One-pot Synthesis of CdS Irregular Nanospheres Hybridized with Oxygen-Incorporated Defect-Rich MoS2 Ultrathin Nanosheets for Efficient Photocatalytic Hydrogen Evolution

2D Monolayer Catalysts: Towards Efficient Water Splitting and Green Hydrogen Production

A viable alternative to non-renewable hydrocarbon fuels is hydrogen gas, created using a safe, environmentally friendly process like water splitting. An important role in water-splitting applications is played by the development of two-dimensional (2D) layered transition metal chalcogenides (TMDCs), transition metal carbides (MXenes), graphene-derived 2D layered nanomaterials, phosphorene, and hexagonal boron nitride. Advanced synthesis methods and characterization instruments enabled an effective application for improved electrocatalytic water splitting and sustainable hydrogen production. Enhancing active sites, modifying the phase and electronic structure, adding conductive elements like transition metals, forming heterostructures, altering the defect state, etc., can improve the catalytic activity of 2D stacked hybrid monolayer nanomaterials. The majority of global research and development is focused on finding safer substitutes for petrochemical fuels, and this review summarizes recent advancements in the field of 2D monolayer nanomaterials in water splitting for industrial-scale green hydrogen production and fuel cell applications.

Photoelectrocatalytic hydrogen evolution reaction stimulated by the surface plasmon resonance effect of copper and silver surrounded with MoS2

Developing plasmonic metal-based photocatalysts can improve the photoelectrocatalytic hydrogen evolution reaction (HER) and overcome the limitations of semiconductor-based photocatalysts. A MoS2@Ag-Cu foam composite electrode was fabricated on a copper foam and employed for photoelectrocatalytic HER. The optical behavior and photoelectrocatalytic HER test results indicate that the surface plasmon resonance effect of copper and silver is the primary source of light absorption. Additionally, molybdenum sulfide was employed as a hot-electron trap to capture the energetic electrons generated from copper and silver, thereby promoting the hydrogen evolution reaction. Its binder-free electrode exhibits the better HER performance and excellent stability. Low-cost plasmonic metals, copper and silver, were used as the source of photocatalysis, providing a novel perspective for enhancing photoelectrocatalytic HER performance.

Synthesis of Phase Junction Cadmium Sulfide Photocatalyst under Sulfur-Rich Solution System for Efficient Photocatalytic Hydrogen Evolution

Photocatalyst with excellent semiconductor properties is the key point to realize the efficient photocatalytic hydrogen evolution (PHE). As a representative binary metal sulfide (BMS) semiconductor, cadmium sulfide (CdS) possesses suitable bandgap of 2.4 eV and negative conduction band potential, which has a great potential to realize efficient visible-light PHE performance. In this work, CdS with unique cubic/hexagonal phase junction is facilely synthesized through a sulfur-rich butyldithiocarbamate acid (BDCA) solution process. The results illustrate that the phase junction can efficiently enhance the separation and transfer of photogenerated electron-hole pairs, resulting in an excellent PHE performance. In addition, the sulfur-rich property of BDCA solution leads to the absence of additional sulfur sources during the synthesis of CdS photocatalyst, which greatly simplifies the fabrication process. The optimal PHE rate of the BDCA-synthesized phase junction CdS photocatalyst is 7.294 mmol g^-1  h^-1 and exhibits a favorable photostability. Moreover, density function theory calculations indicated that the apparent redistribution of charge density in the cubic/hexagonal phase junction regions gives a suitable hydrogen adsorption capacity, which is responsible for the enhanced PHE activity.

ZIF-8 metal organic framework composites as hydrogen evolution reaction photocatalyst: A review of the current state

In the past decade, extensive research has been devoted to synthesis of ZIF-8 materials for catalytic applications. As physico-chemical properties are synthesis-dependent, this review explores different synthesis strategies based the solvent and solvent-free synthesis of zeolitic imidazole framework. Accordingly, the effect of several parameters on the ZIF-8 synthesis were discussed including solvent, deprotonating agents, precursors ratio is delivered. Additionally, the advantages and disadvantages of each synthesis have been discussed and assessed. ZIF-8 textural and structural properties justify its wide use as a stable high surface area MOF in aqueous catalytic reactions. This review includes the applicatios of ZIF-8 materials in photocatalytic hydrogen evolution reaction (HER). The efficiency of the reviewed materials was fairly assessed. Finally, Limitations, drawbacks and future challenges were fully debated to ensure the industrial viability of the ZIFs.

Self-Assembled Zeolitic Imidazolate Framework/CdS Hollow Microspheres with Efficient Charge Separation for Enhanced Photocatalytic Hydrogen Evolution

Enhanced interfacial charge separation is of great importance to high-efficiency photocatalytic hydrogen production. Herein, we successfully fabricated novel ZIF-67/CdS hollow sphere (HS) and ZIF-8/CdS HS heterostructures through an in situ self-assembly process, in which ZIF-67 and ZIF-8 are closely coated on CdS HSs to form "double-shell"-like structures. This hierarchical heterostructure with porous outer layers on the surface of CdS HSs can expose accessible active sites and possess close contact. Upon visible-light illumination, the optimal proportion of ZIF-67/CdS HS displays a hydrogen generation rate of 1721 μmol g^-1 h^-1, which is 11.9 and 3.1 times higher than that of a pure CdS HS (145 μmol g^-1 h^-1) and ZIF-8/CdS HS (555 μmol g^-1 h^-1), respectively. The proposed photocatalytic mechanism is explored: ZIF-8/CdS HS follows the type-II mechanism, and ZIF-67/CdS HS follows the Z-scheme mechanism. The reason for the higher photocatalytic activity of ZIF-67/CdS HS is that ZIF-67 not merely with a porous structure facilitates the diffusion of H₂ gas, but with a well-matched band structure promotes charge transfer and separation.

Recent Progress in the Synthesis and Applications of Composite Photocatalysts: A Critical Review

Photocatalysis is an advanced technique that transforms solar energy into sustainable fuels and oxidizes pollutants via the aid of semiconductor photocatalysts. The main scientific and technological challenges for effective photocatalysis are the stability, robustness, and efficiency of semiconductor photocatalysts. For practical applications, researchers are trying to develop highly efficient and stable photocatalysts. Since the literature is highly scattered, it is urgent to write a critical review that summarizes the state-of-the-art progress in the design of a variety of semiconductor composite photocatalysts for energy and environmental applications. Herein, a comprehensive review is presented that summarizes an overview, history, mechanism, advantages, and challenges of semiconductor photocatalysis. Further, the recent advancements in the design of heterostructure photocatalysts including alloy quantum dots based composites, carbon based composites including carbon nanotubes, carbon quantum dots, graphitic carbon nitride, and graphene, covalent-organic frameworks based composites, metal based composites including metal carbides, metal halide perovskites, metal nitrides, metal oxides, metal phosphides, and metal sulfides, metal-organic frameworks based composites, plasmonic materials based composites and single atom based composites for CO₂ conversion, H₂ evolution, and pollutants oxidation are discussed elaborately. Finally, perspectives for further improvement in the design of composite materials for efficient photocatalysis are provided.

Photoelectrochemical assay based on CdS nanocrystal\hexagonal carbon-nitrogen tube nanocomposite for detection of silver ions

A photochemical assay was reported based on CdS nanocrystal (NC)\hexagonal carbon-nitrogen tube (HCNT) nanocomposite for the detection of Ag⁺. When CdS NCs were combined with HCNT, the photocurrent intensity was increased extensively. After incubation of Ag⁺ with CdS NC\HCNT nanocomposite-modified electrode, Ag₂S was formed on the electrode by the ion-change reaction. As the band gap of Ag₂S cannot match well with HCNT, the photogenerated electron-hole pairs cannot separate efficiently, so the photocurrent intensity decreases. A good linear relationship between the concentration of Ag⁺ in the range from 0.01 to 3 μM and the corresponding photocurrent intensity was obtained with a detection limit of 3.3 nM (S/N = 3). The assay was employed to detect Ag⁺ in lake water and human serum with satisfactory results, which indicated that it might have a broad application in different areas. Photoelectrochemical assay was reported based on CdS nanocrystal\hexagonal carbon-nitrogen tube nanocomposite for detection of Ag^.

Defect-rich cobalt pyrophosphate hybrids decorated Cd0.5Zn0.5S for efficient photocatalytic hydrogen evolution: Defect and interface engineering

Photocatalysts with highly efficient charge separation are of critical significance for improving photocatalytic hydrogen production performance. Herein, a cost-effective and high-performance composite photocatalyst, cobalt-phosphonate-derived defect-rich cobalt pyrophosphate hybrids (CoPPi-M) modified Cd_0.5Zn_0.5S is rationally devised via defect and interface engineering, in which the co-catalyst CoPPi-M delivers a strong interaction with host photocatalyst Cd_0.5Zn_0.5S, rendering Cd_0.5Zn_0.5S/CoPPi-M with a remarkably improved efficiency of charge separation and migration. Besides, Cd_0.5Zn_0.5S/CoPPi-M exhibits a hydrophilic surface with ample access to electrons and a strong reduction ability of electrons. Benefiting from these advantages, the integration of defect-rich cobalt pyrophosphate and Cd_0.5Zn_0.5S enables Cd_0.5Zn_0.5S/CoPPi-M-5% with high photocatalytic H₂ production rate of 6.87 mmol g^-1h^-1, which is 2.46 times higher than that of pristine Cd_0.5Zn_0.5S, and the notable apparent quantum efficiency (AQE) is 20.7% at 420 nm. This work provides a promising route for promoting the photocatalytic performance of non-precious hybrid photocatalyst via defect and interface engineering, and advances energy-generation and environment-restoration devices.

Tailoring the fusion effect of phase-engineered 1T/2H-MoS2 towards photocatalytic hydrogen evolution

Enhanced photocatalytic hydrogen evolution on 30-1T/2H-MoS2 with a higher concentration of the 1T phase was achieved due to the higher availability of electrons and dense active sites after the incorporation of the 1T phase in 2H-MoS2.

Nickel phosphonate-derived Ni2P@N-doped carbon co-catalyst with built-in electron-bridge for boosting the photocatalytic hydrogen evolution

To construct photocatalytic systems that can efficiently convert solar energy to hydrogen energy, numerous studies have been focused on transition metal phosphides (TMPs) co-catalysts, which display low overpotential and cost...

In situ construction of 0D CoWO4 modified 1D Mn0.47Cd0.53S for boosted visible-light photocatalytic H2 activity and photostability

To enhance the photocatalytic activity, loading proper semiconductor with high efficiency and low cost is one of the most valid approaches. Herein, various amounts of CoWO₄ as a novel metal-free material were loaded on Mn_0.47Cd_0.53S (MCS) nanorods for photocatalytic hydrogen production reaction. The CoWO₄/Mn_0.47Cd_0.53S-25 (CW/MCS-25) exhibits the highest hydrogen production rate of 41.53 mmol·h^-1·g^-1 in the Na₂S/Na₂SO₃ system, which is about 2.68 times higher than that of pristine MCS. The Mapping and HRTEM reveals the deposited of CoWO₄ on the MCS. The detailed analyses of XPS, EIS, TRPL spectra and transient photocurrent responses indicate that CoWO₄ and MCS interacted closely and the photogenerated electrons of CoWO₄ can be transferred into MCS. In particular, the introduction of CoWO₄ can further transfer the photogenerated holes of MCS, thereby inhibiting the photocorrosion of MCS and improving photocatalytic activity. This work provides a reference for the exploration of noble metal-free composite material and shows great potential in the photocatalytic application.

Boosting Visible-Light-Driven Photocatalytic Hydrogen Production through Sensitizing TiO2 via Novel Nanoclusters

Improving the light utilization and electron-hole separation efficiency plays a central role in photocatalysis for converting light energy to hydrogen energy. Herein, for the first time, a stable, highly dispersible discrete T4 [Cd₃In₁₇Se₃₁]^5- cluster is developed as a novel photosensitizer to sensitize TiO₂ for photocatalytic hydrogen production. Compared with pristine TiO₂ (near zero) and the T4 clusters (19.5 μmol g^-1 h^-1) that exhibit low hydrogen evolution activities, the T4/TiO₂ composite, constructed from traces of 0.127 mol % T4 cluster-sensitized TiO₂, exhibits a dramatically improved photocatalytic activity of 328.2 μmol g^-1 h^-1, highlighting that the photocatalytic efficiency strongly correlates with that of the T4 cluster. In the meantime, the T4/TiO₂ composites are highly stable, remaining robust in a long-time test of 50 h for photocatalytic hydrogen production. Ultrafast transient absorption spectroscopy, in combination with electrochemical analyses, steady-state and time-resolved photoluminescence, and density functional theory calculations, indicates that the T4 cluster not only serve as a photosensitizer to absorb visible light but also form a heterojunction between the interface of the T4 cluster and TiO₂ to accelerate electron injection. This work highlights the great potential of the stable and highly dispersed discrete metal chalcogenide clusters as high-efficiency photosensitizers for converting solar energy to chemical energy.

3D hollow Bi2O3@CoAl-LDHs direct Z-scheme heterostructure for visible-light-driven photocatalytic ammonia synthesis

In this paper, the novel 3D hollow Z-scheme heterojunction photocatalysts based on Bi₂O₃ and CoAl layered double hydroxides (Bi₂O₃@CoAl-LDHs) were prepared for efficient visible-light-driven photocatalytic ammonia synthesis. The synthesized nanohybrid exhibits excellent photocatalytic ammonia synthesis performance (48.7 μmol·L^-1·h^-1) and structural stability, which is primarily attributed to the fact that Z-scheme heterojunction significantly enhanced lifetime of photogenerated carriers (6.22 ns) and transfer efficiency of surface photogenerated electrons (72.5%). Strict control experiments and nitrogen isotope labeling results show that nitrogen and hydrogen in the produced ammonia come from nitrogen and water in the reactant respectively. Electron paramagnetic resonance (EPR) experiments and density functional theory (DFT) calculations further reveal that the built-in electric field due to the difference between Bi₂O₃ and CoAl-LDHs is the key to constructing the Z-scheme heterojunction. In addition, results of partial density of states (PDOS) show that Co in Bi₂O₃@CoAl-LDHs composite is the active site for photocatalytic N₂ fixation.

A review on vertical and lateral heterostructures of semiconducting 2D-MoS2 with other 2D materials: a feasible perspective for energy conversion

Fossil fuels as a double-edged sword are essential to daily life. However, the depletion of fossil fuel reservoirs has increased the search for alternative renewable energy sources to procure a more sustainable society. Accordingly, energy production through water splitting, CO₂ reduction and N₂ reduction via photocatalytic and electrocatalytic pathways is being contemplated as a greener methodology with zero environmental pollution. Owing to their atomic-level thickness, two-dimensional (2D) semiconductor catalysts have triggered the reawakening of interest in the field of energy and environmental applications. Among them, following the unconventional properties of graphene, 2D MoS₂ has been widely investigated due to its outstanding optical and electronic properties. However, the photo/electrocatalytic performance of 2D-MoS₂ is still unsatisfactory due to its low charge carrier density. Recently, the development of 2D/2D heterojunctions has evoked interdisciplinary research fascination in the scientific community, which can mitigate the shortcomings associated with 2D-MoS₂. Following the recent research trends, the present review covers the recent findings and key aspects on the synthetic methods, fundamental properties and practical applications of semiconducting 2D-MoS₂ and its heterostructures with other 2D materials such as g-C₃N₄, graphene, CdS, TiO₂, MXene, black phosphorous, and boron nitride. Besides, this review details the viable application of these materials in the area of hydrogen energy production via the H₂O splitting reaction, N₂ fixation to NH₃ formation and CO₂ reduction to different value-added hydrocarbons and alcohol products through both photocatalysis and electrocatalysis. The crucial role of the interface together with the charge separation principle between two individual 2D structures towards achieving satisfactory activity for various applications is presented. Overall, the current studies provide a snapshot of the recent breakthroughs in the development of various 2D/2D-based catalysts in the field of energy production, delivering opportunities for future research.

Superior Electrocatalytic Activity of MoS2-Graphene as Superlattice

Evidence by selected area diffraction patterns shows the successful preparation of large area (cm × cm) MoS2/graphene heterojunctions in coincidence of the MoS2 and graphene hexagons (superlattice). The electrodes of MoS2/graphene in superlattice configuration show improved catalytic activity for H2 and O2 evolution with smaller overpotential of +0.34 V for the overall water splitting when compared with analogous MoS2/graphene heterojunction with random stacking.

Light-Induced Formation of MoOxSy Clusters on CdS Nanorods as Cocatalyst for Enhanced Hydrogen Evolution

Metal and metal-oxide particles are commonly photodeposited on photocatalysts by reduction and oxidation reactions, respectively, consuming charges that are generated under illumination. This study reveals that amorphous MoO_xS_y clusters can be easily photodeposited at the tips of CdS nanorods (NRs) by in situ photodeposition for the first time. The as-prepared MoO_xS_y-decorated CdS samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma (ICP) to determine the composition and the possible formation pathways of the amorphous MoO_xS_y clusters. The MoO_xS_y-tipped CdS samples exhibited better hydrogen evolution performance than pure CdS under visible-light illumination. The enhanced activity is attributed to the formation of intimate interfacial contact between CdS and the amorphous MoO_xS_y clusters, which facilitates the charge separation and transfer. Through time-resolved photoluminescence (TRPL) measurements, it was clearly observed that all MoO_xS_y-decorated CdS samples with different loadings of MoO_xS_y showed a faster PL decay when compared to pure CdS, resulting from the effective trapping of photogenerated electrons by the MoO_xS_y clusters. Kelvin probe force microscopy (KPFM) was further used to study the surface potentials of pure CdS NRs and MoO_xS_y-decorated CdS NRs. A higher surface potential on MoO_xS_y-decorated CdS NRs was observed in the dark, indicating that the loading of MoO_xS_y resulted in a lower surface work function compared to pure CdS NRs. This contributed to the effective electron trapping and separation, which was also reflected by the increased photoelectrochemical response. Thus, this study demonstrates the design and facile synthesis of MoO_xS_y-tipped CdS NRs photocatalysts for efficient solar hydrogen production.

Carbon inserted defect-rich MoS2-X nanosheets@CdSnanospheres for efficient photocatalytic hydrogen evolution under visible light irradiation

Carbon -MoS_2-x@CdS (C-MoS_2-x@CdS) core-shell nanostructures with controlled surface sulfur (S) vacancies were prepared via a glucose assisted hydrothermal growth method. The glucose acted as a reducing agent of C-MoS_2-X to partially reduce Mo⁴⁺ ions to Mo³⁺ and served as a carbon source to insert the amorphous carbon into the layered MoS_2-X simultaneously. The presence of Mo³⁺ result in the surface S-vacancies, which can provide more additional active sites and enhance the photocatalytic performance. Moreover, the inserted carbon in layered MoS_2-X enhanced the electron mobility and decreased the resistance electron transfer. Density functional theory (DFT) calculation confirmed that the surface S-vacancies and the amorphous carbon increase the projected density of states at the conduct band edge, which could enhance the photo-absorption and photo-responsibility. The result is consistent with the photocatalytic H₂ production experiment. C2-10%MoS_2-x@CdS presented a high H₂ evolution rate of 61,494 μmol h^-1 g^-1 under visible light irrigation (λ ≥ 420 nm), which is 1.98 times and 158 times higher than that of sample without S-vacancies (10%MoS₂@CdS) and pure CdS, respectively.

Few-layer WS2 nanosheets with oxygen-incorporated defect-sulphur entrapped by a hierarchical N, S co-doped graphene network towards advanced long-term lithium storage performances

Tungsten sulfide (WS₂) with two-dimensional layered graphene-like structure as an anode for lithium-ion batteries (LIBs) has attracted large attention owing to its high theoretical capacity and unique S–W–S layer structure. However, it also always suffers from poor electrical conductivity and volume expansion during lithiation/delithiation process in the practical application. Herein, we demonstrate the successful synergistic regulation of both structural and electronic modulation by simultaneous oxygen incorporation in defect-sulphur WS₂ nanosheets embedded into a conductive nitrogen and sulfur co-doped graphene framework (denoted as O-DS-WS₂/NSG), leading to dramatically enhanced lithium storage. Such a unique structure not only increases the accessible active sites for Li⁺ and enhances the kinetics of ion/electron transport, but also relieves the volume effect of WS₂. Furthermore, the surface defects and heteroatom incorporation can effectively regulate the electronic structure, improve the intrinsic conductivity and offer more active sites. Consequently, electrochemical performance results demonstrate that the obtained O-DS-WS₂/NSG nanocomposites possess great application prospects in LIBs with high specific capacity, superior rate performance as well as excellent cycle stability.

One-step preparation of few-layer oxygen incorporation in defect-sulphur WS₂ nanosheets embedded into the NSG framework exhibits excellent Li-ion storage properties.

Simultaneous manipulation of ion doping and cocatalyst loading into Mn0.3Cd0.7S nanorods toward significantly improved H2 evolution

Ni₂P and Ni²⁺ jointly modified Mn_0.3Cd_0.7S photocatalysts were successfully fabricated via a facile solvothermal method. The loading of Ni₂P and the doping of Ni²⁺ proceeded simultaneously via a one-step process.

Highly efficient and stable photocatalytic properties of CdS/FeS nanocomposites

CdS/FeS nanocomposites were successfully synthesized via a liquid-phase thermal decomposition of a single precursor and an ion adsorption method.

Dynamic charge transfer through Fermi level equilibration in the p-CuFe2O4/n-NiAl LDH interface towards photocatalytic application

The Ni Al LDH–CuFe₂O₄ p–n heterojunction, through vacuum energy level bending, inhibits electron hole recombination and enhances photocatalytic activity.

Designed synthesis of unique ZnS@CdS@Cd0.5Zn0.5S-MoS2 hollow nanospheres for efficient visible-light-driven H2 evolution

Unique ZnS@CdS@Cd_0.5Zn_0.5S-MoS₂ hollow nanospheres with abundant active sites and enhanced light-harvesting and charge separation demonstrate efficient H₂ evolution from visible-light-driven water-splitting.

Construction of titanium dioxide/cadmium sulfide heterojunction on carbon fibers as weavable photocatalyst for eliminating various contaminants

Semiconductor heterojunction powders have exhibited the enhanced photocatalytic activities, but their practical applications have been limited due to their poor recycling performance from flowing wastewater. To solve these problems, with carbon fibers (CFs) as the fixing substrate, we constructed TiO₂/CdS heterojunction as a model on CF surface by utilizing a hydrothermal-chemical bath deposition method. CFs/TiO₂/CdS bundles display a wide photoabsorption with two photoabsorption edges (~410 and 520 nm). Furthermore, CFs/TiO₂/CdS bundles can be weaved into macroscopical cloth (such as weight: 0.1 g, area: 4 × 4 cm²) which have considerable photocurrent density of 5.75 × 10^-6 A/cm². Under visible light irradiation (λ > 400 nm), macroscopic CFs/TiO₂/CdS cloth can degrade 95.44% methylene blue (MB), 64.95% acid orange 7 (AO7), 91.37% tetracycline hydrochloride (TC) and remove 90.70% hexavalent chromium (Cr(VI)) after 120 min, higher than those by CFs/CdS (43.42% MB, 37.42% AO7, 31.76% TC and 30.45% Cr(VI)) or CFs/TiO₂ (12.84% MB, 10.48% AO7, 11.85% TC and 15.58% Cr(VI)). Thus, CFs/TiO₂/CdS can act as a weavable and efficient photocatalyst for eliminating various pollutants from wastewater.

Constructing highly dispersed 0D Co3S4 quantum dots/2D g-C3N4 nanosheets nanocomposites for excellent photocatalytic performance

The development of noble-metal-free catalysts with high efficiency photocatalytic properties is critical to the heterogeneous catalysis. Herein, zero-dimensional (0D) metal sulfide quantum dots/two-dimensional (2D) g-C₃N₄ nanosheets (Co₃S₄/CNNS) nanocomposites are synthesized by a two-step method, including the ways of in-situ deposition and water bath. The highly dispersed Co₃S₄ quantum dots (particle size is 2-4 nm) are evenly and tightly fixed on CNNS, which can be used as co-catalyst to effectively replace noble metals to improve the photocatalytic properties of CNNS. Co₃S₄/CNNS-900 has the apparent quantum efficiency, which is up to 7.85% at 400 nm. At the same time, the H₂ evolution rate of Co₃S₄/CNNS-900 is 20,536.4 μmol g^-1 h^-1, which is 555 times than CNNS. The excellent photocatalytic performance is due to the highly dispersed Co₃S₄ quantum dots on 2D CNNS, which facilitate the formation of more active sites, Co₃S₄/CNNS promotes the separation and migration of photogenerated carriers, shortens the migration distance of photogenerated carriers, and eventually leads to an increase of the photocatalytic performance.

Direct Z-Scheme 2D/2D Photocatalyst Based on Ultrathin g-C3N4 and WO3 Nanosheets for Efficient Visible-Light-Driven H2 Generation

Ultrathin two-dimensional (2D) nanomaterials can not only boost the interfacial charge migration and separation but also provide abundant reactive sites for the photocatalytic H₂ generation. Herein, a kind of direct Z-scheme 2D/2D hybrid nanomaterial is fabricated by post-annealing atomically ultrathin Pt-loaded g-C₃N₄ nanosheets (Pt-CN NSs) with a thickness of ∼4.0 nm and hydrogen-treated WO₃ nanosheets (HWO NSs) with a thickness of ∼2.6 nm. The strong affinity existing between the two types of nanosheets with few-layer stacking results in the formation of atomically ultrathin 2D/2D hybrid nanomaterials (Pt-CN/HWO) with intimate interfacial contact in which the strong electronic interaction and efficient charge separation lead to a direct Z-scheme electron flowing from HWO NSs to CN NSs and then to the Pt cocatalyst for catalyzing the H₂ generation reaction. After optimizing the component ratio, the corresponding Pt-CN/HWO hybrid nanomaterial delivers a significantly boosted photocatalytic H₂ generation activity, up to 6.2 times as high as that of the Pt-CN/WO composite containing Pt-CN NSs and WO₃ nanoplates (WO NPs) without hydrogen treatment. This result reveals that the atomically ultrathin nanosheets in the 2D/2D hybrid nanomaterials can not only deliver strong electronic interaction to promote the Z-scheme mechanism for maintaining the high reduction ability of g-C₃N₄ and high oxidation ability of WO₃ but also alleviate the charge recombination, therefore resulting in the excellent photocatalytic H₂ generation performance.

A Critical Review on Enhancement of Photocatalytic Hydrogen Production by Molybdenum Disulfide: From Growth to Interfacial Activities

Ultrathin 2D molybdenum disulfide (MoS₂ ), which is the flagship of 2D transition-metal dichalcogenide nanomaterials, has drawn much attention in the last few years. 2D MoS₂ has been banked as an alternative to platinum for highly active hydrogen evolution reaction because of its low cost, high surface-to-volume ratio, and abundant active sites. However, when MoS₂ is used directly as a photocatalyst, contrary to public expectation, it still performs poorly due to lateral size, high recombination ratio of excitons, and low optical cross section. Besides, simply compositing MoS₂ as a cocatalyst with other semiconductors cannot satisfy the practical application, which stimulates the pursual of a comprehensive insight into recent advances in synthesis, properties, and enhanced hydrogen production of MoS₂ . Therefore, in this Review, emphasis is given to synthetic methods, phase transitions, tunable optical properties, and interfacial engineering of 2D MoS₂ . Abundant ways of band edge tuning, structural modification, and phase transition are addressed, which can generate the neoteric photocatalytic systems. Finally, the main challenges and opportunities with respect to MoS₂ being a cocatalyst and coherent light-matter interaction of MoS₂ in photocatalytic systems are proposed.

Progress in Electrocatalytic Hydrogen Evolution Based on Monolayer Molybdenum Disulfide

Energy and environmental issues raise higher demands on the development of a sustainable energy system, and the electrocatalytic hydrogen evolution is one of the most important ways to realize this goal. Two-dimensional (2D) materials represented by molybdenum disulfide (MoS2) have been widely investigated as an efficient electrocatalyst for the hydrogen evolution. However, there are still some shortcomings to restrict the efficiency of MoS2 electrocatalyst, such as the limited numbers of active sites, lower intrinsic catalytic activity and poor interlayer conductivity. In this review, the application of monolayer MoS2 and its composites with 0D, 1D, and 2D nanomaterials in the electrocatalytic hydrogen evolution were discussed. On the basis of optimizing the composition and structure, the numbers of active sites, intrinsic catalytic activity, and interlayer conductivity could be significantly enhanced. In the future, the study would focus on the structure, active site, and interface characteristics, as well as the structure-activity relationship and synergetic effect. Then, the enhanced electrocatalytic activity of monolayer MoS2 can be achieved at the macro, nano and atomic levels, respectively. This review provides a new idea for the structural design of two-dimensional electrocatalytic materials. Meanwhile, it is of great significance to promote the study of the structure-activity relationship and mechanism in catalytic reactions.

Recent advances in metal sulfides: from controlled fabrication to electrocatalytic, photocatalytic and photoelectrochemical water splitting and beyond

This review describes an in-depth overview and knowledge on the variety of synthetic strategies for forming metal sulfides and their potential use to achieve effective hydrogen generation and beyond.

Two-dimensional semiconductor transition metal based chalcogenide based heterostructures for water splitting applications

Recent research and development is focused in an intensive manner to increase the efficiency of solar energy conversion into electrical energy via photovoltaics and photo-electrochemical reactions.

A novel n-type CdS nanorods/p-type LaFeO3 heterojunction nanocomposite with enhanced visible-light photocatalytic performance

In this work, a novel n-type CdS nanorods/p-type LaFeO₃ (CdS NRs/LFO) nanocomposite was prepared, for the first time, via a facile solvothermal method. The as-prepared n-CdS NRs/p-LFO nanocomposite was characterized by using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy (EDX), UV-visible diffuse reflection spectroscopy (DRS), vibrating sample magnetometry (VSM), photoluminescence (PL) spectroscopy, and Brunauer–Emmett–Teller (BET) surface area analysis. All data revealed the attachment of the LFO nanoparticle on the surface of CdS NRs. This novel nanocomposite was applied as a novel visible light photocatalyst for the degradation of methylene blue (MB), rhodamine B (RhB) and methyl orange (MO) dyes under visible-light irradiation. Under optimized conditions, the degradation efficiency was 97.5% for MB, 80% for RhB and 85% for MO in the presence of H₂O₂ and over CdS NRs/LFO nanocomposite. The photocatalytic activity of CdS NRs/LFO was almost 16 and 8 times as high as those of the pristine CdS NRs and pure LFO, respectively. The photocatalytic activity was enhanced mainly due to the high efficiency in separation of electron–hole pairs induced by the remarkable synergistic effects of CdS and LFO semiconductors. After the photocatalytic reaction, the nanocomposite can be easily separated from the reaction solution and reused several times without loss of its photocatalytic activity. Trapping experiments indicated that ·OH radicals were the main reactive species for dye degradation in the present photocatalytic system. On the basis of the experimental results and estimated energy band positions, the mechanism for the enhanced photocatalytic activity was proposed.

A novel n–p CdS nanorods/LaFeO₃ (CdS NRs/LFO) heterojunction nanocomposite was prepared via a solvothermal route and applied as a visible-light photocatalyst for enhanced degradation of organic dye pollutants.

Enhanced light trapping and high charge transmission capacities of novel structures for efficient photoelectrochemical water splitting

Excellent PEC efficiency, good reusability and the super stability of trap-like SnS2/TiO2 nanotube arrays (NTs)-based photoanodes are reported. Specifically, the SnS2/TiO2-180 °C (ST-180) photoanode exhibited the highest photocurrent density (1.05 mA cm-2) and an optimal η (0.73%) at 0.5 V (vs. SCE) under simulated light irradiation (AM 1.5G), which are 4.6 and 3.8 times higher than those of pure TiO2 NTs (0.23 mA cm-2 and 0.19%). The IPCE values of ST-180 can reach 21.5% (365 nm) and 13.8% (420 nm), which are much higher than those of pure TiO2 NTs (10.6% at 365 nm and 0.8% at 420 nm). The APCE values of the pure TiO2 NTs photoelectrode are 12.8% (365 nm) and 1.1% (420 nm), while the ST-180 values are 22.3% and 14.2%, respectively. Furthermore, the generation rates of H2 and O2 for the ST-180 photoanode are 47.2 and 23.1 μmol cm-2 h-1 at 0.5 V under AM 1.5G, corresponding to faradaic efficiencies of around 80.1% and 78.3%, respectively. In short, the high-efficiency PEC water splitting performance of this SnS2/TiO2 photoanode results from the enhanced light harvesting ability of the trap-like SnS2 structure, accelerated carrier transportation properties of TiO2 NTs, and effective carrier separation of the type-II heterojunction structure. This work may offer a combinatorial strategy for the preparation of heterojunction structures with high PEC performance and can be a model structure for similar photoanode materials.