Direct Z-scheme Heterojunction Research Articles

2D/2D Bi2MoO6/g-C3N4 direct Z-scheme Van der Waals heterojunction photocatalyst for boosting nitrogen fixation

Although photocatalytic nitrogen fixation is an efficient and environmentally-friendly technology for ammonia synthesis, it still faces challenges such as high recombination of photo-generated carriers and a lack of active sites for the reaction of catalysts. Constructing direct Z-scheme heterojunctions is considered an effective strategy to enhance carrier separation efficiency of catalysts. However, it still encounters the challenge of lacking surface active reaction sites. The 2D Z-scheme Van der Waals heterojunction has the same charge transfer mechanism of direct Z-scheme heterojunctions, ensuring high carrier efficiency and retaining strong redox ability. Additionally, its layered structure provides a large number of reactive sites. In this study, theoretical calculation simulation was employed to predict the properties of Bi2MoO6 (BMO) and g-C3N4 (CN), and to simulate the dynamic behavior of photogenerated carriers. A 2D/2D CN-BMO direct Z-scheme Van der Waals heterojunction was constructed. Remarkably, this heterojunction demonstrated significantly enhanced photocatalytic ammonium generation capabilities. This study provides valuable insights for the development of advanced heterojunction photocatalysts.

ZrS2/Ga2SSe heterojunction: A direct Z-scheme heterojunction with excellent photocatalytic performance across the entire pH range and high solar-to-hydrogen efficiency

Developing photocatalytic water splitting materials for hydrogen production is a crucial strategy for achieving sustainable energy utilization. This study proposes a ZrS2/Ga2SSe van der Waals heterojunction and conducts an in-depth analysis through first-principle calculations. The results show that the heterojunction possesses an indirect bandgap of 1.33 eV, which contributes to its superior optical performance. Its band structure and built-in electric field promote the Z-scheme electron transfer mechanism. High carrier mobility in the heterojunction improves photocatalytic efficiency. Strain engineering further enhances its electronic and optical properties, allowing water splitting across all pH levels within a biaxial strain range of −4% to +2%. Under a −6% compressive strain, there is a 63.06% enhancement in optical performance within the visible light spectrum, and the solar-to-hydrogen efficiency reached 10.93%. Gibbs free energy analysis indicates that the hydrogen evolution reaction, powered by photogenerated electrons, requires only 0.19 eV of energy. Therefore, the ZrS2/Ga2SSe heterojunction is identified as a promising visible-light-driven catalyst for water splitting.

Visible-light-driven photocatalytic for degrading tetracycline wastewater by BiOI/Bi2O3 Z-scheme heterojunction

Direct Z-scheme heterojunctions can exhibit enhanced redox capacity in redox reactions compared to conventional heterojunctions. In this study, BiOI/Bi2O3 Z-scheme heterojunctions were synthesized by a facile co-precipitation and calcination method using BiOI as a precursor, and its photocatalytic activity was investigated by degrading tetracycline antibiotics in aqueous environment. Under visible light, the degradation efficiency of tetracycline reached 80.01 % and the photocatalytic degradation rate constant reached 0.0116 min−1 when the molar ratio of Bi and I in BiOI/Bi2O3 composites was 1:1, which were 2.8 and 4.8 times higher than that of pristine BiOI (0.0041 min−1) and Bi2O3 (0.0024 min−1), respectively. The heterojunctions exposed excellent stability that maintained at 78.80 % after four cyclic tests. The ascendant photocatalytic performance can be attributed to the formation of direct Z-scheme heterojunctions, which improves the separation and transfer efficiency of the photogenerated electron-hole pairs, and ·O2- is the main active substance in the degradation process. This research provides a green and convenient method for preparing photocatalytic heterojunctions, which is conducive to promoting the development of photocatalytic degradation of refractory pollutants under visible light.

HBNC/Janus MoSTe heterojunctions in photocatalytic water splitting for hydrogen production: A first-principles study

Production of clean energy is an efficient way to solve the environmental pollution. We construct hBNC/Janus MoSTe heterojunction as a photocatalyst for hydrogen production from water splitting. The electronic and optical properties of this heterojunction are investigated by the first-principle. The negative binding energy indicates that the process of this heterojunction is exothermic and it tends to exist stably. The 1.42 eV band gap of this heterojunction is suitable for photocatalyst. The results of PDOS show that the band alignment of hBNC/MoSTe is typical type-II. In addition, the built-in electric field makes the path of photo-generated carries belong to Z-scheme. Therefore, the hBNC/MoSTe is a direct Z-scheme heterojunction and has stronger redox properties. The results of Gibbs free energy indicate that the hydrogen evolution reaction (HER) reaction could complete spontaneously under the reduction overpotential (χH2 = 1.38 eV) which is provided by the Photo-generated electrons. The optical coefficient of part visible light is improved compared with monolayer hBNC and MoSTe. Therefore, the h-BNC/MoSTe heterojunction studied here may be a promising candidate for solar-powered Z-scheme photocatalytic water cracking to produce hydrogen, providing a reference for clean energy generation.

Two-dimensional MoSTe/MSi2N4 (M = Mo, W) van der Waals heterojunctions for photocatalytic water-splitting: A first-principles study

Direct Z-scheme heterojunction is a promising candidate for photocatalysts because it effectively separates the photogenerated electrons-hole pairs with strong redox capacity. In this paper, the MoSTe-MSi2N4 (M = Mo, W) heterostructures are constructed, and their stability, electronic structures and photocatalytic performance are investigated. The results demonstrate that the absorption properties of heterojunctions are significantly better than that of monolayers in both visible and ultraviolet light regions. Expressly, heterojunctions have the direct Z-scheme charge transfer mechanism when S surface of MoSTe contacted with MSi2N4 (namely S-M). Further calculation find that the S-M heterojunctions can perform stable photocatalytic water splitting in both acidic and neutral environments, and have better hydrogen evolution reaction. These theoretical predictions suggest that the MoSTe-MSi2N4 heterostructures are high-performance photocatalysts for the preparation of hydrogen gas.

Direct Z-scheme GeC/GaSe heterojunction by first-principles study for photocatalytic water splitting

In this study, we constructed the direct Z-scheme heterojunction by vertically stacking monolayers of GeC and GaSe. And systematically explored its stability, electronic structure, optical absorption characteristics and photocatalytic mechanism with first principles calculations. Our results show that the GeC/GaSe heterojunction possesses an indirect-gap of 1.88 eV and exhibits a staggered energy-band structure. In comparison to the individual monolayers of GeC and GaSe, the GeC/GaSe heterojunction has more excellent absorption of far-ultraviolet and visible light. And the electrons and holes in the GeC/GaSe heterojunction have a transmission path resembling the letter Z. There is also an internal electric field from GeC to GaSe in the heterojunction, which accelerates the photoelectrons and holes along the Z direction when the heterojunction receives light. Furthermore, further studies suggest that the GeC/GaSe heterojunction can be utilized as a photocatalytic material for water splitting under pH = 0–14. Besides, the bandwidth and optical absorption properties of the GeC/GaSe heterojunction can be adjusted by biaxial strains. Moreover, Gibbs free energy calculations during water splitting demonstrate that the GeC/GaSe heterojunction exhibits a highly driven force for both OER and HER. Thus, direct Z-scheme GeC/GaSe heterojunction has the capability to be a promising photocatalyst for water splitting.

Z-Scheme Heterojunction of Hierarchical Cu2S/CdIn2S4 Hollow Cubes to Boost Photoelectrochemical Performance.

The exaltation of light-harvesting efficiency and the inhibition of fast charge recombination are pivotal to the improvement of photoelectrochemical (PEC) performance. Herein, a direct Z-scheme heterojunction is designed of Cu2S/CdIn2S4 by in situ growth of CdIn2S4 nanosheets on the surface of hollow CuS cubes and then annealing at 400°C. The constructed Z-scheme heterojunction is demonstrated with electron paramagnetic resonance and redox couple (p-nitrophenol/p-aminophenol) measurements. Under illumination, it shows the photocurrent 6 times larger than that of hollow Cu2S cubes, and affords outstanding PEC performance over the known Cu2S and CdIn2S4-based photocatalysts. X-ray photoelectron spectroscopy and density functional theory results demonstrate a strong internal electric field formed in Cu2S/CdIn2S4 Z-scheme heterojunction, which accelerates the Z-scheme charge migration, thereby promoting electron-hole separation and enhancing their utilization efficiency. Moreover, the hollow structure of Cu2S is conducive to shortening the charge transport distance and improving light-harvesting capability. In proof-of-concept PEC application, a PEC detection method for miRNA-141 based on the sensitivity of benzo-4-chloro-hexadienone to light absorption on Cu2S/CdIn2S4 modified electrode is developed with good selectivity and a limit of detection of 32 aM. This work provides a simple approach for designing photoactive materials with highly efficient PEC performance.

Hydrothermal synthesis and characterization of 0D/2D SrMoO4/g-C3N4 composite with direct Z-scheme heterojunction: Efficient photocatalytic Ciprofloxacin degradation

Ciprofloxacin (Cip) is a common pollutant that causes sewage problems, and its effective removal is a great contribution to the clean water environment. Direct Zener-scheme (Z-scheme) heterojunction photocatalyst is a promising design idea for the removal of residual antibiotics in water. The goal of this study is to construct a binary composite photocatalyst with Z-scheme heterojunction to effectively remove residual ciprofloxacin in wastewater. Herein, a direct Z-scheme 0D/2D SrMoO4/g-C3N4 (SMOCN) composite photocatalyst was synthesized by ultrasonic-assisted hydrothermal way and its interior information (chemical structure, micromorphology, and physic-optical property) was detected by various characterization instruments (XRD, FT-IR, EDX, XPS, UV–Vis DRS, and PL). Meanwhile, the photocatalytic activity of all-prepared catalysts were estimated by Cip photodegradation experiments under simulated sunlight (500 W Xenon lamp). Among them, 89.9 % of Cip was broken down by 30SMOCN composite within 180 min at pH 7.0, which respectively reached 2.56 times of bare SMO and 2.03 times of bare CN. Furthermore, 85.2 % of Cip targeted molecule is still removed by SMOCN (excellent stability and recyclability) after five cycle runs. Finally, the reasonableness of SMOCN conforming to the direct Z-scheme mechanism is verified by comparison of optical properties, quenching experiment results and photogenerated carrier migration paths: 1) There is optical complementarity between SMO and CN, which is represented by redshifted absorption edge, narrowed band gap and weaken PL intensity. 2) The key active site on the SMOCN composite surface is photogenerated carriers in Cip photocatalytic degradation, which given full play to the direct synergistic catalytic effect between SMO and CN heterojunction. 3) The direct Z-scheme mechanism preserves the carriers of SMOCN with effective photo-redox function, promotes their separation and prolongs their lifetime.

Constructed black phosphorus quantum dots/BiVO4 Z-scheme heterojunction catalysis for efficient Rhodamine b degradation and DFT study

Black phosphorus (BP) is highly regarded in photocatalysis for its bandgap thickness dependency, high hole mobility, and broad visible light absorption. This study introduces a simple hydrothermal method to construct a BP QDs/BiVO4 direct Z-scheme heterojunction. The composite’s crystal structure, morphology, and photochemical properties were comprehensively characterized. The photocatalytic activity was evaluated using Rhodamine B (RhB) degradation under visible light. Notably, BP QDs0.12%/BiVO4 exhibited exceptional performance, achieving a 95.4 % RhB degradation after 100 min, three times higher than BiVO4 alone. The direct Z-scheme heterojunction played a pivotal role in facilitating O2− and h+ involvement in the degradation process. The interfacial interaction between BP QDs and BiVO4 significantly enhanced BiVO4′s visible light absorption, preserving its strong oxidation–reduction capacity. This enhancement was further corroborated by DFT simulation calculations. Overall, this study presents a novel approach for constructing efficient Z-scheme photocatalysts based on BP QDs, laying a solid foundation for their application in the field of photocatalytic degradation.

Cooperation of Strong Electric Field and H2O Dissociation on Co3O4-Decorated SiC Rods for Photodriven CO2 Methanation with 100% Selectivity.

Solar-driven methanation of carbon dioxide (CO2) with water (H2O) has emerged as an important strategy for achieving both carbon neutrality and fuel production. The selective methanation of CO2 was often hindered by the sluggish kinetics and the multiple competition of other C1 byproducts. To overcome this bottleneck, we utilized a biomass synthesis method to synthesize SiC rods and then constructed a direct Z-scheme heterojunction Co3O4/SiC catalyst. The substantial difference in work functions between SiC and Co3O4 served as a significant source of the charge driving force, facilitating the conversion of CO2 to CH4. The high-valent cobalt Co(IV) in Co3O4 acts as an active species to promote efficient dissociation of water. This favorable condition greatly enhanced the likelihood of a high concentration of electrons and protons around a single site on the catalyst surface for CO2 methanation. DFT calculation showed that the energy barrier of CO2 hydrogenation was significantly reduced at the Co3O4/SiC heterojunction interface, which changed the reaction pathway and completely converted the product from CO to CH4. The optimum CH4 evolution rate of Co3O4/SiC samples was 21.3 μmol g-1 h-1 with 100% selectivity. This study has an important guiding significance for the selective regulation of CO2 to CH4 products in photocatalysis applications.

Direct Z-scheme heterojunction impregnated MoS2–NiO–CuO nanohybrid for efficient photocatalyst and dye-sensitized solar cell

In this present work, the preparation of ternary MoS2–NiO–CuO nanohybrid by a facile hydrothermal process for photocatalytic and photovoltaic performance is presented. The prepared nanomaterials were confirmed by physio-chemical characterization. The nanosphere morphology was confirmed by electron microscopy techniques for the MoS2–NiO–CuO nanohybrid. The MoS2–NiO–CuO nanohybrid demonstrated enhanced crystal violet (CV) dye photodegradation which increased from 50 to 95% at 80 min; The degradation of methyl orange (MO) dye increased from 56 to 93% at 100 min under UV–visible light irradiation. The trapping experiment was carried out using different solvents for active species and the Z-Scheme photocatalytic mechanism was discussed in detail. Additionally, a batch series of stability experiments were carried out to determine the photostability of materials, and the results suggest that the MoS2–NiO–CuO nanohybrid is more stable even after four continuous cycles of photocatalytic activity. The MoS2–NiO–CuO nanohybrid delivers photoconversion efficiency (4.92%) explored efficacy is 3.8 times higher than the bare MoS2 (1.27%). The overall results indicated that the MoS2–NiO–CuO nanohybrid nanostructure could be a potential candidate to be used to improve photocatalytic performance and DSSC solar cell applications as well.

Magnetic field-assisted enhancement of photocatalytic activity: Modified Co-POMs direct Z-scheme heterojunction Co4PW9/CeO2 for efficient carrier separation and transport

The study of photocatalysis with multi-field assistance will be a significant research direction in the future, given its capacity to effectively enhance the separation and transportation of photogenerated carriers. In this work, a new type of heterojunction photocatalyst Co4PW9/CeO2 with excellent magnetic response, which is constructed based on cobalt modified polyoxometalates (POMs) and semiconductor CeO2, was successfully prepared. Compared to the photocatalysts previously reported, the composite material Co4PW9/CeO2 developed in our study addresses the limitations associated with the recombination of photogenerated electrons and holes inherent in traditional photocatalysis systems. Numerous techniques analysis result of physicochemical characteristics of composites shows that it efficiently facilitates the separation and migration of photogenerated carriers under the influence of magnetic fields. Upon photostimulation, the oppositely directed Lorentz forces acting on the electrons and holes generated by light effectively hinder the recombination of charge carriers. Concurrently, the charge carriers accumulated at the heterojunction interface undergo rapid migration due to the application of a magnetic field, thereby leading to a substantial increase in the catalytic efficiency of the material. The experimental results of methyl orange model photodegradation demonstrated that Co4PW9/CeO2-IV exhibited superior catalytic performance. The free radical masking experiments and EPR analysis indicated that ∙O2− and ∙OH were the primary active radicals in this catalytic process. The possible photocatalytic mechanism of the heterojunction was discussed in detail. A detailed study of separation and migration behavior of photogenerated carriers when influenced by magnetic fields has been conducted, in which offering a novel perspective for enhancing photocatalytic efficiency.

Electronic structure and photocatalytic performance of Janus MoSSe/Ga2SSe van der Waals heterostructures

Recently, transition metal dichalcogenide photocatalysts have been substantially explored as efficient catalysts for water splitting. This paper systematically investigates the electronic structure and related properties of four, hitherto uninvestigated, Janus MoSSe/Ga2SSe vdW heterostructures using first-principles calculations. The results indicate that two out of the four heterostructures exhibit a type-II energy band arrangement, which facilitates the effective separation of electron-hole pairs in space. Additionally, the electrostatic potential, charge density difference and Bader charges analyses indicate that charge transfer in the interfacial region creates a built-in electric field that effectively inhibits electron and hole complexation, and that one out of the four heterostructures corresponds to a direct Z-scheme heterojunction. The optical absorption coefficients show that the MoSSe/Ga2SSe vdW heterostructures have a broad absorption range from visible to ultraviolet. These findings suggest that the Janus SMoSe/SGa2Se and SMoSe/SeGa2S vdW heterostructures could be suitable for photocatalytic water decomposition. The SMoSe/SGa2Se and SMoSe/SeGa2S vdW heterostructures have high corrected solar-to-hydrogen (STH) efficiency of 11.84% and 10.13%, respectively.

Construction of an In2O3/Bi2S3 Z-Scheme Heterojunction for Enhanced Photocatalytic CO2 Reduction.

Photocatalytic conversion of CO2 to hydrocarbon fuel is a potential strategy to solve energy shortage and mitigate the greenhouse effect. Here, direct Z-scheme heterojunction photocatalysts (In2O3/Bi2S3) without an electron mediator are prepared by a simple hydrolysis method. The In2O3/Bi2S3 composite photocatalysts show greatly boosted photoactivity on CO2 conversion to CO compared with the pristine In2O3 and Bi2S3. The highest CO evolution rate of 2.67 μmol·g-1·h-1 is achieved by In2O3/Bi2S3-3, without any sacrificial agent or cocatalyst, which is about 3.87 times that of In2O3 (0.69 μmol·g-1·h-1). The boosted photocatalytic performance of In2O3/Bi2S3 composite catalysts can be ascribed to the establishment of a Z-scheme heterojunction, improving the photoabsorption and facilitating charge separation and transfer. This study provides a reference for designing and fabricating high-efficiency Z-scheme heterojunction photocatalysts for photocatalytic CO2 reduction.

Z-scheme ferrite nanoparticle/graphite carbon nitride nanosheet heterojunctions for photocatalytic hydrogen evolution

Visible light-driven photocatalytic water splitting has been considered one of the most promising sustainable approaches toward solar fuel production. As a substitute for metal oxide semiconductors, 2D graphitic carbon nitride (gCN) have been suffered a major challenge owing to its moderate bandgap (∼2.8 eV) and the synergistic effect of using spinel metal ferrites with a narrow bandgap (∼1.7 eV–1.9 eV) as a cocatalyst is promising to enhance solar energy conversion efficiency and stability. The as-synthesized gCN/copper ferrite (CFO) nanocomposites exhibit 10-fold augmentation in the photocurrent density (∼5 μA cm−2) compared with pure gCN. Remarkably, the gCN/CFO nanocomposites also exhibit 24 times increment in the rate of photocatalytic H2 evolution (∼488 μmol g−1) in contrast with pure gCN (∼20 μmol g−1 h−1). The amalgamation of gCN with metal ferrites has resulted in the development of direct Z-scheme heterojunction at the interface, facilitating the spatial separation of electrons and holes and boosting photocatalytic performance. Oxygen vacancies enhance the photocatalytic efficacy of the nanocomposites, as confirmed by X-ray photoelectron spectroscopy analysis. Moreover, the as-synthesized composites are highly stable in structure and morphology under light irradiation without considerable reduction in the catalytic performance over several cycles. Therefore, this work presents a facile approach using metal ferrites as co-catalysts to develop graphitic carbon-nitride-based photocatalysts for solar light-assisted green fuel generation.

In situ construction of core-shell NiFe-LDH@ZnIn2S4 direct Z-scheme heterojunction for facilitating photocatalytic H2 evolution

The development of photocatalysts with non-noble metals and the effective separation of photoexcited carriers is a significant strategy for accelerating surface reaction kinetics and promoting water splitting to produce H2. Herein, an exquisite core-shell NiFe-LDH@ZnIn2S4 heterojunction photocatalyst was constructed by in situ decoration of ultrathin ZnIn2S4 nanosheets on the surface of the flower-like NiFe-LDH microsphere. The synthesized 3D hierarchical NiFe@ZIS-25 composite exhibits enhanced photocatalytic H2 evolution activity, reaching 9.12 mmol·h-1·g-1, which is 2.52-fold higher than pure ZnIn2S4. The significant improvement in H2 evolution performance could be attributed to the hierarchical core-shell structure of the NiFe@ZIS-25 photocatalyst, which enhanced the light capture ability. In addition, the interfacial coupling effect of ZnIn2S4 and NiFe-LDH is beneficial to the migration of carriers. More importantly, the construction of Z-scheme heterojunction efficiently promotes the fast translation of photogenerated carriers while preserving a stronger reduction potential to achieve H2 evolution. This work elucidates a rational strategy to develop efficient photocatalysts with hierarchical core-shell structures for water splitting.

Fabrication of NiFe-LDH/MoS2 2D/2D material to construct direct Z-scheme heterojunction for enhanced CO2 photocatalytic reduction under visible light irradiation

In recent years, the utilization of solar energy for conversion of CO2 into fuels has emerged as a promising strategy for mitigating the Greenhouse effect. However, transport efficiency of photogenerated carriers plays a crucial role in determining the efficacy of CO2 photocatalytic reaction. In this paper, a 2D/2D composite material consisting of NiFe-LDH/MoS2, presenting high efficiency in separating photogenerated electron-hole pairs, has been successfully synthesized using a straightforward hydrothermal method. XRD, XPS, FTIR and other characterization results proved that the composite was successfully prepared, and its unique direct Z-scheme heterostructure improved the efficiency of CO2 photocatalytic reduction effectively. The composite material NiFe-LDH/MoS2 demonstrated enhanced rate of photo-induced electron-hole pair separation comparing with pure NiFe-LDH. Apart from this, the charge transfer resistance was reduced simultaneously, the composite material exhibited perfect photocatalytic activity. In photocatalytic reduction reaction experiment, CO yield of NiFe-LDH/MoS2 can reach 10.72 μmol/g, which is 3.93-fold and 4.17-fold that of bare NiFe-LDH and MoS2. The cyclic test also shows that the catalyst has good stability under visible light irradiation.

Influence of metal ions (Me: Fe, Cu, Co, Ni, Mn, Cr) on direct Z-scheme photocatalysts CN/Me-BTC on the degradation efficiency of tetracycline in water environment

BackgroundThe World Health Organization (WHO) reports that antibiotic resistance contributes to approximately 700,000 deaths yearly, with estimate suggesting a rise to 10 million deaths over the next 35 years. MethodsIn this study, direct Z-scheme heterojunction photocatalysts CN/Me-BTC (CN: graphite carbon nitride, Me: metal ions, BTC: benzene-1,3,5-tricarboxylic acid) were successfully synthesized using a hydrothermal combined microwave method, eliminating the need for toxic solvents and featuring a short crystallization time and low reaction temperature. Significant findingsThe study also explores the influence of various metal ions (Fe, Ni, Co, Mn, Cr, and Cu) on the morphological, physicochemical properties, and photocatalytic efficiency of tetracycline (TC) degradation. The CN/Me-BTC photocatalysts exhibit remarkable characteristics, including high visible light absorption, high surface area, low recombination rate between electrons and holes, and fast charge transfer ability.Among the synthesized photocatalysts, CN/FeBTC stands out with the highest efficiency in TC degradation (97.18 %) and degradation rate (decay constant k = 0.0197 min−1), surpassing CN by four times. The study comprehensively investigates factors influencing the TC degradation process, including catalyst mass, pH, antibiotic concentration, participating radicals, anions, and water sources. The mechanism of the photocatalytic process is elucidated based on radical quenching experiments and electrochemical properties.

Elaborate design and construction of direct Z-scheme ZnIn2S4@BiYWO6 heterojunction catalysts for efficient photocatalytic hydrogen production

Photocatalytic Hydrogen production as one of the effective ways to solve the future energy issues has recently become a research hotspot in the field of renewable energy. However, single-component photocatalysts have poor hydrogen production efficiency due to the narrow light-absorption range, susceptibility to photo-corrosion and low catalytic activity. Herein, novel heterojunction photocatalysts of ZnIn2S4@BiYWO6 with different mass ratios were designed and synthesized using a facile two-step hydrothermal method. Experimental results and analyses show that these heterojunction catalysts exhibit extremely excellent photocatalytic performance for hydrogen production. Especially, the hydrogen production rate of 10ZnIn2S4-BiYWO6 is 73 times higher than that of pure ZnIn2S4. Furthermore, enhanced photocatalytic mechanism and carrier transfer pathway in the heterojunction photocatalyst of ZnIn2S4@BiYWO6 were deeply analyzed and explored in the paper, which confirmed that ZnIn2S4@BiYWO6 is a direct Z-scheme heterojunction architecture. Within such a Z-scheme framework, the presence of a built-in electric field at the interface between ZnIn2S4 and BiYWO6 as well as the energy band bending lead to the direct recombination of electrons and holes with low redox capacity, while keeping the electrons and holes with high redox capacity in each component. Consequently, the photocatalytic activity of the Z-scheme heterojunction system has been greatly enhanced. It is believed that the present work provides valuable guidance for the design and construction of novel Z-scheme heterojunction photocatalysts.

Construction of a direct Z-scheme Cs3Bi2Cl9/g-C3N4 heterojunction composite for efficient photocatalytic degradation of various pollutants in water: Performance, kinetics and degradation mechanism

The use of emerging composite materials has been booming to remove environmental pollutants. The aim of this research is to develop a new composite based on Cs3Bi2Cl9 perovskite and graphitic carbon nitride (g-C3N4) to investigate the photocatalytic performance under visible light irradiation. To achieve this, we produce the Cs3Bi2Cl9/g-C3N4 heterojunctions through a simple self-assembly synthesis. The as-synthesized composites are characterized using XRD, FTIR, FESEM, TEM, BET and EDX techniques. The photocatalytic performance of Cs3Bi2Cl9/g-C3N4 is examined in the degradation of various water contaminants, including 4-nitrophenol (4-NP), tetracycline antibiotic (TC), methylene blue (MB) and methyl orange (MO). The experimental results indicate the superior photocatalytic performance of the composites in the degradation of pollutants compared to pure Cs3Bi2Cl9 and g-C3N4. The 10% Cs3Bi2Cl9/g-C3N4 composite achieves the optimal degradation efficiency of 100, 92, 98.7, and 85.1% of 4-NP, TC, MB, and MO, respectively. This superior photocatalytic activity attributes to improved optical and electrochemical properties, including enhanced absorption ability, narrowing band gap, promoted separation efficiency of photogenerated carriers, and a high redox potential, which is confirmed by UV–vis DRS, PL, EIS, and CV analyses. The 10% Cs3Bi2Cl9/g-C3N4 composite also demonstrates high photocatalytic stability after four consecutive cycles. Radical trapping tests show that superoxide radicals (•O2−), holes (h+), and hydroxyl radicals (•OH) contribute to the photocatalytic process. Based on the obtained data, a direct Z-scheme heterojunction mechanism is proposed. Overall, this research offers a new stable photocatalyst with excellent prospect for photocatalytic applications.