In-situ transformation of Bi2WO6 to highly photoreactive Bi2WO6@Bi2S3 nanoplate via ion exchange

Bromine Ion-Intercalated Layered Bi2WO6 as an Efficient Catalyst for Advanced Oxidation Processes in Tetracycline Pollutant Degradation Reaction

The visible-light-driven photocatalytic degradation of pharmaceutical pollutants in aquatic environments is a promising strategy for addressing water pollution problems. This work highlights the use of bromine-ion-doped layered Aurivillius oxide, Bi2WO6, to synergistically optimize the morphology and increase the formation of active sites on the photocatalyst's surface. The layered Bi2WO6 nanoplates were synthesized by a facile hydrothermal reaction in which bromine (Br-) ions were introduced by adding cetyltrimethylammonium bromide (CTAB)/tetrabutylammonium bromide (TBAB)/potassium bromide (KBr). The as-synthesized Bi2WO6 nanoplates displayed higher photocatalytic tetracycline degradation activity (~83.5%) than the Bi2WO6 microspheres (~48.2%), which were obtained without the addition of Br precursors in the reaction medium. The presence of Br- was verified experimentally, and the newly formed Bi2WO6 developed as nanoplates where the adsorbed Br- ions restricted the multilayer stacking. Considering the significant morphology change, increased specific surface area, and enhanced photocatalytic performance, using a synthesis approach mediated by Br- ions to design layered photocatalysts is expected to be a promising system for advancing water remediation.

One-pot solvothermal synthesis of Bi/Bi2S3/Bi2WO6 S-scheme heterojunction with enhanced photoactivity towards antibiotic oxytetracycline degradation under visible light

A novel noble-metal-free ternary Bi/Bi₂S₃/Bi₂WO₆ S-scheme heterojunction and Schottky junction was successfully synthesized by one-pot solvothermal method. UV-Vis spectroscopy showed improved light absorption in the ternary composite structure. Electrochemical impedance spectroscopy and photoluminescence spectroscopy confirmed the reduced interfacial resistivity and photogenerated charge recombination rate of the composites. Using oxytetracycline (OTC) as model pollutant, Bi/Bi₂S₃/Bi₂WO₆ presented high photocatalytic activity towards OTC degradation, where the removal rate of Bi/Bi₂S₃/Bi₂WO₆ was 1.3 and 4.1 times higher than that of Bi₂WO₆ and Bi₂S₃ under visible light irradiation in 15 min, respectively. The excellent visible photocatalysis activity was attributed to the SPR effect of metal Bi and the direct S-scheme heterojunction of Bi₂S₃ and Bi₂WO₆ with the matched energy band structure, which led to the increased electron transfer rate and high separation efficiency of the photogenerated election-hole pairs. After seven cycles, the degradation efficiency for 30 ppm OTC with Bi/Bi₂S₃/Bi₂WO₆ only decreased 20.4%. In the degradation solution, the composite photocatalyst leached only 16 ng/L Bi and 26 ng/L W of metal with high photocatalytic stability. Moreover, free radical quenching experiment and electron spin-resonance spectroscopy experiment revealed that ·O₂^-, ¹O₂, h⁺ and ·OH played crucial roles in the photocatalytic degradation of OTC. Based on the analysis of high performance liquid chromatography-mass spectrometry for the intermediates in the degradation process, the degradation pathway was provided. Finally, combined with ecotoxicological effect analysis, the decreased toxicity of OTC after degradation towards rice seedlings was confirmed.

Research progress in metal sulfides for photocatalysis: From activity to stability

Metal sulfides are a type of reduction semiconductor photocatalysts with narrow bandgap and negative conduction band potential, which make them have unique photocatalytic performance in solar-to-fuel conversion and environmental purification. However, metal sulfides also suffer from low quantum efficiency and photocorrosion. In this review, the strategies to improve the photocatalytic activity of metal sulfide photocatalysts by stimulating the charge separation and improving light-harvesting ability are introduced, including morphology control, semiconductor coupling and surface modification. In addition, the recent research progress aiming at improving their photostability is also illustrated, such as, construction of hole transfer heterojunctions and deposition of hole transfer cocatalysts. Based on the electronic band structures, the applications of metal sulfides in photocatalysis, namely, hydrogen production, degradation of organic pollutants and reduction of CO₂, are summarized. Finally, the perspectives of the promising future of metal-sulfide based photocatalysts and the challenges remaining to overcome are also presented.

Yolk-shell shaped Au-Bi2S3heterostructure nanoparticles for controlled drug release and combined tumor therapy

To fabricate a novel stimuli-responsive system enabling controlled drug release and synergistic therapy, yolk-shell shaped bismuth sulfide modified with Au nanoparticles (Au-Bi₂S₃) was prepared. The Au-Bi₂S₃nanomaterial with heterojunction structure exhibited excellent photothermal conversion efficiency and considerable free radicals yield under laser irradiation. The drug delivery capacity was confirmed by co-loading Berberine hydrochloride (BBR) and a phase change material 1-tetradecanol (PCM), which could be responsible for NIR light induced thermal controlled drug release.In vitroinvestigation demonstrated that Au-Bi₂S₃has cell selectivity, and with the assistance of the properties of Au-Bi₂S₃, the loaded drug could give full play to their cancer cell inhibition ability. Our work highlights the great potential of this nanoplatform which could deliver and control Berberine hydrochloride release as well as realize the synergistic anti-tumor strategy of photothermal therapy, photodynamic therapy and chemotherapy for tumor therapy.

Modifying SnS2 With Carbon Quantum Dots to Improve Photocatalytic Performance for Cr(VI) Reduction

The photoreduction for hazardous Cr(VI) in industrial wastewater has been considered a "green" approach with low-cost and easy-to-go operation. SnS₂ is a promising narrow bandgap photocatalyst, but its low charge carrier separation efficiency should be solved first. In this work, N-doped carbon quantum dots (CQDs) were prepared and loaded onto SnS₂ nanoparticles via an in situ method. The resulting composite samples (NC@SnS₂) were characterized, and their photocatalytic performance was discussed. SnS₂ nanoparticles were obtained as hexagonal ones with a bandgap of 2.19 eV. The optimal doping level for NC@SnS₂ was citric acid: urea:SnS₂ = 1.2 mmol:1.8 mmol:3.0 mmol. It showed an average diameter of 40 nm and improved photocatalytic performance, compared to pure SnS₂, following a pseudo-first-order reaction with a kinetic rate constant of 0.1144 min^-1. Over 97% of Cr(VI) was photo-reduced after 30 min. It was confirmed that modification of SnS₂ with CQDs can not only improve the light-harvesting ability but also stimulate the charge separation, which therefore can enhance the photoreactivity of SnS₂ toward Cr(VI) reduction. The excellent stability of NC@SnS₂ indicates that it is promising to be practically used in industrial wastewater purification.

Two-Dimensional Nanostructures in the World of Advanced Oxidation Processes

Two-dimensional compounds with nanostructural features are attracting attention from researchers worldwide. Their multitude of applications in various fields and vast potential for future technology advancements are successively increasing the research progress. Wastewater treatment and preventing dangerous substances from entering the environment have become important aspects due to the increasing environmental awareness, and increasing consumer demands have resulted in the appearance of new, often nonbiodegradable compounds. In this review, we focus on using the most promising 2D materials, such as MXenes, Bi2WO6, and MOFs, as catalysts in the modification of the Fenton process to degrade nonbiodegradable compounds. We analyze the efficiency of the process, its toxicity, previous environmental applications, and the stability and reusability of the catalyst. We also discuss the catalyst’s mechanisms of action. Collectively, this work provides insight into the possibility of implementing 2D material-based catalysts for industrial and urban wastewater treatment.

Visible light photodegradation of 2,4-dichlorophenol using nanostructured NaBiS2: Kinetics, cytotoxicity, antimicrobial and electrochemical studies of the photocatalyst

Removal of the hazardous and endocrine-disrupting 2,4-dichlorophenol (2,4-DCP) from water bodies is crucial to maintain the sanctity of the ecosystem. As a low bandgap material (1.37 eV), NaBiS₂ was hydrothermally prepared and used as a potential photocatalyst to degrade 2,4-DCP under visible light irradiation. NaBiS₂ appeared to be highly stable and remained structurally undeterred despite thermal variations. With a surface area of 6.69 m²/g, NaBiS₂ has enough surface-active sites to adsorb the reactive molecules and exhibit a significant photocatalytic activity. In alkaline pH, the adsorption of 2,4-DCP on NaBiS₂ appeared to decrease whereas, the acidic and neutral environments favoured the degradation. An increase in the photocatalyst dosage enhanced the degradation efficiency from 81 to 86 %, because of higher vacant adsorbent sites and the electrostatic attraction between NaBiS₂ and 2,4-DCP. The dominant scavengers degraded 2,4-DCP by forming a coordination bond between chlorine's lone pair of electrons and the vacant orbitals of bismuth, following the order hole> OH > singlet oxygen. Being non-toxic to both natural and aquatic systems, NaBiS₂ exhibits antifungal properties at higher concentrations. Finally, the electron-rich NaBiS₂ is an excellent electrocatalyst that effectively degrades organic pollutants and is a promising material for industrial and environmental applications.

Tetragonal/orthorhombic-bismuth tungstate homojunction formed through in situ bismuth induced phase transformation as highly efficient photocatalyst for pollutant degradation

Tetragonal/orthorhombic-bismuth tungstate (t/o-Bi₂WO₆) homojunctions of high photocatalytic efficiencies were fabricated through a novel in situ Bi induced phase transformation. The photocatalytic efficiencies of t-Bi₂WO₆ were greatly enhanced via formation of the homojunction. Photocatalytic degradation of rhodamine B (RhB), a recalcitrant organic pollutant, under simulated sunlight illumination was investigated as a demonstration for the efficiency enhancement. A 6.22 folds improvement was achieved with formation of the homojunction in terms of reaction rate constants. The homojunction catalyst was demonstrated to be photocatalytically stable over a five cycles operation. The t/o-Bi₂WO₆ homojunction enhances separation and utilization efficiency of photo-generated charge carriers and thus greatly boosts the catalytic efficiency. Trapping tests and electron spin resonance spectroscopy were conducted to reveal that singlet oxygen (¹O₂), hole (h⁺), electrons (e^-), and superoxide anion radical (O₂^-) are the main working reactive species for RhB degradation. Density functional theory (DFT) calculations were performed to prove the feasibility of Bi induced phase transformation of t-Bi₂WO₆ to o-Bi₂WO₆. The present development offers a new design route for high efficiency photocatalysts for water pollution control.

Construction of S-scheme Bi2WO6/g-C3N4 heterostructure nanosheets with enhanced visible-light photocatalytic degradation for ammonium dinitramide

Photocatalysis technology is considered as a promising environmental remediation strategy. Herein, photocatalytic degradation of ammonium dinitramide (ADN, main component of propellant) was investigated over Bi₂WO₆/g-C₃N₄ (BWO/CN) heterostructure nanosheets prepared by a one-step in-situ hydrothermal method. The operating conditions including ADN initial concentration, catalyst dosage, initial pH, temperature and green oxidizer (hydrogen peroxide) were optimized systematically. Under optimal conditions, the photocatalytic degradation rate of ADN over BWO/CN can reach 98.93% after 80 min visible-light irradiation. Besides, the composite has excellent stability for ADN treatment and nitrate ions are the major degradation products. Furthermore, S-scheme heterojunction mechanism was proposed to explain the extremely high REDOX performance of BWO/CN composite.

Near-Infrared-Driven Photocatalysts: Design, Construction, and Applications

Photocatalysts, which utilize solar energy to catalyze the oxidation or reduction half reactions, have attracted tremendous interest due to their great potential in addressing increasingly severe global energy and environmental issues. Solar energy utilization plays an important role in determining photocatalytic efficiencies. In the past few decades, many studies have been done to promote photocatalytic efficiencies via extending the absorption of solar energy into near-infrared (NIR) light. This Review comprehensively summarizes the recent progress in NIR-driven photocatalysts, including the strategies to harvest NIR photons and corresponding photocatalytic applications such as the degradation of organic pollutants, water disinfection, water splitting for H₂ and O₂ evolution, CO₂ reduction, etc. The application of NIR-active photocatalysts employed as electrocatalysts is also presented. The subject matter of this Review is designed to present the relationship between material structure and material optical properties as well as the advantage of material modification in photocatalytic reactions. It paves the way for future material design in solar energy-related fields and other energy conversion and storage fields.

Selective and sensitive visible-light-prompt photoelectrochemical sensor of paracetamol based on Bi2WO6 modified with Bi and copper sulfide

Paracetamol (PA) is a ubiquitous non-steroidal anti-inflammatory drug, mainly used to treat headaches, arthritis and osteoarthritis and other diseases. In this work, a novel label free photoelectrochemical (PEC) sensor based on Bi-CuS/Bi2WO6 has been developed for the detection of PA, which was fabricated by a simple two-step hydrothermal process. It was found that Bi-CuS/Bi2WO6 with a CuS/Bi2WO6 heterojunction and surface plasmon resonance (SPR) effect of Bi possesses enhanced charge transfer and absorption wavelengths under visible light, particularly when compared to pristine Bi2WO6 films, thus producing an increase in the observed photocurrent. The photocurrent was increased after adding PA. And the photocurrent increment was linear with PA concentration in the range from 0.01-60 μM with a detection limit of 2.12 nM. Moreover, the PEC sensor also exhibited high anti-interference property and acceptable stability. In the present study, a Bi-CuS/Bi2WO6 photoelectrode is considered a promising candidate for carrying out PEC analysis.

Recycling of spent alkaline Zn-Mn batteries directly: Combination with TiO2 to construct a novel Z-scheme photocatalytic system

Recycling of spent alkaline Zn-Mn batteries (S-AZMB) has always been a focus of attention in environmental and energy fields. However, the current research mostly concentrated in the recovery of purified materials, and ignores the direct reuse of S-AZMB. Herein, we propose a new concept for the first time that unpurified S-AZMB can be used as raw materials for preparation of Z-scheme photocatalytic system in combination with TiO₂. A series of characterizations and experiments confirm that the combination with S-AZMB not only extends the response of TiO₂ to visible light, but also significantly enhances the separation ability of photogenerated electron-hole pairs. In the toluene removal experiment, the degradation kinetic rate of Z-scheme TiO₂@S-AZMB photocatalyst reaches 21.0 and 10.5 times than that of TiO₂ and S-AZMB, respectively. More notably, this S-AZMB based Z-scheme photocatalyst can maintain structural and photocatalytic performance stability in cyclic catalytic reactions. We believe that this work not only expands the research concept of recycling S-AZMB, but also provides a new idea for designing highly efficient Z-scheme photocatalysts.

Effective charge kinetics steering in surface plasmons coupled two-dimensional chemical Au/Bi2WO6-MoS2 heterojunction for superior photocatalytic detoxification performance

Developing and designing a rational heterojunction with efficient charge kinetics properties have been a research hotspot for improving photocatalytic performance. Herein, a surface plasmons coupled two-dimensional chemical Au/Bi₂WO₆-MoS₂ heterojunction was synthesized. In thus a system, Au nanoparticles are tightly attached to the sides of Bi₂WO₆ nanosheets, conducting a HEI effect with additional visible light response to inject "hot electrons" into Bi₂WO₆, resulting in additional charge generation. Meanwhile, few-layer MoS₂ nanosheets were chemically assembled onto ultrathin Bi₂WO₆ nanosheets via interfacial SO bonds to form a intimate 2D-2D nanojunction, the separated and injected electrons on the surface of Bi₂WO₆ were further directional transfer to MoS₂ nanosheets through SO bonds for detoxification of heavy metal ions Cr(VI), and the corresponding holes left on Bi₂WO₆ nanosheets were applied for simultaneous degradation of tetracycline antibiotic. The photocatalytic detoxification activity of Au/Bi₂WO₆-MoS₂ was nearly 4.84, 3.47 and 1.90 times higher than that of pristine Bi₂WO₆, Au/Bi₂WO₆ and Bi₂WO₆-MoS₂ composites, which could be ascribed to the effective charge kinetics steering and well manipulation of charge flow by virtue of the rational structural and compositional features. This work provides a new perspective for the construction of high-activity detoxification photocatalysts through steering charge kinetics.

In situ preparation of Bi2S3 nanoribbon-anchored BiVO4 nanoscroll heterostructures for the catalysis of Cr(vi) photoreduction

Novel Bi₂S₃ nanoribbon-anchored BiVO₄ nanoscroll heterostructures were fabricated, showing enhanced photocatalytic activity for Cr(vi) reduction under UV-visible light illumination.

Graphene oxide mediated co-generation of C-doping and oxygen defects in Bi2WO6 nanosheets: a combined DRIFTS and DFT investigation

In order to efficiently control air pollutants using photocatalytic technology, the co-generation of C-doping and oxygen vacancies (OVs) in Bi₂WO₆ (BWO) nanosheets was achieved by a graphene oxide (GO)-mediated hydrothermal method. The photocatalytic performance was highly improved with the synergistic effects of C-doping and OVs. The experimental characterization and DFT calculations were closely combined to reveal that the C element could serve as both an electron acceptor and channel for charge transfer to promote charge separation. Meanwhile, the OVs could induce the formation of a defect level in the band gap which increases the production of ˙OH as the primary reactive species by introducing more light-generated holes into the valence band. Meanwhile, the OVs could enhance the generation of ˙O₂^- species via the promotion of O₂ adsorption and activation on the catalyst surface. Moreover, the reaction intermediates were monitored and the mechanism of photocatalytic NO oxidation was proposed based on in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The design concept of photocatalyst modification with C-doping and OVs could offer a novel strategy to enhance the performance for environmental applications.

Enhanced performance of alkali-modified Bi2WO6/Bi0.15Ti0.85O2 toward photocatalytic oxidation of HCHO under visible light

Photocatalytic oxidation of formaldehyde (HCHO) is considered as one of the promising ways to resolve indoor air HCHO pollution. TiO₂ has been well known as the most extended application in photocatalysis due to its strong oxidizing ability and stability. Owing to high activity under visible light irradiation, TiO₂ and Bi₂O₃ doping mixed with Bi₂WO₆ was analyzed in this study. The formation of two kinds of heterojunction caused efficient charge separation, leading to the effective reduction in the recombination of photo-generated electron and hole. The special structure and enhanced performance of these catalysts were analyzed. For the first time, the loading of alkali salts was researched for photocatalytic oxidation. In order to understand the reaction mechanism of alkali salts enhanced effects, the catalysts were investigated by using BET, XRD, UV-Vis, FT-IR, SEM, and XPS. The results found more than 2 wt% of Na₂SO₄ loading and the mixed methods with different solutions were key factors affecting the performance of catalysts. Nearly 92% HCHO conversion could be completed over Bi₂WO₆/Bi_0.15Ti_0.85O₂ (Na₂SO₄), and the concentration of HCHO was only 0.07 mg/m³ for 24 h, which was below the limit of specification in China. The results also indicated that the solution mixing method was more favorable to increase the HCHO conversion due to decrease the size of Bi_0.15T_i0.85O₂ particles. The catalysts with Na₂SO₄ loading provided more surface-adsorbed oxygen that facilitated the desorption of CO₂ and markedly increased the photocatalytic oxidation of HCHO. Graphical abstract Plausible mechanism over W-Bi2WO6/ Bi0.15Ti0.85O2-Na2SO4 (1:4) catalysts.

Synthesis of Bi2WO6/Na-bentonite composites for photocatalytic oxidation of arsenic(iii) under simulated sunlight

Novel Bi₂WO₆/bentonite (denoted as BWO/BENT) composites were prepared via a typical hydrothermal process and employed for the photocatalytic oxidation of arsenic(iii) (As(iii)). The properties of the prepared samples were characterized through X-ray diffraction, transmission and scanning electron microscopy, UV-visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy. Effects of the BENT ratio on the As(iii) removal were explored under simulated sunlight, and the best photocatalytic effect was observed for the composite with BWO : BENT = 7 : 3 w/w. Compared with the pure BWO, the BWO/BENT composites exhibited an improved photocatalytic ability in the removal of As(iii), which was mainly ascribed to the enlarged specific surface area and the suppressed electron–hole recombination by the incorporated BENT. Furthermore, photo-generated holes (h⁺) and superoxide radicals ·O₂⁻ were confirmed to be the major contributors to the oxidation of As(iii), and an associated mechanism of photocatalytic oxidation of As(iii) over BWO/BENT composites was proposed.

Novel Bi₂WO₆/bentonite (denoted as BWO/BENT) composites were prepared via a typical hydrothermal process and employed for the photocatalytic oxidation of arsenic(iii) (As(iii)).

Bi4O5I2 flower/Bi2S3 nanorod heterojunctions for significantly enhanced photocatalytic performance

The excellent photocatalytic reduction of Cr(vi) over Bi₄O₅I₂/Bi₂S₃ heterojunctions is ascribed to the synergetic effects of Bi₂S₃ sensitization and intimate contact between Bi₄O₅I₂ flowers and Bi₂S₃ nanorods.

Photocatalytic Oxidation of Acetone Over High Thermally Stable TiO2 Nanosheets With Exposed (001) Facets

Anatase TiO₂ (A-TiO₂) usually exhibits superior photocatalytic activity than rutile TiO₂ (R-TiO₂). However, the phase transformation from A-TiO₂ to R-TiO₂ will inevitably happens when the calcination temperature is up to 600°C, which hampers the practical applications of TiO₂ photocatalysis in hyperthermal situations. In this paper, high energy faceted TiO₂ nanosheets (TiO₂-NSs) with super thermal stability was prepared by calcination of TiOF₂ cubes. With increase in the calcination temperature from 300 to 600°C, TiOF₂ transforms into TiO₂ hollow nanoboxes (TiO₂-HNBs) assembly from TiO₂-NSs via Ostwald Rippening process. Almost all of the TiO₂-HNBs are disassembled into discrete TiO₂-NSs when calcination temperature is higher than 700°C. Phase transformation from A-TiO₂ to R-TiO₂ begins at 1000°C. Only when the calcination temperature is higher than 1200°C can all the TiO₂-NSs transforms into R-TiO₂. The 500°C-calcined sample (T500) exhibits the highest photoreactivity toward acetone oxidation possibly because of the production of high energy TiO₂-NSs with exposed high energy (001) facets and the surface adsorbed fluorine. Surface oxygen vacancy, due to the heat-induced removal of surface adsorbed fluoride ions, is responsible for the high thermal stability of TiO₂-NSs which are prepared by calcination of TiOF₂ cubes.