MoS2-Stratified CdS-Cu2-xS Core-Shell Nanorods for Highly Efficient Photocatalytic Hydrogen Production

Tailoring Copper Single-Atoms-Stabilized Metastable Transition-Metal-Dichalcogenides for Sustainable Hydrogen Production

Unconventional 1T' phase transition metal dichalcogenides (TMDs) show great potential for hydrogen evolution reaction (HER). However, they are susceptible to transitioning into the stable 2H phase, which reduces their catalytic activity and stability. Herein, we present a scalable approach for designing thermally stable 1T'-TMDs hollow structures (HSs) by etching Cu1.94S templates from pre-synthesized Cu1.94S@TMDs heterostructures, including 1T'-MoS2, MoSe2, WS2, and WSe2 HSs. Furthermore, taking 1T'-MoS2 HSs as an example, the etched Cu ions can be firmly adsorbed on their surface in the form of single atoms (SAs) through Cu-S bonds, thereby elevating the phase transition temperature from 149 °C to 373 °C. Due to the advantages conferred by the 1T' phase, hollow structure, and synergistic effect between Cu SAs and 1T'-MoS2 supports, the fabricated 1T'-MoS2 HSs demonstrate superior HER performance. Notably, their high-phase stability enables continuous operation of designed 1T'-MoS2 HSs for up to 200 hours at an ampere-level current density without significant activity decay. This work provides a universal method for synthesizing highly stable 1T'-TMDs electrocatalysts, with a particular focus on the relationship between their phase and catalytic stability.

Molybdenum Disulfide Induced Phase Control Synthesis of Multi-dimensional Co3S4-MoS2 Heteronanostructures via Cation Exchange

Phase control over cation exchange (CE) reactions has emerged as an important approach for the synthesis of nanomaterials (NMs), enabling precise determination of their reactivity and properties. Although factors such as crystal structure and morphology have been studied for the phase engineering of CE reactions in NMs, there remains a lack of systematic investigation to reveal the impact for the factors in heterogeneous materials. Herein, we report a molybdenum disulfide induced phase control method for synthesizing multidimensional Co3S4-MoS2 heteronanostructures (HNs) via cation exchange. MoS2 in parent Cu1.94S-MoS2 HNs are proved to affect the thermodynamics and kinetics of CE reactions, and facilitate the formation of Co3S4-MoS2 HNs with controlled phase. This MoS2 induced phase control method can be extended to other parent HNs with multiple dimensions, which shows its diversity. Further, theoretical calculations demonstrate that Co3S4 (111)/MoS2 (001) exhibits a higher adhesion work, providing further evidence that MoS2 enables phase control in the HNs CE reactions, inducing the generation of novel Co3S4-MoS2 HNs. As a proof-of-concept application for crystal phase- and dimensionality-dependent of cobalt sulfide based HNs, the obtained Co3S4-MoS2 heteronanoplates (HNPls) show remarkable performance in hydrogen evolution reactions (HER) under alkaline media. This synthetic methodology provides a unique design strategy to control the crystal structure and fills the gap in the study of heterogeneous materials on CE reaction over phase engineering that are otherwise inaccessible.

Protonated Z-scheme CdS-covalent organic framework heterojunction with highly efficient photocatalytic hydrogen evolution

The low efficiency of photocatalytic hydrogen production from water is mainly suffer from limited light absorption, charge separation and water delivery to the active centers. Herein, an inorganic-organic Z-scheme heterojunction (CdS-COF-Ni) is constructed by in-situ growth of CdS nanosheets on the porphyrin-based covalent organic framework with nickel ions (COF-Ni) in the porphyrin centers. A built-in electric field is formed at the interface, which accelerates the separation and transfer of photogenerated charges. Moreover, through the surface protonation treatment in ascorbic acid (AC) solution, the hydrophilicity of the obtained composite is obviously increased and facilitates the transport of water molecules to the photocatalytic centers. Under the synergistic effect of the interfacial interaction and surface protonation treatment, the photocatalytic hydrogen production rate is optimized to be 18.23 mmol h-1 g-1 without adding any cocatalysts, which is 21 times that of CdS. After a series of photoelectrochemical measurements, in situ X-ray photoelectron spectroscopy (XPS) analysis, and density functional theory (DFT) calculations, it is found that the photocatalytic charge transfer pathway conforms to the Z-scheme mechanism, which not only greatly accelerates the separation and transfer of photogenerated charges, but also retains a high reduction capacity for water splitting. This work offers a good strategy for constructing highly efficient organic-inorganic heterojunctions for water splitting.

Surface Plasmon Resonance-Mediated Photocatalytic H2 Generation

The limited yield of H2 production has posed a significant challenge in contemporary research. To address this issue, researchers have turned to the application of surface plasmon resonance (SPR) materials in photocatalytic H2 generation. SPR, arising from collective electron oscillations, enhances light absorption and facilitates efficient separation and transfer of electron-hole pairs in semiconductor systems, thereby boosting photocatalytic H2 production efficiency. However, existing reviews predominantly focus on SPR noble metals, neglecting non-noble metals and SPR semiconductors. In this review, we begin by elucidating five different SPR mechanisms, covering hot electron injection, electric field enhancement, light scattering, plasmon-induced resonant energy transfer, and photo-thermionic effect, by which SPR enhances photocatalytic activity. Subsequently, a comprehensive overview follows, detailing the application of SPR materials-metals, non-noble metals, and SPR semiconductors-in photocatalytic H2 production. Additionally, a personal perspective is offered on developing highly efficient SPR-based photocatalysis systems for solar-to-H2 conversion in the future. This review aims to guide the development of next-gen SPR-based materials for advancing solar-to-fuel conversion.

Cu1.94S-ZnS-CdS ternary heteronanoplates with efficient carrier transfer for enhanced photocatalytic hydrogen evolution

Incorporating precise morphology control and efficient carrier separation into single-nanoparticle heterojunctions to achieve high photocatalytic efficiency remains a significant challenge. Here, we synthesized Cu1.94S-ZnS-CdS ternary heteronanoplates (HNPs) with a continuous sublattice structure using cation exchange reactions. Femtosecond transient absorption spectroscopy (TAS) confirms that ternary heterojunction enhances carrier separation efficiency, demonstrating both rapid separation (∼0.2 ps) and an extended lifetime (∼1512 ps). The synergistic combination results in a significantly enhanced hydrogen evolution rate of 2.012 mmol·g-1·h-1, which is 17 times and 183 times higher than that achieved by pure CdS and ZnS, respectively. Furthermore, there is no significant decrease in the activity of Cu1.94S-ZnS-CdS in photocatalytic hydrogen evolution after 288 days of placement. Our work offers an alternative approach for designing noble-metal-free photocatalysts with precisely defined materials and interfaces, aiming to enhance both photocatalytic hydrogen evolution efficiency and stability.

Enhanced Photocatalytic Hydrogen Production Activity Driven by TiO2/(MoP/CdS): Insights from Powder Particles to Thin Films

Transitioning from powder photocatalysts to thin film photocatalysts is one of the necessary steps toward industrializing photocatalytic hydrogen production. Herein, we reported the integration of non-noble metal cocatalyst MoP decorated with TiO2 and CdS, forming TiO2/(MoP/CdS) for ultraviolet-visible light utilization. The designed powder TiO2/(MoP/CdS) composites achieved a superior hydrogen production rate of 42.2 mmol g-1 h-1, which is 30.1 times that of TiO2/CdS, performing the highest activity among the TiO2-CdS-based composite photocatalysts. Moreover, we fabricated a thin film from TiO2/(MoP/CdS) powder, which exhibited comparable photocatalytic activity for hydrogen production, achieving 35.5 mmol g-1 h-1 and maintaining long-term stability for 150 h. The outstanding performance was attributed to the ability of the TiO2/(MoP/CdS) composite photocatalysts to absorb both visible and ultraviolet light. Additionally, the heterojunction formed between TiO2 and CdS also played a significant role in the overall photocatalyst activity. This cost-effective catalyst holds promise for future large-scale industrial applications.

Materials Advances in Photocatalytic Solar Hydrogen Production: Integrating Systems and Economics for a Sustainable Future

Photocatalytic solar hydrogen generation, encompassing both overall water splitting and organic reforming, presents a promising avenue for green hydrogen production. This technology holds the potential for reduced capital costs in comparison to competing methods like photovoltaic-electrocatalysis and photoelectrocatalysis, owing to its simplicity and fewer auxiliary components. However, the current solar-to-hydrogen efficiency of photocatalytic solar hydrogen production has predominantly remained low at ≈1-2% or lower, mainly due to curtailed access to the entire solar spectrum, thus impeding practical application of photocatalytic solar hydrogen production. This review offers an integrated, multidisciplinary perspective on photocatalytic solar hydrogen production. Specifically, the review presents the existing approaches in photocatalyst and system designs aimed at significantly boosting the solar-to-hydrogen efficiency, while also considering factors of cost and scalability of each approach. In-depth discussions extending beyond the efficacy of material and system design strategies are particularly vital to identify potential hurdles in translating photocatalysis research to large-scale applications. Ultimately, this review aims to provide understanding and perspective of feasible pathways for commercializing photocatalytic solar hydrogen production technology, considering both engineering and economic standpoints.

Engineered Two-Dimensional Transition Metal Dichalcogenides for Energy Conversion and Storage

Designing efficient and cost-effective materials is pivotal to solving the key scientific and technological challenges at the interface of energy, environment, and sustainability for achieving NetZero. Two-dimensional transition metal dichalcogenides (2D TMDs) represent a unique class of materials that have catered to a myriad of energy conversion and storage (ECS) applications. Their uniqueness arises from their ultra-thin nature, high fractions of atoms residing on surfaces, rich chemical compositions featuring diverse metals and chalcogens, and remarkable tunability across multiple length scales. Specifically, the rich electronic/electrical, optical, and thermal properties of 2D TMDs have been widely exploited for electrochemical energy conversion (e.g., electrocatalytic water splitting), and storage (e.g., anodes in alkali ion batteries and supercapacitors), photocatalysis, photovoltaic devices, and thermoelectric applications. Furthermore, their properties and performances can be greatly boosted by judicious structural and chemical tuning through phase, size, composition, defect, dopant, topological, and heterostructure engineering. The challenge, however, is to design and control such engineering levers, optimally and specifically, to maximize performance outcomes for targeted applications. In this review we discuss, highlight, and provide insights on the significant advancements and ongoing research directions in the design and engineering approaches of 2D TMDs for improving their performance and potential in ECS applications.

In-situ and wavelength-dependent photocatalytic strain evolution of a single Au nanoparticle on a TiO2 film

Photocatalysis is a promising technique due to its capacity to efficiently harvest solar energy and its potential to address the global energy crisis. However, the structure-activity relationships of photocatalyst during wavelength-dependent photocatalytic reactions remains largely unexplored because it is difficult to measure under operating conditions. Here we show the photocatalytic strain evolution of a single Au nanoparticle (AuNP) supported on a TiO2 film by combining three-dimensional (3D) Bragg coherent X-ray diffraction imaging with an external light source. The wavelength-dependent generation of reactive oxygen species (ROS) has significant effects on the structural deformation of the AuNP, leading to its strain evolution. Density functional theory (DFT) calculations are employed to rationalize the induced strain caused by the adsorption of ROS on the AuNP surface. These observations provide insights of how the photocatalytic activity impacts on the structural deformation of AuNP, contributing to the general understanding of the atomic-level catalytic adsorption process.

Quasi-type-II Cu-In-Zn-S/Ni-MOF heterostructure with prolonged carrier lifetime for photocatalytic hydrogen production

Visible-driven photocatalytic hydrogen production using narrow-bandgap semiconductors has great potential for clean energy development. However, the widespread use of these semiconductors is limited due to problems such as severe charge recombination and slow surface reactions. Herein, a quasi-type-II heterostructure was constructed by combining bifunctional Ni-based metal-organic framework (Ni-MOF) nanosheets with BDC (1,4-benzenedicarboxylic acid) linker coupled with Cu-In-Zn-S quantum dots (CIZS QDs). This heterostructure exhibited a prolonged charge carrier lifetime and abundant active sites, leading to significantly improved hydrogen production rate. The optimized rate achieved by the CIZS/Ni-MOF heterostructure was 2642 μmol g-1 h-1, which is 5.28 times higher than that of the CIZS QDs. This improved performance can be attributed to the quasi-type-II band alignment between the CIZS QDs and Ni-MOF, which facilitates effective delocalization of the photogenerated electrons within the system. Additional photoelectrochemical tests confirmed the well-maintained photoluminescence and prolonged charge carrier lifetime of the CIZS/Ni-MOF heterostructure. This study provides valuable insights into the use of multifunctional MOFs in the development of highly efficient composite photocatalysts, extending beyond their role in light harvesting and charge separation.

Induced dipole moments in amorphous ZnCdS catalysts facilitate photocatalytic H2 evolution

Amorphous semiconductors without perfect crystalline lattice structures are usually considered to be unfavorable for photocatalysis due to the presence of enriched trap states and defects. Here we demonstrate that breaking long-range atomic order in an amorphous ZnCdS photocatalyst can induce dipole moments and generate strong electric fields within the particles which facilitates charge separation and transfer. Loading 1 wt.% of low-cost Co-MoSx cocatalysts to the ZnCdS material increases the H2 evolution rate to 70.13 mmol g-1 h-1, which is over 5 times higher than its crystalline counterpart and is stable over the long-term up to 160 h. A flexible 20 cm × 20 cm Co-MoSx/ZnCdS film is prepared by a facile blade-coating technique and can generate numerous observable H2 bubbles under natural sunlight, exhibiting potential for scale-up solar H2 production.

Visible light-induced hole transfer in single-nanoplate Cu1.81S-CdS heterostructures

The separation and transfer of photogenerated carriers in semiconducting materials are essential processes that determine the efficiency of optoelectronic devices and photocatalysts, and transient absorption spectroscopy provides a powerful support for exploring the diffusion and recombination of photogenerated electrons and holes. Herein, high-quality Cu1.81S nanoplates were synthesized by a hot injection method, and were used as starting templates for the preparation of Cu1.81S-CdS heterojunctions and CdS nanoplates by cation exchange. Their carrier dynamics were investigated by transient absorption spectroscopy, which revealed that photogenerated holes may be transferred from the CdS phase to the Cu1.81S phase under 400 nm excitation. This process is in the opposite direction to the hole transfer induced by near-infrared localized surface plasmon resonance in copper sulfide heterostructures. Moreover, density functional theory calculations were used to further explain the visible light-induced hole transport process. This transfer is a potential way to increase the rate of H2 production and enhance the photostability of the catalyst.

Recent advances in the role of MXene based hybrid architectures as electrocatalysts for water splitting

The development of non-noble metal based and cost-effective electrocatalysts for water splitting has attracted significant attention due to their potential in production of clean and green hydrogen fuel. Discovered in 2011, a family of two-dimensional transition metal carbides, nitrides, and carbonitrides, have demonstrated promising performance as electro catalysts in the water splitting process due to their high electrical conductivity, very large surface area and abundant catalytic active sites. However, their-long term stability and recyclability are limited due to restacking and agglomeration of MXene flakes. This problem can be solved by combining MXene with other materials to create their hybrid architectures which have demonstrated higher electrocatalytic performance than pristine MXenes. Electrolysis of water encompasses two half-cell reactions, hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode. Firstly, this concise review explains the mechanism of water splitting. Then it provides an overview of the recent advances about applications of MXenes and their hybrid architectures as HER, OER and bifunctional electrocatalysts for overall water splitting. Finally, the recent challenges and potential outlook in the field have been presented. This concise review may provide further understanding about the role of MXene-based hybrid architectures to develop efficient electrocatalysts for water splitting.

Self-Assembly of Mixed-Dimensional GeS1- x Sex (1D Nanowire)-(2D Plate) Van der Waals Heterostructures

The integration of dissimilar materials into heterostructures is a mainstay of modern materials science and technology. An alternative strategy of joining components with different electronic structure involves mixed-dimensional heterostructures, that is, architectures consisting of elements with different dimensionality, for example, 1D nanowires and 2D plates. Combining the two approaches can result in hybrid architectures in which both the dimensionality and composition vary between the components, potentially offering even larger contrast between their electronic structures. To date, realizing such heteromaterials mixed-dimensional heterostructures has required sequential multi-step growth processes. Here, it is shown that differences in precursor incorporation rates between vapor-liquid-solid growth of 1D nanowires and direct vapor-solid growth of 2D plates attached to the wires can be harnessed to synthesize heteromaterials mixed-dimensional heterostructures in a single-step growth process. Exposure to mixed GeS and GeSe vapors produces GeS1- x Sex van der Waals nanowires whose S:Se ratio is considerably larger than that of attached layered plates. Cathodoluminescence spectroscopy on single heterostructures confirms that the bandgap contrast between the components is determined by both composition and carrier confinement. These results demonstrate an avenue toward complex heteroarchitectures using single-step synthesis processes.

Defect-induced atomic-level intimate interface of a hollow Ov-CeO2/CdS photocatalyst with a Z-scheme to boost hydrogen evolution

Construction of Z-scheme heterojunction catalysts with high-speed charge transfer channels for efficient photocatalytic hydrogen production from water splitting is still a challenge. In this work, a lattice-defect-induced atom migration strategy is proposed to construct an intimate interface. The oxygen vacancies of cubic CeO₂ obtained from a Cu₂O template are used to induce lattice oxygen migration and form SO bonds with CdS to form a close contact heterojunction with a hollow cube. The hydrogen production efficiency reaches ∼12.6 mmol·g^-1·h^-1 and maintains a high value over 25 h. A series of photocatalytic tests combined with density functional theory (DFT) calculations show that the close contact heterostructure not only promotes the separation/transfer of photogenerated electron-hole pairs but also regulates the intrinsic catalytic activity of the surface. A large number of oxygen vacancies and SO bonds at the interface participate in charge transfer, which accelerates the migration of photogenerated carriers. The hollow structure improves the ability to capture visible light. Therefore, the synthesis strategy proposed in this work, as well as the in-depth discussion of the interface chemical structure and charge transfer mechanism, provides new theoretical support for the further development of photolytic hydrogen evolution catalysts.

Methylthio-functionalized UiO-66 to promote the electron-hole separation of ZnIn2S4 for boosting hydrogen evolution under visible light illumination

Solar-driven water splitting offers a leading-edge approach to storing abundant and intermittent solar energy and producing hydrogen as a clean and sustainable energy carrier. More importantly, constructing well-designed photocatalysts is a promising approach to develop clean hydrogen energy. In this paper, flower spherical UiO-66-(SCH₃)₂/ZnIn₂S₄ (UiOSC/ZIS) photocatalysts are successfully synthesized by a simple two-step hydrothermal method, and they exhibit high hydrogen production activity in light-driven water splitting. The optimized 30-UiOSC/ZIS (the content of UiOSC was 30 mg) composite exhibits optimal hydrogen production activity with a hydrogen production of 3433 μmol g^-1 h^-1, which is 5 and 235 times higher than that of pure ZIS and UiOSC, respectively. In addition, a long-cycling stability test has shown that the UiOSC/ZIS composite has good stability and recyclability. Experimental and characterization results show the formation of a type-II heterojunction between UiOSC and ZIS. This effectively suppresses the recombination of electrons-holes and promotes the carrier transfer, thus significantly improving the hydrogen production performance. This research further promotes the application of UiO-66-(SCH₃)₂ in the field of photocatalytic hydrogen production and provides a reference for the rational design of UiO-66-based composite photocatalysts.

2D Transition Metal Dichalcogenides for Photocatalysis

Two-dimensional (2D) transition metal dichalcogenides (TMDs), a rising star in the post-graphene era, are fundamentally and technologically intriguing for photocatalysis. Their extraordinary electronic, optical, and chemical properties endow them as promising materials for effectively harvesting light and catalyzing the redox reaction in photocatalysis. Here, we present a tutorial-style review of the field of 2D TMDs for photocatalysis to educate researchers (especially the new-comers), which begins with a brief introduction of the fundamentals of 2D TMDs and photocatalysis along with the synthesis of this type of material, then look deeply into the merits of 2D TMDs as co-catalysts and active photocatalysts, followed by an overview of the challenges and corresponding strategies of 2D TMDs for photocatalysis, and finally look ahead this topic.

PtS quantum dots/Nb2O5 nanosheets with accelerated charge transfer for boosting photocatalytic H2 production

The rapid recombination rate of charges limits the improvement of photocatalytic hydrogen evolution performance related to semiconductor photocatalysts. An effective strategy to accelerate charge separation and transfer is the design and construction of new high-efficiency cocatalysts on photocatalysts. Herein, a system of PtS quantum dots/Nb₂O₅ nanosheets (PtS/Nb₂O₅) was constructed via the in situ vapor phase (ISVP) synthesis process. The conclusions from ultrafast femtosecond-resolved TA spectroscopy indicated that the lifetime of the photogenerated charges of PtS/Nb₂O₅ (6073.75 ps) was shortened markedly in contrast to that of Nb₂O₅ (6634.05 ps), manifesting the facilitated separation and transfer of photogenerated charges caused by the quantum-dot-structured PtS cocatalyst. The enhanced charge separation and transfer capacity contributes to an excellent H₂ production rate of 182.5 μmol h^-1 for PtS/Nb₂O₅, which is up to 3.4 and 12.2 times that of Pt/Nb₂O₅ and Nb₂O₅, respectively. This work brings up new avenues for constructing unique and effective photocatalysts via the cocatalyst design.

Selective-Epitaxial Hybrid of Tripartite Semiconducting Sulfides for Enhanced Solar-to-Hydrogen Conversion

The design and synthesis of advanced semiconductors is crucial for the full utilization of solar energy. Herein, colloidal selective-epitaxial hybrid of tripartite semiconducting sulfides CuInS₂ Cd(In)SMoS₂ heteronanostructures (HNs) via lateral- and vertical-epitaxial growths, followed by cation exchange reactions, are reported. The lateral-epitaxial CuInS₂ and Cd(In)S enable effective visible to near-infrared (NIR) solar spectrum absorption, and the vertical-epitaxial ultrathin MoS₂ offer sufficient edge sulfur sites for the hydrogen evolution reaction (HER). Furthermore, the integrated structures exhibit unique epitaxial-staggered type II band alignments for continuous charge separation. They achieve the H₂ evolution rate up to 8 mmol h^-1 g^-1 , which is ≈35 times higher than bare CdS and show no deactivation after long-term cycling, representing one of the most efficient and robust noble-metal-free photocatalysts. This design principle and transformation protocol open a new way for creating all-in-one multifunctional catalysts in a predictable manner.

Recent advances in solution assisted synthesis of transition metal chalcogenides for photo-electrocatalytic hydrogen evolution

Hydrogen evolution from water splitting is considered to be an important renewable clean energy source and alternative to fossil fuels for future energy sustainability. Photocatalytic and electrocatalytic water splitting is considered to be an effective method for the sustainable production of clean energy, H₂. This perspective especially emphasizes research advances in the solution-assisted synthesis of transition metal chalcogenides for both photo and electrocatalytic hydrogen evolution applications. Transition metal chalcogenides (CdS, MoS₂, WS₂, TiS₂, TaS₂, ReS₂, MoSe₂, and WSe₂) have received intensified research interest over the past two decades on account of their unique properties and great potential across a wide range of applications. The photocatalytic activity of transition metal chalcogenides can further be improved by elemental doping, heterojunction formation with noble metals (Au, Pt, etc.), non-chalcogenides (MoS₂, In₂S₃, NiS_1-X), morphological tuning, through various solution-assisted synthesis processes, including liquid-phase exfoliation, heat-up, hot-injection methods, hydrothermal/solvothermal routes and template-mediated synthesis processes. In this review we will discuss recent developments in transition metal chalcogenides (TMCs), the role of TMCs for hydrogen production and various strategies for surface functionalization to increase their activity, different synthesis methods, and prospects of TMCs for hydrogen evolution. We have included a brief discussion on the effect of surface hydrogen binding energy and Gibbs free energy change for HER in electrocatalytic hydrogen evolution.

Ni2P NPs loaded on methylthio-functionalized UiO-66 for boosting visible-light-driven photocatalytic H2 production

The UiO-66 family shows promising photocatalytic prospects in water splitting for hydrogen evolution under visible light irradiation due to its suitable band gap and adequate active sites. In this work, novel Ni₂P/UiO-66-(SCH₃)₂ composites were prepared by a simple solvothermal method. These as-synthesized samples were fully characterized by XRD, SEM, TEM, HRTEM, EDS, and XPS methods. The effectiveness of visible light driven photocatalytic water-splitting to produce hydrogen was investigated in the presence of sacrificial agents. The results showed that the optimal hydrogen yield of 5 wt% Ni₂P/UiO-66-(SCH₃)₂ is 3724.22 μmol g^-1 h^-1, reaching almost 187 times that of pristine UiO-66-(SCH₃)₂ (19.93 μmol g^-1 h^-1). Meanwhile, long term cycling stability tests also showed that Ni₂P/UiO-66-(SCH₃)₂ composites present an excellent photocatalytic H₂ production stability. Photoelectrochemical performance analysis revealed that the high catalytic activity of the composite materials could be associated with the synergistic effect of UiO-66-(SCH₃)₂ and Ni₂P. Light stimulates UiO-66-(SCH₃)₂ to generate electrons and holes, and Ni₂P as a cocatalyst could effectively transmit electrons and boost photogenerated charge separation. This work provides a reference for exploring UiO-66 family catalysts with good catalytic activity.

3D/2D Heterojunction of CeO2/Ultrathin MXene Nanosheets for Photocatalytic Hydrogen Production

Two-dimensional (2D) nanomaterials benefit from the high specific surface area, unique surface properties, and quantum size effects, which have attracted widespread scientific attention. MXenes add many members to the 2D material family, mainly metal conductors, most of which are dielectrics, semiconductors, or semimetals. With excellent electron mobility, beneficial to electron-hole separation, and large functional groups that can be tightly coupled with other materials, MXenes have broad application prospects in photocatalysis. Meanwhile, the application of CeO₂-based materials in organic catalysis, photocatalytic water splitting, and photodegradation of organic pollutants has been extensively explored, and studies have found that CeO₂-based materials show good photocatalytic performance. In view of this, we synthesized regular octahedral CeO₂ with a homojunction in one step by a hydrothermal method and compounded it with ultrathin 2D material MXene, which exhibited fast carrier migration efficiency and a good interfacial effect, making the material show excellent photocatalytic activity. The results showed that the photocatalytic H₂ evolution performance of the MXene/CeO₂ heterojunction was significantly improved. In this study, a low-cost catalyst with high photocatalytic activity was prepared, presenting a new research idea for achieving a combined 3D/2D photocatalytic system.

Directional Damping of Plasmons at Metal-Semiconductor Interfaces

ConspectusOver the past decade, it has been shown that surface plasmons can enhance photoelectric conversion in photovoltaics, photocatalysis, and other optoelectronic applications through their plasmonic absorption and damping processes. However, plasmonically enhanced devices have yet to routinely match or exceed the efficiencies of traditional semiconductor devices. The effect of plasmonic losses dissipates the absorbed photoenergy mostly into heat and that has hampered the realization of superior next-generation plasmonic optoelectronic devices. Several approaches are being explored to alleviate this situation, including using gain to compensate for the plasmonic losses, designing and synthesizing alternative low-loss plasmonic materials, and reducing activation barriers in plasmonic devices and physical thicknesses of photoabsorber layers to lower the plasmonic losses. A newly proposed plasmon-induced interfacial charge-transfer transition (PIICTT) mechanism has proven to be effective in minimizing energy loss during interfacial charge transfer. The PIICTT leads to a damping of metallic plasmonics by directly generating excitons at the plasmonic metal/semiconductor heteronanostructures. This novel concept has been proven to overcome some of the limitations of electron-transfer inefficiencies, renewing a focus on surface plasmon damping processes with the goal that the plasmonic excitation energies of metal nanoparticles can be more efficiently transferred to the adjacent semiconductor components in the absence and presence of an effective interlayer of carrier-selective blocking layer (CSBL). Several theoretical and experimental studies have concluded that efficient plasmon-induced ultrafast hot-carrier transfer was observed in plasmonic-metal/semiconductor heteronanostructures. The PIICTT mechanism may well be a general phenomenon at plasmonic metal/semiconductor, metal/molecule, semiconductor/semiconductor, and semiconductor/molecule heterointerfaces. Thus, the PIICTT presents a new opportunity to limit energy loss in plasmonic-metal nanostructures and increase device efficiencies based on plasmonic coupling. The nonradiative damping of surface plasmons can impact the energy flux direction and thereby provide a new process beyond light trapping, focusing, and hot carrier creation.In this Account, we draw much attention to the benefits of interfacial plasmonic coupling, highlighting recent pioneering discoveries in which plasmon-induced interfacial charge- and energy-transfer processes enable the generation of hot charge carriers near the plasmonic-metal/semiconductor interfaces. This process is likely to increase the photoelectric conversion efficiency, constituting "plasmonic enhancement". We also discuss recent advances in the dynamics of surface plasmon relaxation and highlight exciting new possibilities for plasmonic metals and their interactions with strongly attached semiconductors to provide directional energy fluxes. While this new research area comes on the heels of much elaborate research on both metal and semiconductor nanomaterials, it provides a subtle but important refinement in understanding the optoelectronic properties of materials with far-reaching consequences from fundamental interface science to technological applications. We hope that this Account will contribute to a more systematic description of interface-coupled plasmonics, both fundamentally and in terms of applications toward the design of plasmonic heterostructured devices.

Confinement Matters: Stabilization of CdS Nanoparticles inside a Postmodified MOF toward Photocatalytic Hydrogen Evolution

Insights into developing innovative routes for the stabilization of photogenerated charge-separated states by suppressing charge recombination in photocatalysts is a topic of immense importance. Herein, we report the synthesis of a metal-organic framework (MOF)-based composite where CdS nanoparticles (NPs) are confined inside the nanosized pores of Zr⁴⁺-based MOF-808, namely, CdS@MOF-808. Anchoring l-cysteine into the nanospace of MOF-808 via postsynthetic ligand exchange allows the capture of Cd²⁺ ions from their aqueous solution, which are further utilized for in situ growth of CdS NPs inside the nanosized MOF pores. The formation of CdS@MOF-808 opens up a possibility for visible-light photocatalysis as CdS NPs (1-2 nm) are a well-studied semiconductor system with a band gap of ∼2.6 eV. The confinement of the CdS NPs inside the MOF pores, close to the Zr⁴⁺ cluster, opens up a shorter electron transfer route from CdS to the catalytic Zr⁴⁺ cluster and shows a high rate of H₂ evolution (10.41 mmol g^-1 h^-1) from water with a loading of 3.56 wt % CdS. In contrast, a similar composite in which CdS NPs are stabilized on the external surface of MOF-808 reveals poor activity (0.15 mmol g^-1 h^-1). CdS NPs stabilized on the MOF-808 surface show slower and inefficient electron transfer kinetics compared to CdS stabilized inside the nanospace of the MOF, as realized by the transient absorption measurements. Therefore, this work unveils the critical role of stabilizing the photosensitizer NPs in close proximity of the catalytic sites in MOF systems towards developing highly efficient H₂ evolution photocatalysts.

Synergetic metal-semiconductor interaction: Single-atomic Pt decorated CdS nano-photocatalyst for highly water-to-hydrogen conversion

Solar driven water-to-hydrogen conversion is a promising technology for the typical sustainable production mode, so increasing efforts are being devoted to exploit high-performance photocatalytic materials. Cadmium sulfide (CdS) is widely used to prepare highly active photocatalysts owing to its merits of broadband-light harvesting and feasible band structure. However, the slow photo-carriers' migration in CdS body structure generally results in high-frequency carriers recombination, which leads to unsatisfied photoactivity. Metallic single-atom surface decoration is an effective method to build the strong metal-support interaction for promotion of photo-carriers' migration. Herein, a simple light-induced reduction procedure was proposed to decorate single-atomic Pt on the surface of CdS nanoparticles for highly photocatalytic HER activity. Research showed that the synergetic metal (Pt)-semiconductor (CdS) interaction significantly promoted the body-to-surface (BTS) photo-carriers' migration of CdS, thereby the high light-to-fuel conversion efficiency (AQY_{500 nm} = 25.70%) and 13.5-fold greater simulated sunlight driven HER rate of bare CdS was achieved by this CdS-Pt nano-photocatalyst. Based on the photo-electrochemical analysis and density functional theory calculations, the remarkably improved HER photoactivity can be attributed to the enhanced light-harvesting, promoted BTS electron migration and reduced reaction energy barriers. This study provides a facile procedure to obtain CdS based photocatalyst with metallic single-atom sites for high-performance HER photocatalysis.

Ultrafast interfacial charge evolution of the Type-II cadmium Sulfide/Molybdenum disulfide heterostructure for photocatalytic hydrogen production

The interfacial charge dynamics was crucial for semiconductor heterostructure photocatalysis. Through the rational design of the heterostructure interface, heterojunction expressed variable recombination and migration dynamics for excited carriers. Herein, followed by a typical chemical bath strategy with the hexagonal cadmium sulfide (CdS) overlapped on the exfoliated molybdenum disulfide (MoS₂) film, we developed a cadmium sulfide/molybdenum disulfide (CdS-MoS₂) nano-heterojunction and investigated the interfacial charge dynamics for photocatalytic hydrogen evolution. Photoelectron spectroscopy detected an energetic offset between CdS and MoS₂, revealing the formation of an interfacial electric field with efficient charges separation. Through transient absorption spectra, we demonstrated the type-II contact at the CdS-MoS₂ interface. Driven by the electric field, the excited carriers separated and rapidly migrated to sub-band defects of CdS within the first 500 fs. The carriers-restricted defects provided catalytic active sites, endowing CdS-MoS₂ a highly efficient photocatalytic capability. Consequentially, the CdS-MoS₂ achieved an enhanced hydrogen evolution rate of 2.3 mmol·g^-1·h^-1 with significantly stronger photocurrent density. This work gave an insight to the channel of interfacial separation and migration for excited carriers, which could contribute to the interfacial engineering of advanced heterojunction photocatalysts.

Crystal structure dependent cation exchange reactions in Cu2-xS nanoparticles

Because of high mobility of Cu⁺ in crystal lattice, Cu_2-xS nanoparticles (NPs) utilized as cation exchange (CE) templates to produce complicated nanomaterials has been extensively investigated. Nevertheless, the structural similarity of commonly used Cu_2-xS somewhat limits the exploration of crystal structure dependent CE reactions, since it may dramatically affect the reaction dynamics and pathways. Herein, we select djurleite Cu_1.94S and covellite CuS nanodisks (NDs) as starting templates and show that the crystal structure has a strong effect on their CE reactions. In the case of djurleite Cu_1.94S NDs, the Cu⁺ was immediately substituted by Cd²⁺ and solid wurtzite CdS NDs were produced. At a lower reaction temperature, these NDs were partially substituted, giving rise to the formation of Janus-type Cu_1.94S/CdS NDs, and this process is kinetically and thermodynamically favorable. For covellite CuS NDs, they were transformed into hollow CdS NDs under a more aggressive reaction condition due to the unique disulfide covalent bonds. These disulfide bonds distributed along [0 0 1] direction were gradually ruptured/reduced and CuS@CdS core-shell NDs could be obtained. Our findings suggest that not only the CE reaction kinetics and thermodynamics, but also the intermediates and final products are intimately correlated to the crystal structure of the host material.

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.

Molybdenum disulfide loading on a Z-scheme graphitic carbon nitride and lanthanum nickelate heterojunction for enhanced photocatalysis: Interfacial charge transfer and mechanistic insights

Interfacial design and the co-catalyst effect are considered to be effective to achieve separation and transport of photogenerated carriers in composite photocatalysts. In this study, a Z-scheme heterojunction was successfully combined with a co-catalyst to achieve a highly efficient LaNiO₃/g-C₃N₄/MoS₂ photocatalyst. MoS₂ flakes were loaded on a hybrid material surface, which was formed by LaNiO₃ nanocubes embedded on layered g-C₃N₄, and a good heterostructure with multiple attachment sites was obtained. Experimental studies confirmed that the Z-scheme heterojunction completely preserves the strong redox ability of the photogenerated electrons and holes. As a cocatalyst, MoS₂ further promoted interfacial charge separation and transport. The synergistic effect of the Z-scheme heterojunction and co-catalyst effectively realized the transfer of photogenerated carriers from "slow transfer" to "high transfer" and promoted water decomposition and pollutant degradation. Results revealed that under simulated sunlight irradiation, LaNiO₃/g-C₃N₄/MoS₂ composites exhibit superior hydrogen evolution of 45.1 μmol h^-1, which is 19.1 times that of g-C₃N₄ and 4.9 times that of LaNiO₃/g-C₃N₄, respectively. Moreover, the LaNiO₃/g-C₃N₄/MoS₂ Z-scheme photocatalyst exhibited excellent photocatalytic performance for antibiotic degradation and heavy-metal ion reduction under visible light. This study might provide some insights into the development of photocatalysts for solar energy conversion and environmental remediation.

Hollow MoS2-supported MAPbI3 composites for effective photocatalytic hydrogen evolution

A facile and effective electrostatic adsorption method was developed to fabricate H-MoS2/MAPbI3 composites, which improved hydrogen evolution activity and stability.

Solar-Driven Gas-Phase Moisture to Hydrogen with Zero Bias

Band structure engineering offers a perfect route to tune the transport properties of electrons and holes independently, especially in semiconductors for water splitting. Here, we explore the possibility of achieving a bias-free single-step solar to chemical energy conversion using gas-phase moisture as the reactant while generating hydrogen as the reaction product. A metal-based superhygroscopic hydrogel scavenges moisture from the ambient environment and serves as the water source. The FeOOH/BiVO₄ heterojunction works as the photoanode wherein the interface allows the transport of electrons to the outer layer, resulting in an upward band bending. Concomitantly, the negative charges will accumulate on the Cu₂O surface in the FeOOH/Cu₂O photocathode, inducing a downward band bending. With the use of the hydrogel, photoanode, and photocathode, a device for directly splitting the moisture absorbed from the ambient air is realized, generating a photocurrent of 0.75 mA cm^-2 under the one-sun intensity of cool daylight without any additional bias. The solar-cell-assisted device can split 6 mg of moisture in 10 h, and the hydrogel can absorb more than 30 mg of moisture in the same period.

Photocatalytic H2O Overall Splitting into H2 Bubbles by Single Atomic Sulfur Vacancy CdS with Spin Polarization Electric Field

Low efficient transfer of photogenerated charge carriers to redox sites along with high surface reaction barrier is a bottleneck problem of photocatalytic H₂O overall splitting. Here, in the absence of cocatalysts, H₂O overall splitting has been achieved by single-atomic S vacancy hexagonal CdS with a spin polarization electric field (PEF). Theoretical and experimental results confirm that single-atomic S vacancy-induced spin PEF with opposite direction to the Coulomb field accelerates charge carrier transport dynamics from the bulk phase to surface-redox sites. By systematically tuning the spin PEF intensity with single-atomic S vacancy content, common pristine CdS is converted to a photocatalyst that can efficiently complete H₂O overall splitting by releasing a great number of H₂ bubbles under natural solar light. This work solves the bottleneck of solar energy conversion in essence by single atom vacancy engineering, which will promote significant photocatalytic performance enhancement for commercialization.

An electron donor-acceptor organic photoactive composite with Schottky heterojunction induced photoelectrochemical immunoassay

A signal enhancement photoelectrochemical (PEC) immunoassay system induced by the composite (PTCs@Au) of electron donor-acceptor with Schottky heterojunction was designed. Carcinoembryonic antigen (CEA) was selected as a model target. Initially, the capture anibody (Ab1) was linked to gold nanoparticles electrodeposited on glassy carbon electrode and sealed by bovine serum albumin. Meanwhile, the organic semiconductor (PTCs) with the structure of electron donor-acceptor was synthetized from perylene tetracarboxylic dianhydride (acceptor) and dopamine (donor) via amidation reaction. Then PTCs@Au composite with Schottky heterojunction was formed through gold nanoparticles in situ reduction and functionalization with PTCs. Next, the detection antibody was labeled by PTCs@Au composite (Ab2-PTCs@Au) as an immuno-probe. The PTCs@Au was introduced via sandwich immune reaction leading to enhancement PEC signal without additional electron donor nor acceptor for achieving quantitative detection of CEA under external light. The proposed immunoelectrode showed dynamic ranges of 0.5 fg mL^-1 to 10 pg mL^-1 and 10 pg mL^-1 to 1 μg mL^-1 with the detection limit of 0.17 fg mL^-1. In addition, this PEC strategy with acceptable selectivity and stability can be potentially applied to detect other targets by choosing appropriate target recognition unit.

Core-shell structure of sulphur vacancies-CdS@CuS: Enhanced photocatalytic hydrogen generation activity based on photoinduced interfacial charge transfer

To regulate the charge flow of the photocatalyst in photocatalytic hydrogen reactions is highly desirable. In this study, a highly efficient sulphur vacancies-CdS@CuS core-shell heterostructure photocatalyst (denoted CdS-SV@CuS) was developed through the surface modification of CdS-sulphur vacancies (SV) nanoparticles by CuS based on photoinduced interfacial charge transfer (IFCT). This novel photocatalyst with modulated charge transfer was prepared by hydrothermal treatment and subsequent cation-exchange reactions. The SV confined in CdS and the IFCT facilitate the charge carrier's efficient spatial separation. The optimized CdS-SV@CuS(5%) catalyst exhibited a remarkably higher H₂ production rate of 1654.53 μmol/g/h, approximately 6.7 and 4.0 times higher than those of pure CdS and CdS-SV, respectively. The high photocatalytic performance is attributed to the rapid charge separation, caused by the intimate interactions between CdS-SV and CuS in the core-shell heterostructure. This is the first time that a straightforward method is adopted to construct a metal sulphide core-shell structure for superior H₂-production activity by IFCT.

Cu-Sb-S Ternary Semiconductor Nanoparticle Plasmonics

Semiconductor plasmonics is a recently emerging field that expands the chemical and physical bandwidth of the hitherto well-established noble metallic nanoparticles. Achieving tunable plasmonics from colloidal semiconductor nanocrystals has drawn enormous interest and is promising for plasmon-related applications. However, realizing this goal of tunable semiconductor nanocrystals is currently still a synthetic challenge. Here, we report a colloidal synthesis strategy for highly dispersed, platelet-shaped, antimony-doped copper sulfide semiconductor nanocrystals (Sb_y-Cu_xS NCs) with a dominant localized surface plasmon resonance (LSPR) band tunable from the near-infrared into the midvisible spectral range. This work presents the synthesis and quantifies the resulting plasmonic features. It furthermore elucidates the underlying carrier concentration requirements to realize a continuum of LSPR spectra. Building on our previous work on binary plasmonics Cu_xS, Cu_xSe, and Cu_xTe NCs, the present method introduces a much wider and finer tunability with ternary semiconductor plasmonics.

Preparation of CdSy Se1- y -MoS2 Heterostructures via Cation Exchange of Pre-Epitaxially Synthesized Cu2- χ Sy Se1- y -MoS2 for Photocatalytic Hydrogen Evolution

Construction of 2D transition metal dichalcogenide (TMD)-based epitaxial heterostructures with different compositions is important for various promising applications, including electronics, photonics, and catalysis. However, the rational design and controlled synthesis of such kind of heterostructures still remain challenge, especially for those consisting of layered TMDs and other non-layered materials. Here, a facile one-pot, wet-chemical method is reported to synthesize Cu_{2- χ} S_y Se_{1- y} -MoS₂ heterostructures in which two types of different epitaxial configurations, i.e., vertical and lateral epitaxies, coexist. The chalcogen ratio (S/Se) in Cu_{2- χ} S_y Se_{1- y} and the loading amount of MoS₂ in the heterostructures can be tuned. Impressively, the obtained Cu_{2- χ} S_y Se_{1- y} -MoS₂ heterostructures can be transformed to CdS_y Se_{1- y} -MoS₂ without morphological change via cation exchange. As a proof-of-concept application, the obtained CdS_y Se_{1- y} -MoS₂ heterostructures with controllable compositions are used as photocatalysts, exhibiting distinctive catalytic activities toward the photocatalytic hydrogen evolution under visible light irradiation. The method paves the way for the synthesis of different TMD-based lateral epitaxial heterostructures with unique properties for various applications.

2D WS2 co-catalysts induce the growth of CdS and enhance the photocatalytic performance

Here, we obtain WS₂ nanosheets with near-infrared absorption which can replace the precious metal Pt as excellent cocatalysts.

Harnessing photo/electro-catalytic activity via nano-junctions in ternary nanocomposites for clean energy

Though solar energy availability is predicted for centuries, the diurnal and asymmetrical nature of the sun across the globe presents significant challenges in terms of harvesting sunlight. Photo/electro-catalysis, currently believed to be the bottleneck, promises a potential solution to these challenges along with a green and sustainable environment. This review aims to provide the current highlights on the application of inorganic-semiconductor-based ternary nanocomposites for H2 production and pollutant removal. Various engineering strategies employing integration of 2D materials, 1D nanorods, and/or 0D nanoparticles with inorganic semiconductors to create multiple nano-junctions have been developed for the excellent photocatalytic activity. Following a succinct description of the latest progress in photocatalysts, a discussion on the importance of ternary electrocatalysts in the field of next-generation supercapacitors has been included. Finally, the authors' perspectives are considered briefly, including future developments and critical technical challenges in the ever-growing field of photo/electro-catalysis.

A Microorganism Bred TiO2/Au/TiO2 Heterostructure for Whispering Gallery Mode Resonance Assisted Plasmonic Photocatalysis

The TiO₂/Au nanostructure has been acknowledged as one of the most classic visible-light active photocatalysts due to the surface plasmon resonance (SPR) of Au nanoparticles. In many cases, the SPR effect only features weak visible light absorption in conventional TiO₂/Au nanostructures. Here, we demonstrate a design of TiO₂/Au/TiO₂ with a combination of whispering gallery mode (WGM) resonances and SPR for efficient visible-light-driven photocatalysis. Escherichia coli (E. coli) were used as natural reactants as well as a template to construct an E. coli-like TiO₂/Au/TiO₂ nanostructure. Using numerical simulations, we show that the E. coli-like TiO₂ capsule acts as the WGM resonator to interplay with the SPR effect of the Au NPs on TiO₂ surface, which leads to a significant increase of visible light absorption and the local field enhancement at the Au-TiO₂ interface. Accordingly, with the synergistic effect of WGM and SPR, the E. coli-like TiO₂/Au/TiO₂ nanostructure exhibits enhanced photocatalytic activity in the visible range. Our work reveals a promising bioapproach to a design highly visible light active plasmonic photocatalyst.