Confinement of ultrasmall CoFe2O4 nanoparticles in hierarchical ZnIn2S4 microspheres with enhanced interfacial charge separation for photocatalytic H2 evolution

A compendium of all-in-one solar-driven water splitting using ZnIn2S4-based photocatalysts: guiding the path from the past to the limitless future

Photocatalytic water splitting represents a leading approach to harness the abundant solar energy, producing hydrogen as a clean and sustainable energy carrier. Zinc indium sulfide (ZIS) emerges as one of the most captivating candidates attributed to its unique physicochemical and photophysical properties, attracting much interest and holding significant promise in this domain. To develop a highly efficient ZIS-based photocatalytic system for green energy production, it is paramount to comprehensively understand the strengths and limitations of ZIS, particularly within the framework of solar-driven water splitting. This review elucidates the three sequential steps that govern the overall efficiency of ZIS with a sharp focus on the mechanisms and inherent drawbacks associated with each phase, including commonly overlooked aspects such as the jeopardising photocorrosion issue, the neglected oxidative counter surface reaction kinetics in overall water splitting, the sluggish photocarrier dynamics and the undesired side redox reactions. Multifarious material design strategies are discussed to specifically mitigate the formidable limitations and bottleneck issues. This review concludes with the current state of ZIS-based photocatalytic water splitting systems, followed by personal perspectives aimed at elevating the field to practical consideration for future endeavours towards sustainable hydrogen production through solar-driven water splitting.

Photothermal-Enhanced S-Scheme Heterojunction of Hollow Core-Shell FeNi2S4@ZnIn2S4 toward Photocatalytic Hydrogen Evolution

Herein, guided by the results of density functional theory prediction, the study rationally designs a hollow core-shell FeNi2S4@ZnIn2S4 (FNS@ZIS) Step-scheme (S-scheme) heterojunction for photocatalytic H2 evolution with photothermal-assisted. The hollow FNS spheres offered substrate for coating the ZIS nanosheets, which can inhibit ZIS nanosheets from agglomerating into pellet, enrich the active site, increase specific surfaces, and raise the light absorption. Notably, due to its excellent photothermal properties, FNS core generated heat unceasingly inside under visible-light irradiation and effectively prevent the heat loss of the reaction system, which increased the local temperature of photocatalysts and thus accelerated the charge migration. In addition, the S-scheme heterojunction construction via in situ growth has a tight interface, which can facilitate the separation and transfer of carriers and achieve high redox potential. Owning to the distinctive construction, the hollow core-shell FNS@ZIS S-scheme heterojunction show extraordinary stability and photocatalytic H2 evolution rate with 7.7 mmol h-1 g-1, which is ≈15.2-fold than pristine ZIS. Based on the double evidence of theoretical predictions and experimental confirmations, the photothermal effect and electron transfer mechanism of this innovative material are investigated in depth by the following infrared thermography technology and deep DFT calculations.

Harnessing the Power of Light: The Synergistic Effects of Crystalline Carbon Nitride and Ti3C2Tx MXene in Photocatalytic Hydrogen Production

Photocatalytic hydrogen evolution is an environmentally friendly means of energy generation. Although g-C3N4 possesses fascinating features, its inherent shortcomings limit its photocatalytic applications. Therefore, modifying the intrinsic properties of g-C3N4 and introducing cocatalysts are essential to ameliorate the photocatalytic efficiency. To achieve this, metal-like Ti3C2Tx is integrated with crystalline g-C3N4 via a combined salt-assisted and freeze-drying approach to form crystalline g-C3N4/Ti3C2Tx (CCN/TCT) hybrids with different Ti3C2Tx loading amounts (0, 0.2, 0.3, 0.4, 0.5, 1, 5, 10 wt.%). Benefiting from the crystallization of CN, as evidenced by the XRD graph, and the marvelous conductivity of Ti3C2Tx supported by EIS plots, CCN/TCT/Pt loaded with 0.5 wt.% Ti3C2Tx displays an elevated H2 (2) should be subscripted evolution rate of 2651.93 µmol g-1 h-1 and a high apparent quantum efficiency of 7.26% (420 nm), outperforming CN/Pt, CCN/Pt, and other CCN/TCT/Pt hybrids. The enhanced performance is attributed to the synergistic effect of the highly crystalline structure of CCN that enables fleet charge transport and the efficient dual cocatalysts, Ti3C2Tx and Pt, that foster charge separation and provide plentiful active sites. This work demonstrates the potential of CCN/TCT as a promising material for hydrogen production, suggesting a significant advancement in the design of CCN heterostructures for effective photocatalytic systems.

Poly Meta-Aminophenol (PmAP) as a Solid-State Electron Mediator in the Z-Scheme, Ag3PO4/CoFe2O4 Heterojunction: Mineralization of Highly Concentrated Bisphenol-A and Reactive Dyes Water Pollutants

This study demonstrated the effectiveness of poly meta-aminophenol (PmAP) as a solid electron mediator in the Z-scheme photocatalytic system for organic pollutants (viz. bisphenol-A and reactive dyes) mineralization and also illustrated how PmAP transported the photogenerated electrons from an O2-emitting photocatalyst (Ag3PO4) to a H2-emitting photocatalyst (CoFe2O4) enabling enhanced photocatalytic activity under visible light irradiation. The PmAP/Ag3PO4-CoFe2O4 (PAC-10), was prepared by a two-step process and characterized by various analytical methods to assess the impact of PmAP on optical, photocatalytic, and electrochemical characteristics of the CoFe2O4 (CFO)/Ag3PO4 composite. The morphological investigation revealed that the PmAP sheet was nicely decorated with evenly distributed Ag3PO4 and CoFe2O4 particles. The M-S plot and impedance analyses were used to assess the electrochemical capabilities of the catalyst. Z-scheme charge transfer pathways were well supported by the radical trapping experiment and HRTEM analysis of Pt photodeposited PAC-10 photocatalysts during the photoreaction. Because of its magnetic nature and ease of synthesis, the PAC-10 offers an easily recyclable Z-scheme photocatalytic system that has the potential for purifying wastewater with high concentrations (up to 100 mg/L) of organic pollutants within 30 min of visible light exposition.

Dipole Moment and Built-In Polarization Electric Field Induced by Oxygen Vacancies in BiOX for Boosting Piezoelectric-Photocatalytic Removal of Uranium(VI)

Piezoelectric-photocatalysis is distinguished by its piezoelectricity as an external force that induces deformation within the catalyst to engender a polarized electric field compared to conventional photocatalysis. Herein, the piezoelectric photocatalyst BiOBr has been expertly synthesized via a plasma process and applied for piezoelectric-photocatalysis removal of uranium(VI) for the first time. The abundant surface oxygen vacancies (OVs) could induce a dipole moment and built-in electric field, which endows BiOBr with excellent separation and transport efficiency of photogenerated charges to actuate more charges to participate in the piezoelectric-photocatalytic reduction process. Consequently, under visible light and ultrasound (150 W and 40 kHz), the removal rate constant of OVs-BiOBr-30 (0.0306 min-1) was 2.4, 30.6, and 6 times higher than those of BiOBr (0.01273 min-1), ultrasound, or photocatalysis, respectively. The piezoelectric-photocatalytic synergy is also universal for BiOX (X = Cl, Br, or I) to accelerate the reduction rate of uranium(VI). This work highlights the role of piezoelectric-photocatalysis in the treatment of uranium-containing wastewater, which is of great significance for resource conservation and environmental remediation.

Synthesize magnetic ZnFe2O4@C/Cd0.9Zn0.1S catalysts with S-scheme heterojunction to achieve extraordinary hydrogen production efficiency

Suppressing the electron-hole recombination rate of catalyst legitimately is one of the effective strategies to improve photocatalytic hydrogen evolution. Herein, carbon-coated metal oxide, ZnFe2O4@C (ZFO@C), nanoparticles were synthesized and employed to couple with quadrupedal Cd0.9Zn0.1S (CZS) via an ordinary ultrasonic self-assembly method combined with calcination to form a novel ZFO@C/CZS catalyst with step-scheme (S-scheme) heterojunction. The photocatalytic hydrogen evolution reaction (HER) was conducted to verify the enhanced photoactivity of ZFO@C/CZS. The optimal ZFO@C/CZS exhibits an extraordinary photocatalytic HER rate of 111.3 ± 0.9 mmol g-1 h-1 under visible-light irradiation, corresponding to an apparent quantum efficiency as high as (76.2 ± 0.9)% at 450 nm. Additionally, the as-synthesized ZFO@C/CZS composite exhibits high stability and recyclability. The excellent photocatalytic hydrogen evolution performance should arise from the formed S-scheme heterojunction and the unique ZFO@C core-shell structure, which inhibit electron hole recombination as well as provide more reactive sites. The pathway of S-scheme charge transfer was validated through density functional theory calculations and electrochemical measurements. This work provides a rational strategy for the synthesis of unique magnetic S-scheme heterojunction photocatalysts for water splitting under visible light irradiation.

Constructed a novel of Znln2S4/S-C3N4 heterogeneous catalyst for efficient photodegradation of tetracycline

Despite S-doped C3N4 can exhibit more efficient photo-reactivity than pure C3N4, there is still some space to further improve the detaching efficiency of electron-hole and enhance the photocatalytic efficiency of S-C3N4. The construction of heterojunction is an effective method to promote the photocatalytic efficiency. ZnIn2S4, as a novel photocatalyst, its VB (1.37 V) and CB (- 1.09 V) can match with S-C3N4. Therefore, we hope to construct the ZnIn2S4/S-C3N4 heterojunction for boosting the photocatalytic activity of S-C3N4. In this paper, ZnIn2S4/S-C3N4 heterojunction was prepared through hydrothermal method using S-C3N4, ZnCl2, InCl3·4H2O, and thioacetamide as raw materials and heated at 160 °C for 16 h. The optimum 18% ZnIn2S4/S-C3N4 nanocomposites exhibit dramatically enhanced photocatalytic performance for degradation of tetracycline with 86.3% removal rate within 120 min, higher than 50% degradation efficiency of pure S-C3N4. And in the process of photodegradation for tetracycline, the largest contribution rate is the photo-excited cavity (h+), followed by ·O2- and ·OH. Herein, we have provided a good example for removing antibiotic residues by using S-C3N4-based heterojunction towards environmental remediation.

Construction of magnetically recoverable MnZnFe2O4@Ag3PO4 Z-scheme photocatalyst for rapid visible-light-driven phenol degradation

Visible-light-driven magnetic heterojunction as a promising photocatalysts has received much attention in environmental remediation. In this work, novel Z-scheme heterojunction MnZnFe₂O₄@Ag₃PO₄ (MZFO@APO) magnetic photocatalysts with excellent visible-light-driven photocatalytic activity are successfully constructed and characterized. The photocatalytic activity for phenol degradation is measured, and photodegradation mechanism is investigated with EPR, radical trapping experiments, and LC-MS. It turns out that the heterojunction introduced MZFO exhibits good adsorption effect on visible light and the direct Z-scheme bandgap alignment of MZFO and APO significantly improves charge separation and electron transfer, outperforming that of pure APO. MZFO@APO-40% with 40% APO content shows the rapid photodegradation performance, obtaining a 100% removal efficiency of phenol (25 mg L^-1) after 12-min visible light irradiation, and its kinetic constants are approximately 25.3 and 4.9 times higher than that of P25 TiO₂ and pure APO, respectively. Especially, MZFO@APO-40% also possesses a high magnetic separation property and can be efficiently reused for 5 cycles. Additionally, EPR and radical trapping experiments confirm that h⁺, O₂^-, and ¹O₂ are the main active species in the photocatalytic process. Hydroquinone and small molecular organic acids such as maleic acid and oxalic acid are detected by LC-MS, which further indicates that the pathway of phenol degradation involves hydroxylation, open-ring reactions, and mineralization reactions. The novel addition of MZFO in photocatalyst construction has the potential to promote its application in environmental remediation.

Construction of a p-n heterojunction based on magnetic Mn0.6Zn0.4Fe2O4 and ZnIn2S4 to improve photocatalytic performance

To improve the photocatalytic performance of Mn_0.6Zn_0.4Fe₂O₄ (MZFO) and ZnIn₂S₄ (ZIS) for organic pollutants, the p-n MZFO@ZIS heterojunctions with different weight percentage (10 ~ 40%) of MZFO are constructed from spent batteries and added indium ion via a green bioleaching and hydrothermal method. Structural, optical, and photocatalytic properties for the heterojunctions are investigated systematically by XRD, FT-IR, SEM-EDX, TEM, BET, VB-XPS, UV-vis DRS, PL, etc. The results confirm that p-n junction significantly improves the visible light adsorption and the separation efficiency of photogenerated carriers. Specifically, MZFO-25%@ZIS shows the highest photodegradation performance toward Congo red (CR), and its reactive kinetic constant is about 9.6, 7.8, and 7.0 times higher than that of P25 TiO₂, MZFO, and ZIS, respectively, and MZFO-25%@ZIS still possesses a high reusability and simple magnetic separation after 5 cycles of reuse. The radical trapping experiments and electronic paramagnetic resonance (EPR) tests show that ·O₂^-, ·OH, and h⁺ are the most important active substance for degrading CR. The pathways for the CR degradation are further proposed based on the intermediate analysis. DFT + U calculations confirm that the high charge density of Zn-O, Fe-O, and Zn-S bonds in the MZFO and ZIS molecules provides the electrons for the sufficient production of free radicals. This work also provides a novel high value-added strategy for the green utilization of spent batteries.

Antibacterial Z-scheme ZnIn2S4/Ag2MoO4 composite photocatalytic nanofibers with enhanced photocatalytic performance under visible light

Considering the biocompatibility of natural proteins and the strong photo-redox capability of Z-scheme heterojunctions, we fabricated Z-scheme ZnIn₂S₄/Ag₂MoO₄@Zein (Z ZA) photocatalytic membranes via electrospinning and in-situ precipitation for enrofloxacin (ENR) degradation. Z ZA exhibit a fiber structure wrapped with ZnIn₂S₄/Ag₂MoO₄ heterojunctions. Photocatalytic studies and various characterization results certified that the Z-scheme structure between ZnIn₂S₄ and Ag₂MoO₄ significantly increases the lifetime and separation efficiency of photogenerated carriers, which in turn enhances the photodegradation of ENR. The degradation rate of Z ZA-10 (ZnIn₂S₄/10 wt% Ag₂MoO₄@Zein) with the highest catalytic activity could reach 100% within 120 min compared with other samples. For ENR degradation, •O₂^- radicals were certified to be the primary active species by trapping experiments, and several possible conversion pathways of ENR in photocatalytic reactions were proposed. Furthermore, the antibacterial rates of Z ZA-20 (ZnIn₂S₄/20 wt% Ag₂MoO₄@Zein) against B. subtilis, P. aeruginosa, S. aureus, and E. coli could reach 90.09%, 89.78%, 84.34%, and 95.31%, respectively. Antibacterial evaluations and cytotoxicity assays demonstrated that Z ZA photocatalytic films had desirable antibacterial properties and low cytotoxicity, rendering them safe and effective for use in the treatment of antibiotic wastewater.

Constructing 3D magnetic flower-like Fe3O4@SiO2@Co3O4@BiOCl heterojunction photocatalyst for degrading rhodamine B

In this work, the 3D magnetic flower-like Fe₃O₄@SiO₂@Co₃O₄@BiOCl heterojunction photocatalyst was successfully prepared. The combination of BiOCl with Co₃O₄ favored to increase specific surface area and separate photo-generated carriers of the resulting composite, resulting in the improvement of catalytic efficiency. The photocatalytic activities of Fe₃O₄@SiO₂@Co₃O₄@BiOCl were researched in details. In 50 min of visible light, the degradation efficiency for rhodamine B (RhB) of Fe₃O₄@SiO₂@Co₃O₄@BiOCl was 98.41%. It still maintained 94.22% even after three tests. Furthermore, the photodegradation mechanisms were also investigated, indicating that the improved efficiency was ascribed to the superior separation of photo-induced electron-hole pairs. This study supplies a new perception to fabricate photocatalysts for actual uses.

M-Carboxylic Acid Induced Formation of New Coordination Polymers for Efficient Photocatalytic Degradation of Ciprofloxacin

Four new 2−3D materials were designed and synthesized by hydrothermal methods, namely, {[(L1·Cu·2H2O) (4,4-bipy)0.5] (β-Mo8O26)0.5·H2O} (1), {[(L1·Cu)2·(4,4-bipy)] (Mo5O16)} (2), {Co(L1)2}n (3), and {[(L1)2][β-Mo8O26]0.5·5H2O} (4). [L1=5-(4-aminopyridine) isophthalic acid]. The degradation of ciprofloxacin (CIP) in water by compounds 1−4 was studied under visible light. The experimental results show that compounds 1−4 have obvious photocatalytic degradation effect on CIP. In addition, for compound 1, the effects of temperature, pH, and adsorbent dosage on photocatalytic performance were also investigated. The stability of compound 1 was observed by a cycle experiment, indicating that there was no significant change after three cycles of CIP degradation.

Construction of a ZnIn2S4/Au/CdS Tandem Heterojunction for Highly Efficient CO2 Photoreduction

Photocatalytic CO₂ reduction technology is of great importance to alleviate energy crisis and environmental pollution; however, it remains a serious challenge due to the fast recombination of carriers. In this study, we report a three-dimensional structure of a ZnIn₂S₄/Au/CdS composite photocatalyst for the CO₂ reduction reaction, where Au nanoparticles (NPs) are evenly anchored on the surface of ZnIn₂S₄ by photodeposition and Au NPs are wrapped around by CdS. In ZnIn₂S₄/Au/CdS composite photocatalysts, Au NPs act as a bridge to construct a "semiconductor-metal-semiconductor" tandem electron transfer mechanism (ZnIn₂S₄ → Au → CdS) heterojunction, which greatly promotes the transfer of photogenerated electrons. It is worth noting that Au NPs, as a local surface plasmon resonance (LSPR) effect excited source to generate excited-state electrons, further improve the photoreduction CO₂ activity. Under UV-vis light irradiation, the CO yield of ZnIn₂S₄/Au/CdS can reach 63.07 μmol·g^-1·h^-1, which is higher than that of 6.37 μmol·g^-1·h^-1 for pure ZnIn₂S₄, 0.93 μmol·g^-1·h^-1 for CdS, 8.9 μmol·g^-1·h^-1 for ZnIn₂S₄/CdS, 31.04 μmol·g^-1·h^-1 for ZnIn₂S₄/Au, and 5.37 μmol·g^-1·h^-1 for CdS/Au. In addition, the ternary ZnIn₂S₄/Au/CdS composite photocatalyst has good cyclic stability. This study broadens the idea of designing photocatalysts with good carrier separation efficiency.

Interior and Surface Synergistic Modifications Modulate the SnNb2O6/Ni-Doped ZnIn2S4 S-Scheme Heterojunction for Efficient Photocatalytic H2 Evolution

Interior and surface synergistic modifications can endow the photocatalytic reaction with tuned photogenerated carrier flow at the atomic level. Herein, a new class of 2D/2D SnNb₂O₆/Ni-doped ZnIn₂S₄ (SNO/Ni-ZIS) S-scheme heterojunctions is synthesized by a simple hydrothermal strategy, which was used to evaluate the synergy between interior and surface modifications. Theoretical calculations show that the S-scheme heterojunction boosts the desorption of H atoms for rapid H₂ evolution. As a result, 25% SNO/Ni_0.4-ZIS exhibits significantly improved PHE activity under visible light, roughly 4.49 and 2.00 times stronger than that of single ZIS and Ni_0.4-ZIS, respectively. In addition, 25% SNO/Ni_0.4-ZIS also shows superior structural stability. This work provides advanced insight for developing high-performance S-scheme systems from photocatalyst design to mechanistic insight.

Structural, optical and photocatalytic properties of magnetic recoverable Mn0.6Zn0.4Fe2O4@Zn0.9Mn0.1O heterojunction prepared from waste Mn-Zn batteries

Green, simple and high value-adding technology is crucial for realizing waste batteries recycling. In this work, the magnetically recyclable Mn_0.6Zn_0.4Fe₂O₄@Zn_0.9Mn_0.1O (MZFO@ZMO) heterojunctions are prepared from waste Mn-Zn batteries via a green bioleaching and sample co-precipitation method. The as-prepared catalysts with different Zn_0.9Mn_0.1O weight percentage (25%, 50% and 75%) have been comprehensively characterized in structure, optics, photoelectrochemistry and photocatalytic activity. Characterization results indicate that MZFO@ZMO heterojunctions with the core-shell structure, demonstrates excellent absorption intensity in the visible light region, outperforming that of individual ZnO and Zn_0.9Mn_0.1O. Especially, the staggered bandgap alignment of Mn_0.6Zn_0.4Fe₂O₄ and Zn_0.9Mn_0.1O greatly enhances electron transfer and charge separation in the binary heterojunction system. The optimized MZFO@50%-ZMO shows the highest photodegradation performance toward methylene blue (MB) under the visible light irradiation, with a 99.7% of photodegradation efficiency of 20 mg L^-1 of MB within 90 min, and its reactive kinetic constants is about 7.2, 10.8 and 21.7 times higher than that of Zn_0.9Mn_0.1O, P25 TiO₂ and Mn_0.6Zn_0.4Fe₂O₄, respectively. The MB photocatalytic mechanism is investigated in the scavenger and 5,5-dimethylpyrroline-N-oxide (DMPO) spin-trapping electron spin resonance (ESR) experiments, and h⁺ and *O₂^- are identified as the major active species for MB degradation. In addition, MZFO@50%-ZMO also exhibits a good reusability and high magnetic separation properties after six successive cycles. This new material indicates the advantages of low costs, simple reuse and great potential in application.

Anchoring ZnIn2S4 nanosheets on ZSM-5 for boosting photocatalytic Cr(vi) reduction

ZSM-5@ZnIn2S4 is constructed for highly efficient photocatalytic Cr(vi) reduction.

Interface engineering of Co9S8/CdIn2S4 ohmic junction for efficient photocatalytic H2 evolution under visible light

The design and development of high-performance photocatalysts from three aspects of simultaneous enhancement of light harvest, carrier migration rate, and redox reaction rate is still a great challenge. Herein, a novel Co₉S₈/CdIn₂S₄ ohmic junction with a robust internal electric field (IEF) is successfully prepared via hydrothermal and in situ synthesis methods and is used for effective photocatalytic H₂ evolution (PHE). Under simulated visible light irradiation, the PHE rate of 5% Co₉S₈/CdIn₂S₄ can reach 1083.6 μmol h^-1 g^-1, which is 6.4 times higher than that of CdIn₂S₄ (170.5 μmol h^-1 g^-1). The enhanced PHE performance is mainly ascribed to the improved light harvest and carrier separation efficiency and fast surface H₂ evolution kinetics. Moreover, Co₉S₈ nanotubes serve as promising Co-based cocatalysts that can evidently enhance PHE activity. Additionally, Co₉S₈/CdIn₂S₄ shows superior stability because the photogenerated carrier transfer path restrains the photocorrosion behavior. The photocatalytic mechanism is proposed based on experimental results and DFT calculations. This work offers new insights for the design and development of highly active photocatalysts from interface engineering.

Boosting H2 Production over C60 -Mediated NH2 -MIL-125(Ti)/Zn0.5 Cd0.5 S S-Scheme Heterojunction via Enhanced Interfacial Carrier Separation

Improving greatly the separation efficiency of interfacial charge carrier is a major challenge in photocatalysis. Herein, a new class of C₆₀ -mediated NH₂ -MIL-125(Ti)/Zn_0.5 Cd_0.5 S S-scheme heterojunction with enhanced interfacial charge carrier separation is designed and synthesized. The constructed S-scheme heterojunction thermodynamically favors photocatalytic H₂ evolution because of the large driving force resulting from its strong redox abilities. As a consequence, the optimum proportion of C₆₀ -mediated NH₂ -MIL-125(Ti)/Zn_0.5 Cd_0.5 S S-scheme heterojunction displays comparable H₂ evolution activity with a rate of 7825.20 µmol h^-1 g^-1 under visible light irradiation, which is about 93.05 times, 6.38 times and 2.65 times higher than that of 2% C₆₀ /NH₂ -MIL-125(Ti), Zn_0.5 Cd_0.5 S and 45% NH₂ -MIL-125(Ti)/Zn_0.5 Cd_0.5 S, and outperforms the majority of the previously reported MOFs-based photocatalysts. Spectroscopic characterizations and theory calculations indicate that the S-scheme heterojunction can powerfully promote the separation of photogenerated carriers. This work offers a new insight for future design and development of highly active MOFs-based photocatalysts.

ZnIn2 S4 -Based Photocatalysts for Energy and Environmental Applications

As a fascinating visible-light-responsive photocatalyst, zinc indium sulfide (ZnIn₂ S₄ ) has attracted extensive interdisciplinary interest and is expected to become a new research hotspot in the near future, due to its nontoxicity, suitable band gap, high physicochemical stability and durability, ease of synthesis, and appealing catalytic activity. This review provides an overview on the recent advances in ZnIn₂ S₄ -based photocatalysts. First, the crystal structures and band structures of ZnIn₂ S₄ are briefly introduced. Then, various modulation strategies of ZnIn₂ S₄ are outlined for better photocatalytic performance, which includes morphology and structure engineering, vacancy engineering, doping engineering, hydrogenation engineering, and the construction of ZnIn₂ S₄ -based composites. Thereafter, the potential applications in the energy and environmental area of ZnIn₂ S₄ -based photocatalysts are summarized. Finally, some personal perspectives about the promises and prospects of this emerging material are provided.

Constructing high-performance H3PW12O40/CoS2 counter electrodes for quantum dot sensitized solar cells by reducing the surface work function of CoS2

A low cost H₃PW₁₂O₄₀ (PW₁₂)/CoS₂ complex is prepared and used as a counter electrode (CE) to combine with sandwich quantum dot sensitized solar cells (QDSSCs) composed of a TiO₂/CdS/CdSe/ZnS photoanode and polysulfide electrolyte to study their photovoltaic properties via a simple hydrothermal method. Under standard simulated sunlight, the photoelectric conversion efficiency (PCE) of 2%PW₁₂ (PW₁₂-2/CoS₂) doped CEs was 6.29%, which was significantly 67.7% higher than those of QDSSCs based on undoped CoS₂ CEs (3.75%). Due to the introduction of PW₁₂, the nanoparticles forming the hollow structure of CoS₂ changed from regular octahedra to rough nanoparticles, which increase the active sites. At the same time, the work function of CoS₂ decorated with PW₁₂ is decreased. This study and discovery demonstrate that POMs can be used to optimize CE materials and improve the photoelectric conversion efficiency of QDSSCs, which provide an experimental and theoretical basis for subsequent investigations.

Rational design of n-Bi12TiO20@p-BiOI core-shell heterojunction for boosting photocatalytic NO removal

Bismuth titanate (Bi₁₂TiO₂₀) with unique sillenite structure has been shown to be an excellent photocatalyst for environmental remediation. However, the narrow light-responsive range and rapid recombination of photoinduced electrons-holes limit the photocatalytic performance of Bi₁₂TiO₂₀. To overcome the limitations, a practical and feasibleway is to fabricate heterojunctions by combining Bi₁₂TiO₂₀ with suitable photocatalysts. Here, using a facile chemical precipitation method, a novel and hierarchical core-shell structure of n-Bi₁₂TiO₂₀@p-BiOI (BTO@BiOI) heterojunction was rationally designed and synthesized by loading BiOI nanosheets on BTO nanofibers. The constructed BTO@BiOI composites exhibited significant charge transfer ability due to the synergistic effects of the built-in electric field between BTO and BiOI as well as close interfacial contacts. In addition, the narrow bandgapcharacteristics of the BiOI led to wide light absorption ranges. Therefore, the BTO@BiOI heterojunction exhibited an improved photocatalytic performance under visible light irradiation. The NO removal efficiency of optimal BTO@BiOI was 45.7%, which was significantly higher compared tothat of pure BTO (3.6%) or BiOI (23.1%). Moreover, the cycling experiment revealed that BTO@BiOI composite has a good stability and reusability. The possible mechanism of photocatalytic NO oxidation over BTO@BiOI was investigated in detail.

Hierarchical fabrication of hollow Co2P nanocages coated with ZnIn2S4 thin layer: Highly efficient noble-metal-free photocatalyst for hydrogen evolution

The directional synthesis of transition metal phosphides was considered to be an effective strategy to solve the overdependence of noble metals on photocatalytic hydrogen evolution (PHE) reactions. Inspiringly, this work reported a facile method for constructing hollow Co₂P nanocages (Co₂P NCGs) that derived from ZIF-67 by calcining and phosphiding procedure in nitrogen atmosphere to act as non-noble metal cocatalysts. Followed with further coating thin-layered ZnIn₂S₄ (ZIS) on the surface of Co₂P NCGs through a hydrothermal reaction, the hierarchical robust Co₂P/ZnIn₂S₄ nanocages (Co₂P/ZIS NCGs) were then delicately fabricated as efficient photocatalysts for PHE reactions. The uniquely hollow structure of Co₂P NCGs largely diffused the photogenerated chargers that induced from ZIS and the closely interfacial contact significantly promoted the separation and transfer of electrons from ZIS to Co₂P according to density functional theory (DFT) calculation, synergistically resulting in an efficient hydrogen generation performance. PHE results showed that an efficient H₂ evolution rate of 7.93 mmol/g/h over 10% Co₂P/ZIS NCGs was achieved, about 10 times higher than that of pristine ZnIn₂S₄. More importantly, the hierarchically hollow Co₂P/ZIS NCGs exhibited ascendant PHE activity in comparison with that of 1% noble metal (Pt, Au, Ag) loaded ZnIn₂S₄ with superior sustainability, all indicating the efficient and stable photocatalysts of Co₂P/ZIS NCGs for PHE reactions.

Boosting charge carrier separation efficiency by constructing an intramolecular DA system towards efficient photoreduction of CO2

The charge carrier excitation–recombination process between the donor and acceptor, and the photocatalytic reduction of CO₂ to CO over CN based DA composites.

Bimetallic phosphide NixCo1−xP decorated flower-like ZnIn2S4 for enhanced photocatalytic hydrogen evolution

2%Ni_0.1Co_0.9P–ZIS exhibited the highest photocatalyst hydrogen production rate of 3839 μmol g⁻¹ h⁻¹ under visible light irradiation (λ > 420 nm), which is 5.4 times higher than pure ZIS (714 μmol g⁻¹ h⁻¹).

Biomimetic design and synthesis of visible-light-driven g-C3N4 nanotube @polydopamine/NiCo-layered double hydroxides composite photocatalysts for improved photocatalytic hydrogen evolution activity

In the practical process of photocatalytic H₂ evolution, optimizing the ability of light absorption and charge spatial separation is the top priority for improving the photocatalytic performance. In this study, we elaborately engineer neoteric g-C₃N₄ nanotube@polydopamine(pDA)/NiCo-LDH (LPC) composite photocatalyst by combining hydrothermal and calcination method. In the LPC composite system, the one-dimensional (1D) g-C₃N₄ nanotubes with larger specific surface area can afford more active sites and conduce to shorten the charge migration distance, as well as the high-speed mass transfer in the nanotube can accelerate the reaction course. The g-C₃N₄/NiCo-LDH type-II heterojunction can efficaciously stimulate the spatial separation of photo-produced charge. In addition, pDA as heterojunction metal-free interface mediums can provide multiple action (π-π* electron delocalization effect, adhesive action and photosensitization). The optimized LPC nanocomposite displays about 3.3-fold high photoactivity for H₂ evolution compared with the g-C₃N₄ nanotube under solar light irradiation. In addition, the cycle experiment result shows that the LPC composite photocatalyst possesses superior stability and recyclability. The resultant g-C₃N₄@pDA/NiCo-LDH composite photocatalyst displays the potential practical application in the field of energy conversion.