Oxygen vacancy mediated single unit cell Bi2WO6 by Ti doping for ameliorated photocatalytic performance

A Review on Bi2WO6-Based Materials for Photocatalytic CO2 Reduction

Photocatalytic reduction of CO2 (PCR) technology offers the capacity to transmute solar energy into chemical energy through an eco-friendly and efficacious process, concurrently facilitating energy storage and carbon diminution, this innovation harbors significant potential for mitigating energy shortages and ameliorating environmental degradation. Bismuth tungstate (Bi2WO6) is distinguished by its robust visible light absorption and distinctive perovskite-type crystal architecture, rendering it highly efficiency in PCR. In recent years, numerous systematic strategies have been investigated for the synthesis and modification of Bi2WO6 to enhance its photocatalytic performance, aiming to achieve superior applications. This review provides a comprehensive review of the latest research progress on Bi2WO6 based materials in the field of photocatalysis. Firstly, outlining the fundamental principles, associated reaction mechanisms and reduction pathways of PCR. Then, the synthesis strategy of Bi2WO6-based materials is introduced for the regulation of its photocatalytic properties. Furthermore, accentuating the extant applications in CO2 reduction, including metal-Bi2WO6, semiconductor-Bi2WO6 and carbon-based Bi2WO6 composites etc. while concludes with an examination of the future landscape and challenges faced. This review hopes to serve as an effective reference for the continuous improvement and implementation of Bi2WO6-based photocatalysts in PCR.

One-Step Self-Assembled WO3/rGO Microspheres Photoanode Assembled Efficient Photocatalytic Fuel Cells for Simultaneous Organic Pollutant Degradation and Electricity Generation

Photocatalytic fuel cells (PFCs) present a promising and environmentally friendly approach to simultaneously treat organic pollutants in wastewater and electricity generation. The development of photoanodes with high light absorption and carrier mobility is essential for enhancing the performance of PFCs but remains challenging. Herein, a one-step self-assembly strategy was adopted to develop flower-like WO3/rGO microspheres for PFC devices. Attributed to the abundant surface-active sites, enhanced light harvesting, and efficient separation of photogenerated charge carriers, the WO3/rGO photoanode demonstrated superior rhodamine B (RhB) degradation rate (90% in 2 h), maximum power density (4.74 μW/cm2), and maximum photocurrent density (0.096 mA/cm2), 1.4, 2.4, and 4.0 times higher than the corresponding pure WO3 photoanode, respectively. Density functional theory (DFT) calculations reveal that the built-in electric field formed between the interface of WO3 and rGO promotes the transfer of photogenerated electrons from WO3 to rGO, thus exerting a significant impact on improving the migration and separation of photoinduced charge carriers. Moreover, by combining experimental and theoretical results, a complete PFC operation mechanism for the PFC system was proposed. This study focuses on the strategy of constructing rGO-doped photocatalysts to enhance the interfacial charge transfer mechanism, providing a promising approach for the development of high-performance photoanodes in PFC systems.

Sonochemical regulation of oxygen vacancies for Bi2WO6 nanosheet-based photoanodes to promote photoelectrochemical performance

Integration of oxygen vacancies (Vo) into nanostructured semiconductor-based photocatalysts has been recognized as a promising strategy for enhancing the performance of photoelectrochemical (PEC) water splitting. However, precisely controlling the Vo concentration in photocatalysts via an effective and tunable approach remains challenging. Herein, a series of optimized bismuth tungstate (Bi2WO6) nanosheet-based photoanodes with varying concentrations of Vo were prepared by a sonochemical method with in situ cavitation detection, which enables accurate manipulation of the acoustic cavitation intensity applied to the surface of Bi2WO6 photoanodes in alkaline solution. Based on the analysis of the Vo concentration and sound field characteristics, the mechanism of sonochemical regulation of Vo in Bi2WO6 nanosheets was interpreted. Specifically, the increase in Vo concentration can be attributed to the enhancement of Bi-O bond dissociation. This enhancement is influenced not only by the intensified impact of shear force and the generation of active radicals by transient cavitation, but also by the accelerated diffusion of the reactant, a result of stable cavitation. By optimizing the transient and stable cavitation intensity, a Vo-rich Bi2WO6 photoanode was obtained without altering the microstructure of Bi2WO6 nanosheets. The presence of high concentration Vo facilitates the interfacial chemical reactivity and the transmission of photogenerated carriers, leading to the drastic promotion of the PEC water splitting performance. The transient photocurrent density of the Vo-rich Bi2WO6 photoanode reaches 69.2 μA cm-2 (1.23 V vs. RHE), 7.86 times that of the untreated Bi2WO6 photoanode. Additionally, the charge injection efficiency increases to 35.4%. This work provides a controllable and effective method for defect engineering of nanostructured semiconductor-based electrodes.

Synergistic effect of excellent carriers separation and efficient high level energy electron utilization on Bi3+-Ce2Ti2O7/ZnIn2S4 heterostructure for photocatalytic hydrogen production

The separation of photogenerated carriers and the efficient utilization of high-level energy electrons (HLEEs) are the key processes for improving the performance of photocatalysts. Herein, Ce2Ti2O7/ZnIn2S4 (CTOZIS) and Bi3+-doped Ce2Ti2O7/ZnIn2S4 (BCTOZIS) photocatalyst were successfully synthesized through hydrothermal method. The photocatalytic hydrogen production of CTOZIS and BCTOZIS was 1233.7 μmol g-1 and 4168.5 μmol g-1 under visible light irradiation (λ ≥ 420 nm) within 5 h, which was 2.3 and 7.6 times than that of pure ZnIn2S4, respectively. X-ray photoelectron spectroscopy, photoluminescence spectroscopy and electrochemical characterization demonstrated that after Bi3+ doping, the electron-hole pairs recombination of BCTOZIS was inhibited, which may be ascribed to the establishment of a Z-scheme heterojunction and the presence of oxygen vacancy and Ce4+/Ce3+ redox center. The doping of Bi3+ resulted in the adjustment of the valence band position of Ce2Ti2O7 from 1.98 V to 1.92 V. This adjustment enabled direct transfer of HLEEs generated in Ce2Ti2O7 to the conduction band of ZnIn2S4 for hydrogen production with a wavelength below 423 nm. The synergistic effect of conventional Z-scheme electron transfer and the unique utilization of HLEEs boosted the photocatalytic performance of BCTOZIS. This study affords an innovative insight for designing visible-light-driven photocatalysts with high photocatalytic activity.

Comprehensive Insights into the Family of Atomically Thin 2D-Materials for Diverse Photocatalytic Applications

2D materials with their fascinating physiochemical, structural, and electronic properties have attracted researchers and have been used for a variety of applications such as electrocatalysis, photocatalysis, energy storage, magnetoresistance, and sensing. In recent times, 2D materials have gained great momentum in the spectrum of photocatalytic applications such as pollutant degradation, water splitting, CO2 reduction, NH3 production, microbial disinfection, and heavy metal reduction, thanks to their superior properties including visible light responsive band gap, improved charge separation and electron mobility, suppressed charge recombination and high surface reactive sites, and thus enhance the photocatalytic properties rationally as compared to 3D and other low-dimensional materials. In this context, this review spot-lights the family of various 2D materials, their properties and their 2D structure-induced photocatalytic mechanisms while giving an overview on their synthesis methods along with a detailed discussion on their diverse photocatalytic applications. Furthermore, the challenges and the future opportunities are also presented related to the future developments and advancements of 2D materials for the large-scale real-time photocatalytic applications.

An experimental design study of photocatalytic activity of the Z-scheme silver iodide/tungstate binary nano photocatalyst

A binary AgI/ Ag2WO4 photocatalyst was fabricated and characterized by SEM, XRD, UV-Vis DRS, and FT-IR. It was then used to photodegrade sodium ceftriaxone (CTX) in an aqueous solution. The band gap energies of 2.95, 2.78, and 2.62 eV were obtained by the Kubelka-Munk model for Ag2WO4, AgI, and AgI/Ag2WO4 catalysts. The samples have pHPZC values of 6.9, 4.2, and 6.6, respectively. The synergistic photocatalytic activity of the coupled system depended on the AgI:Ag2WO4 mole ratio and grinding time (optimums:mole ratio of 4:1 and time 30 min). The experimental design was used for optimizing the conditions and a quadratic model well-processed the data based on the model F value of 131.87 > F0.05,14,13 = 2.55 and LOF F value of 0.78 < F0.05,10,3 = 8.78. The optimized RSM run included the irradiation time of 85 min, 3.5 mg/L of CTX sample at pH 9, and a catalyst dose of 1.0 g/L. Under the optimized conditions, about 63% of CTX molecules were photodegraded. In the study of the scavenging agents, the direct Z-scheme mechanism accumulated electrons in the CB-AgI and the holes in the VB-Ag2WO4 level, as stronger reducing and oxidizing centers than the accumulated electrons and holes of the type (II) heterojunction mechanism. Compared to a CTX oxidation potential of about 0.06 V, the direct Z-scheme mechanism is more favorable to reduce or oxidize it.

Fabrication of 2D/1D Bi2WO6/halloysite nanotubes photocatalyst towards water purification: a support effect onin situconstruction and electron-hole separation

In this research work, a reusable and efficient 2D/1D heterogeneous structured photocatalyst based on amine-functionalized halloysite nanotubes (MHNTs) and Bi2WO6nanosheet (BWO) was prepared using a facile hydrothermal method for decomposing PPCPs under simulated sunlight. On the degradation of tetracycline hydrochloride (TCH), the effects of composite catalysts prepared under various conditions were discussed. The results showed that over BWO/MHNTs with a mass ratio was 3:1, the synthesizing temperature was 120 °C and the precursor pH value was 1, the TCH (10 mg l-1) degradation efficiency reached 100% after 1 h irradiation of simulated sunlight. Moreover, BWO/MHNTs composites kept good recovery and stable photocatalytic activity after 5 cycles. The excellent dispersion of Bi2WO6on the surface of clay minerals and the oxygen vacancy enhanced electron-hole separation may be responsible for the its high activity and stability. Futhermore, the radical capture test demonstrated that ·O-2was primarily responsible for the photodegradation of TCH. Thus, BWO/MHNTs composites exhibit a good application prospect in the field of sunlight-driven photocatalytic degradation towards PPCPs pollutants in water.

Imperfect makes perfect: defect engineering of photoelectrodes towards efficient photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting for hydrogen evolution has been considered as a promising technology to solve the energy and environmental issues. However, the solar-to-hydrogen (STH) conversion efficiencies of current PEC systems are far from meeting the commercial demand (10%) due to the lack of efficient photoelectrode materials. The recent rapid development of defect engineering of photoelectrodes has significantly improved the PEC performance, which is expected to break through the bottleneck of low STH efficiency. In this review, the category and the construction methods of different defects in photoelectrode materials are summarized. Based on the in-depth summary and analysis of existing reports, the PEC performance enhancement mechanism of defect engineering is critically discussed in terms of light absorption, carrier separation and transport, and surface redox reactions. Finally, the application prospects and challenges of defect engineering for PEC water splitting are presented, and the future research directions in this field are also proposed.

Bismuth tungstate Bi2WO6: a review on structural, photophysical and photocatalytic properties

This review paper provides a comprehensive overview of the recent trends in bismuth tungstate (Bi₂WO₆) research, covering its structural, electrical, photoluminescent, and photocatalytic properties. The structural characteristics of bismuth tungstate are explored in detail, including its different allotropic crystal structures with respect to its isotypic materials. The electrical properties of bismuth tungstate, such as its conductivity and electron mobility, are also discussed, along with its photoluminescent properties. The photocatalytic activity of bismuth tungstate is a particular focus, with recent advances in doping and co-doping strategies with metals, rare earth and other elements summarized. The limitations and challenges of using bismuth tungstate as a photocatalyst are also examined, such as its low quantum efficiency and susceptibility to photodegradation. Finally, recommendations for future research directions are provided, including the need for further studies on the underlying mechanisms of photocatalytic activity, the development of more efficient and stable bismuth tungstate-based photocatalysts, and the exploration of new applications in fields such as water treatment and energy conversion.

Oxygen Vacancy Mediated Band-Gap Engineering via B-Doping for Enhancing Z-Scheme A-TiO2/R-TiO2 Heterojunction Photocatalytic Performance

Fabrication of Z-scheme heterojunction photocatalysts is an ideal strategy for solving environmental problems by providing inexhaustible solar energy. A direct Z-scheme anatase TiO₂/rutile TiO₂ heterojunction photocatalyst was prepared using a facile B-doping strategy. The band structure and oxygen-vacancy content can be successfully tailored by controlling the amount of B-dopant. The photocatalytic performance was enhanced via the Z-scheme transfer path formed between the B doped anatase-TiO₂ and rutile-TiO₂, optimized band structure with markedly positively shifted band potentials, and the synergistically-mediated oxygen vacancy contents. Moreover, the optimization study indicated that 10% B-doping with the R-TiO₂ to A-TiO₂ weight ratio of 0.04 could achieve the highest photocatalytic performance. This work may provide an effective approach to synthesize nonmetal-doped semiconductor photocatalysts with tunable-energy structures and promote the efficiency of charge separation.

Insights into the formation of environmentally persistent free radicals during photocatalytic degradation processes of ceftriaxone sodium by ZnO/ZnIn2S4

At present, the researches on photocatalysis were mainly focused on the design, improvement and development of catalysts, and less attention was paid to the existing characteristics of environmentally persistent free radicals (EPFRs) during the process of photocatalytic oxidation. In this study, A flower-like Z-type heterojunction ZnO/ZnIn₂S₄ (ZnO/ZIS) and typical antibiotic ceftriaxone sodium (CS) were taken as study objects, concentrating on the generation characteristics of EPFRs during the degradation of CS by ZnO/ZIS, and clarifying the degradation mechanism of CS in which EPFRs participated. The results showed that the degradation efficiency of 10 mg/L CS by 0.40 g/L ZnO/ZIS reached 85.3% in 150 min under the irradiation of 500 W xenon lamp. It was clear that ·O₂^- and h⁺ play major roles in CS degradation by ZnO/ZIS under visible light, and ·OH plays an auxiliary role. Furthermore, the formation mechanism of EPFRs during photocatalytic degradation processes of CS by ZnO/ZIS were first investigated thoroughly via experimental analysis and density functional theory (DFT) calculations. The concentration level of EPFRs centered on oxygen atoms is 10¹¹ spin/mm³, which were generated in the process of degradation of CS by ZnO/ZIS under visible light. The production of EPFRs chiefly includes two procedures: chemical adsorption and transfer of electrons. The adsorption energy of precursor P8 on ZnIn₂S₄ side is -1.91 eV, the electrons transferred from precursor P8 and P11 to ZnO/ZnIn₂S₄ heterojunction. Surprisingly, EPFRs have little negative effects on the degradation process of CS by ZnO/ZIS. The study was not only a key field in the development of photocatalysis technology, but also a new way to study the removal mechanism of antibiotics.

Electrostatic interaction and surface S vacancies synergistically enhanced the photocatalytic degradation of ceftriaxone sodium

ZnIn₂S₄ ultrathin 2D nanosheets with a positive surface charge are synthesized by a hydrothermal method and different contents of surface S vacancies are induced via heat treatment of as-prepared ZnIn₂S₄ (ZIS). As the S vacancies contents increased, the photocatalytic degradation efficiency of ceftriaxone (CTRX) sodium is promoted. Especially, ZIS-300 shows the best degradation efficiency (88.8%) for an initial CTRX concentration of 10 mg L^-1 in 2 h. It is found that S vacancies cause the electron density of surface metal atoms (Zn, In) to be decreased, which makes the effective adsorption and activation of ceftriaxone anions through electrostatic adsorption interactions. Meanwhile, S vacancies also serve as active centers to promote the absorption of O₂ and gather electrons to form •O₂^- species. The photogenerated holes quickly transfer to the surface of the catalyst to directly degrade the adsorbed CTRX. Thus, the photocatalytic CTRX degradation efficiency is significantly improved. Finally, a possible mechanism for over defective ZIS is proposed. This work provides a feasible strategy for the efficient degradation of antibiotics from the perspective of electrostatic adsorption and molecule activation.

Tuning oxygen vacancy in Bi2WO6 by heteroatom doping for enhanced photooxidation-reduction properties

Heteroatom doping was recently regarded as an effective method to tune the band gap and improve the separation and transfer of photogenerated electron-hole pairs in semiconductor photocatalysts. Herein, a novel S,F-codoped Bi2WO6 (S,F-Bi2WO6) with suitable oxygen vacancies was synthesized via the hydrothermal-calcination and post-sulfurization, for efficient Cr(VI) reduction and methyl orange (MO) degradation under visible light. The amount of surface oxygen vacancies could be controlled by adjusting the S/F ratio during the doping process, which modulated the band structure and photogenerated charge behavior of Bi2WO6. The optimal S0.10F-Bi2WO6 exhibited an excellent photooxidation-reduction performance, which Cr(VI) reduction and MO degradation efficiencies were 1.6 and 2.6 times than those of the pristine Bi2WO6 without oxygen vacancy under visible-light, respectively. The enhanced photooxidation-reduction performance was because the right amount of oxygen vacancies could effectively narrow the bandgap and improve the separation efficiency of electron-hole pairs. Thus, this work offered a mild and simply approach for preparing heteroatom doped Bi2WO6 and a potential to be extended to the synthesis of other doped materials for environmental remediation.

Synergistic Effect of Amorphous Ti(IV)-Hole and Ni(II)-Electron Cocatalysts for Enhanced Photocatalytic Performance of Bi2WO6

Bi2WO6 has become a common photocatalyst due to its advantages of simple synthesis and high activity. However, the defects of pure Bi2WO6 such as low light reception hinder its application in photocatalysis. In this study, based on the modification of Bi2WO6 with Ti(IV) as a cavity co-catalyst, new Ni- and Ti-doped nanosheets of Bi2WO6 (Ni/Ti-Bi2WO6) were prepared by a one-step wet thermal impregnation method and used for the photocatalytic degradation of tetracycline. The experimental results showed that the photocatalytic activity of Ni/Ti-Bi2WO6 modified by the two-component catalyst was significantly better than those of pure Bi2WO6 and Ti-Bi2WO6 modified with Ti(IV) only. The photocatalytic effect of Ni/Ti-Bi2WO6 with different Ni/Ti molar ratios was investigated by the degradation of TC. The results showed that 0.4Ni/Ti-Bi2WO6 possessed the best photocatalytic performance, with a degradation rate of 92.9% at 140 min TC. The results of cycling experiments showed that the catalyst exhibited high stability after five cycles. The scavenger experiment demonstrated that the h+ and O2− were the main reactive species. The enhanced photocatalytic activity of Bi2WO6 could be attributed to the synergistic effect between the Ti(IV) as a hole cocatalyst and Ni(II) as an electron cocatalyst, which effectively promoted the separation of photogenerated carriers.

Panax notoginseng powder -assisted preparation of carbon-quantum-dots/BiOCl with enriched oxygen vacancies and boosted photocatalytic performance

Low activity of photocatalysts is a serious bottleneck to the practical application of photocatalytic technology. In this paper, a series of BiOCl composite photocatalysts containing carbon quantum dots (CQDs) were successfully prepared by adding Panax notoginseng powder (PNP) to the solvothermal synthesis system of BiOCl as a template agent and a raw material for 0D CQDs. CQDs/BiOCl exhibit 2D flake structures and 3D flower-like microspheres self-assembled from thin flakes, holding rich oxygen vacancies (OVs). After detailed characterization, it was found that the amount of OVs on BiOCl could be regulated according to the amount of PNP added. The CQDs/OVs-BiOCl photocatalysts exhibit higher photogenerated charge separation efficiency and photocatalytic activity than the bare BiOCl. When the mass ratio of PNP/BiOCl is 1.0%, the photocatalyst demonstrates the maximum degradation activity for rhodamine B (RhB) and perfluorooctanoic acid (PFOA). In view of the solid observations, a photocatalytic enhancement mechanism of CQDs/BiOCl was elucidated.

Boosted photocatalytic effect of binary AgI/Ag2WO4 nanocatalyst: characterization and kinetics study towards ceftriaxone photodegradation

In modern chemistry, great interest has been paid to introducing outstanding photocatalysts for degrading organic pollutants. Herein, a highly efficient binary AgI/Ag₂WO₄ photocatalyst was prepared from AgI and Ag₂WO₄ nanoparticles (NPs) and characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), electrochemical impedance spectroscopy (EIS), and Fourier transform infrared (FT-IR) techniques. In the Scherrer model, the average crystallite sizes of 34.9, 42.0, and 24.1 nm were estimated for the AgI, Ag₂WO₄, and the binary catalyst, while the values were 91, 13, and 85 nm by the Williamson-Hall model. FTIR confirmed the presence of W-O-W, O-W-O, Ag-I, and O-Ag-O bonds in the coupled material. DRS results showed absorption edge wavelengths of 451, 462, and 495 nm (corresponding to the band gap values of 2.75, 2.68, and 2.51 eV) for Ag₂WO₄, AgI, and AgI/Ag₂WO₄ catalyst, respectively. Synergistic photocatalytic activity of the coupled system was achieved towards ceftriaxone (CTX) in an aqueous solution (about 33% 10 ppm CTX solution was degraded without any optimization in the initial conditions of catal dose 0.3 g/L (Ag₂WO₄:AgI with mole ratio 1:2 and 30 min abrasion time), and irrad. time 45 min, C_CTX). This boosted effect depended on the AgI:Ag₂WO₄ mole ratio and grinding time for the mechanical preparation of the binary catalyst (optimums: mole ratio of 4:1 and time 30 min). The photodegradation kinetics obeyed the Hinshelwood model with the apparent first-order rate constant (k) of 0.013 min^-1 (t_1/2 = 53.30 min). Performing the COD on the photodegraded CTX solutions got a Hinshelwood plot with a slope of 0.019 min^-1 (t_1/2 = 36.5 min).

Engineering controllable oxygen vacancy defects in iron hydroxide oxide immobilized on reduced graphene oxide for boosting visible light-driven photo-Fenton-like oxidation

Visible light-driven photo-Fenton-like technology is a promising advanced oxidation process for water remediation, while the construction of effective synergetic system remains a great challenge. Herein, iron hydroxide oxide (α-FeOOH) with controllable oxygen vacancy defects were engineered on reduced graphene oxide (rGO) nanosheets (named as OVs-FeOOH/rGO) through an in-situ redox method for boosting visible light-driven photo-Fenton-like oxidation. By adjusting the pH environment to modulate the redox reaction kinetics between graphene oxide (GO) and ferrous salt precursors, the oxygen vacancy concentration in α-FeOOH could be precisely controlled. With optimized oxygen vacancy defects obtained at pH 5, the OVs-FeOOH/rGO displayed superior photo-Fenton-like performance for Rhodamine B degradation (99% within 40 mins, rate constant of 0.2278 mg^-1 L min^-1) with low H₂O₂ dosage (5 mM), standing out among the reported photo-Fenton-like catalysts. The catalyst also showed excellent reusability, general applicability, and tolerance ability of realistic environmental conditions, which demonstrates great potential for practical applications. The results reveal that moderate oxygen vacancy defects can not only strengthen absorption of visible light and organic pollutants, but also promote the charge transfer to simultaneously accelerate the photogenerated electron-hole separation and Fe(III)/Fe(II) Fenton cycle, leading to the remarkable photo-Fenton-like oxidation performance. This work sheds light on the controllable synthesis and mechanism of oxygen vacancy defects to develop efficient photo-Fenton-like catalysts for wastewater treatment.

Interfacial charge dynamics in type-II heterostructured sulfur doped-graphitic carbon nitride/bismuth tungstate as competent photoelectrocatalytic water splitting photoanode

Sluggish charge transfers at the electrode/electrolyte interface and fast recombination of electron-hole pairs limit the photoelectrocatalytic water-splitting ability of the bismuth tungstate (Bi₂WO₆). To address these issues, sulfur doped-graphitic carbon nitride/bismuth tungstate (S-g-C₃N₄/Bi₂WO₆) heterostructured hybrid material with different wt% of S-g-C₃N₄ were constructed via an ultrasonic approach. The formation of heterostructure offers well-separated electron-hole pairs, thereby improving the charge transfer process, and boosting water oxidation kinetics on the surface of modified electrodes. Electrochemical impedance analysis confirms the rapid charge transfer process and quick electrochemical reaction at the electrode/electrolyte interface, which quenches the charge recombination process. The S-g-C₃N₄/Bi₂WO₆ with 3 wt% of S-g-C₃N₄ photoanode delivers ~43, ~18 and ~2-folds higher applied bias photon-to-current efficiency than S-g-C₃N₄, Bi₂WO₆, and g-C₃N₄/Bi₂WO₆ (3 wt% of g-C₃N₄) photoanodes, respectively. From the combination of UV-Vis, XPS valance band, and Mott-Schottky analysis the plausible band edge positions of the Bi₂WO₆ and S-g-C₃N₄ were calculated. Based on the band structure, we have concluded that the S-g-C₃N₄/Bi₂WO₆ hybrid photoanode follows a type-II charge transfer mechanism to promote the photoelectrocatalytic water splitting ability.

Investigation of the Kinetics and Reaction Mechanism for Photodegradation Tetracycline Antibiotics over Sulfur-Doped Bi2WO6-x/ZnIn2S4 Direct Z-Scheme Heterojunction

The rational design of direct Z-scheme heterostructural photocatalysts using solar energy is promising for energy conversion and environmental remediation, which depends on the precise regulation of redox active sites, rapid spatial separation and transport of photoexcited charge and a broad visible light response. The Bi₂WO₆ materials have been paid more and more attention because of their unique photochemical properties. In this study, S²⁻ doped Bi₂WO_6-x coupled with twin crystal ZnIn₂S₄ nanosheets (Sov−BWO/T−ZIS) were prepared as an efficient photocatalyst by a simple hydrothermal method for the removal of tetracycline hydrochloride (TCH). Multiple methods (XRD, TEM, XPS, EPR, UV vis DRS, PL etc.) were employed to systematically investigate the morphology, structure, composition and photochemical properties of the as-prepared samples. The XRD spectrum indicated that the S²⁻ ions were successfully doped into the Sov−BWO component. XPS spectra and photoelectrochemical analysis proved that S²⁻ served as electronic bridge and promoted captured electrons of surface oxygen vacancies transfer to the valence band of T−ZIS. Through both experimental and in situ electron paramagnetic resonance (in situ EPR) characterizations, a defined direct Z-scheme heterojunction in S-BWO/T−ZIS was confirmed. The improved photocatalytic capability of S-BWO/T−ZIS results ascribed that broadened wavelength range of light absorption, rapid separation and interfacial transport of photoexcited charge, precisely regulated redox centers by optimizing the interfacial transport mode. Particularly, the Sov−50BWO/T−ZIS Z-scheme heterojunction exhibited the highest photodegradation rate was 95% under visible light irradiation. Moreover, this heterojunction exhibited a robust adsorption and degradation capacity, providing a promising photocatalyst for an organic pollutant synergistic removal strategy.

Oxygen vacancy BiO2-x/Bi2WO6 synchronous coupling with Bi metal for phenol removal via visible and near-infrared light irradiation

The introduction of oxygen-defects has been a versatile strategy to enhance photocatalysis efficiency. In this work, a 2D/3D Bi/BiO_2-x/Bi₂WO₆ heterojunction photocatalyst with rich oxygen-defective was in sequence prepared through a facile solvothermal method, which displays favorable photocatalytic activity towards organic contaminants under visible-NIR light irradiation. The enhancement in photocatalytic performance can be attributed to the synergistic effect between oxygen-vacancy-rich heterojunction and the localized surface plasmon resonance induced by metallic Bi. The functional group interaction, surface morphology, crystal structure, element composition, and tuned bandgap were investigated by FT-IR, SEM, Raman shift, ICP-MS, and XPS technique. The spectrum response performance of the photocatalyst was verified by UV-visible DRS analysis. Results of photodegradation experiments toward organic contaminants showed that the prepared photocatalyst can degrade 90% of phenol in 20 mins under visible-NIR light irradiation, both Z-scheme heterojunction and the introduction of Bi metal contribute to the enhancement in the photocatalytic activity. The results of the DFT calculation suggest that the valence band-edge hybridization within BiO_2-x and Bi₂WO₆ can effectively enhance the photocatalytic performance by increasing the migration efficiencies of electron-hole pairs. Moreover, a possible mechanism was proposed on the results of EIS, ESR and GC-MS tests. This work offers a novel insight for synthesizing efficient visible-NIR light photocatalysis by activating the semiconductors with Bi metal.

Ordered Ti-doped FeVO4 nanoblock photoanode with improved charge properties for efficient solar water splitting

Highly photoactive FeVO₄ photoanodes with ordered nanoblock morphology and uniform Ti-doping were prepared by drop-casting mixed Ti and V precursors onto FeOOH nanorod films and following an annealing process. The results indicate that Ti⁴⁺ is uniformly doped into the FeVO₄ lattice by substituting V⁵⁺ and provides an increased number of O₂^- vacancies. The optimized film thickness and doping level are 620 nm and 0.3%, respectively. Compared to the undoped sample, the Ti-doped photoanode showed ~ 219% enhancement in photocurrent at 1.0 V vs Ag/AgCl under back illumination of AM 1.5, reaching a state-of-the-art value of ~ 1.47 mA cm^-2, and also achieved stable and efficient overall water splitting activity with evolution rates of 28.3 and 14.1 μmol cm^-2h^-1 for H₂ and O₂, respectively. The excellent PEC performance could be attributed to the remarkably enhanced charge carrier concentration and conductivity, and the facilitated charge transfer kinetics across the semiconductor/electrolyte interface, as a result of Ti-doping.

Understanding the hierarchical behavior of Bi2WO6 with enhanced photocatalytic nitrogen fixation activity

Hierarchical Bi2WO6 nanostructures self-assembled with planar arranged nanosheets and dispersed Bi2WO6 nanosheets were synthesized with different dosages of EG via a simple hydrothermal route. The Bi2WO6 photocatalysts were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). A control experiment was conducted to test the effect of EG dosage on the growth mechanism and behavior of the highly (010) exposed hierarchical lamellar nanostructures and dispersed nanosheets. The photocatalytic nitrogen fixation rate of the hierarchical Bi2WO6 nanostructures was estimated to be 948 μmol g-1 h-1 across the full spectrum, which was 23% higher than that of the dispersed nanosheets (770 μmol g-1 h-1) due to chemisorption on the hierarchical structures and enhanced surface oxygen vacancies (OVs).

Visible-light-driven photo-Fenton degradation of ceftriaxone sodium using SnS2/LaFeO3 composite photocatalysts

The LaFeO3-based heterostructure photocatalyst and photo-Fenton process are combined to effectively treat ceftriaxone sodium (CRS) contaminant under visible light.

Promoting superoxide generation in Bi2WO6 by less electronegative substitution for enhanced photocatalytic performance: an example of Te doping

Doping with elements with lower electronegativity, like Te, shifts the band potentials of Bi2WO6 to the point that superoxide radical generation is feasible. As a result, an optimum of 2.5 at% Te doping improves the activity of Bi2WO6 by 48 times.