Excellent Charge Separation of NCQDs/ZnS Nanocomposites for the Promotion of Photocatalytic H2 Evolution

Carbon Quantum dots (CQDs) are widely studied because of their good optical and electronic characteristics and because they can easily generate photocarriers. Nitrogen-doped CQDs (NCQDs) may exhibit improved hydrophilic, optical, and electron-transfer properties, which are conducive to photocatalytic hydrogen evolution. In this paper, NCQD-modified ZnS catalysts were successfully prepared. Under the irradiation of the full spectrum, the H2 evolution rate of the optimal catalyst 0.25 wt % NCQDs/ZnS achieves 5.70 mmol g-1 h-1, which is 11.88, 43.84, and 5.14 times the values of ZnS (0.48 mmol g-1 h-1), NCQDs (0.13 mmol g-1 h-1), and CQDs/ZnS (1.11 mmol g-1 h-1), respectively. Furthermore, it shows good stability, indicating that the modification of NCQDs prevents the photocorrosion and oxidation of ZnS. The enhanced performance is due to NCQD loading, which promotes the separation of photogenerated carriers, optimizes the structures, and increases the specific surface area. This work highlights the fact that NCQD-modified ZnS may afford a new strategy to synthesize ZnS-based photocatalysts with enhanced H2 production performance.

Tuning Electrons Migration of Dual S Defects Mediated MoS2-x/ZnIn2S4-x Toward Highly Efficient Photocatalytic Hydrogen Production

Photocatalytic hydrogen production is a prevalent method for hydrogen synthesis. However, high recombination rate of photogenerated carriers and high activation energy barrier of H remain persistent challenge. Here, the two-step hydrothermal method is utilized to prepare dual S-defect mediated catalyst molybdenum sulfide/zinc indium sulfide (MSv/ZISv), which has high hydrogen production rate of 8.83 mmol g-1h-1 under simulated sunlight. The achieved rate is 21.91 times higher than pure ZnIn2S4 substrate. Defects in ZIS within MSv/ZISv modify the primitive electronic structure by creating defect state that retaining good reducing power, leading to the rapid separation of electron-hole pairs and the generation of additional photogenerated carriers. The internal electric field further enhances the migration toward to cocatalyst. Simultaneously, the defects introduced on the MoS2 cause electron rearrangement, leading to electron clustering on both S vacancies and edge S. Thereby MSv/ZISv exhibits the lowest activation energy barrier and |ΔGH*|. This work explores the division of synergies between different types of S defects, providing new insights into the coupling of defect engineering.

Controllable Synthesis, Formation Mechanism, and Photocatalytic Activity of Tellurium with Various Nanostructures

Telluriums (Te) with various nanostructures, including particles, wires, and sheets, are controllably synthesized by adjusting the content of polyvinylpyrrolidone (PVP) in a facile solvothermal reaction. Te nanostructures all have complete grain sizes with excellent crystallinity and mesopore structures. Further, the formation mechanisms of Te nanostructures are proposed to be that the primary nuclei of Te are released from the reduction of TeO32- using N2H4·H2O, and then grow into various nanostructures depending on the different content of PVP. These nanostructures of Te all exhibit the photocatalytic activities for the degradation of MB and H2 production under visible light irradiation, especially Te nanosheets, which have the highest efficiencies of degradation (99.8%) and mineralization (65.5%) at 120 min. In addition, compared with pure Te nanosheets, the rate of H2 production increases from 412 to 795 μmol∙h-1∙g-1 after the introduction of Pt, which increases the output by nearly two times. The above investigations indicate that Te with various nanostructures is a potential photocatalyst in the field of degradation of organic pollutants and H2 fuel cells.

Graphitic Carbon Nitride Nanosheets Decorated with Zinc-Cadmium Sulfide for Type-II Heterojunctions for Photocatalytic Hydrogen Production

In this study, we fabricated graphitic carbon nitride (g-C3N4) nanosheets with embedded ZnCdS nanoparticles to form a type II heterojunction using a facile synthesis approach, and we used them for photocatalytic H2 production. The morphologies, chemical structure, and optical properties of the obtained g-C3N4-ZnCdS samples were characterized by a battery of techniques, such as TEM, XRD, XPS, and UV-Vis DRS. The as-synthesized g-C3N4-ZnCdS photocatalyst exhibited the highest hydrogen production rate of 108.9 μmol·g-1·h-1 compared to the individual components (g-C3N4: 13.5 μmol·g-1·h-1, ZnCdS: 45.3 μmol·g-1·h-1). The improvement of its photocatalytic activity can mainly be attributed to the heterojunction formation and resulting synergistic effect, which provided more channels for charge carrier migration and reduced the recombination of photogenerated electrons and holes. Meanwhile, the g-C3N4-ZnCdS heterojunction catalyst also showed a higher stability over a number of repeated cycles. Our work provides insight into using g-C3N4 and metal sulfide in combination so as to develop low-cost, efficient, visible-light-active hydrogen production photocatalysts.

Ni-anchored g-C3N4 for improved hydrogen evolution in photocatalysis

In this study, we present a facile wet chemical method for synthesizing Ni-modified polymeric carbon nitride (g-C3N4) nanosheets. X-ray absorption fine structure spectroscopy (XAFS) reveals the formation of a unique Ni-N structure, resulting from Ni atoms anchoring in cavities of g-C3N4. The Ni anchoring on the surface N sites modifies the electronic structure of g-C3N4, demonstrating remarkable effectiveness even at low anchoring amounts. The as-prepared Ni/g-C3N4 catalysts show robust performance for photocatalytic hydrogen evolution under visible light irradiation, attributed to the unique Ni-N interactions. Specifically, the photocatalytic H2 production rate of the Ni/CN-45 catalyst reached 8482.14 μmol·g-1·h-1 with an apparent quantum efficiency (AQE) of 0.75% under light irradiation at 427 nm. This rate surpasses most of the previously reported g-C3N4 based photocatalysts and is nearly 8 times higher than that of the pure g-C3N4 catalyst (1116.07 μmol·g-1·h-1).&#xD.

S-Scheme and Schottky Junction Synchronous Regulation Boost Hierarchical CdS@Nb2O5/Nb2CTx (MXene) Heterojunction for Photocatalytic H2 Production

Photocatalytic water cracking hydrogen (H₂) production is a promising clean energy production technology. Therefore, a ternary CdS@Nb₂O₅/Nb₂CT_x (MXene) heterojunction with hierarchical structure was designed to promote photocatalytic H₂ evolution. When Na₂S/Na₂SO₃ and lactic acid were used as sacrificial agents, the hydrogen evolution reaction (HER) rates of the optimized photocatalyst were 1501.7 and 2715.8 μmol g^-1 h^-1, with 12.4% and 26.1% apparent quantum efficiencies (AQE) at 420 nm, respectively. Its HER performance was 10.9-fold higher than that of pure CdS and remained 87% activity after five rounds of cycle tests. Such an enhancement stems from the excellent light absorption properties, tight interfacial contact, fast charge transfer channel, and sufficient active sites. Mechanism analysis demonstrates that S-scheme and Schottky junction synchronous regulation boost hierarchical CdS@Nb₂O₅/Nb₂CT_x for photocatalytic H₂ production. This work creates possibilities for manufacturing Nb-based MXene photocatalysts for converting solar energy and other applications.

Metal Complex/ZnS-Modified Ni Foam as Magnetically Stirrable Photocatalysts: Roles of Redox Mediators and Carrier Dynamics Monitored by Operando Synchrotron X-ray Spectroscopy

Magnetically stirrable photocatalysts binding the ZnS-decorated Ni foam with the metal complex cocatalyst as a redox mediator and light-absorbing composition were investigated. Loading metal complex can improve light absorption, surface hydrophilicity, interfacial charge migration, and H₂ production activity. The variation of the metal valences of the composite photocatalysts in an operando environment (with sacrificial agent solution) with and without light irradiation was investigated by X-ray absorption near-edge structure (XANES) spectra and Fourier-transformed extended X-ray absorption fine structure (EXAFS) spectra to monitor the charge carrier dynamics of photocatalysis and explain how the macrocyclic Cu complex (CuC) acted as a redox mediator better than the Ni complex. The smaller valence difference of copper valence in ZS/CuC for dark and light states revealed that the Cu complex facilitates a reversible electron transfer between the ZnS photocatalyst and H⁺. Loading the Cu complex can improve the separation of photogenerated carriers by the redox couple of complexes, leading to a significantly improved photocatalytic H₂ production activity of 8150 μmol h^-1 g^-1. The reactants can flow through these magnetically stirrable Ni foam-based photocatalysts by magnetic-field-driven stirring, which improves the contact between photocatalysts and the sacrificial agents. The operando synchrotron provides new insights for understanding the roles of redox mediators.

Enhanced Charge Separation for Efficient Photocatalytic H2 Production by Long-Lived Trap-State-Induced Interfacial Charge Transfer

Photogeneration of charge carriers in semiconductors provides the scientific fundamental for photocatalytic water splitting. However, an ongoing challenge is the development of a new mechanism promoting charge carrier separation. Here we propose a trap-state-induced interfacial charge-transfer transition mechanism (TSICTT), in which electrons in long-lived trap states recombine with holes on the valence band (VB) of the semiconductor, thus prolonging the electron lifetime. We demonstrate this concept in the Sr₄Al₁₄O₂₅:Eu²⁺, Dy³⁺/CdS (SAO/CdS) heterostructure, where trapped electrons with a lifetime of up to several hours in the SAO persistent luminescence phosphor (PLP) can continuously consume holes on the VB of CdS nanoparticles (NPs). We discover that the interfacial interaction and the work function difference between SAO and CdS are crucial for the TSICTT, which finally contributes to the improved H₂ production from 34.4 to 1212.9 μmol g_CdS^-1 h^-1 under visible-light irradiation. This model introduces a new strategy to manipulate charge carrier transport for the effective utilization of solar energy.

Crystal Facet Engineering and Hydrogen Spillover-Assisted Synthesis of Defective Pt/TiO2-x Nanorods with Enhanced Visible Light-Driven Photocatalytic Activity

Hydrogen spillover can assist the introduction of defects such as Ti³⁺ and concomitant oxygen vacancies (V_O) in a TiO₂ crystal, thereby inducing a new level below the conduction band to improve the conductivity of photogenerated electrons and the visible light absorption property of TiO₂. Meanwhile, crystal facet engineering offers a promising approach to achieve improved activity by influencing the recombination step of the photogenerated electrons and holes. In this study, with the aim of achieving enhanced visible light-driven photocatalytic activity, rutile TiO₂ nanorods with different aspect ratios were synthesized by crystal facet engineering, and Pt-deposited TiO_2-x nanorods (Pt/TNR) were then obtained via reduction treatment assisted by hydrogen spillover. The reduction treatment at 200 °C induced the formation of surface Ti³⁺ exclusively, whereas surface Ti³⁺ and V_O were formed by performing the reduction at 600 °C. The Pt/TNR with a higher aspect ratio reduced at 200 °C exhibited the highest activity in photocatalytic H₂ production under visible light irradiation owing to the synergistic effect of the introduction of Ti³⁺ defects and the spatial charge carrier separation induced by crystal facet engineering.

Enhancing Photocatalytic Hydrogen Production via the Construction of Robust Multivariate Ti-MOF/COF Composite

Titanium metal-organic frameworks (Ti-MOFs), as an appealing type of artificial photocatalysts, have shown great potentials in the field of solar energy conversion due to their well-studied photo-redox activity similar to TiO 2 and good optical responsiveness of linkers serving as the antenna to absorb visible-light. Although enormous efforts have been dedicated to developing Ti-MOFs with high photocatalytic activity, their solar energy conversion performances are still poor. Herein, a covalent-integrated strategy has been implemented to construct a series of multivariate Ti-MOF/COF hybrid materials, PdTCPP⸦PCN-415(NH 2 )/TpPa (composites 1, 2, and 3), featuring excellent visible-light utilization, suitable band gap, and high surface area for photocatalytic H 2 production. Notably, the resulting composites demonstrated remarkably enhanced visible-light-driven photocatalytic H 2 evolution performance, especially for the composite 2 with the maximum H 2 evolution rate of 13.98 mmol g -1 h -1 (turn-over frequency (TOF) = 227 h -1 ), which is much higher than the prototypical counterparts, PdTCPP⸦PCN-415(NH 2 ) (0.21 mmol g -1 h -1 ) and TpPa (6.51 mmol g -1 h -1 ). Our work thereby suggests a new approach to develop highly efficient photocatalysts for photocatalytic H 2 evolution reaction and beyond.

Disordered-Layer-Mediated Reverse Metal-Oxide Interactions for Enhanced Photocatalytic Water Splitting

In heterogeneous catalysts, metal-oxide interactions occur spontaneously but often in an undesired way leading to the oxidation of metal nanoparticles. Manipulating such interactions to produce highly active surface of metal nanoparticles can warrant the optimal catalytic activity but has not been established to date. Here we report that a prior reduced TiO₂ support can reverse the interaction with Pt nanoparticles and augment the metallic state of Pt, exhibiting a 3-fold increase in hydrogen production rate compared to that of conventional Pt/TiO₂. Spatially resolved electron energy loss spectroscopy of the Ti valence state and the electron density distribution within Pt nanoparticles provide direct evidence supporting that the Pt/TiO₂/H₂O triple junctions are the most active catalytic sites for water reduction. Our reverse metal-oxide interaction scheme provides a breakthrough in the stagnated hydrogen production efficiency and can be applied to other heterogeneous catalyst systems composed of metal nanoparticles with reducible oxide supports.

Regulating the Electronic Structure and Water Adsorption Capability by Constructing Carbon-Doped CuO Hollow Spheres for Efficient Photocatalytic Hydrogen Evolution

Copper(II) oxide featuring a narrow bandgap and low toxicity has been frequently applied in the visible-light-driven photocatalytic hydrogen evolution, but it suffers from large intrinsic overpotential and low water adsorption capacity. Herein, we report a self-templated strategy for the preparation of carbon-doped CuO hollow spheres (C-CuO HSs) through thermal transformation of a hierarchical MOF. The hierarchical Cu-MOFs not only act as a template to form interior voids during the thermal transformation, but also serve as precursors to dope C atoms into the CuO lattice. The as-synthesized C-CuO HSs exhibits remarkable photocatalytic performance with a H₂ evolution rate of 67.3 mmol/g/h and the apparent quantum efficiency of 25.3 % at 520 nm in the present of eosin-Y photosensitizer. The high performance of C-CuO HSs is attributed to the hierarchical porous structure and modulated electronic structure of CuO by C-doping with well exposed reactive sites, high water adsorption capability, and low water reduction reaction barrier. The results presented in this work might shed light on the design of high-performance photocatalysts for various energy-related applications.

Boosting the Photocatalytic Ability of g-C3N4 for Hydrogen Production by Ti3C2 MXene Quantum Dots

The big challenging issues in photocatalytic H₂ evolution are efficient separation of the photoinduced carriers, the stability of the catalyst, enhancing quantum efficiency, and requiring photoinduced electrons to enrich on photocatalysts' surface. Herein, Ti₃C₂ MXene quantum dots (QDs) possess the activity of Pt as a co-catalyst in promoting the photocatalytic H₂ evolution to form heterostructures with g-C₃N₄ nanosheets (NSs) (denoted g-C₃N₄@Ti₃C₂ QDs). The photocatalytic H₂ evolution rate of g-C₃N₄@Ti₃C₂ QD composites with an optimized Ti₃C₂ QD loading amounts (100 mL) is nearly 26, 3 and 10 times higher than pristine g-C₃N₄ NSs, Pt/g-C₃N₄, and Ti₃C₂ MXene sheet/g-C₃N₄, respectively. The Ti₃C₂ QDs increase the specific surface area of g-C₃N₄ and boost the density of the active site. Besides, metallic Ti₃C₂ QDs possess excellent electronic conductivity, causing the improvement of carrier transfer efficiency.

Sub-5 nm Ultra-Fine FeP Nanodots as Efficient Co-Catalysts Modified Porous g-C3N4 for Precious-Metal-Free Photocatalytic Hydrogen Evolution under Visible Light

Sub-5 nm ultra-fine iron phosphide (FeP) nano-dots-modified porous graphitic carbon nitride (g-C₃N₄) heterojunction nanostructures are successfully prepared through the gas-phase phosphorization of Fe₃O₄/g-C₃N₄ nanocomposites. The incorporation of zero-dimensional (0D) ultra-small FeP nanodots co-catalysts not only effectively facilitate charge separation but also serve as reaction active sites for hydrogen (H₂) evolution. Herein, the strongly coupled FeP/g-C₃N₄ hybrid systems are employed as precious-metal-free photocatalysts for H₂ production under visible-light irradiation. The optimized FeP/g-C₃N₄ sample displays a maximum H₂ evolution rate of 177.9 μmol h^-1 g^-1 with the apparent quantum yield of 1.57% at 420 nm. Furthermore, the mechanism of photocatalytic H₂ evolution using 0D/2D FeP/g-C₃N₄ heterojunction interfaces is systematically corroborated by steady-state photoluminescence (PL), time-resolved PL spectroscopy, and photoelectrochemical results. Additionally, an increased donor density in FeP/g-C₃N₄ is evidenced from the Mott-Schottky analysis in comparison with that of parent g-C₃N₄, signifying the enhancement of electrical conductivity and charge transport owing to the emerging role of FeP. The density functional theory calculations reveal that the FeP/g-C₃N₄ hybrids could act as a promising catalyst for the H₂ evolution reaction. Overall, this work not only paves a new path in the engineering of monodispersed FeP-decorated g-C₃N₄ 0D/2D robust nanoarchitectures but also elucidates potential insights for the utilization of noble-metal-free FeP nanodots as remarkable co-catalysts for superior photocatalytic H₂ evolution.

Tuning Band Alignments and Charge-Transport Properties through MoSe2 Bridging between MoS2 and Cadmium Sulfide for Enhanced Hydrogen Production

Transition-metal dichalcogenide materials play a major role in the state-of-the-art innovations for energy conversion because of potential applications resulting from their unique properties. These materials additionally show inordinate potential toward the progress of hygienic power sources to deal with increasing environmental disputes at the time of skyrocketing energy demands. Herein, we report earth-abundant, few-layered, MoSe₂-bridged MoS₂/cadmium sulfide (CdS) nanocomposites, which reduce photogenerated electron and hole recombination by effectively separating charge carriers to achieve a high photocatalytic efficiency. Accordingly, the MoSe₂-bridged MoS₂/CdS system produced effective hydrogen (193 μmol·h^-1) as that of water using lactic acid as a hole scavenger with the irradiation of solar light. The presence of few-layered MoSe₂ bridges in MoS₂/CdS successfully separates photogenerated charge carriers, thereby enhancing the shuttling of electrons on the surface to active edge sites. To the best of our knowledge, this few-layered MoSe₂-bridged MoS₂/CdS system exhibits the most effective concert among altogether-reported MoS₂-based CdS composites. Notably, these findings with ample prospective for the development of enormously real photocatalytic systems are due to their economically viable and extraordinary efficiency.

From UV to Near-Infrared Light-Responsive Metal-Organic Framework Composites: Plasmon and Upconversion Enhanced Photocatalysis

The exploitation of photocatalysts that harvest solar spectrum as broad as possible remains a high-priority target yet grand challenge. In this work, for the first time, metal-organic framework (MOF) composites are rationally fabricated to achieve broadband spectral response from UV to near-infrared (NIR) region. In the core-shell structured upconversion nanoparticles (UCNPs)-Pt@MOF/Au composites, the MOF is responsive to UV and a bit visible light, the plasmonic Au nanoparticles (NPs) accept visible light, whereas the UCNPs absorb NIR light to emit UV and visible light that are harvested by the MOF and Au once again. Moreover, the MOF not only facilitates the generation of "bare and clean" Au NPs on its surface and realizes the spatial separation for the Au and Pt NPs, but also provides necessary access for catalytic substrates/products to Pt active sites. As a result, the optimized composite exhibits excellent photocatalytic hydrogen production activity (280 µmol g^-1 h^-1 ) under simulated solar light, and the involved mechanism of photocatalytic H₂ production under UV, visible, and NIR irradiation is elucidated. Reportedly, this is an extremely rare study on photocatalytic H₂ production by light harvesting in all UV, visible, and NIR regions.

Single Pt Atoms Confined into a Metal-Organic Framework for Efficient Photocatalysis

It is highly desirable yet remains challenging to improve the dispersion and usage of noble metal cocatalysts, beneficial to charge transfer in photocatalysis. Herein, for the first time, single Pt atoms are successfully confined into a metal-organic framework (MOF), in which electrons transfer from the MOF photosensitizer to the Pt acceptor for hydrogen production by water splitting under visible-light irradiation. Remarkably, the single Pt atoms exhibit a superb activity, giving a turnover frequency of 35 h^-1 , ≈30 times that of Pt nanoparticles stabilized by the same MOF. Ultrafast transient absorption spectroscopy further unveils that the single Pt atoms confined into the MOF provide highly efficient electron transfer channels and density functional theory calculations indicate that the introduction of single Pt atoms into the MOF improves the hydrogen binding energy, thus greatly boosting the photocatalytic H₂ production activity.

Cocatalyzing Pt/PtO Phase-Junction Nanodots on Hierarchically Porous TiO2 for Highly Enhanced Photocatalytic Hydrogen Production

Phase-junctions between a cocatalyst and its semiconductor host are quite effective to enhance the photocatalytic activity and are widely studied, while reports on the phase-juncted cocatalyst are still rare. In this work, we report the deposition of the Pt/PtO phase-juncted nanodots as cocatalyst via NaOH modification of an interconnected meso-macroporous TiO₂ network with high surface area and inner-particle mesopores to enhance the performance of photocatalytic H₂ production. Our results show that NaOH modification can largely influence Pt/PtO phase-juncted nanodot formation and dispersity. Compared to the TiO₂ nanoparticles, the hierarchically meso-macroporous TiO₂ network containing 0.18 wt % Pt/PtO phase-juncted cocatalyst demonstrates a highest photocatalytic H₂ rate of 13 mmol g^-1 h^-1 under simulated solar light, and possesses a stable cycling activity without obvious decrease after five cycles. Such high H₂ production performance can be attributed to both the phase-juncted Pt/PtO providing more active sites while PtO suppresses the undesirable hydrogen back reaction, and the special hierarchically porous TiO₂ network with inner-particle mesopores presenting short diffusion path lengths for photogenerated electrons and enhanced light harvesting efficiency. This work suggests that Pt/PtO phase-juncted cocatalyst on hierarchically porous TiO₂ nanostructures is a promising strategy for advanced photocatalytic H₂ production.

Bare Cd1-xZnxS ZB/WZ Heterophase Nanojunctions for Visible Light Photocatalytic Hydrogen Production with High Efficiency

In this work, we report the synthesis of Cd1-xZnxS zinc blende/wurtzite (ZB/WZ) heterophase nanojunctions with highly efficient charge separation by a solvothermal method in a mixed solution of diethylenetriamine (DETA) and distilled water. l-Cysteine was selected as a sulfur source and a protecting ligand for stabilization of the ZB/WZ homojunction. The optimal ternary chalcogenide Cd0.7Zn0.3S elongated nanocrystals (NCs) without any cocatalyst loading show very high visible light photocatalytic activity with H2 production efficiency of 3.13 mmol h(-1) and an apparent quantum efficiency of 65.7% at 420 nm. This is one of the best visible light photocatalysts ever reported for photocatalytic hydrogen production without any cocatalysts. The charge separation efficiency, having a critical role in enhancing photocatalytic activity for hydrogen production, was significantly improved. Highly efficient charge separation with a prolonged carrier lifetime is driven by the internal electrostatic field originating from the type-II staggered band alignment at the ZB/WZ junctions, as confirmed by steady and time-resolved photoluminescence spectra. Further, the strong binding between the l-cysteine ligand and Cd1-xZnxS elongated nanocrystals protects and stabilizes NCs; the l-cysteine ligand at the interface could trap holes from Cd1-xZnxS NCs, while photogenerated electrons transfer to Cd1-xZnxS catalytic sites for proton reduction. Our results demonstrate that Cd1-xZnxS ZB/WZ heterophase junctions stabilized by l-cysteine molecules can effectively separate charge carriers and achieve highly visible light photocatalytic hydrogen production. The present study provides a new insight into the design and fabrication of advanced materials with homojunction structures for photocatalytic applications and optoelectronic devices.

Ga-Promoted Photocatalytic H2 Production over Pt/ZnO Nanostructures

Photocatalytic H2 generation is investigated over a series of Ga-modified ZnO photocatalysts that were prepared by hydrothermal methods. It is found that the structural, textural, and optoelectronic properties remarkably depend on the Ga content. The photocatalytic activity is higher in samples with Ga content equal to or lower than 5.4 wt %, which are constituted by Zn1-xGaxO phases. Structural, textural, and optoelectronic characterization, combined with theoretical calculations, reveals the effect of Ga in the doped ZnO structures. Higher Ga incorporation leads to the formation of an additional ZnGa2O4 phase with spinel structure. The presence of such a phase is detrimental for the textural and optoelectronic properties of the photocatalysts, leading to a decrease in H2 production. When Pt is used as the cocatalyst, there is an increase of 1 order of magnitude in the activity with respect to the bare photocatalysts. This is a result of Pt acting as an electron scavenger, decreasing the electron-hole recombination rate and boosting the H2 evolution reaction.

Metallic 1T-LixMoS2 Cocatalyst Significantly Enhanced the Photocatalytic H2 Evolution over Cd0.5Zn0.5S Nanocrystals under Visible Light Irradiation

In the present work, metallic 1T-LixMoS2 is utilized as a novel cocatalyst for Cd0.5Zn0.5S photocatalyst. The obtained LixMoS2/Cd0.5Zn0.5S hybrids show excellent photocatalytic performance for H2 generation from aqueous solution containing Na2S and Na2SO3 under splitting visible light illumination (λ ≥ 420 nm) without precious metal cocatalysts. It turns out that a certain amount of intercalating Li(+) ions ultimately drives the transition of MoS2 crystal from semiconductor triagonal phase (2H phase) to metallic phase (1T phase). The distinct properties of 1T-LixMoS2 promote the efficient separation of photoexcited electrons and holes when used as cocatalyst for Cd0.5Zn0.5S photocatalyst. As compared to 2H-MoS2 nanosheets only having edge active sites, photoinduced electrons not only transfer to the edge sites of 1T-LixMoS2, but also to the plane active sites of 1T-LixMoS2 nanosheets. The content of LixMoS2 in hybrid photocatalysts influences the photocatalytic activity. The optimal 1T-LixMoS2 (1.0 wt %)/Cd0.5Zn0.5S nanojunctions display the best activity for hydrogen production, achieving a hydrogen evolution rate of 769.9 μmol h(-1), with no use of noble metal loading, which is about 3.5 times higher than that of sole Cd0.5Zn0.5S, and 2 times higher than that of 2H-MoS2 (1.0 wt %)/Cd0.5Zn0.5S samples. Our results demonstrate that Li(+)-intercalated MoS2 nanosheets with high conductivity, high densities of active sites, low cost, and environmental friendliness are a prominent H2 evolution cocatalyst that might substitute for noble metal for potential hydrogen energy applications.