Integrating electronic structure regulation and dynamic active sites construction on NixCd1-xS-Ni0 photocatalyst for efficient hydrogen evolution

Regulating electronic structure and enriching active sites of photocatalysts are effective strategies to promote hydrogen evolution. Herein, a unique NixCd1-xS-Ni0 photocatalyst, including the surface nickel (Ni) doping and atomic Ni0 anchoring sites, is successfully prepared by Ni2+ ions exchange reaction (Ni2++ CdS → NixCd1-xS) and in-situ photo-induction of Ni0(Ni2++NixCd1-xS→hνNixCd1-xS-Ni0), respectively. As to Ni doping, the Ni replaced cadmium (Cd) atoms introduce hybridized states around the Fermi level, modulating the electronic structure of adjacent S atoms and optimizing the photocatalytic activity of sulfur (S) atoms. Besides, photogenerated Ni0 atoms, anchored on unsaturated S atoms, act as charge transfer bridges to reduce Ni2+ ions in the solution to Ni clusters (NixCd1-xS-Ni0→ne-NixCd1-xS-Ni). Subsequently, the displacement reaction of Ni clusters with protons (H+) spontaneously proceeds to produce hydrogen (H2) in an acidic solution (NixCd1-xS-Ni→2H+H2↑+Ni2++NixCd1-xS-Ni0). The equilibrium of photo-deposition/dissolution of Ni clusters realizes the construction of dynamic active sites, providing sustainable reaction centers and enhancing surface redox kinetics. The NixCd1-xS-Ni0 exhibits a high hydrogen evolution rate of 428 mmol·h-1·g-1 with a quantum efficiency of 75.6 % at 420 nm. This work provides the optimal S electronic structure for photocatalytic H2 evolution and constructs dynamic Ni clusters for chemical replacement reaction. This work provides the optimal S electronic structure for photocatalytic H2 evolution and constructs dynamic Ni clusters for displacement reaction, opening a dual pathway for efficient water reduction.

Surface Coordination of Pd/ZnIn2S4 toward Enhanced Photocatalytic Activity for Pyridine Denitrification

New surface coordination photocatalytic systems that are inspired by natural photosynthesis have significant potential to boost fuel denitrification. Despite this, the direct synthesis of efficient surface coordination photocatalysts remains a major challenge. Herein, it is verified that a coordination photocatalyst can be constructed by coupling Pd and CTAB-modified ZnIn₂S₄ semiconductors. The optimized Pd/ZnIn₂S₄ showed a superior degradation rate of 81% for fuel denitrification within 240 min, which was 2.25 times higher than that of ZnIn₂S₄. From the in situ FTIR and XPS spectra of 1% Pd/ZnIn₂S₄ before and after pyridine adsorption, we find that pyridine can be selectively adsorbed and form Zn⋅⋅⋅C-N or In⋅⋅⋅C-N on the surface of Pd/ZnIn₂S₄. Meanwhile, the superior electrical conductivity of Pd can be combined with ZnIn₂S₄ to promote photocatalytic denitrification. This work also explains the surface/interface coordination effect of metal/nanosheets at the molecular level, playing an important role in photocatalytic fuel denitrification.

Interfacial Assembly of Ti3 C2 Tx /ZnIn2 S4 Heterojunction for High-Performance Photodetectors

Two-dimensional (2D) materials have emerged as prospective candidates for electronics and optoelectronics applications as they can be easily fabricated through liquid exfoliation and used to fabricate various structures by further subsequent processing methods in addition to their extraordinary and unique optoelectronic properties. Herein, the Ti3 C2 Tx /ZIS heterostructure with nanometer-thick Ti3 C2 Tx -MXene and ZnIn2 S4 (ZIS) films is fabricated by successive interfacial assembly of liquid exfoliated 2D MXene and ZnIn2 S4 nanoflakes. Benefiting from the superior light-harvesting capability and low dark current of ZnIn2 S4 , the limited absorbance, large scattering coefficient, and high dark current disadvantages of MXene are ameliorated. Meanwhile, the separation and transport of photogenerated carriers in ZnIn2 S4 are improved due to the excellent electrical conductivity of Ti3 C2 Tx nanoflakes. As a result, the as-prepared Ti3 C2 Tx /ZIS heterostructure photodetector has excellent optoelectronic characteristics in terms of a high responsivity of 1.04 mA W-1 , a large specific detectivity up to 1 × 1011  Jones, a huge on/off ratio at around 105 , and an ultralow dark current at ≈10-12  A. This work demonstrates a convenient method to construct heterostructured photodetectors by liquid exfoliated 2D nanoflakes, the as-fabricated Ti3 C2 Tx /ZIS heterostructured photodetectors show promising application potential for low-cost, reliable, and high-performance photodetectors.

Unexpected High-Performance Photocatalytic Hydrogen Evolution in Co@NCNT@ZnIn2 S4 Triggered by Directional Charge Separation and Transfer

The structural design of photocatalysts is highly related to the separation and transfer of photogenerated carriers, which is essential for the improvement of photocatalytic hydrogen evolution performance. Here, the hybrid photocatalyst M@NCNT@ZIS (M: Fe, Co, Ni; NCNT: nitrogen-doped carbon nanotube; ZIS: ZnIn₂ S₄ ) with a hierarchical structure is rationally designed and precisely synthesized. The unique hollow structure with a large specific surface area offers abundant reactive sites, thus increasing the adsorption of reactants. Importantly, the properly positioned metal nanoparticles realize the directional charge migration from ZIS to M@NCNT, which significantly improves the efficiency of charge separation. Furthermore, the intimate interface between M@NCNT and ZIS effectively facilitates charge migration by shortening the transfer distance and providing numerous transport channels. As a result, the optimized Co@NCNT@ZIS exhibits a remarkable photocatalytic hydrogen evolution efficiency (43.73 mmol g^-1 h^-1 ) without Pt as cocatalyst. Experimental characterizations and density functional theory calculations demonstrate that the synergistic effect between hydrogen adsorption and interfacial charge transport is of great significance for improving photocatalytic hydrogen production performance.

Metal-organic framework (MOF)-5/CuO@ZnIn2S4 core-shell Z-scheme tandem heterojunctions for improved charge separation and enhanced photocatalytic performance

Interface engineering is regarded as an effective strategy for charge separation. Metal-organic framework (MOF)-5/CuO@ZnIn₂S₄ core-shell Z-scheme tandem heterojunctions with a three-dimensional floral spherical shape are prepared by a two-step solvothermal and oxidative method. The flower spherical core-shell structure enhances multiple reflections and refractions of light and thus improves light utilization efficiently. In addition, this core-shell structure can supply sufficient active sites for photocatalytic reactions. Meanwhile, the composition of Z-scheme tandem heterojunctions and the photothermal effect contributed to the spatial charge separation and accelerated the photocatalytic process. The photocatalytic hydrogen production rate of MOF-5/CuO@ZnIn₂S₄ (1938.3 μmol g^-1 h^-1) is 18 times higher than that of pristine MOF-5, and the photocatalytic degradation efficiency of 2,4-dichlorophenol and phenol can reach up to 98.7% and 97.3%, respectively. In addition, multiple cycle experiments demonstrate high stability, which is favorable for practical applications.

A Review on MXene Synthesis, Stability, and Photocatalytic Applications

Photocatalytic water splitting, CO₂ reduction, and pollutant degradation have emerged as promising strategies to remedy the existing environmental and energy crises. However, grafting of expensive and less abundant noble-metal cocatalysts on photocatalyst materials is a mandatory practice to achieve enhanced photocatalytic performance owing to the ability of the cocatalysts to extract electrons efficiently from the photocatalyst and enable rapid/enhanced catalytic reaction. Hence, developing highly efficient, inexpensive, and noble-metal-free cocatalysts composed of earth-abundant elements is considered as a noteworthy step toward considering photocatalysis as a more economical strategy. Recently, MXenes (two-dimensional (2D) transition-metal carbides, nitrides, and carbonitrides) have shown huge potential as alternatives for noble-metal cocatalysts. MXenes have several excellent properties, including atomically thin 2D morphology, metallic electrical conductivity, hydrophilic surface, and high specific surface area. In addition, they exhibit Gibbs free energy of intermediate H atom adsorption as close to zero and less than that of a commercial Pt-based cocatalyst, a Fermi level position above the H₂ generation potential, and an excellent ability to capture and activate CO₂ molecules. Therefore, there is a growing interest in MXene-based photocatalyst materials for various photocatalytic events. In this review, we focus on the recent advances in the synthesis of MXenes with 2D and 0D morphologies, the stability of MXenes, and MXene-based photocatalysts for H₂ evolution, CO₂ reduction, and pollutant degradation. The existing challenges and the possible future directions to enhance the photocatalytic performance of MXene-based photocatalysts are also discussed.

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.

Morphology engineering and photothermal effect derived from perylene diimide based derivative for boosting photocatalytic hydrogen evolution of ZnIn2S4

The construction of excellent photocatalysts for splitting water into hydrogen is highly desirable to realize carbon neutralization. In this work, an innovative and well-designed S-scheme photocatalyst composed of ultrathin ZnIn₂S₄ (ZIS) nanosheets uniformly anchored on the surface of organic semiconductor PDIIM is successfully fabricated. Within the heterojunction, perylene diimide with an imidazole group (PDIIM) is strategically applied as a structure template, which plays a crucial role in optimizing the morphology, increasing the active sites of sulfur vacancies, providing the additional photothermal effect, and promoting photogenerated charge separation of the catalyst. The photocatalytic H₂ generation rate of the ZIS/PDIIM heterojunction with an optimized mass ratio reaches up to 13.04 mmol/g/h, which is 2.64 times and 14.02 times higher than that of pristine ZIS and PDIIM, respectively. The outstanding photocatalytic activity is attributed to the synergistic effect of the above advantages. Importantly, the photothermal effect induced by PDIIM belonging to the perylene diimide-based derivative was discovered to accelerate photocatalytic H₂ generation for the first time. This work provides valuable insight into the utilization of perylene diimide-based derivatives in the construction of multi-effect enhancement photocatalysts and their application in photothermal-assisted photocatalytic hydrogen evolution.

One-pot in-situ hydrothermal synthesis of ternary In2S3/Nb2O5/Nb2C Schottky/S-scheme integrated heterojunction for efficient photocatalytic hydrogen production

MXene-derived photocatalysts continue to fascinate the research community in developing photo-driven green and sustainable fuel production. However, the efficiency of MXene-derived photocatalyst is still low due to the wide bandgap and high recombination rate of photo-excited charge carriers. Here, we have synthesized the Nb₂C MXene-derived ternary photocatalyst via one-pot in-situ hydrothermal method for photocatalytic hydrogen (H₂) evolution. The partial oxidation of Nb₂C MXene into Nb₂O₅ nanorods and coupling with In₂S₃ nanoparticles via in-situ chemical anchoring were the key factors toward high efficiency and long-term stability during photocatalytic H₂ evolution. The optimized ternary photocatalyst composite manifested the highest H₂ evolution efficiency at 68.8 µmol g^-1 h^-1, which was 11 and 7.5 times higher than the Nb₂O₅/Nb₂C (NNC) and pure In₂S₃ photocatalyst, respectively. Moreover, the photocatalytic stability of the optimized ternary photocatalyst composite was analyzed for five consecutive cycles, and above 87% activity retention was observed even after the fifth cycle without any obvious decline. The separation efficiency of photoexcited charge carriers could be attributed to the synergic effect of the In₂S₃/Nb₂O₅ heterojunction and the redox reactions at different sites of the composite. More importantly, the participation of Schottky junction and S-scheme heterojunction charge transfer for the obtained novel ternary photocatalyst was evaluated via ultraviolet photoelectron spectroscopy (UPS) and electron paramagnetic resonance (EPR). This research will provide additional insight into the extended potential of MXene-derived ternary photocatalysts towards efficient H₂ production to meet future global energy demands.

MXenes as Emerging Materials: Synthesis, Properties, and Applications

Due to their unique layered microstructure, the presence of various functional groups at the surface, earth abundance, and attractive electrical, optical, and thermal properties, MXenes are considered promising candidates for the solution of energy- and environmental-related problems. It is seen that the energy conversion and storage capacity of MXenes can be enhanced by changing the material dimensions, chemical composition, structure, and surface chemistry. Hence, it is also essential to understand how one can easily improve the structure-property relationship from an applied point of view. In the current review, we reviewed the fabrication, properties, and potential applications of MXenes. In addition, various properties of MXenes such as structural, optical, electrical, thermal, chemical, and mechanical have been discussed. Furthermore, the potential applications of MXenes in the areas of photocatalysis, electrocatalysis, nitrogen fixation, gas sensing, cancer therapy, and supercapacitors have also been outlooked. Based on the reported works, it could easily be observed that the properties and applications of MXenes can be further enhanced by applying various modification and functionalization approaches. This review also emphasizes the recent developments and future perspectives of MXenes-based composite materials, which will greatly help scientists working in the fields of academia and material science.

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.

Robust S-scheme hierarchical Au-ZnIn2S4/NaTaO3: Facile synthesis, superior photocatalytic H2 production and its charge transfer mechanism

Designing Step-scheme (S-scheme) heterojunction with the directional charge transfer pathway has been considered as a promising strategy for realizing effective spatial separation of photo-generated carriers in a photocatalytic system by utilizing broadband solar energy. Herein, the novel and ternary S-scheme heterojunction photocatalysts were fabricated by embedding Au nanoparticles (NPs) on the surface of ZnIn₂S₄/NaTaO₃ composites through a facile two-step hydrothermal method for the first time. As expected, it showed an enhanced hydrogen evolution rate of 11404 μmol g^-1 h^-1, which was approximately 58 and 10 times higher than that of the pristine NaTaO₃ nanocubes (197 μmol g^-1 h^-1) and ZnIn₂S₄ microspheres (1180 μmol g^-1 h^-1) under simulated sunlight irradiation, respectively. An intimate heterojunction interface as well as Au nanoparticles as electron reservoir and reactive sites, which enhanced light absorption capacity and accelerated charge carrier separation, was answerable to the huge promotion in the photocatalytic performance. Most notably, XPS, EPR analysis and density functional theory (DFT) calculation results, revealed that the presence of strong interfacial electric fields promoted superior separation efficiency in the Au-ZnIn₂S₄/NaTaO₃ S-scheme heterojunction. This innovative work may shed light on a more appealing and meaningful approach to modify sodium tantalate for the promising application in photocatalytic hydrogen generation.

Sensitive photoelectrochemical determination of T4 polynucleotide kinase using AuNPs/SnS2/ZnIn2S4 photoactive material and enzymatic reaction-induced DNA structure switch strategy

We report here Au nanoparticles (AuNPs)/SnS₂/ZnIn₂S₄ as a high-performance active material for sensitive photoelectrochemical (PEC) determination of T4 polynucleotide kinase (T4 PNK) using an enzymatic reaction-induced DNA structure switch strategy. To construct the PEC biosensor, a double-stranded DNA probe consisting of a CdS quantum dots (QDs)-labeled single-stranded DNA (sDNA) and its complementary DNA (cDNA) is immobilized on the AuNPs/SnS₂/ZnIn₂S₄ photoactive material. T4 PNK can catalyze the phosphorylation of 5'-OH-terminated sDNA in the double-stranded DNA probe when ATP is present, and λ-exonuclease can catalyze the degradation of the phosphorylated sDNA into small fragments. Then the cDNA forms a hairpin structure so that CdS QDs and AuNPs are in close contact, which can induce exciton-plasma interactions between CdS QDs and AuNPs. The exciton-plasma interactions significantly boost the photocurrent, enabling the "signal on" PEC determination of T4 PNK in the range of 10^-4 - 1 U mL^-1 with a detection limit of 6 × 10^-5 U mL^-1. The PEC biosensor can also be used to screen enzyme inhibitors.

Recent advances and challenges in 2D/2D heterojunction photocatalysts for solar fuels applications

Although photocatalytic technology has emerged as an effective means of alleviating the projected future fuel crisis by converting sunlight directly into chemical energy, no visible-light-driven, low-cost, and highly stable photocatalyst has been developed to date. Due to considerably higher interfacial contact with numerous reactive sites, effective charge transmission and separation ability, and strong redox potentials, the focus has now shifted to 2D/2D heterojunction systems, which have exhibited effective photocatalytic performance. The fundamentals of 2D/2D photocatalysis for different applications and the classification of 2D/2D materials are first explained in this paper, followed by strategies to improve the photocatalytic performance of various 2D/2D heterojunction systems. Following that, current breakthroughs in 2D/2D metal-based and metal-free heterojunction photocatalysts, as well as their applications for H₂ evolution via water splitting, CO₂ reduction, and N₂ fixation, are discussed. Finally, a brief overview of current constraints and predicted results for 2D/2D heterojunction systems is also presented. This paper lays out a strategy for developing efficient 2D/2D heterojunction photocatalysts and sophisticated technology for solar fuel applications in order to address the energy issue.

Surface Modification of 2D Photocatalysts for Solar Energy Conversion

2D materials show many particular properties, such as high surface-to-volume ratio, high anisotropic degree, and adjustable chemical functionality. These unique properties in 2D materials have sparked immense interest due to their applications in photocatalytic systems, resulting in significantly enhanced light capture, charge-transfer kinetics, and surface reaction. Herein, the research progress in 2D photocatalysts based on varied compositions and functions, followed by specific surface modification strategies, is introduced. Fundamental principles focusing on light harvesting, charge separation, and molecular adsorption/activation in the 2D-material-based photocatalytic system are systemically explored. The examples described here detail the use of 2D materials in various photocatalytic energy-conversion systems, including water splitting, carbon dioxide reduction, nitrogen fixation, hydrogen peroxide production, and organic synthesis. Finally, by elaborating the challenges and possible solutions for developing these 2D materials, the review is expected to provide some inspiration for the future research of 2D materials used on efficient photocatalytic energy conversions.

Boosting photocatalytic CO2 reduction via Schottky junction with ZnCr layered double hydroxide nanoflakes aggregated on 2D Ti3C2Tx cocatalyst

Designing efficient photocatalysts is vital for the photoreduction of CO₂ to produce solar fuels, helping to alleviate issues of fossil fuel depletion and global warming. In this work, a novel ZnCr-LDH/Ti₃C₂T_x Schottky junction is successfully synthesized using an in situ coprecipitation method. ZnCr-LDH nanoflakes collectively grow on the surface of Ti₃C₂T_x MXene nanosheets. When using Ti₃C₂T_x MXene as a cocatalyst in the prepared heterojunction, the light absorption intensity, photo-induced electron separation and migration efficiency increase. As a result, the composite ZnCr-LDH/Ti₃C₂T_x results in significant improvement in the performance of photocatalytic CO₂ reduction under simulated solar irradiation. The optimized sample ZCTC25 has the highest photocatalytic CO₂ reduction rates of 122.45 μmol g^-1 CO and 19.95 μmol g^-1 CH₄ (after 6 h of irradiation). These values are approximately 2.65 times higher than those of pristine ZnCr-LDH. The product selectivity towards CO is 86%. This work provides a new method for the construction of novel 2D semiconductor photocatalysts and enriches the application of an unusual type of layered double hydroxides in the photoreduction of CO₂.

Sulfur Vacancies Enriched 2D ZnIn2S4 Nanosheets for Improving Photoelectrochemical Performance

Vacancies engineering based on semiconductors is an effective method to enhance photoelectrochemical activity. Herein, we used a facile one-step solvothermal method to prepare sulfur vacancies modified ultrathin two-dimensional (2D) ZnIn2S4 nanosheets. The photon-to-current efficiency of sulfur vacancies modified ultrathin 2D ZnIn2S4 nanosheets is 1.82-fold than ZnIn2S4 nanosheets without sulfur vacancies and 2.04-fold than multilayer ZnIn2S4. The better performances can be attributed to the introduced sulfur vacancies in ZnIn2S4, which influence the electronic structure of ZnIn2S4 to absorb more visible light and act as the electrons trapping sites to suppress the recombination of photo-generated carriers. These results provide a new route to designing efficient photocatalyst by introducing sulfur vacancies.

Photocatalytic degradation mechanism of phenanthrene over visible light driven plasmonic Ag/Ag3PO4/g-C3N4 heterojunction nanocomposite

Visible light driven plasmonic Ag/Ag₃PO₄/g-C₃N₄ heterojunction nanocomposite with regular morphology was prepared via a modified facile method. The two-dimensional ultrathin g-C₃N₄ nanosheet is uniformly wrapped on the surface of Ag₃PO₄ nanopolyhedron. A charge transfer bridge was built between Ag₃PO₄ nanopolyhedron and g-C₃N₄ nanosheet due to the reduction of Ag nanoparticles. This structure can inhibit the recombination of photogenerated electron-hole pairs and promote the transfer of photogenerated carriers, so as to produce more active species for participating in the photocatalytic reaction. In addition, the surface plasmon resonance (SPR) of appropriate Ag nanoparticles enhanced the absorption and utilization of visible light. Compared with Ag₃PO₄ and Ag/Ag₃PO₄, Ag/Ag₃PO₄/g-C₃N₄ showed higher photocatalytic activity. Under visible light irradiation, the degradation rate of phenanthrene (PHE) was 0.01756 min^-1, which was 3.14 times and 2.38 times that of Ag₃PO₄ and Ag/Ag₃PO₄, respectively. After four cycles of photocatalytic reaction, the Ag/Ag₃PO₄/g-C₃N₄ photocatalyst still maintained high photocatalytic activity. The active sites of PHE were predicted by Gaussian simulation calculation and combined with intermediate products identification of GC-MS, the possible degradation pathway of PHE was speculated. This research has reference significance for the construction of plasmonic heterojunction photocatalyst in the field of environmental pollution remediation.

Promoting Charge Separation in Hollow-Structured C/MoS2@ZnIn2S4/Co3O4 Photocatalysts via Double Heterojunctions for Enhanced Photocatalytic Hydrogen Evolution

A reasonable design of samples with efficient spatial separation for photoinduced electron-hole pairs toward the photocatalytic hydrogen evolution reaction (HER) has gained significant attention. Herein, a new C/MoS₂@ZnIn₂S₄/Co₃O₄ composite with a core-shell structure is designed toward photocatalytic hydrogen production on C/MoS₂ and Co₃O₄ dual electron collectors. Co₃O₄ nanoparticles as the co-catalyst would form a Schottky junction with ZnIn₂S₄ nanosheets while the C/MoS₂ hollow core would form the step-scheme (S-scheme) heterojunction with ZnIn₂S₄ sheets, which provides a dual photogenerated electron transfer pathway during the light irradiation process. In addition, the unique core-shell architecture offers large contact interfaces favoring the exposure of rich active sites, which facilitated the separation and the transfer of charges. Consequently, all these factors endowed the C/MoS₂@ZnIn₂S₄/Co₃O₄ composite with enhanced light absorption ability and an increased hydrogen evolution rate of 6.7 mmol·g^-1·h^-1 under 420 nm light irradiation, which is about 23.4- and 4.5-fold that of ZnIn₂S₄ and CMZ, respectively. This work offers a guideline for designing efficient composite photocatalysts toward the photocatalytic HER.

In Situ Growth of Three-Dimensional MXene/Metal-Organic Framework Composites for High-Performance Supercapacitors

In this study, we propose a versatile method for synthesizing uniform three-dimensional (3D) metal carbides, nitrides, and carbonitrides (MXenes)/metal-organic frameworks (MOFs) composites (Ti₃ C₂ T_X /Cu-BTC, Ti₃ C₂ T_X /Fe,Co-PBA, Ti₃ C₂ T_X /ZIF-8, and Ti₃ C₂ T_X /ZIF-67) that combine the advantages of MOFs and MXenes to enhance stability and improve conductivity. Subsequently, 3D hollow Ti₃ C₂ T_X /ZIF-67/CoV₂ O₆ composites with excellent electron- and ion-transport properties derived from Ti₃ C₂ T_X /ZIF-67 were synthesized. The specific capacitance of the Ti₃ C₂ T_X /ZIF-67/CoV₂ O₆ electrode was 285.5 F g^-1 , which is much higher than that of the ZIF-67 and Ti₃ C₂ T_X /ZIF-67 electrode. This study opens a new avenue for the design and synthesis of MXene/MOF composites and complex hollow structures with tailorable structures and compositions for various applications.

Dual-Functional Photocatalysis for Cooperative Hydrogen Evolution and Benzylamine Oxidation Coupling over Sandwiched-Like Pd@TiO2 @ZnIn2 S4 Nanobox

Photocatalytic hydrogen evolution (PHE) over semiconductor photocatalysts is usually constrained by the limited light-harvesting and separation of photogenerated electron-hole pairs. Most of the reported systems focusing on PHE are facilitated by consuming the photoinduced holes with organic sacrificial electron donors (SEDs). The introduction of the SEDs not only causes the environmental problem, but also increases the cost of the reaction. Herein, a dual-functional photocatalyst is developed with the morphology of sandwiched-like hollowed Pd@TiO₂ @ZnIn₂ S₄ nanobox, which is synthesized by choosing microporous zeolites with sub-nanometer-sized Pd nanoparticles (Pd NPs) embedded as the sacrificial templates. The ternary Pd@TiO₂ @ZnIn₂ S₄ photocatalyst exhibits a superior PHE rate (5.35 mmol g^-1 h^-1 ) and benzylamine oxidation conversion rate (>99%) simultaneously without adding any other SEDs. The PHE performance is superior to the reported composites of TiO₂ and ZnIn₂ S₄ , which is attributed to the elevated light capture ability induced by the hollow structure, and the enhanced charge separation efficiency facilitated by the ultrasmall sized Pd NPs. The unique design presented here holds great potential for other highly efficient cooperative dual-functional photocatalytic reactions.

One-Step MOF-Templated Strategy to Fabrication of Ce-Doped ZnIn2 S4 Tetrakaidecahedron Hollow Nanocages as an Efficient Photocatalyst for Hydrogen Evolution

Achieving structure optimizing and component regulation simultaneously in the ZnIn2 S4 -based photocatalytic system is an enormous challenge in improving its hydrogen evolution performance. 3D hollow-structured photocatalysts have been intensively studied due to their obvious advantages in solar energy conversion reactions. The synthesis of 3D hollow-structured ZnIn2 S4 , however, is limited by the lack of suitable template or synthesis methods, thereby restricting the wide application of ZnIn2 S4 in the field of photocatalysis. Herein, Ce-doped ZnIn2 S4 photocatalysts with hollow nanocages are obtained via one-step hydrothermal method with an ordered large-pore tetrakaidecahedron cerium-based metal-organic frameworks (Ce-MOFs) as template and Ce ion source. The doping of Ce and the formation of ZnIn2 S4 tetrakaidecahedron hollow nanocages with ultrathin nanosheet subunits are simultaneously induced by the Ce-MOFs, making this groundbreaking work. The Ce-doped ZnIn2 S4 with a nonspherical 3D hollow nanostructure inherit the tetrakaidecahedron shape of the Ce-MOF templates, and the shell is composed of ultrathin nanosheet subunits. Both theoretical and experimental results indicate that the doping of Ce and the formation of hollow nanocages increase light capture and the separation of photogenerated charge carriers.

High-Stability Ti3C2-QDs/ZnIn2S4/Ti(IV) Flower-like Heterojunction for Boosted Photocatalytic Hydrogen Evolution

The practical application of photocatalytic H₂-evolution is greatly limited by its sluggish charge separation, insufficient active sites, and stability of photocatalysts. Zero-dimensional (0D) Ti₃C₂ MXene quantum dots (MQDs) and amorphous Ti(IV) have been proven to be potential substitutes for noble co-catalyst to accelerate the separation of photogenerated electron-hole pairs and prevent the self-oxidation of photocatalysts, leading to better photocatalytic H₂-evolution performance with long-term stability. In this study, amorphous Ti(IV) and MQDs co-catalysts were successfully deposited on ZnIn₂S₄ (ZIS) microspheres composed of ultra-thin nanosheets via a simple impregnation and self-assembly method (denoted as MQDs/ZIS/Ti(IV)). As expected, the optimal MQDs/ZIS/Ti(IV) sample exhibited a photocatalytic H₂-evolution rate of 7.52 mmol·g⁻¹·h⁻¹ and excellent photostability without metallic Pt as the co-catalyst in the presence of Na₂S/Na₂SO₃ as hole scavenger, about 16, 4.02 and 4.25 times higher than those of ZIS, ZIS/Ti(IV), and MQDs/ZIS, respectively. The significantly enhanced photocatalytic H₂-evolution activity is attributed to the synergistic effect of the three-dimensional (3D) flower-like microsphere structure, the amorphous Ti(IV) hole co-catalyst, and a Schottky junction formed at the ZIS–MQDs interface, which offers more active sites, suppresses self-photocorrosion, and photo-generates the charge recombination of ZIS.

Ti3C2Tx MXene Nanoflakes Embedded with Copper Indium Selenide Nanoparticles for Desalination and Water Purification through High-Efficiency Solar-Driven Membrane Evaporation

Solar-driven interface evaporation recently emerges as one of the most promising methods for seawater desalination and wastewater purification, mainly due to its low energy consumption. However, there still exist special issues in the present material system based on conventional noble metals or two-dimensional (2D) nanomaterials etc., such as high costs, low light-to-heat conversion efficiencies, and unideal channels for water transport. Herein, a composite photothermal membrane based on Ti₃C₂T_x MXene nanoflakes/copper indium selenide (CIS) nanoparticles is reported for highly efficient solar-driven interface evaporation toward water treatment applications. Results indicate that the introduction of CIS improves the spatial accessibility of the membrane by increasing the interlayer spacings and wettability of MXene nanoflakes and enhances light absorption capability as well as reduces reflection for the photothermal membrane. Simultaneously, utilization of the MXene/CIS composite membrane improves the efficiency of light-to-heat conversion probably due to formation of a Schottky junction between MXene and CIS. The highest water evaporation rate of 1.434 kgm^-2 h^-1 and a maximum water evaporation efficiency of 90.04% as well as a considerable cost-effectiveness of 62.35 g h^-1/$ are achieved by using the MXene/CIS composite membrane for solar interface evaporation, which also exhibits excellent durability and light intensity adaptability. In addition, the composite photothermal membrane shows excellent impurity removal ability, e.g., >98% for salt ions, >99.8% for heavy metal ions, and ∼100% for dyes molecules. This work paves a promising avenue for the practical application of MXene in the field of water treatment.

Sulfur Vacancy and Ti3 C2 Tx Cocatalyst Synergistically Boosting Interfacial Charge Transfer in 2D/2D Ti3 C2 Tx /ZnIn2 S4 Heterostructure for Enhanced Photocatalytic Hydrogen Evolution

Constructing an efficient photoelectron transfer channel to promote the charge carrier separation is a great challenge for enhancing photocatalytic hydrogen evolution from water. In this work, an ultrathin 2D/2D Ti3 C2 Tx /ZnIn2 S4 heterostructure is rationally designed by coupling the ultrathin ZnIn2 S4 with few-layered Ti3 C2 Tx via the electrostatic self-assembly strategy. The 2D/2D Ti3 C2 Tx /ZnIn2 S4 heterostructure possesses larger contact area and strong electronic interaction to promote the charge carrier transfer at the interface, and the sulfur vacancy on the ZnIn2 S4 acting as the electron trap further enhances the separation of the photoinduced electrons and holes. As a consequence, the optimal 2D/2D Ti3 C2 Tx /ZnIn2 S4 composite exhibits a high photocatalytic hydrogen evolution rate of 148.4 µmol h-1 , which is 3.6 times and 9.2 times higher than that of ZnIn2 S4 nanosheet and flower-like ZnIn2 S4 , respectively. Moreover, the stability of the ZnIn2 S4 is significantly improved after coupling with the few-layered Ti3 C2 Tx . The characterizations and density functional theory calculation demonstrate that the synergistic effect of the sulfur vacancy and Ti3 C2 Tx cocatalyst can greatly promote the electrons transfer from ZnIn2 S4 to Ti3 C2 Tx and the separation of photogenerated charge carriers, thus enhancing the photocatalytic hydrogen evolution from water.

Piezoelectric effect enhanced photocatalysis in environmental remediation: State-of-the-art techniques and future scenarios

Photocatalysis has been widely used as an advanced oxidation process to control pollutants effectively. However, environmental photocatalysis' decontamination efficiency is restricted to the photogenerated electron-hole pairs' rapid recombination. Recently, emerging investigations have been directed to generate internal electric field by piezoelectric effect to enhance the separation efficiency of photogenerated charge carriers for better photocatalytic performance; however, there are still huge knowledge gaps on the rational application of piezo-photocatalysis in environmental remediation and disinfection. Thus, we have conducted a comprehensive review to better understand the physicochemical properties of piezoelectric materials (non-centrosymmetric crystal structures, piezoelectric coefficient, Young's modulus, and etc.) and current study states. We also elucidated the strategy of piezo-photo catalysis system constructions (mono-component, core-shell structure, and etc.) and underlying mechanisms of enhanced remediation performance. Addressing the current challenges and future scenarios (degradation of organic pollutants, disinfection, and etc.), the present review would shed light on the advanced wastewater treatment development towards sustainable control of emerging containments.

Spatial carrier separation in cobalt phosphate deposited ZnIn2S4 nanosheets for efficient photocatalytic hydrogen evolution

Developing photocatalyst with effective charge separation and fast surface reaction kinetics is crucial to high-efficiency photocatalytic H₂ evolution. Herein we spatially separate the reductive and oxidative reaction sites of ZnIn₂S₄ nanosheet and accelerate the hole transfer process by simply depositing cobalt phosphate (CoH_xPO_y, noted as Co-Pi), a non-precious co-catalyst, on its basal plane. Theoretical calculations combined with comprehensive characterizations reveal that Zn vacancies induced deep local energy levels serve as hole trap states to pin the photogenerated holes on (001) surface of ZnIn₂S₄. Upon Co-Pi deposition, Co atoms preferentially bond with S atoms nearby the Zn vacancies of ZnIn₂S₄. Taking advantage of the formation of Co-S bonds, Co-Pi acts as a hole receptor to extract the trapped holes effectively. As the photocatalytic activity of ZnIn₂S₄ is caused by active S atoms on its edge side, deposition of Co-Pi on planar side of nanosheets helps electron-hole migration to different facets. As a result of inert facet activation and spatial carrier separation, Co-Pi/ZnIn₂S₄ exhibits a superior photocatalytic H₂ evolution rate of 10.19 mmol g^-1h^-1 under visible light, which is superior to most of reported ZnIn₂S₄-based photocatalysts. This work will provide novel insights into the activation of inert basal planes of two-dimensional photocatalysts.

Sheet-on-sheet TiO2/Bi2MoO6 heterostructure for enhanced photocatalytic amoxicillin degradation

Developing sheet-on-sheet (2D/2D) heterostructure with built-in electric field (BIEF) is effective in boosting the performance of photocatalysts for emerging contaminants degradation. Herein, the 2D/2D microtopography and (-)TiO₂/(+)Bi₂MoO₆ BIEF were precisely integrated into hierarchical nanosheets, which can provide the basis and driving force for charge transfer both in in-plane and interface of heterojunction. The prepared photocatalyst (TiO₂/Bi₂MoO₆) showed high-efficiency and stable performance for photocatalytic amoxicillin (AMX) degradation, which was 18.2 and 5.7 times higher than TiO₂ and Bi₂MoO₆, respectively. More importantly, TiO₂/Bi₂MoO₆ showed more efficient photocatalytic activity and photogenerated charge separation than TiO₂@Bi₂MoO₆ (different morphology). Besides, four possible pathways of AMX degradation were proposed depending on Gaussian calculations and intermediates analysis by GC-MS and HPLC-TOFMS. This work sheds light on the design and construction of unique 2D/2D heterostructure photocatalysts for AMX degradation.