Facile synthesis of sphere-like structured ZnIn2S4-rGO-CuInS2 ternary heterojunction catalyst for efficient visible-active photocatalytic hydrogen evolution

Ammonia-Treated Graphene Oxide/ZnIn2S4 Composite for Enhanced Photocatalytic Hydrogen Production under Visible Light Irradiation

In the pursuit of solar-driven photocatalytic energy generation, environmental remediation, and carbon neutrality, the development of semiconductor-based heterojunction photocatalysts presents a promising strategy. However, the photocatalytic efficiency of pristine ZnIn2S4 (ZIS) is hindered by rapid electron-hole recombination and a relatively small surface area. Meanwhile, pure graphene oxide (GO) is not an ideal photocatalyst due to its inappropriate bandgap and the presence of oxygenated functional groups. To overcome these limitations, a surfactant-assisted ZIS synthesis was combined with ammonia-treated GO (NGO) to form an NGO/ZIS composite that enhances light absorption, charge carrier separation and transport, and overall hydrogen production efficiency under visible light illumination. Among the evaluated materials, 0.1NGO/ZIS exhibited the highest hydrogen evolution rate (18.8 mmol·g-1 h-1), demonstrating enhancements of 3-fold and 940-fold increased compared to pristine ZIS (5.8 mmol·g-1 h-1) and NGO (0.02 mmol·g-1 h-1), respectively. This superior photocatalytic performance is attributed to improved interfacial charge transfer between NGO and ZIS, facilitated by the incorporation of amine and amide groups into GO. Furthermore, density functional theory (DFT) calculations were conducted to validate the impact of ammonia treatment on GO and support the experimental findings. The synthesized photocatalysts were characterized by using X-ray diffraction (XRD), Fourier-transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), diffuse reflectance sorption spectroscopy (DRS), photoluminescence (PL), electrochemical impedance spectroscopy (EIS), electron spin resonance (ESR), and time-resolved photoluminescence (TRPL) analyses. This study presents a simple yet effective approach to fabricating NGO/ZIS composites, contributing to the advancement of high-performance photocatalysts for sustainable energy applications.

Designing CuO@rGO-MoS2 Nanocomposite with Bird's-Nest Like Structure as Peroxymonosulfate Activator for the Efficient Degradation of Rhodamine B

A straightforward, single-stage hydrothermal approach was utilized to synthesize a unique CuO@rGO-MoS2 nanocomposite, featuring a nest-mimicking architecture. It has highly efficient heterogeneous catalyzed property that can catalyze and activate the peroxymonosulfate (PMS) by means of radical (•OH, SO4•-, and O2•-) and nonradical (1O2) pathways to generate ROS for the rapid degradation of the organic dye rhodamine B (Rh.B). Graphene oxide, which has high specific surface, serves as an excellent carrier which achieves a homogeneous dispersion of the main catalyst component and gives a series of oxygen-containing functional groups that become active centers for nonradical route activation. Through experimental and DFT calculation, it was revealed that MoS2 as a cocatalyst accelerated the redox cycle of the Cu active center during the activation of PMS via catalysis, further enhancing the catalytic activity of the nanocomposites. And thus the CuO@rGO-MoS2/PMS system with bird's-nest like structure achieves rapid degradation of Rh.B in a short period, and the decomposition efficiency of Rh.B reaches 99% within 30 min duration of the reaction. Besides, this system exhibits excellent resistance to environmental interference, demonstrating commendable degradation efficiency across broad pH spectrum (pH 5-11) and high levels of common interfering ions (Cl-, NO3-, SO42-, etc.). To conclude, this study tried to propose and validate a catalyst design idea based on catalytic activation of peroxymonosulfate by selecting appropriate main catalysts, cocatalysts, and catalyst carriers to achieve improved catalytic performance and stability of the catalysts, and the synthesized catalysts CuO@rGO-MoS2 by this design strategy have shown good degradation performances in real wastewater.

Synergistically-mediated highly-efficient visible-light-driven hydrogen evolution activity using Ohmic/Schottky-type dual-junctions and sulfur vacancy

Enabling highly-efficient multiplex-optimization photocatalysts is critical to overcome the bottlenecks of hydrogen evolution reaction efficiency and photostability. Herein, novel CoS/Sv-ZnIn2S4/MoS2 composites are successfully synthesized through an in situ technique. Taking advantage of the synergistic effect of sulfur vacancy, Schottky-type MoS2/Sv-ZnIn2S4 junction and Ohmic-type CoS/Sv-ZnIn2S4 junction, the light absorption, electron/hole separation efficiency, charge transfer rate and hydrogen reduction reaction dynamic can be significantly enhanced. As a result, an impressive photocatalytic hydrogen evolution rate of 18.43 mmol g-1 h-1 is achieved under the visible-light irradiation. Furthermore, apparent quantum efficiencies of 72.14 % and 9.91 % are also achieved under 350 and 420 nm monochromatic light irradiation. This work presents an in situ perspective to design multiplex-optimization photocatalytic system for highly-efficient hydrogen production.

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.

The construction of Z-scheme heterojunction ZnIn2S4@CuO with enhanced charge transfer capability and its mechanism study for the visible light degradation of tetracycline

In this study, copper oxide (CuO) was prepared by the microwave-assisted hydrothermal technique subsequently, CuO was grown in situ onto different rare metal compounds to prepare Z-scheme heterojunctions to improve the degradation efficiency of tetracycline (TC) in water environments. Various characterization proved the successful synthesis of all composite materials, and the formation of tight heterojunction interfaces, among which, the core-shell structure ZnIn2S4@CuO exhibited excellent photocatalytic degradation capability. Research results indicated that the degradation efficiency of ZnIn2S4@CuO for TC (50 mg/L) in the water environment reached 95.8 %, and the degradation rate is 2.41 times and 12.93 times that of CuO and ZnIn2S4 alone, respectively, the reason is because of the introduction of ZnIn2S4, Z-scheme heterojunction structures and internal electric field (IEF) is constructed and formed to extend the visible light response range of photocatalysts to improve electron-hole separation efficiency, and enhance charge transfer. In addition, ZnIn2S4@CuO-2 exhibited good stability and reproducibility, with no significant loss of activity after five cycles. Finally, the precise locations of free radical attack on TC were investigated by the combined use of high-resolution mass spectrometry (HR-MC) and frontier electron densities (FEDs), and a reasonable degradation pathway was provided. The results of this research provide a new and viable approach to overcome the limitations of conventional photocatalytic materials in terms of limited visible light absorption range and fast carrier recombination rates, which offers promising prospects for a wide range of applications in the field of wastewater purification.

Photocatalysis oxidative desulfurization of dibenzothiophene in extremely deep liquid fuels on the Z-scheme catalyst ZnO-CuInS2-ZnS intelligently integrated with carbon quantum dots: performance, mechanism, and stability

In this study, we improved the electrochemical and photocatalytic properties of the ZnO-CuInS2-ZnS (ZCZ) material by integrating with carbon quantum dots (CQD) with particle sizes from 2 to 5 nm. The integration of ZnO-CuInS2-ZnS with carbon quantum dots (ZnO-CuInS2-ZnS/CQD:ZCZ-CQD) enhanced the visible light absorption, significantly reduced the electron-hole recombination rate, and facilitated the electron transfer and separation processes as confirmed by UV-visible diffuse reflectance spectroscopy (UV-vis DRS), photoluminescence (PL), and electrochemical impedance spectroscopy (EIS). The successful integration of ZCZ with carbon quantum dots was confirmed using X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM) methods. The ZCZ/CQD photocatalyst removed up to 98.32% of DBT after 120 minutes of reaction, maintained over 90% durability after 10 cycles, and retained its structure without any changes. The ZCZ photocatalyst integrated with CQD enhances faster dibenzothiophene (DBT) removal by 4.46, 3.24, 2.53, and 1.72 times compared to ZnO, CuInS2, ZnS, and ZnO-CuInS2-ZnS, respectively. Factors influencing the oxidation process of DBT including the mass of the photocatalyst, initial DBT concentration, stability, and reaction kinetics were studied. Through active species trapping experiments, this study demonstrated that the formation of ˙O2 - and ˙OH radicals determines the reaction rate. The mechanism of photocatalysis on ZCZ-CQD materials and the intermediate products formed in the process of photocatalytic oxidative desulfurization of dibenzothiophene is proposed based on electrochemical measurements and GC-MS results.

Microwave-assisted synthesis of ZnS@CuInxSy for photocatalytic degradation of coloured and non-coloured pollutants

Copper indium sulfide (CuInS2) exhibits strong visible light absorption and thus has the potential for good photocatalytic activity; however, rapid charge recombination limits its practical usage. An intriguing strategy to overcome this issue is to couple CuInS2 with another semiconductor to form a heterojunction, which can improve the charge carrier separation and, hence, enhance the photocatalytic activity. In this study, photocatalysts comprising CuInS2 with a secondary CuS phase (termed CuInxSy) and CuInxSy loaded with ZnS (termed ZnS@CuInxSy) were synthesized via a microwave-assisted method. Structural and morphological characterization revealed that the ZnS@CuInxSy photocatalyst comprised tetragonal CuInS2 containing a secondary phase of hexagonal CuS, coupled with hexagonal ZnS. The effective band gap energy of CuInxSy was widened from 2.23 to 2.71 as the ZnS loading increased from 0 to 30%. The coupling of CuInxSy with ZnS leads to long-lived charge carriers and efficient visible-light harvesting properties, which in turn lead to a remarkably high activity for the photocatalytic degradation of brilliant green (95.6% in 5 h) and conversion of 4-nitrophenol to 4-nitrophenolate ions (95.4% in 5 h). The active species involved in these photocatalytic processes were evaluated using suitable trapping agents. Based on the obtained results, photocatalytic mechanisms are proposed that emphasize the importance of h+, O2•-, and OH- in photocatalytic processes using ZnS@CuInxSy.

Enhanced piezo-photocatalytic performance in ZnIn2S4/BiFeO3 heterojunction stimulated by solar and mechanical energy for efficient hydrogen evolution

An emerging approach that employs both light and vibration energy on binary photo-/piezoelectric semiconductor materials for efficient hydrogen (H2) evolution has garnered considerable attention. ZnIn2S4 (ZIS) is recognized as a promising visible-light-activated photocatalyst. However, its effectiveness is constraint by the slow separation dynamics of photoexcited carriers. Density functional theory (DFT) predictions have shown that the integration of piezoelectric BiFeO3 (BFO) is conducive to the reduction of the H2 adsorption free energy (ΔGH*) for the photocatalytic H2 evolution reaction, thereby enhancing the reaction kinetics. Informed by theoretical predictions, piezoelectric BFO polyhedron particles were successfully synthesized and incorporated with ZIS nanoflowers to create a ZIS/BFO heterojunction using an ultrasonic-assisted calcination method. When subjected to simultaneous ultrasonic treatment and visible-light irradiation, the optimal ZIS/BFO piezoelectric enhanced (piezo-enhanced) heterojunction exhibited a piezoelectric photocatalytic (piezo-photocatalytic) H2 evolution rate approximately 6.6 times higher than that of pristine ZIS and about 3.0 times greater than the rate achieved under light-only conditions. Moreover, based on theoretical predictions and experimental results, a plausible mechanism and charge transfer route for the enhancement of piezo-photocatalytic performance were studied by the subsequent piezoelectric force microscopy (PFM) measurements and DFT calculations. The findings of this study strongly confirm that both the internal electric field of the step-scheme (S-Scheme) heterojunction and the alternating piezoelectric field generated by the vibration of BFO can enhance the transportation and separation of electron-hole pairs. This study presents a concept for the multipath utilization of light and vibrational energy to harness renewable energy from the environment.

Improved solar-driven water purification using an eco-friendly and cost-effective aerogel-based interfacial evaporator with exceptional photocatalytic capabilities

As a promising solution to address the global challenge of freshwater scarcity, solar-powered interfacial steam generation has undergone notable advancements. This study introduces a novel solar-driven interfacial evaporation membrane (ZnIn2S4@SiO2/ACSA, ZSAS) comprising a ZnIn2S4@SiO2 composite and a black sodium alginate aerogel infused with activated carbon. The ZSAS membrane demonstrates exceptional light absorption and thermal insulation, leading to elevated surface temperatures and reduced heat dissipation into the bulk water. Furthermore, the incorporation of AC reinforces the mechanical properties of the ZSAS membrane and enhances the water purification performance. These collective features result in an impressive evaporation rate of 1.485 kg m-2 h-1 and a high photothermal conversion efficiency of 91.2% under 1 sun irradiation for the optimal ZSAS membrane. Moreover, the optimal ZSAS membrane can effectively remove salts, heavy metal ions, and organic pollutants, benefitting from its superior evaporation separation effect and the photocatalytic properties of the ZnIn2S4@SiO2 composite.

Emergence of CuInS2 derived photocatalyst for environmental remediation and energy conversion

Hydrogen production, catalytic organic synthesis, carbon dioxide reduction, environmental purification, and other major fields have all adopted photocatalytic technologies due to their eco-friendliness, ease of use, and reliance on sunlight as the driving force. Photocatalyst is the key component of photocatalytic technology. Thus, it is of utmost importance to produce highly efficient, stable, visible-light-responsive photocatalysts. CIS stands out among other visible-light-response photocatalysts for its advantageous combination of easy synthesis, non-toxicity, high stability, and suitable band structure. In this study, we took a brief glance at the synthesis techniques for CIS after providing a quick introduction to the fundamental semiconductor features, including the crystal and band structures of CIS. Then, we discussed the ways doping, heterojunction creation, p-n heterojunction, type-II heterojunction, and Z-scheme may be used to modify CIS's performance. Subsequently, the applications of CIS towards pollutant degradation, CO2 reduction, water splitting, and other toxic pollutants remediation are reviewed in detail. Finally, several remaining problems with CIS-based photocatalysts are highlighted, along with future potential for constructing more superior photocatalysts.

Copper indium sulfide quantum dots in photocatalysis

Since the advent of photocatalytic technology, scientists have been searching for semiconductor materials with high efficiency in solar energy utilization and conversion to chemical energy. Recently, the development of quantum dot (QD) photocatalysts has attracted much attention because of their unique characteristics: small size, quantum effects, strong surface activity, and wide photoresponse range. Among ternary chalcogenide semiconductors, CuInS₂ QDs are increasingly examined in the field of photocatalysis due to their high absorption coefficients, good matching of the absorption range with sunlight spectrum, long lifetimes of photogenerated electron-hole pairs and environmental sustainability. In this review paper, the structural and electronic properties, synthesis methods and various photocatalytic applications of CuInS₂ QDs are systematically expounded. The current research status on the photocatalytic properties of materials based on CuInS₂ QD is discussed combined with the existing modification approaches for the enhancement of their performances. Future challenges and new development opportunities of CuInS₂ QDs in the field of photocatalysis are then prospected.

Trace Cu+-dominated band structure engineering in CuxIn0.25ZnSy for promoting photocatalytic H2 evolution

As an attractive semiconductor photocatalyst, (CuInS₂)_x-(ZnS)_y has been intensively studied in photocatalysis, due to its unique layered structure and stability. Here, we synthesized a series of Cu_xIn_0.25ZnS_y photocatalysts with different trace Cu⁺-dominated ratios. The results show that doping with Cu⁺ ions leads to an increase in the valence state of In and the formation of a distorted S structure, simultaneously inducing a decrease in the semiconductor bandgap. When the doping amount of Cu⁺ ions is 0.04 atomic ratio to Zn, the optimized Cu_0.04In_0.25ZnS_y photocatalyst with a bandgap of 2.16 eV shows the highest catalytic hydrogen evolution activity (191.4 μmol.h^-1). Subsequently, among the common cocatalysts, Rh loaded Cu_0.04In_0.25ZnS_y gives the highest activity of 1189.8 μmol·h^-1, corresponding to an apparent quantum efficiency of 49.11 % at 420 nm. Moreover, the internal mechanism of photogenerated carrier transfer between semiconductors and different cocatalysts is analyzed by the band bending phenomenon.

A novel Fe/Mo co-catalyzed graphene-based nanocomposite to activate peroxymonosulfate for highly efficient degradation of organic pollutants

A novel 3D α-FeOOH@MoS₂/rGO nanocomposite was successfully fabricated by a simple in situ hydrothermal method. It is a highly efficient heterogeneous catalyst in activation of peroxymonosulfate (PMS) for rapid degradation of rhodamine B (RhB), with 99.9% of RhB removed within 20 min. The introduction of rGO contributes to uniform dispersion and sufficient contact of α-FeOOH and MoS₂ nanosheets. Highly active Mo(IV) enhances the reduction of Fe(III), improves Fe(III)/Fe(II) conversion and promotes the generation of O₂1, which ensures an improved catalytic activity. MoS₂/rGO hybrid can effectively solve the problem of material reunion and make α-FeOOH exhibit excellent catalytic performance. The α-FeOOH@MoS₂-rGO/PMS system is a co-catalytic system based on the active components of α-FeOOH and MoS₂. The main reactive oxygen species in the α-FeOOH@MoS₂-rGO/PMS system are O₂1, SO₄^.- and ⋅O₂^-, which contribute to a high reactivity over a wide range of pH (5-9). Besides, this system is highly resistant to anions (Cl^-, SO₄^2-) and natural organic matter (humic acid), and can be widely used for degradation of common organic pollutants. The α-FeOOH@MoS₂/rGO is a promising Fenton-like catalyst for refractory organic wastewater treatment.

Chalcogenides and Chalcogenide-Based Heterostructures as Photocatalysts for Water Splitting

Chalcogenides are essential in the conversion of solar energy into hydrogen fuel due to their narrow band gap energy. Hydrogen fuel could resolve future energy crises by substituting carbon fuels owing to zero-emission carbon-free gas and its eco-friendliness. The fabrication of different metal chalcogenide-based photocatalysts with enhanced photocatalytic water splitting have been summarized in this review. Different modifications of these chalcogenides, including coupling with another semiconductor, metal loading, and doping, are fabricated with different synthetic routes that can remarkably improve the photo-exciton separation and have been extensively investigated for photocatalytic hydrogen generation. In this direction, this review is undertaken to provide an overview of the enhanced photocatalytic performance of the binary and ternary chalcogenide heterostructures and their mechanisms for hydrogen production under irradiation of light.

Bismuth quantum dots anchored one-dimensional CdS as plasmonic photocatalyst for pharmaceutical tetracycline hydrochloride pollutant degradation

Earth abundant metal based plasmonic photocatalysis is one of the most proficient approaches to degrade the emergent organic pollutants in contaminated water. Here, we report that using one-dimensional CdS/zero-dimensional Bi quantum dot (QD) heterostructures (1D/0D CdS/Bi HSs) were obtained via a simple solvothermal reaction. The results specified that the Bi QDs were grown onto CdS NRs through the reduction of Bi³⁺ ions. The Bi modified CdS HSs were employed as a photocatalyst for pharmaceutical pollutant tetracycline degradation and the optimized sample showed the maximum photocatalytic degradation activity of 90% under visible light radiation within 60 min, which is greater than the pure CdS (52%) under identical conditions. Based on the structural characterizations and degradation efficiency, the obtained CdS/Bi is a promising photocatalyst for the treatment of wastewater which contains emerging pollutants such as organic dyes and pharmaceutical antibiotics during the industrial processes. The boosted photocatalytic degradation efficiency is credited to the doped Bi³⁺ species; surface plasmon resonance effect that raised from metallic Bi QDs and proficient photoinduced charge carriers separation.

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 a Z-scheme ZnIn2S4-S/CNTs/RP nanocomposite with modulated energy band alignment for enhanced photocatalytic hydrogen evolution

Energy band structures greatly determine the charge separation and transfer properties in heterojunction photocatalysts and consequently their photocatalytic activities. Herein, a well-designed Z-scheme ZnIn₂S₄-S/CNTs/RP (ZIS-S/CNTs/RP) nanocomposite was fabricated according to an energy band alignment steering strategy to realize superior photocatalytic H₂ evolution performance. The ZIS-S/CNTs/RP nanocomposite shows an efficient photocatalytic H₂ evolution rate of 1639.9 μmol g^-1h^-1, which is noticeably higher than that of pristine red phosphorus (RP) and CNTs/RP and ZIS-S/RP composites, as well as those of the compared heterojunctions using bulk RP or ZnIn₂S₄. Owing to the modification of nanosized RP and the introduction of sulfur vacancies in ZnIn₂S₄, a tailored energy band alignment of the heterojunction with a higher reduction potential and larger Fermi level potential difference was achieved, which resulted in significantly increased photogenerated electron-hole separation efficiency and a more efficient Z-scheme charge transfer mechanism, thus promoting the photocatalytic activity of ZIS-S/CNTs/RP. This work aims to provide a novel effective strategy for the construction of high-performance heterojunction photocatalysts by energy band engineering.