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Low-overpotential layered hydroxides (LDHs) with high theoretical capacity are promising electrodes for supercapaterry and oxygen evolution reaction; however, the low electronic conductivity and insufficient active sites of bulk LDHs increase the internal resistance and reduce the capacity and oxygen-production efficiency of electrodes. Herein, we prepared a polyaniline-coated NiCo-layered double hydroxide intercalated with MoO42− (M-LDH@PANI) composite electrode using a two-step method. As the amount of MoO42− in the LDH increases, acicular microspheres steadily evolve into flaky microspheres with a high surface area, providing more active electrochemical sites. Moreover, the amorphous PANI coating of M-LDH boosts the electronic conductivity of the composite electrode. Accordingly, the M-LDH@PANI at an appropriate level of MoO42− exhibits significantly enhanced energy storage and catalytic performance. Experimental analyses and theoretical calculations reveal that a small amount of MoO42− is conducive to the expansion of LDH interlayer spacing, while an excessive amount of MoO42− combines with the H atoms of LDH, thus competing with OH−, resulting in reduced electrochemical performance. Moreover, M-LDH flaky microspheres can efficiently modulate deprotonation energy, greatly accelerating surface redox reactions. This study provides an explanation for an unconventional mechanism, and a method for the modification of LDH-based materials for anion intercalation.

The two-dimensional semiconductor photocatalytic material has excellent photocatalytic H2 evolution activity. In order to further improve the hydrogen production activity of g-C3N4, this study improved the preparation process of g-C3N4 and obtained a new photocatalyst (name H-CN) with a higher absorption range, larger specific surface area, and faster hydrogen production activity. Compared with the originally prepared g-C3N4, the H-CN absorption range has been improved, and the utilization of visible light has reached 650 nm. When the doping amount of Pt cocatalyst was 1.0 wt%, the H-CN demonstrates excellent photocatalytic hydrogen production activity, with a hydrogen production rate of 4.3 mmol h−1·g−1, which was 7.0 times higher than that pure 1.0 wt% Pt/g-C3N4. The fluorescence spectroscopy of H-CN showed better separation of carriers and longer lifetime. This study has guiding significance for the preparation of subsequent ultra-thin nanosheet photocatalysts and the establishment of high-efficiency photocatalytic systems.

Bi2WO6/Bi2MoO6 heterostructured photocatalys had been synthesized by a refluxing method. And the photocatalytic activity of Bi2WO6/Bi2MoO6 heterostructured photocatalysts was better than Bi2WO6. The enhancement in photocatalysis activity belonged to the match of energy level between the Bi2MoO6 and Bi2WO6. In order to further enhance the photocatalytic activity of Bi2WO6/Bi2MoO6, Bi2WO6/Bi2MoO6 was used to activate peroxymonosulfate to photodegradate methylene blue. The mechanism of activating peroxymonosulfate was proved by radical quenching experiment which revealed that sulfate radicals governed the removal of methylene blue.

An understanding of the high photocatalytic performance reported for MoS2/BiOI nanocomposite is far from satisfactory. Here, the interfacial interaction and electronic properties of a MoS2/BiOI heterostructure were investigated systematically for the first time by first-principle calculations incorporating a semi-empirical dispersion-correction scheme. Our results confirm the reasonable existence of van der Waals interactions and a favorable Z-scheme mechanism, based on the typical interfacial cohesive energy and the energy level lineup at the interface. Analyzing the charge density differences and work functions, the built-in electric field is formed along the direction from MoS2 to BiOI after the interface equilibrium, and facilitates the separation of photoinduced electron–hole pairs in the interface. Additionally, it can be inferred that the incorporation of MoS2 into BiOI increases the carrier mobility and improves light harvesting, in agreement with the previously reported experimental data. Our work provides an insight into the mechanism of the enhanced visible-light photocatalytic activity of a MoS2/BiOI heterostructure, and helps to design other new heterostructure combinations.

Herein, a wide-spectrum (∼678 nm) responsive Bi8(CrO4)O11 photocatalyst with a theoretical solar spectrum efficiency of 42.0% was successfully constructed. Bi8(CrO4)O11 showed highly efficient and stable photocatalytic water oxidation activity with a notable apparent quantum efficiency of 2.87% (420 nm), superior to many reported wide-spectrum driven photocatalysts. Most remarkably, its strong oxidation ability also enables the simultaneous degradation and complete mineralization for phenol, and its excellent performance is about 23.0 and 2.9 times higher than CdS and P25-TiO2, respectively. Its high activity is ascribed to the giant internal electric field induced by its large crystal dipole, which accelerates the rapid separation of photogenerated electron–hole pairs. Briefly, the discovery of wide-spectrum bismuth chromate and the mechanism of exponentially enhanced photocatalytic performance by increasing the crystal dipole throw light on improving solar energy conversion.

A two-dimensional (2D)/three-dimensional (3D) hybrid heterostructure has recently emerged as an effective method for improving photocatalytic efficiency. In this work, we perform a comprehensive first-principles study of the structural, electronic, and optical properties of a novel 3D-SiC/2D-MoS2 heterostructure. The calculation results reveal that the SiC(0001) surface/MoS2 monolayer-integrated heterostructure in Schottky contact with a new chemical bonding contributed to the surface adhesion and optoelectronic properties. Meanwhile, the valence and conduction band-edge positions of SiC and MoS2 changed with the Fermi level and formed a desired type-II band alignment, which greatly facilitate the rapid separation of photogenerated carriers. Moreover, the surface state of SiC(0001) can be removed when combined with MoS2, and their band gap is also reduced. Furthermore, Bader charge and charge density difference indicated that there is a remarkable separated distribution of electrons and holes at the inter...

Nitrogen reduction reactions (NRRs) under mild conditions retain an enormous challenge in effective N2 activation on metal-based catalysts. Here, by spin-polarized DFT calculations, we systematically investigated the potential of single transition-metal atoms (Sc to Zn, Nb to Cd, W, Pt and Au) supported on the experimentally available WS2 nanosheets with sulfur vacancies as catalysts for N2 fixation and conversion. The results confirm that the WS2 nanosheet with sulfur vacancies is a good platform for anchoring single transition-metal atoms. Based on proposed several criteria, it is found that the single Ni atoms anchored to sulfur vacancies possess outstanding catalytic activity of NRR. Here, the Ni-WS2 nanosheet acts as likely Lewis-acid system and accepts electrons from the N2*, which causes the weakening of N–N bond. Reaction energy diagrams of the NRRs show that the whole NRRs on Ni-WS2 surface prefer to occur along the alternating associative pathway, and form the ammonia without the requirement of energy input. Overall, our results reveal that the Ni-WS2 system is a quite promising single-atom catalyst with less energy-consuming and good stability for NRRs. These findings could motivate more experimental and theoretical researches to further explore the potential of single transition-metal atoms anchored to two-dimensional substrate materials for NRRs.

Understanding is far from satisfactory on the high photocatalytic performances of g-C3N4/WS2 nanocomposites which are experimentally reported. Here, we investigate systematically for the first time the interfacial interactions and electronic properties of triazine-based g-C3N4/WS2 nanocomposites by first-principles calculations. The results confirm the reasonable existence of vdW interaction and typical direct Z-scheme mechanism based on the prominent interfacial binding energies and the energy level lineup at interface. Both energy band structures and work functions show that the conduction and valence band edges of the g-C3N4 layer are more negative than those of the WS2 layer after their intimate contact, respectively. Meanwhile, the interfacial interaction makes WS2 with negative charges and g-C3N4 with positive charges, forming a built-in electric field from g-C3N4 to WS2. Thus, photogenerated e––h+ pairs are separated to different places with prolonged lifetime and high redox potential. This work shines some lights on a direct Z-scheme mechanism for the g-C3N4/WS2 heterostructured photocatalyst.

Controlling the p-type electrical transport behavior of nanoelectronic devices remains a grand challenge in reducing the Schottky barrier. To address this issue, we systematically investigate the effect of asymmetric Se doping on the interlayer interaction and electronic properties of a MoS2(1−x)Se2x/graphene heterostructure by first-principles calculations incorporating a semiempirical dispersion–correction scheme. The results show that the interfacial binding can be enhanced by Se doping inside the interface, while the effect of Se doping outside the interface is negligible on the interfacial binding. The type and height of the Schottky barrier can be tuned by changing the concentration and sites of the Se dopant at the interface. Further, it is found that by increasing the concentration of the Se dopant inside the interface the transition from an n-type Schottky barrier to a p-type can be realized, and a low p-type Schottky barrier is gained at the interface for highly efficient charge transfer. Lastly, it is confirmed that the redistribution of the interfacial charge leads to a shift of the Fermi level, and thus determines the type and height of the Schottky barrier. These conclusions provide rational evidence for the asymmetric doping concepts to design and fabricate MoS2-based field effect transistors.

The surface properties of BiPO4 exert a significant effect on the photocatalytic performance under ultraviolet irradiation, but they have not been well explored, either experimentally or theoretically. Herein, for the first time, we systematically studied the structures and energetics of four low-index stoichiometric surfaces of monazite BiPO4 using density functional theory. A new scheme is proposed to correct the surface energy and compare this with the average surface energy. Both of the two schemes for the surface energies indicate that the order of the surface energies is (100) < (010) < (011) < (001), which is not completely consistent with their surface dangling bond densities. The main reason is incomplete PO4 tetrahedrons, namely, the existence of dangling P–O bonds in the bare (001) plane. However, only dangling Bi–O bonds are found in the other three low-index surfaces. It is obvious that the dangling bond density of the Bi atoms and the intact PO4 tetrahedrons are two crucial factors in the surface stability. Correspondingly, the differences in the planar-averaged electron density and the work function are presented to describe the charge distribution close to the surface. Furthermore, the equilibrium morphology calculated using the Wulff construction suggests that the (001), (010), (011) and (100) facets account for 15%, 33%, 16% and 36%, respectively. The two low-energy (100) and (010) facets dominate in the Wulff shape and make up almost 69% of the total crystal shape area. This work will provide theoretical guidance for the further design of effective BiPO4-based photocatalysts.

In this work, we aimed to develop a novel method for the target preparation of multicomponent composites Au@CdS/g-C3N4 towards high visible light photocatalytic activity with the assistance of L-cysteine biomolecules. Through the interaction of L-cysteine biomolecules with Au nanoparticles and g-C3N4 bulks, CdS layer were in-situ precipitated on the surface of Au nanoparticles to form core-shell structure Au@CdS and Z-scheme structure Au@CdS-g-C3N4 with good interface bonding in composites. By taking advantage of this feature, the highest reaction rate constant of 8%Au@CdS/g-C3N4 for methyl orange dye and phenol degradation was 3.08- and 1.48-folds higher than pure g-C3N4 bulks, which was ascribed to the strong interaction between different substances for efficient charges transferring and separation as evidenced by the studies of X-ray photoelectron spectroscopy, steady-state and transient photoluminescence spectroscopy. This work highlights the utilization of biomolecules for the target preparation of composites and its application on environmental remediation.

Although g-C3N4/BiPO4 heterojunctions have shown high photocatalytic performance experimentally, understanding is far from satisfactory on the relevance of the interlayer interaction and energy levels at interface. Herein, the energy level alignment at g-C3N4/BiPO4 interface is systematically explored by first-principles calculations incorporating semiempirical dispersion-correction schemes. The results indicate that a stable interface with the chemical adsorption can be formed between g-C3N4 and BiPO4. Interestingly, a typical type-II band alignment at g-C3N4/BiPO4 interface is found based on the analysis of the energy band structures and work functions, where the valence and conduction band edges of the BiPO4 layer are higher than those of the g-C3N4 layer after the actual contact of BiPO4 and g-C3N4, respectively. Especially, both charge density difference and Mulliken population show that a built-in electric field is formed with the direction from g-C3N4 to BiPO4 after interfacial equilibrium, and fac...

Bi2WO6 nanosheets were synthesized by a hydrothermal method with H2WO4 for the first time. The band structure of Bi2WO6 was investigated on the basis of density functional theory calculations. Bi2WO6 photocatalysts showed photocatalytic activity for the degradation of methylene blue under visible light irradiation. Kinetic studies using radical scavenger technologies suggested that holes were the dominant photo-oxidants. After hybridization with C3N4, the photocatalytic activity of Bi2WO6 was obviously enhanced. The enhanced photocatalytic activity of the C3N4/Bi2WO6 photocatalysts could be attributed to the effective separation of photogenerated e-/h+ pairs. The photogenerated holes on the valence band of Bi2WO6 can transfer to the highest occupied molecular orbital of C3N4via the well-developed interface, causing a reduction in the probability of e-/h+ recombination; consequently, large numbers of photogenerated holes led to the enhancement of the photocatalytic activity.

Interfacial interactions and electronic properties of graphene/CH3NH3PbI3 heterojunctions were investigated by first-principles calculations incorporating semiempirical dispersion-correction scheme to describe van der Waals interactions. Two lattice match configurations between graphene and CH3NH3PbI3(0 0 1) slab were constructed in parallel contact and both of them were verified to form remarkable van der Waals heterojunctions with similar work functions. Our calculated energy band structures show that the Dirac-cone of graphene and the direct band gap of CH3NH3PbI3 are still preserved in the heterojunctions, thus graphene can be a promising candidate either as a capping or supporting layer for encapsulating CH3NH3PbI3 layer. It is identified that the Schottky barrier of graphene/CH3NH3PbI3 heterojunctions can be controlled by the interlayer distance and affected by the stacking pattern of graphene and CH3NH3PbI3. The 3D charge density differences present the build-in internal electric field from graphene to CH3NH3PbI3 after interface equilibrium and thus, a low n-type Schottky barrier is needed for high efficient charge transferring in the interface. The possible mechanism of the band edge modulations in the heterojunctions and corresponding photoinduced charge transfer processes are also described.

Bismuth vanadate (BiVO4)-based photocatalysts as a typical solar-water-splitting material have attracted much interest due to their moderate band gap, fine hole conductivity and good stability. In this work, we perform a comprehensive first-principles study of the structural, electronic and optical properties of a black phosphorus BP/BiVO4 heterostructure, which was realized with remarkable performance in pure water splitting in a very recent experiment. Firstly, the optoelectronic properties and charge transport between BP and BiVO4 are systematically elucidated. We find that the positions of the valence/conduction band edge of BP and BiVO4 change with the Fermi level and form a type-II heterostructure with a high optical absorption coefficient. Furthermore, the charge density difference and Bader charge analysis indicated that the internal electric field will facilitate the separation of e−/h+ pairs at the BP/BiVO4 interface and restrain the carrier recombination. Therefore, the present work provides insightful understanding of the physical mechanism and superior photocatalytic performance of this new synthesized system and offers instructions for fabricating superior BiVO4-based heterostructure photocatalysts.

The manipulation of the constituents of novel hetero-photocatalysts is an effective method for improving photocatalytic efficiency, but a theoretical understanding of the relationship between interlayer interaction and photocatalytic activity is still lacking. Herein, the interfacial interactions and electronic properties of MoS2/graphene oxide (GO) heterojunctions with various O concentrations were explored systematically by first-principles calculations. The results indicate that MoS2 and GO can form a stable van der Waals heterojunction, and enhance the built-in internal electric field from GO to the MoS2 surface with the increase in O concentration after interfacial equilibrium. It is inferred that the photogenerated electrons and holes naturally accumulate in the conduction band of GO and the valence band of MoS2, respectively, under the built-in internal electric field driving, indicating the formation of direct Z-scheme heterojunctions. In addition, a red shift of the light absorption edge and the shift up of the conduction band edge of MoS2/GO heterojunctions are observed with an increase in O concentration. It can be concluded that the O atom plays a crucial role in the energy band alignment of MoS2/GO heterojunctions for the improvement of photocatalytic performance. These results are beneficial to understand and design layered MoS2/GO photocatalytic systems or as cocatalysts with other semiconductors.

The photoelectrochemical properties of g-C3N4 sheet are modified by the π-π stacking interaction with graphene, and the corresponding role of graphene on the surface chemical reactions is investigated by density functional theory. The calculated cohesive energies and the lattice mismatch energies indicate that g-C3N4 and graphene are in parallel contact and can form a stable heterojunction. According to our calculated energy band structures and work functions of g-C3N4/graphene heterojunctions, the band edge modulations by graphene are discussed and corresponding photoinduced charge transfer processes are analyzed in detail. It is found that the incorporating of graphene into g-C3N4 facilitates the separation of photoinduced e–/h+ pairs and the oxidation capacity enhancement of the photoinduced holes with the downshifting of the valence band edge of g-C3N4 layer. It is identified that the inhomogeneous onsite energies between interlayer and the band edge modulations are induced by the inhomogeneous charge redistribution between interlayer caused by graphene. Further, the initial dynamic reaction processes of oxygen atoms in g-C3N4/graphene heterojunctions also confirm the significant role of graphene on the surface chemical reactions.

A reflux method to synthesize ultrathin polycrystalline TiO2(B) nanosheets (NSs) which are assembled by single crystals, and further stacked into nanoflower structures, is described. On the basis of the theoretical calculations and experiments, H2O2 can easily substitute the ethylene glycol adsorbed on the surface of TiO2(B) NSs, forming H2O2–NS due to the lower adsorption energy and the unique structural features of ultrathin TiO2(B) nanosheets. TiO2(B) NSs and the H2O2 system can be accelerated to generate superoxide radicals under heat or light and thus exhibit a great degradation property on dye molecules; the total organic carbon (TOC) removal rate was 6 times higher than that for H2O2 alone. Meanwhile, TiO2(B) NSs and the H2O2 system have a good application on the selective oxidation due to the reactive species of superoxide radicals avoiding overoxidization of benzyl alcohol. The conversion of benzyl alcohol oxidized to benzaldehyde in water solution under low temperature and atmospheric pressure w...

The interface properties of the hybrid graphene/BiVO4(001) heterojunction were investigated by first-principle calculations incorporating semiempirical dispersion-correction schemes to correctly describe van der Waals interactions. The results indicate that graphene and BiVO4 are in contact and form a stable heterojunction. After equilibration of the graphene/BiVO4 interface, their energy levels are adjusted with the shift of their Fermi levels based on calculated work functions. In addition, electrons in the upper valence band of BiVO4 can be excited to the conduction band under irradiation, and then arrive at the C pz orbital of graphene, in which the electrons cannot migrate back to BiVO4 and thus are trapped in graphene. Thus, substantial holes are accumulated in the BiVO4(001) surface, facilitating the separation of photogenerated e−/h+ pairs. The calculated charge density difference unravels that the charge redistribution drives the interlayer charge transfer from graphene to the BiVO4(001) surface. It is identified that the hybridization between the two components induces an increase of optical absorption of BiVO4 in the visible-light region. A deep understanding of the microcosmic mechanisms of interface interaction and charge transfer in this system would be helpful for fabricating BiVO4-based heterojunction photocatalysts.

The surface modification to inhibit charge recombination was utilized in dye-sensitized solar cells (DSSCs) and self-powered ultraviolet (UV) sensors based on SnO 2 hierarchical microspheres by TiO 2 modification. For DSSCs with SnO 2 photoelectrodes modified by TiO 2 , the power conversion efficiency (PCE) was improved from 1.40% to 4.15% under standard AM 1.5G illumination (100 mW/cm 2 ). The electrochemical impedance spectroscopy and open-circuit voltage decay measurements indicated that the charge recombination was effectively inhibited, resulting in long electron lifetime. For UV sensors with SnO 2 photoelectrodes modified by TiO 2 layer, the self-powered property was more obvious, and the sensitivity and response time were enhanced from 91 to 6229 and 0.15 s to 0.055 s, respectively. The surface modification can engineer the interface energy to inhibit charge recombination, which is a desirable approach to improve the performance of photoelectric nanodevice.

A ternary composite photocatalyst CdS/Au/g-C3N4 was synthesized by a facile two-step photoreduction method. In this hybrid structure, CdS nanoparticles and CdS@Au core–shell nanoparticles are homogeneously deposited on the surface of g-C3N4 to produce two different structures CdS–g-C3N4 and CdS@Au–g-C3N4. The microstructure analysis results of the composition, chemical states, and optical properties of as-prepared ternary hybrid reveal that a strong interaction exists between CdS nanoparticles, CdS@Au nanoparticles and the g-C3N4 bulk. The ternary composite CdS/Au/g-C3N4 exhibits significantly enhanced photocatalytic activity for RhB degradation under visible light irradiation compared with the binary composites CdS/g-C3N4, Au/g-C3N4 and pure g-C3N4. Meanwhile, CdS/Au/g-C3N4 also demonstrates good photostability in the recycling test of RhB degradation. The active species in the photocatalytic reaction over CdS/Au/g-C3N4 are detected as O2˙− and h+. The superior photocatalytic performance of CdS/Au/g-C3N4 should be attributed to the enhanced separation efficiency of photogenerated electrons–holes induced by the formed heterojunctions CdS–g-C3N4 and Z-scheme structure CdS@Au–g-C3N4 where Au nanoparticles serve as electrons mediator.

In this work, a special hybrid structure with 2D configuration comprising of g-C3N4, reduced graphene oxide (RGO), and BiOI (g-C3N4/BiOI/RGO) was rationally constructed and immobilized on Ni foam with RGO functioned as electron transfer mediator and binder. The immobilized 2D g-C3N4/BiOI/RGO hybrid structure exhibited the enhanced photocatalytic CO2 reduction to CO and the methyl orange (MO) degradation efficiency under visible light irradiation. Particularly, the hybrid heterojunction with a mass ratio 6% of BiOI to g-C3N4 displayed the highest CO yield and degradation rate constant for MO, which was 1.6 times and 3 times of g-C3N4/RGO binary heterojunction immobilized on Ni foam. The enhanced photocatalytic activity was ascribed to the rapid charge separation. More importantly, combined with the theoretical calculations on the work functions of g-C3N4, rGO and BiOI, the experimental results clarified the charges transfer route of g-C3N4/BiOI/RGO heterojunction conforming to the Z-scheme mechanism.

The hydrogen adsorption properties of Ti and Ni atoms as media on single-walled carbon nanotube (SWCNT) have been studied by density functional theory (DFT) incorporating a pragmatic method to correctly describe van der Waals interactions. The results show that both Ti and Ni atoms can reliably adhere to single-walled carbon nanotube, respectively, making strong TM[Formula: see text]C bonds. Meantime, it is found that the average adsorption energies of H2 by Ti and Ni atoms are decreased with the increase of the amount of H2 adsorption. Ti or Ni atoms can bind up to no more than six H2 molecules on a carbon nanotube. It is inferred that these transition metals (TMs) can adsorb molecular hydrogen through likely Kubas-type interaction. By comparing the interaction energies among TM and H atoms, it can be identified that the hydrogen adsorption properties of Ti atoms are superior to those of Ni atoms at certain conditions. The present investigation is useful in the wider development of carbon-based nanomaterials as potential high-capacity H2 storage media.