhaust gases. The reaction energy barriers of acidic gases dissociated process on Pt decorated phosphorene are relatively low and the reaction processes are significantly exothermic, indicating that the dissociation process is favorable.

The charge-compensated N–F co-doping in combination with N or F mono-doping has been adopted to reduce the band-gap of KNbO $$_{3}$$ so as to improve its photocatalytic efficiency under visible light for hydrogen generation by water splitting. The relative positions of N–F co-doping into O-sites of KNbO $$_{3}$$ are considered to simulate the samples prepared by different experimental techniques. It is energetically unfavorable to form N mono-doped KNbO $$_{3}$$ under any conditions, and the presence of F favors the N doping into KNbO $$_{3}$$ . Although N doping reduces the effective band-gap, the localized states above the Fermi level and the presence of charge-compensated oxygen defect will accelerate the electron-hole recombination and thus reduce photocatalytic efficiency, while F doping hardly affects the band-gap. The defect introduced by N doping has been completely passivated in the N–F co-doped system. All the N–F co-doped configurations considered here have suitable band-gaps to absorb visible light with respect to the water redox level. Even the N–F co-doped system with lower dopant concentration harvests obviously longer wavelength of visible light as compared to the pure system.

As a new type of promising photovoltaic material, organic–inorganic hybrid perovskites (OIHPs) have attracted particular attention owing to their rapid increase in power conversion efficiency (PCE). It is quite remarkable that within several years PCEs have speedily exceeded the value of 20% from the original 3.8% in 2009. Nevertheless, the existence of heavy metal lead in the prototype perovskite MAPbI3 poses a great threat to human health and the living environment. To explore potential alternatives, we choose the congener elements of Ge and Sn as partial substituents for lead. By virtue of density functional theory calculations, the electronic structures and optical properties of Ge/Sn-doped perovskite compounds have been investigated involving GGA-PBE and DFT-SOC levels. The simulations indicate that the optical absorption coefficient is significantly enhanced due to the use of Ge/Sn dopants. Moreover, it is revealed that the absorption spectra shift towards the near infrared and even the middle infrared, and meanwhile, the band gap can be tuned by means of the Ge/Sn doping. Additionally, optical property analyses imply that the effect of spin–orbit coupling (SOC) plays a positive role for the application of OIHP materials in the photovoltaic field. These results shed a new light on a deep understanding of the nature of a range of functional materials constituted of OIHPs.

In this work, we employ hybrid density functional theory calculations to design a two-dimensional layered CdS/C2N heterostructure for visible light photocatalytic water splitting to produce hydrogen. The calculation results show that the conduction band minimum (CBM) and the valence band maximum (VBM) of C2N monolayers are lower than those of CdS nanosheets by about 0.76 eV and 0.44 eV, respectively. The type-II band alignment, density of states, Bader charge analysis, and charge density difference of the CdS/C2N heterostructure indicate that the photogenerated electrons migrate from the CdS monolayer to the C2N monolayer, favoring the separation and transfer of photogenerated charge carriers, which restrains the recombination of photogenerated carriers and enhances the photocatalytic efficiency. The calculated band gap and optical absorption spectra reveal that the two-dimensional layered CdS/C2N heterostructure may be a potential photocatalyst for photo-electrochemical water splitting because of its appropriate band gap and excellent visible light absorption behavior. Moreover, the electronic and optical properties of the CdS/C2N heterostructure can be effectively modulated by the strain. These findings suggest that the C2N sheets are a promising candidate as metal-free co-catalysts for CdS photocatalysts, and also provide valuable information for experimentalists to design highly active and efficient visible light photocatalysts for water splitting.

Bi3.15Nd0.85Ti2.99Mn0.01O12 (BNTM) thin films with (200)-orientations, (117)-orientations, and mixed-orientations were prepared by sol-gel methods. The influence of orientations on polarization fatigue behaviors of BNTM thin films were systematically investigated at both low and elevated temperatures. It was found that the changed trends of the polarization fatigue of (200)-oriented and (117)-oriented BNTM thin films at elevated temperatures were opposite. The fatigue properties become exacerbated for the (200)-oriented ones and become improved for the (117)-oriented ones, while the reduction of remanent polarization first decreases and then increases for the mixed-oriented ones. It can be assumed that the different roles played by domain walls and interface layer with increasing T in these thin films have caused such differences, which was certified by the lower activation energies (0.12–0.13 eV) of (200)-oriented BNTM thin films compared to those of BNTM thin films (0.17–0.31 eV) with other orientations through the temperature-dependent impedance spectra analysis. With the aid of piezoresponse force microscopy (PFM), the non-neutral tail-to-tail or head-to-head polarization configurations with greater probabilities for (117)-oriented and mixed-oriented thin films were found, while a majority of the neutral head-to-tail polarization configurations can be observed for (200)-oriented ones.

Shuttle effect of lithium polysulfide (LiPS) and slow sulfur redox kinetics have seriously impeded the commercial application of lithium-sulfur (Li-S) batteries. Here, to solve these issues, a synergistic engineering strategy is proposed to rationally fabricate porous core–shell Co@CoO1-x nanosheets array grown on carbon cloth (CC/Co@CoO1-x) as a sulfur host. The porous two-dimensional (2D) nanosheets array structure endows CoO1-x shells with highly exposed active sites, leading to strong LiPS adsorption ability. Besides, abundant oxygen vacancies (OVs) enhance the electrical conductivities of CoO1-x shells and facilitate the breakage of the S-S bond in adsorbed LiPS. Furthermore, the underneath metallic Co cores with few grain boundaries coupled with CC form integrated and continuous conductive networks, which achieves fast electron transfer from CC to CoO1-x surfaces to accelerate the immobilized LiPS conversion. Due to the synergistic effect of sulfophilic CoO1-x shells and conductive Co cores, the CC/Co@CoO1-x host enables a high-performance Li-S battery with excellent performance even at a high sulfur loading of 5.1 mg cm−2. This work highlights the effectiveness of combination 2D core–shell heterostructure with OVs to inhibit shuttle effect of LiPS and meanwhile boost sulfur conversion, which can guide the future design of high-performance sulfur hosts.

In this theoretical study, the double-hole-mediated codoping strategy has been adopted to improve the photocatalytic activity of cubic KNbO3 as compared with the corresponding individual doping. The strong double-hole-mediated dopant–dopant coupling significantly reduces the effective bandgaps for the anionic–anionic (N–N, P–P, N–P, C–S) codoped systems with removing the appearing acceptor states above the Fermi level. No dopant–O coupling occurs in the cationic–anionic (V–C, Ti–P, Ti–N, Zr–P, Zr–N, Sc–S, Y–S) codoped systems. The V–C and Ti–P codoping could lead to narrowed bandgaps without unfilled localized states appearing above the Fermi level. N, Ti, Zr, Sc, Y monodoping and Ti–N, Zr–P, Zr–N, Sc–S, Y–S codoping introduce unoccupied impurity states between the valence band maximum and conduction band minimum, which makes them unfavorable for photocatalysis as these impurity states may serve as electron–hole recombination centers. For P–P, N–P, and C–S codoped systems, the intermediate states are high...

Interface characteristics of Co2MnSi/Ag/Co2MnSi trilayer have been investigated by means of first-principles. The most likely interface is formed by connecting MnSi-termination to the bridge site between two Ag atoms. As annealed at high temperature, the formation of interface DO3 disorder is most energetically favorable. The spin polarization is reduced by both the interface itself and interface disorder due to the interface state occurs in the minority-spin gap. As a result, the magneto-resistance ratio has a sharp drop based on the estimation of a simplified modeling.

Monodoping with Mo, Cr, and N atoms, and codoping with Mo-N and Cr-N atom pairs, are utilized to adjust the band structure of NaNbO3 , so that NaNbO3 can effectively make use of visible light for the photocatalytic decomposition of water into hydrogen and oxygen, as determined by using the hybrid density functional. Codoping is energetically favorable compared with the corresponding monodoping, due to strong Coulombic interactions between the dopants and other atoms, and the effective band gap and stability for codoped systems increase with decreasing dopant concentration and the distance between dopants. The molybdenum, chromium, and nitrogen monodoped systems, as well as chromium-nitrogen codoped systems, are unsuitable for the photocatalytic decomposition of water by using visible light, because defects introduced by monodoping or the presence of unoccupied states above the Fermi level, which promotes electron-hole recombination processes, suppress their photocatalytic performance. The Mo-N codoped NaNbO3 sample is a promising photocatalyst for the decomposition of water by using visible light because Mo-N codoping can reduce the band gap to a suitable value with respect to the water redox level without introducing unoccupied states.

The dehydrogenation of pristine and defective h-BN sheets-supported ammonia borane (AB) systems is investigated by the first-principles method. The results show that nitrogen or boron atoms at the edges of vacancies are used as hydrogen acceptors which plays a crucial role in the process of dehydrogenation between the defective h-BN sheets and AB. The energy barriers to the transfer of hydrogen from AB to the defective h-BN sheets are low and the processes are significantly exothermic, indicating that these reactions are thermodynamically favorable. The hydrogenated defective h-BN sheets (protonic and hydridic hydrogens transfer from AB to the defective h-BN sheets) further react with AB to release H2 with low reaction barriers. Our theoretical study demonstrates that the defective h-BN sheets can be the effective metal-free catalysts. Furthermore, the potential advantage of such dehydrogenation process is the fact that no other elements are being introduced into the system.

The BiOX/BiOY (X, Y = F, Cl, Br, I, X ≠ Y) systems have been investigated as possible visible light photocatalysts in contrast with the BiOX (X = F, Cl, Br, I) systems by using hybrid density functional calculations. All the BiOX/BiOY systems have indirect bandgaps, and all the bandgaps of BiOX/BiOY systems we considered are between the bandgaps of BiOX and BiOY systems. The calculated bandgaps for BiOF/BiOCl, BiOF/BiOBr, BiOF/BiOI, BiOCl/BiOBr, BiOCl/BiOI, and BiOBr/BiOI are respectively 3.86, 3.41, 2.74, 2.99, 2.30, and 2.23 eV. The maximum absorption wavelength increases in the order of BiOF, BiOF/BiOCl, BiOCl, BiOF/BiOBr, BiOCl/BiOBr, BiOBr, BiOF/BiOI, BiOCl/BiOI, BiOBr/BiOI, and BiOI. The conduction band edges for all the BiOX/BiOY systems originate from Bi 6p states, but the valance band edges are contributed by different electronic states. Besides, the relative positions of X p states and Y p states for BiOX/BiOY systems are different, which should be attributed to the different p orbital energies of X and Y atoms. Due to the conduction band maximum is lower than the hydrogen reduction potential, all the BiOX and BiOX/BiOY systems are thermodynamically unfavorable for hydrogen production. Meanwhile, owing to the suitable bandgaps and band edge positions, the BiOF/BiOI, BiOCl/BiOBr, BiOCl/BiOI, and BiOBr/BiOI superlattices are possible visible light photocatalysts for degradation of organic pollutants.

The geometric structures, adsorption energies and energy barriers are determined to comprehend XO 2 (X = C, N, S) gases adsorption and dissociation on pristine and defective graphene supported Pt13 using density functional theory. The pristine graphene supported Pt13 has stronger adsorption capacity for XO 2 gases compared with that of XO 2 on defective graphene supported Pt13. It is more morphological changes of Pt13 and more electron transfer between XO 2 and Pt13 that lead to the stronger adsorption of XO 2 on pristine graphene supported Pt13. The energy barriers of XO 2 on pristine graphene supported Pt13 are also smaller than that of XO 2 on defective graphene supported Pt13, which indicates that the dissociation of XO 2 on pristine graphene supported Pt13 is more likely to occur.

Restacking diverse two dimensional (2D) nanosheets into a bilayer van der Waals (vdW) heterojunction opens up a promising platform for designing high performance photocatalyst. In this work, by employing HSE06 hybrid functional, we have systematically studied the electronic and optical properties of GaSe/g-C3N4 bilayer heterojunction, whose different layers with a interlayer spacing of 3.49 A at equilibrium are bound together through the vdW interaction. Our computations indicate that the GaSe/g-C3N4 heterostructure, whose bandedge positions can stride over the redox levels of water and bandgap is much smaller than that of GaSe monolayer, is suitable for photocatalytic water splitting. By applying strains in the range from 6% pressure to 6% tension, these bandgaps of GaSe/g-C3N4 heterojunction can be narrowed to the range of 1.70–2.84 eV. Particularly, GaSe/g-C3N4 heterojunction with 6% tension, whose conduction band minimum (CBM) and valence band maximum (VBM) are situated at different slabs, can realize the efficient separation of electron–hole pairs. Meanwhile, GaSe/g-C3N4 heterojunction with 6% tension, whose bandgap decreases to 2.31 eV, can make the utmost of the sunlight. In contrast with GaSe and g-C3N4 monolayers, the distinct red shifts of optical absorption appear in GaSe/g-C3N4 heterojunctions with 6% tension, which results in the narrowing of the bandgaps. Even in the VIS region about 460 nm, there is an absorption peak in the optical absorption spectrum of GaSe/g-C3N4 heterojunctions with 6% tension. Therefore, GaSe/g-C3N4 heterojunctions should have promising applications as photocatalysts for water decomposition to generate hydrogen.

Density functional theory (DFT) and the bond order-length-strength mechanism are used to investigate the electronic, bonding, and magnetic behaviours of Sc atoms adsorbed on the surface of lithium (Li) (1 1 0). The results indicate that Sc atoms form two-dimensional (2D) geometric structures including larger decagon, trapezoid decagon, decagon, octagon, and quadrangle structures on the Li (1 1 0) surface. The total magnetic moments of these structures are respectively 4.75, 1.84, 3.44, 3.32, and −0.427 μB. Further, the residual spin spectrum (RSS) correlation clearly indicates that the quadrangle structure has anti-ferromagnetic property; this finding should open up a new study direction for the design of novel 2D magnetic materials.

Engineering suitable tin selenide (SnSe) anode for sodium ion batteries (SIBs) with both excellent cycling durability and remarkable rate capability has received enormous attention. The effective regulation of morphology and size has been shown to promote electrochemical performance. The irregular shape and micron size of obtained SnSe by conventional construction methods (high energy ball milling) is detrimental to the anode performance. Herein, SnSe quantum-dots (E-SnSe) and SnSe nanoparticles (B-SnSe) are synthesized by means of a feasible electrospinning technique together with subsequent high-temperature selenylation and high energy ball milling, respectively, and both are examined as anode materials for SIBs. As compared to B-SnSe electrode, the E-SnSe electrode delivers a larger discharge capacity of 268 mAh g−1 after 750 cycles at 2 A g−1 and more remarkable cycling durability over 1500 cycles even at much higher rate of 5 A g−1, which is the best cycling stability reported so far for SnSe-based anodes. The significantly enhanced performance is attributed to unique three-dimensional (3D) conductive carbon network structure of E-SnSe, which could boost rapid electron/sodium ion transport with the remarkable contribution of pseudocapacitance and dramatically improve the structure evolution of SnSe resulted from the conversion and alloying process. Furthermore, the assembled Na3V2(PO4)3@C//E-SnSe full cell shows an output voltage of above 2.0 V, ultralong cycle life of 1500 cycles with a high reversible discharge capacity of about 100 mAh g−1 at 1 A g−1 and superior rate capability with 86.4% capacity retention after 35 cycles, showing the potential application prospects in a large scale energy storage field.

In this work, graphene-like ZnO (g-ZnO)-based two-dimensional (2D) heterostructures (ZnO/WS₂ and ZnO/WSe₂) were designed as water-splitting photocatalysts based on the hybrid density functional. The dependence of photocatalytic properties on the rotation angles and biaxial strains were investigated. The bandgaps of ZnO/WS₂ and ZnO/WSe₂ are not obviously affected by rotation angles but by strains. The ZnO/WS₂ heterostructures with appropriate rotation angles and strains are promising visible water-splitting photocatalysts due to their appropriate bandgap for visible absorption, proper band edge alignment, and effective separation of carriers, while the water oxygen process of the ZnO/WSe₂ heterostructures is limited by their band edge positions. The findings pave the way to efficient g-ZnO-based 2D visible water-splitting materials.

In this study, a pulp beating machine was used to premix the pulp fibers with high density polyethylene (HDPE) particles in water. The wet or pre-dried pulp fiber/HDPE mixture was then melt-compounded by a twin screw extruder. For further improving the dispersion of pulp fiber, some mixture was forced to pass through the twin-screw extruder twice. The resulting mixture was compression molded to the composite. The fiber distribution was observed by the aid of an optic and scanning electron microscope. The mechanical and rheological properties and creep resistance of the composites were characterized. Test results demonstrate that when the wet pulp fiber/HDPE mixture was subjected to pre-pressing and oven drying prior to extrusion compounding, the resulting composites exhibited homogeneous fiber distribution, superior flexural property, creep-resistance, and high storage modulus. Particularly, its flexural strength and modulus were 57% and 222% higher, respectively, than that of the neat HDPE, while the composites prepared without pre-dried were 19% and 100% higher, respectively. Drying the wet mixture in advance is more effective than re-passing through the extruder for improving the fiber dispersion and composite performance.

Photocatalytic water-splitting for hydrogen generation is a promising way to solve the energy crisis, yet the design of efficient photocatalysts is still a challenge. By utilization of first principles calculations, we predict the photocatalytic properties of monolayer boron phosphide (BP) based BP/XY2 (X = Mo, W; Y = S, Se) composites of different rotated configurations. Our results suggest that the BP/XY2 composites can be stably formed, and the narrowed bandgaps ensure these composites are suitable for absorbing visible light. The bandgaps and band edge positions are slightly affected by the rotation angles. The BP/MoS2, BP/MoSe2, and BP/WSe2 are type II heterostructures. Furthermore, the transferred charge from BP to XY2 layers leads to the formation of electric fields, which efficiently separate the photoinduced carriers. The band alignments of BP/MoS2, BP/MoS2, BP/MoSe2, and BP/WSe2 satisfy the requirements of overall water-splitting within the pH scope of 3.6-7.9, 6.8-7.9, 4.0-8.0, and 8.7-8.8. This work will provide valuable insight for designing efficient water-splitting photocatalysts.