Z-scheme Heterojunction Structure Research Articles

Z-scheme Bi2WO6/KCN heterojunction towards efficient photocatalytic degradation of tetracycline hydrochloride

Antibiotic overuse raises environmental concerns, boosting the demand for efficient removal from pharmaceutical wastewater. Photocatalysis, particularly using semiconductor photocatalysts, offers a promising solution and garners significant scientific interest. In this study, a cyanamide defective carbon nitride (KCN) and Bi2WO6(BWO) heterojunction photocatalyst (2-BWO@KCN) was developed, analyzed, and employed for the photocatalytic degradation of tetracycline hydrochloride (TC) under visible light. The as-synthesized heterojunction 2-BWO@KCN sample demonstrates superior performance compared to pure BWO, CN, KCN, and the heterojunction with pure CN (i.e., 2-BWO@CN) in terms of degrading TC and generating photocurrent under visible light. The study found that the degradation efficiency was affected by the dosage of 2-BWO@KCN and the presence of coexisting ions. Under optimal conditions, the degradation efficiency could reach 87% within 20 min of illumination. Additionally, through comprehensive experimental analysis, the degradation pathway, band structure, and mechanism were thoroughly explored. The superior photocatalytic performance of 2-BWO@KCN was attributed to its Z-scheme heterojunction structure, which significantly reduced the recombination of photogenerated electron and hole (e−/h+) pairs. The radicals (•OH/•O2−) produced were identified using ESR, and their role in tetracycline degradation was further analyzed through active species trapping experiments.

Highly-efficient photocatalytic hydrogen evolution enabled by piezotronic effects in SrTiO3/BaTiO3 nanofiber heterojunctions

The synergistic effect between piezoelectric and photocatalytic behaviors presents an interesting avenue to enhance the water-splitting processes for hydrogen production. Through a combination of experimental findings and theoretical calculations, we propose that the piezoelectric field inherent in these materials may decrease the bandgap of piezo-photocatalysts, while the Z-scheme heterojunction structure facilitates electron transfer. Leveraging the synergistic effects of heterojunction formation and piezoelectric assistance, we demonstrate that the incorporated piezoelectric BaTiO3 significantly enhances the hydrogen evolution rate of hybrid SrTiO3/BaTiO3 nanofibers to 1950.2 μmol·g–1·h–1. This surpasses the rates achieved by pure SrTiO3 and BaTiO3 counterparts by 2.4 and 4.1 times, respectively, and notably exceeds those of perovskite-based piezo-photocatalysts ever reported. The present work offers a valuable pathway for piezoelectric-assisted photocatalytic mechanism insight and sustainable hydrogen production, toward a remarkable advancement in pursuit of efficient and environmentally-friendly energy solutions.

Visible-light-induced degradation of rhodamine B by double Z-scheme magnetic ATP-g-C3N4/SnFe2O4/Bi2WO6 heterojunctions: Performance and mechanism

A magnetic ternary double Z-scheme ATP-g-C3N4/SnFe2O4/Bi2WO6 (AG/SFO/BWO) heterojunction was prepared by a simple and green hydrothermal process, which was successfully used in the dye degradation. AG/7.5 %SFO/BWO catalyst demonstrated outstanding visible-light-induced degradation, achieving an impressive 96.72 % degradation of rhodamine B (RhB) in 2 h. Compared with Bi2WO6 (BWO) and SnFe2O4/Bi2WO6 (SFO/BWO), the degradation efficacy was increased about 1.65 and 1.16 times, respectively. After being used for five batches, the degradation rate of RhB remained over 90 %. Moreover, AG/7.5 %SFO/BWO showcased remarkable efficacy in degrading methylene blue (MB), Congo red (CR), and tetracycline (TC). Bacterial toxicity test indicated the toxicity of dyes was rapidly decreased in 24 h. Physicochemical properties and morphological characteristics of the prepared photocatalysts were investigated by various methods, including XRD, FTIR, XPS, SEM, TEM, BET, VSM, UV–vis, and EIS. AG/7.5 %SFO/BWO, utilizing a dual-Z scheme pathway, efficiently absorbed broad light, yielding multiple active agents, primarily hole (h+) and superoxide radical •O2−. The double Z-scheme heterojunction structure enhanced the electron-hole separation and ensured a stable photochemical environment. UPLC-HRMS was used to identify intermediates during the RhB degradation. Its degradation pathway and catalytic mechanism were illustrated systematically. The bio-toxicity (acute toxicity, developmental toxicity, and mutagenicity) of the intermediates was also evaluated by T.E.S.T.

Insight into Fe-O-Bi electron migration channel in MIL-53(Fe)/Bi4O5I2 Z-scheme heterojunction for efficient photocatalytic decontamination

Building a heterojunction is a fascinating option to guarantee sufficient carrier separation and transfer efficiency, but the mechanism of charge migration at the heterojunction interface has not been thoroughly studied. Herein, MIL-53(Fe)/Bi4O5I2 photocatalyst with a Z-scheme heterojunction structure is constructed, which achieves efficient photocatalytic decontamination under solar light. Driven by the newly-built internal electric field (IEF), the formation of Fe-O-Bi electron migration channel allows for rapid separation and transfer of charge carriers at the heterojunction interface, confirmed by the material characterization and density functional theory (DFT) calculation. The narrower band gap and improved visible light response also contribute to the enhanced photocatalytic activity of composite materials. With levofloxacin as the target pollutant, the optimal MIL-53(Fe)/Bi4O5I2 achieves complete removal of pollutant within 150 min, the photocatalysis rate of which is ca. 4.4 and 26.0 times that of pure Bi4O5I2 and MIL-53(Fe), respectively. Simultaneously, the optimal composite material exhibits satisfactory photodegradation of seven fluoroquinolones, and the photocatalysis rates are as follows: lomefloxacin > ciprofloxacin > enrofloxacin > norfloxacin > pefloxacin > levofloxacin > marbofloxacin. DFT calculations reveal a positive relationship between degradation rate and Fukui index (ƒ0) of main carbon atoms in seven fluoroquinolones. This study sheds light on the existence of electron migration channels at Z-scheme heterojunction interface to ensure sufficient photoinduced carrier transfer, and reveals the influence of pollutant structure on photolysis rate.

Novel C4P2 monolayers: forming Z-scheme heterojunction and Janus structure for high-efficiency metal-free photocatalytic water splitting.

Metal-free two-dimensional (2D) semiconductors have garnered significant attention in the realm of photocatalytic water splitting, primarily owing to their inherent clean, stable, and efficient photoresponsive properties. Motivated by it, we have proposed two types of stable C4P2 monolayers with indirect band gaps, mediocre carrier mobility and excellent optical absorption in visible-light and ultraviolet regions. Although the too-low work function of monolayer α-C4P2 and the too-high work function of monolayer β-C4P2 make them only suitable for single-side redox reaction in photocatalytic water splitting, the creation of an α-C4P2/β-C4P2 Z-scheme heterojunction, combined with the Janus monolayer γ-C4P2 that integrates features of both α and β structures, effectively addresses this limitation, fulfilling the prerequisites for comprehensive photocatalytic water splitting. Furthermore, the calculations indicate that the α-C4P2/β-C4P2 Z-scheme heterojunction and Janus monolayer γ-C4P2 not only demonstrate improved carrier mobility and optical absorption but also feature internal electric fields that effectively enhance driving energy and photo-induced charge separation. Notably, Janus monolayer γ-C4P2 achieves a high electron mobility of ∼105 cm2 V-1 s-1 and an impressive solar-to-hydrogen conversion efficiency of 25.62%.

The powerful combination of 2D/2D Ni-MOF/carbon nitride for deep desulfurization of thiophene in fuel: Conversion route, DFT calculation, mechanism

2D/2D Ni-MOF/g-C3N4 nanocomposite was utilized for desulfurization. The multilayer pore structure and high specific surface area of Ni-MOF/g-C3N4 promote the adsorption and conversion of thiophene. In addition, the two-dimensional structure exposes more active centers and shortens photogenerated carrier migration to the material surface distance, it enhances photogenerated charge transfer. The Ni-MOF and g-C3N4 construct a Z-scheme heterojunction structure with tight contact, it effectively enhances the material's photocatalytic redox ability. In the light, the material generates more photocarriers for the production of free radicals including hydroxyl radicals, holes, and superoxide radicals. The higher carrier concentration of Ni-MOF/g-C3N4 promotes the activation and oxidation of thiophene, consequently enhancing the photocatalytic desulfurization capability. The results showed that the conversion of thiophene was 98.82 % in 3 h under visible light irradiation. Radical capture experiments and analysis using electron paramagnetic resonance spectroscopy demonstrated that superoxide radicals, holes, and hydroxyl radicals played crucial roles in PODS (photocatalytic oxidative desulfurization). In addition, DFT (density functional theory) calculations were conducted to determine the paths of electron migration and TH (thiophene) adsorption energy. Finally, a mechanism for photocatalytic desulfurization was proposed based on the comprehensive analysis of theoretical calculations and experimental studies.

Matched micro-geometrical configuration leading to hetero-interfacial intimate contact of MoS2@UiO-66-NH2 Z-scheme heterojunction for efficient photocatalytic CO2 reduction

Z-scheme heterojunction is an effective strategy in photocatalysis, when hetero-interfacial intimate contact is the center of high-performance Z-scheme heterojunction structure. Here, x-MoS2 [x = plate (p), flower (f), and solid sphere (s)] with extensive optical absorption and high conductivity and stable UiO-66-NH2(y) (y = 100, 300, and 500 nm) with rich Lewis's acid sites were integrated to a series of x-MoS2@UiO-66-NH2(y) Z-scheme heterojunctions, which were fully characterized and used for photocatalytic reduction of CO2 (pCO2RR) into CH4 and CO. In response to the difficult modification of MoS2 and loose contact of composite bulk materials, the micro-geometric configurations on the size of UiO-66-NH2 and the morphology of MoS2 were optimized to achieve an intimate contact. The Z-scheme heterojunction f-MoS2@UiO-66-NH2 (100 nm) with perfectly matched micro-geometric configuration exhibited an excellent electron consumption rate (Rele) of 263.78 μmol g–1 h–1 and a high CH4 yield of 27.18 μmol g–1 h–1 with a selectivity of 82.44%, being far superior to most MoS2- and MOFs-based heterojunctions. Comprehensive investigations with extensive photoelectric characterizations, control experiments, and density functional theory (DFT) calculations demonstrate that the excellent photocatalytic performance of f-MoS2@UiO-66-NH2 (100 nm) could be attributed to that (i) the low size of UiO-66-NH2 strengthens mutual alignment and increases outer surface to maximize heterointerface contact with MoS2, accelerating the interfacial charge transfer; (ii) the hierarchical structure of f-MoS2 with optimal basal plane curvature greatly reduces contact barriers to present a high charge throughput with a charge excitation rate of 1.967 mV, smooth initiating the 8-electron CO2 methanation. Additionally, the durability of f-MoS2@UiO-66-NH2 (100 nm) was also investigated.

Boosting photocatalytic H2 evolution on UIO-66-NH2/covalent triazine-based frameworks composites by constructing a covalent heterojunction.

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have been proved as efficient catalysts for photocatalytic hydrogen (H2) evolution, thanks to their tunable functionalities, permanent porosity, excellent visible light response, and physicochemical stability. Herein, a series of photocatalysts (termed NUBC) was fabricated by loading different amounts of Zr-UiO-66-NH2 (NU) onto a benzoic acid-modified covalent triazine-based framework (BC) based on post-synthetic covalent modification. The resulting NUBC catalysts exhibited a type-II Z-scheme heterojunction structure formed via the amide covalent bonds between the amine groups on NU and carboxyl groups on BC. The optimal loading of NU on BC is 30 wt.% (30NUBC) and the corresponding photocatalytic H2 evolution rate was 378 μmol h-1 g-1, almost 445 and 2 times than that of NU and BC, respectively. The synergistic effect between the type-II Z-scheme heterojunctions and amide bonds was conducive to boosting visible light harvesting and facilitating charge transportation and separation. Furthermore, the prepared NUBC catalysts show great reusability and stability. Overall, this work sheds light on the design of novel MOF/COF hybrid materials and provides a systematic exploration of their photocatalytic H2 evolution properties.

In2S3@TiO2/In2S3 Z-Scheme Heterojunction with Synergistic Effect for Enhanced Photocathodic Protection of Steel.

In this work, a TiO2/In2S3 heterojunction film was successfully synthesized using a one-step hydrothermal method and applied in the photocathodic protection (PCP) of 304SS. The octahedral In2S3 and In2S3@TiO2 nanoparticles combined and coexisted with each other, with In2S3 quantum dots growing on the surface of TiO2 to form In2S3@TiO2 with a wrapping structure. The composite photoelectrode, which includes TiO2 with a mixed crystalline phase and In2S3, exhibited significantly enhanced PCP performance for 304SS compared with pure In2S3 and TiO2. The In2S3@TiO2/In2S3 composites with 0.3 g of P25 titanium dioxide (P25) showed the best protection performance, resulting in a cathodic shift of its OCP coupled with 304SS to -0.664 VAgCl. The electron transfer tracking results demonstrate that In2S3@TiO2/In2S3 forms a Z-scheme heterojunction structure. The enhanced PCP performance could be attributed to the synergistic effect of the mixed crystalline phase and the Z-scheme heterojunction system. The mixed crystalline phase of TiO2 provides more electrons, and these electrons are gathered at higher energy potentials in the Z-scheme system. Additionally, the built-in electric field further promotes the more effective electrons transfer from photoelectrode to the protected metals, thus, leading to enhanced photoelectrochemical cathodic protection of 304SS.

Lattice-matched controllable construction of nanometer scale CdS/TiO2 hollow nanoboxes Z-scheme heterojunctions based on micrometer and sub-nanometer CdS for comparison of visible photocatalytic activity

Size effect exerts a significant influence on the photocatalytic properties of materials. Nanometer CdS/TiO2 hollow nanoboxes (TiO2-HNBs) (tetragonal phase) Z-scheme heterojunctions were lattice-matched controllably fabricated by using cubic TiOF2 as a template and loading with micrometer CdS micron rods (hexagonal phase) or sub-nanometer CdS quantum dots (cubic phase) through one-pot template ultrasonic hydrothermal method. The morphology, constitution, physical property, as well as photocatalytic properties of as-prepared samples were investigated comprehensively. Under visible light irradiation (λ ≥ 420 nm), the hydrogen production rates of CdS micron rods, CdS nanorods/TiO2-HNBs (CT-7), CdS quantum dots/TiO2-HNBs (CTQ-7) and CdS quantum dots was 1642.61, 455.35, 148.92 and 1025.53 μmol/g/h, which was 26.39, 7.32, 2.39 and 16.48 times that of TiO2-HNBs, respectively. Meanwhile, the photodegradation rate of Rhodamine B by CdS micron rods, CT-7, CTQ-7 and CdS quantum dots within 60 min was 69.59%, 99.90%, 89.96% and 40.70%, which were 4.77, 6.85, 6.17 and 2.79 times that of P25, respectively. CdS micron rods had the largest size but the strongest photo-hydrogen production properties. Due to its Z-scheme heterojunction structure and Ti-S bond, CT-7 exhibited enhanced electron-hole separation rate and electron transfer rate, resulting in superior RhB degradation performance. Although CdS quantum dots had the smallest size, it did not boast the best performance, indicating that smaller size does not necessarily correlate with better photocatalytic performance. This study provides a reference for comparing the performance of photocatalytic materials with different sizes.

Using waste silver metal in synthesis of Z-scheme Ag@WO3-CeO2 heterojunction to increase photodegradation and electrochemical performances

Design of a Z-scheme heterojunction structure is eco-friendly due to its multi-nanocatalyst performances like wastewater treatment, antibacterial and electrochemical activity. Herein, Ag was extracted from waste batteries in a nitric acid leaching manner. Also, WO3 nanorods and WO3-CeO2 were synthesized by the surfactant-assisted hydrothermal acidic and sol–gel methods, respectively. Silver nanoparticles were doped by wet impregnation method to prepare ternary (Ag@WO3-CeO2) and binary (Ag@WO3 and Ag@CeO2) heterojunctions. The band gap of the prepared Ag@WO3-CeO2 was remarkably diminished in comparison with the rest of the sample (from 2.73 to 2.59 eV). The Langmuir-Hinslewood model showed that ternary systems can degrade methylene blue twice as much as WO3-CeO2 and seven times more than single-component systems. This was due to the presence of silver as a mediator for the transfer of photogenerated electrons between two semiconductors. Also, methylene blue was degraded by more than 90.8% efficiency. Electrochemical impedance spectroscopy (EIS) analysis confirmed that the charge transfer resistance of Ag@WO3-CeO2 was decreased by more than 50%. The results of bactericidal activeness confirmed elevated inhibition capability of Ag@WO3-CeO2 towards E.coli with 99% degradation. X-ray fluorescence (XRF) results confirmed that 98% of silver can be re-extracted after 5 photocatalytic uses which is a material with green technology.

Synergistic effect of bimetallic cobalt-based sulfide enhances the performance of ZnSe photocatalytic hydrogen evolution by Z-scheme

In this work, ZnSe/ZnCo2S4 (ZCS) composites were synthesized by simple hydrothermal method and Z-scheme heterojunctions were formed. Under the simulated sunlight environment, The results show that the hydrogen production efficiency of 70 wt% ZnSe/ZCS composites was as high as 3402.4 μmol·g−1·h−1, which is 4.37 and 94.44 times that of ZnSe and ZCS monomers, respectively, and the apparent quantum efficiency (AQY) reaches 10.5%. Among them, the Z-scheme heterojunction improves the redox ability of the material, which is more conducive to charge separation, and ZCS also promotes absorption of visible light of ZnSe/ZCS. In addition, the Z-scheme heterojunction structure and material stability were verified by XPS, ESR.This work provides a new way to improve ZnSe in the field of photocatalytic hydrogen evolution.

Integration of high visible-light-driven ternary dual Z-scheme AgVO3-InVO4/g-C3N4 heterojunction nanocomposite for enhanced uranium(VI) photoreduction separation

With deepening application of nuclear power technology, the problem of water ecological environment pollution caused by uranium (U(VI)) is becoming increasingly serious. Photoreduction separation of U(VI) on photocatalysts is considered as an effective strategy to solve uranium pollution. In this work, a novel ternary dual Z-scheme AgVO3-InVO4/g-C3N4 heterojunction (Z-AIGH) nanocomposite with high surface area (73.45 m2 g−1, Z-AIGH2) was designed. The batch adsorption experiment in dark environment showed that Z-AIGH2 nanocomposite had an excellent U(VI) adsorption performance. As for photocatalytic experiments, Z-AIGH2 exhibited a rapid photocatalytic response for separating U(VI) without any organic sacrifice agents. The U(VI) separation rate on Z-AIGH2 nanocomposite was over 98.7% after only 20.0 min visible light irradiation (T = 298 K, CU(Ⅵ) = 10.0 mg L−1, m/V = 0.1 g L−1 and pH = 7.0). Z-AIGH2 nanocomposite also showed good selectivity and cycle stability. The U(VI) removal rate of Z-AIGH2 nanocomposite after fifth cycles was about 96.1% (T = 298 K, CU(Ⅵ) = 10.0 mg L−1, m/V = 0.1 g L−1 and pH = 7.0). High photocatalytic activity of Z-AIGH2 for U(VI) was attributed to the construction of ternary dual Z-scheme heterojunction structure and ant nest-like hole structure. Based on above results, Z-AIGH2 nanocomposite had great potential for water environment renovation.

A step closer to real practice: Integrated tandem photocatalysis-biofilm process towards degradation of crude oil

Intimately coupled photocatalysis and biodegradation (ICPB) systems represent a promising wastewater treatment technology. The implementation of ICPB systems for oil spill treatment is a pressing concern. In this study, we developed an ICPB system comprising BiOBr/modified g-C3N4 (M-CN) and biofilms for the treatment of oil spills. The results demonstrate that the ICPB system achieved the rapid degradation of crude oil, outperforming the single photocatalysis and biodegradation methods by degrading 89.08 ± 5.36% within 48 h. The combination of BiOBr and M-CN formed a Z-scheme heterojunction structure, enhancing the redox capacity. The interaction between the holes (h+) and the negative charge on the biofilm surface promoted the separation of electrons (e−) and h+, thereby accelerating the degradation process of crude oil. Moreover, ICPB system maintained an excellent degradation ratio after three cycles and its biofilms progressively adapted to the adverse effects of crude oil and light. The microbial community structure remained stable throughout the degradation of crude oil, with Acinetobacter and Sphingobium identified as the dominant genera in biofilms. The proliferation of the Acinetobacter genus appeared to be the main factor contributing to the promotion of crude oil degradation. Our work demonstrates that the integrated tandem strategies perhaps represent a feasible pathway toward practical crude oil degradation.

Efficient visible-light driven photodegradation of sulfonamide antibiotics using a Z-scheme Ag2O/Bi-nicotinate nanocomposite

In this article, a two-dimensional bismuth complex (Bi-nic) was successfully synthesized via hydrothermal method using nicotinic acid (nic) as ligand. Then, Ag2O/Bi-nic nanocomposites with high visible-light driven photocatalytic activity were prepared at 60 °C, 80 °C and 100 °C, respectively, using Bi-nic as precursor. The synthesized Ag2O/Bi-nic nanocomposites were structurally characterized by XRD, FT-IR, EDX, XPS and DRS. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images displayed that Ag2O nanoparticles with an average size of 20 nm distributed on the surface of Bi-nic nano-sheets. The Ag2O/Bi-nic composites exhibited excellent photocatalytic activities in degradation of sulfonamide antibiotics under visible light. Under the catalysis of Ag2O/Bi-nic-80, the degradation efficiencies of sulfadiazine and sulfamethoxazole antibiotics were up to 94% and 93% after irradiating for 160 and 60 min, respectively. Ag2O and Bi-nic form a Z-scheme heterojunction structure in the Ag2O/Bi-nic nanocomposite, which allows electrons to transfer from the conduction band of Bi-nic to the valence band of Ag2O. It is revealed that the photogenerated e− and h+ can be effectively separated on the interfacial between Ag2O nanoparticle and Bi-nic nanosheet, which significantly improved the photocatalytic activity of Ag2O/Bi-nic.

Facile synthesis of Bi2WO6/Bi2MoO6 Z-scheme heterojunction for dye degradation and Cr(VI) reduction

Dyeing wastewater has been one of the severe pollutant crises along the textile industry development, and the design of effective photocatalysts is the attractive strategy for wastewater remediation. Herein, Bi2WO6/Bi2MoO6 microspheres with the high surface area of 12.16 m2/g were prepared by the solvothermal synthesis method, and the hybrid photocatalyst exhibited outstanding solar absorption, photoelectric conversion and photocatalytic performances. The photoelectric tests indicated that the sample photoelectrode exhibite high transient visible light-driven photocurrent value (1.91 μA/cm2) and low interface resistance. The photocatalytic rate constants for rhodamine B (RhB), methylene blue (MB) photodegradation achieved 1.65 × 10-2 min−1 and 3.78 × 10-2 min−1. The main active species for dye photodegradation were O2 radicals, and the preparation and photocatalytic mechanisms were proposed. Furthermore, the as-prepared photocatalyst also showed high photoremoval of Cr(VI) under visible light irradiation, and the high photocatalytic efficiency (68.57%) was obtained after 160 min irradiation. The excellent photoelectrochemical performance was mainly ascribed to the outstanding photoelectron separation and transportation from Z-scheme heterojunction structure construction. The investigation about Bi2WO6/Bi2MoO6 photocatalysts would provide a feasible route for novel photocatalyst design toward photocatalytic dyeing wastewater purification.

Visible-light-driven photocatalytic degradation of tetracycline hydrochloride by Z-scheme Ag3PO4/1T@2H-MoS2 heterojunction: Degradation mechanism, toxicity assessment, and potential applications

Residual antibiotics in wastewater threaten living organisms and the ecosystem, while the photocatalytic process is recognized as one of the most eco-friendly and promising technologies for the treatment of antibiotic wastewater. In this study, a novel Z-scheme Ag3PO4/1T@2H-MoS2 heterojunction was synthesized, characterized, and used for the visible-light-driven photocatalytic degradation of tetracycline hydrochloride (TCH). It was found that Ag3PO4/1T@2H-MoS2 dosage and coexisting anions had significant effects on the degradation efficiency, which could reach up to 98.9 % within 10 min under the optimal condition. Combing experiments and theoretical calculations, the degradation pathway and mechanism were thoroughly investigated. The excellent photocatalytic property of Ag3PO4/1T@2H-MoS2 was achieved attributed to the Z-scheme heterojunction structure, which remarkably inhibited the recombination of photoinduced electrons and holes. The potential toxicity and mutagenicity for TCH and generated intermediates were evaluated, which revealed the ecological toxicity of antibiotic wastewater was reduced effectively during the photocatalytic degradation process.

Synthesis of SiO2-doped BiOX (X = Cl, Br) II-type heterojunctions and 2H-MoS2-doped SiO2@BiOX Z-scheme heterojunctions: A comparative study

In this research, II-type SiO2@BiOX (X = Cl, Br) was synthesized by loading SiO2 microspheres onto 2D layered BiOX using a simple one-step hybrid solvothermal method. On this basis, the two-dimensional bismuth oxyhalide layer was modified by using 2H-MoS2 layer and compounded with SiO2 microspheres to form 2H-MoS2@SiO2@BiOX (X = Cl, Br) Z-scheme heterostructured photocatalysts. The energy band structure and photogenerated carrier transport mechanism of the composite photocatalysts were analyzed by various characterization methods, and the transport efficiency of photogenerated carriers of II-type heterojunction and Z-scheme heterojunction were compared. The differences in photocatalytic activities of II-type heterojunctions and Z-scheme heterojunctions were shown by microscopic mechanisms and macroscopic phenomena. The photocatalytic degradation experiments showed that the doping of 2H-MoS2 acted as a conducting medium in the p-BiOX/n-SiO2 heterostructure, which changed the photogenerated electron transfer and formed the Z-scheme heterojunction structure, thus promoting the photocatalytic activity. In this study, the structure of BiOX-based composite photocatalyst was optimized and constructed, and a new idea was provided for the design and construction of II-type heterojunction and Z-scheme heterojunction photocatalysts.

WO3@ZnO Nanoarrays as the Photoanode for Photoelectrochemical Production of H2O2

WO3@ZnO core–shell nanoarrays with a Z-scheme heterojunction structure have been fabricated by combining electrodeposition and dropping process and used as photoanodes for the production of hydrogen peroxide (H2O2). The photocurrent density of the WO3@ZnO nanoarray photoanode is 1.57 mA∙cm−2 at the applied potential of 1.8 V vs reversible hydrogen electrode, which exhibits almost 4 time larger than that of pure ZnO nanoarray photoanode. A high photoconversion efficiency to the production of H2O2 (0.53%) and Faradic efficiency (33%) are also reached by this WO3@ZnO nanoarray photoanode under Air-Mass 1.5 Global (AM 1.5 G, 100 mW∙cm−2). This work provides an effective approach for the application of Z-scheme heterojunction in the photoelectrochemical synthesis of H2O2.

Visible-light-driven Z-scheme ternary Fe3O4/TiO2/g-C3N4 nanocomposite as reusable photocatalyst for efficient removal of dyes and chromium in water

In this work, a highly efficient magnetic recyclable Z-scheme ternary Fe3O4/TiO2/g-C3N4 heterojunction photocatalyst is designed through the hydrothermal method. The prepared photocatalysts were characterized by XRD, FTIR, Raman, TGA, BET, UV–vis DRS, PL, TEM, and XPS techniques. The superior photocatalytic degradation efficiency of ternary photocatalyst is about 98.2 and 95% for RhB and MB, respectively, under simulated solar light irradiation. The photocatalytic degradation rate constant of RhB and MB over ternary Fe3O4/TiO2/g-C3N4 photocatalyst were 6.8, 7.5, and 2.4 folds higher (RhB); and 4.7, 7.8, and 3.4 folds higher (MB) than pure TiO2, pristine g-C3N4, and Fe3O4/TiO2 photocatalysts, respectively. Ternary photocatalyst also exhibits remarkable photocatalytic performance in the photoreduction of Cr(VI) with about 95.6% reduction efficiency attained in 50 min. The increase in photocatalytic activity of the ternary photocatalyst is accredited to the enhancement in electron-hole pair separation and the construction of the Z-scheme heterojunction structure. The simultaneous photodegradation and photoreduction of organic dyes and Cr(VI) reveal that ternary photocatalysts could be utilized in real-world wastewater applications.