Modulation of Bi2 MoO6 -Based Materials for Photocatalytic Water Splitting and Environmental Application: a Critical Review

Ternary heterojunction of cross-linked benzene Polymer/Bi2MoO6-Graphene oxide catalysts promote efficient adsorption and photocatalytic removal of oxytetracycline

Antibiotics are refractory degradable organic pollutants that present a significant hazard to water environments. In this work, a ternary composite (KB/BMO-GO) comprising of graphene oxide (GO), Bi2MoO6 (BMO), and a cross-linked benzene polymer (KB) was synthesized and applied to promote the synergistic adsorption-photocatalytic degradation of the refractory pollutant, oxytetracycline (OTC). The inclusion of GO and KB in the composite enhanced the OTC adsorption performance of the catalysts, and the construction of Z-scheme heterojunction promoted the photogenerated charge separation efficiency and broadened the range of light absorption, thereby enhancing the photocatalytic performance. Moreover, we compared the performance of catalysts loaded with different mass ratios of KB (x% KB/BMO-GO). Among them, the 15 % KB/BMO-GO catalyst sample had the best OTC degradation performance. Specifically, 15 % KB/BMO-GO could adsorb 69.7 % of OTC in 30 min, reaching an OTC degradation rate of 93.3 % under visible light irradiation. h+ and 1O2 are the main active substances in the photocatalytic process. In addition, the catalysts are acid-alkali and salt-resistant, as well as good reusability. This study provides a valuable reference for the preparation of highly efficient photocatalysts for synergistic adsorption-photodegradation processes.

Fe-Doped g-C3N4/Bi2MoO6 Heterostructured Composition with Improved Visible Photocatalytic Activity for Rhodamine B Degradation

The binary heterostructured semiconducting visible light photocatalyst of the iron-doped graphitic carbon nitride/bismuth molybdate (Fe-g-C3N4/Bi2MoO6) composite was prepared by coupling with Fe-doped g-C3N4 and Bi2MoO6 particles. In the present study, a comparison of structural characteristics, optical properties, and photocatalytic degradation efficiency and activity between Fe-doped g-C3N4 particles, Bi2MoO6 particles, and Fe-g-C3N4/Bi2MoO6 composite was investigated. The results of X-ray diffraction (XRD) examination indicate that the hydrothermal Bi2MoO6 particles have a single orthorhombic phase and Fourier transform infrared (FTIR) spectroscopy analysis confirms the formation of Fe-doped g-C3N4. The optical bandgaps of the Fe-doped g-C3N4 and Bi2MoO6 particles are 2.74 and 2.73 eV, respectively, as estimated from the Taut plots obtained from UV-Vis diffuse reflectance spectroscopy (DRS) spectra. This characteristic indicates that the two semiconductor materials are suitable for absorbing visible light. The transmission electron microscopy (TEM) micrograph reveals the formation of the heterojunction Fe-g-C3N4/Bi2MoO6 composite. The results of photocatalytic degradation revealed that the developed Fe-g-C3N4/Bi2MoO6 composite photocatalyst exhibited significantly better photodegradation performance than the other two single semiconductor photocatalysts. This property can be attributed to the heterostructured nanostructure, which could effectively prevent the recombination of photogenerated carriers (electron-hole pairs) and enhance photocatalytic activity. Furthermore, cycling test showed that the Fe-g-C3N4/Bi2MoO6 heterostructured photocatalyst exhibited good reproducibility and stability for organic dye photodegradation.

Recent progress in defect-engineered metal oxides for photocatalytic environmental remediation

Rapid industrial advancement over the last few decades has led to an alarming increase in pollution levels in the ecosystem. Among the primary pollutants, harmful organic dyes and pharmaceutical drugs are directly released by industries into the water bodies which serves as a major cause of environmental deterioration. This warns of a severe need to find some sustainable strategies to overcome these increasing levels of water pollution and eliminate the pollutants before being exposed to the environment. Photocatalysis is a well-established strategy in the field of pollutant degradation and various metal oxides have been proven to exhibit excellent physicochemical properties which makes them a potential candidate for environmental remediation. Further, with the aim of rapid industrialization of photocatalytic pollutant degradation technology, constant efforts have been made to increase the photocatalytic activity of various metal oxides. One such strategy is the introduction of defects into the lattice of the parent catalyst through doping or vacancy which plays a major role in enhancing the catalytic activity and achieving excellent degradation rates. This review provides a comprehensive analysis of defects and their role in altering the photocatalytic activity of the material. Various defect-rich metal oxides like binary oxides, perovskite oxides, and spinel oxides have been summarized for their application in pollutant degradation. Finally, a summary of existing research, followed by the existing challenges along with the potential countermeasures has been provided to pave a path for the future studies and industrialization of this promising field.

One-Step Decoration of Subnanometer MoOx Clusters on Bi11VO19 Nanotubes for Visible-Light-Driven Water Oxidation

For the sluggish reaction kinetics due to a four-electron transfer process, water oxidation is always a major obstacle to solar splitting of water to hydrogen. It remains a tough challenge to develop efficient nonnoble-metal photocatalysts for water oxidation. Herein, we decorate the host photocatalyst of Bi11VO19 nanotubes with the coatalyst of subnanometer MoOx clusters (denoted as Bi11VO19/MoOx hetero-nanotubes) via a one-step cation-exchange solvothermal reaction using Na2V6O16 nanowires as the hard template. It is observed that the morphology and microstructure of Bi11VO19/MoOx hetero-nanotubes vary with the dosage of Mo source and polyvinylpyrrolidone, as well as with the solvent composition. The optimized Bi11VO19/MoOx hetero-nanotubes significantly enhance the photooxidation of water to oxygen with visible light, delivering an oxygen production rate of 790 μmol g-1 h-1, which is 12 times that of bare Bi11VO19 nanotubes. In situ X-ray photoelectron spectroscopy and (photo)electrochemical characterization suggest that the enhanced photoactivity may be caused by the decorated cocatalyst of MoOx clusters, which extracts electrons from Bi11VO19 nanotubes, leaving an abundance of holes for water photooxidation. This work demonstrates a potential strategy to develop photocatalysts for energy conversion by constructing Bi11VO19-based nanostructures.

Recent Progress in Photocatalytic Degradation of Water Pollution by Bismuth Tungstate

Photocatalysis has emerged as a highly promising, green, and efficient technology for degrading pollutants in wastewater. Among the various photocatalysts, Bismuth tungstate (Bi2WO6) has gained significant attention in the research community due to its potential in environmental remediation and photocatalytic energy conversion. However, the limited light absorption ability and rapid recombination of photogenerated carriers hinder the further improvement of Bi2WO6's photocatalytic performance. This review aims to present recent advancements in the development of Bi2WO6-based photocatalysts. It delves into the photocatalytic mechanism of Bi2WO6 and summarizes the achieved photocatalytic characteristics by controlling its morphology, employing metal and non-metal doping, constructing semiconductor heterojunctions, and implementing defective engineering. Additionally, this review explores the practical applications of these modified Bi2WO6 photocatalysts in wastewater purification. Furthermore, this review addresses existing challenges and suggests prospects for the development of efficient Bi2WO6 photocatalysts. It is hoped that this comprehensive review will serve as a valuable reference and guide for researchers seeking to advance the field of Bi2WO6 photocatalysis.

Dual Z-scheme BiOI/Bi2S3/MgIn2S4 composite photocatalyst for effective photocatalytic degradation of Congo red

The demand and use of dyes in modern life are increasing, and dye pollution has become a widespread concern worldwide; therefore, it is essential to develop novel environmentally friendly materials to deal with dye wastewater. Herein, a novel visible-light-driven ternary catalyst (BiOI/Bi2S3/MgIn2S4) was fabricated by employing the hydrothermal method. Compared to BiOI, the synthesized ternary catalyst exhibited better photocatalytic performance to decompose Congo red under visible light. Congo red was completely degraded after 0.5 h (0.5 g/L photocatalyst BiOI/Bi2S3/MIS-1) in the presence of visible light, which was 16.83 and 9.94 times of that of pure BiOI and MgIn2S4, respectively. A repetitive experiment showed that the BiOI/Bi2S3/MIS-1 could be reusable to degrade Congo red, demonstrating that it has excellent mechanical properties. The enhanced photocatalytic capability was due to addition of BiOI and Bi2S3, which increased the charge separation as well as suppressed the recombination of photo-induced holes and electrons. Electron paramagnetic resonance technique and free radical trapping tests were employed to determine the radicals produced in BiOI/Bi2S3/MgIn2S4 in the presence of visible light, indicating that ·O2- and h+ were major active species to decompose Congo red under photocatalytic process. Seventeen main intermediates or reaction products were identified by UPLC-MS. The tentative degradation pathway of Congo red was also proposed.

Boron-doped graphene quantum dot/bismuth molybdate composite photocatalysts for efficient photocatalytic nitrogen fixation reactions

Bismuth molybdate (BMO) is a promising visible-driven photocatalyst and constructing heterojunctions in BMO-based materials is an effective way to enhance photocatalytic performance. In this study, boron-doped graphene quantum dots (BGQDs) were synthesized by one-step pyrolysis and carbonization, followed by the preparation of bismuth molybdate/boron-doped graphene quantum dots (BGQDs/BMO) heterojunction photocatalysts using in-situ growth method. The introduction of BGQDs significantly improved the photocatalytic nitrogen fixation activity under the irradiation of visible light and without scavengers. The highest NH3 yield was achieved with BGQDs/BMO-10, which was 3.48 times higher than pure phase BMO. This improvement was due to the formation of Z-scheme heterojunctions between BGQDs and BMO with the synergistic mechanism of interfacial charge transport and the generation of more protons. This study provides useful guidance for enhancing the visible-light nitrogen fixation performance of BMO materials.

Synergistic effects of rare earth doping and carbon quantum dots on BiOF/Bi2MoO6 heterojunctions for enhanced visible-near-infrared photocatalysis

Herein, we designed and synthesized a series of rare earth doped BiOF/Bi₂MoO₆ heterojunctions. The doping locations of rare earth ions were altered to determine the influence on the visible and near-infrared photocatalytic activity of heterojunctions. It is experimentally and theoretically confirmed that doping with Tm³⁺/Yb³⁺ in one semiconductor of the heterojunction produces superior photocatalytic efficiency than doping in both semiconductors. In addition, the near infrared photocatalytic efficiency strongly relied on upconversion luminescence from the Re³⁺ doped semiconductor in the heterojunction. By further modifying with CQDs, the CQDs/BiOF:Tm³⁺,Yb³⁺/Bi₂MoO₆ sample shows excellent visible and near-infrared photocatalytic performance, with 90% degradation of RhB occurring in the first 20 min under visible irradiation. This can be attributed to the large BET area, efficient photoinduced carrier separation and the upconversion process of the composite. This research will provide a systematic solution for realizing full-spectrum responsive and highly efficient photocatalysis by combination of rare earth ion doping, quantum dot modification and Z-scheme heterojunctions.

Efficient visible-light-driven S-scheme AgVO3/Ag2S heterojunction photocatalyst for boosting degradation of organic pollutants

The traditional semiconductor photocatalysts for solving the related environmental aggravation are often challenged by the recombination of photogenerated carriers. Designing an S-scheme heterojunction photocatalyst is one of the keys to tackling its practical application problems. This paper reports an S-scheme AgVO₃/Ag₂S heterojunction photocatalyst constructed via a straightforward hydrothermal approach that exhibits outstanding photocatalytic degradation performances to the organic dye Rhodamine B (RhB) and antibiotic Tetracycline hydrochloride (TC-HCl) driven by visible light. The results show that AgVO₃/Ag₂S heterojunction with a molar ratio of 6:1 (V6S) possesses the highest photocatalytic performances, 99% of RhB can be almost degraded by 0.1 g/L V6S within 25 min light illumination, and about 72% of TC-HCl can be photodegraded with the act of 0.3 g/L V6S under 120 min light irradiation. Meanwhile, the AgVO₃/Ag₂S system exhibits superior stability and maintains high photocatalytic activity after 5 repeated tests. Moreover, the EPR measurement and radical capture test identify that superoxide radicals and hydroxyl radicals mainly contribute to the photodegradation process. The present work demonstrates that constructing an S-scheme heterojunction can effectively inhibit the recombination of carriers, providing insights into the fabrication of applied photocatalysts for practical wastewater purification treatment.

One-step fabrication of Cu-doped Bi2MoO6 microflower for enhancing performance in photocatalytic nitrogen fixation

This study enhances the photocatalytic N₂ immobilization performance of Bi₂MoO₆ through Cu doping. Cu-doped Bi₂MoO₆ was synthesized via a simple solvothermal method. Various characterizations were implemented to examine the influence of Cu doping on the properties of Bi₂MoO₆. Results indicated that the doped Cu element had a valence state of + 2 and substituted the position of Bi³⁺. Cu doping exerted minimal effect on the morphology of Bi₂MoO₆ but largely influenced the energy band structure. The band gap was slightly narrowed, and the conduction band was raised, such that Cu-doped Bi₂MoO₆ could generate more electrons with stronger reducibility. Moreover, importantly, Cu doping reduced work function and improved charge separation efficiency, which was considered the major cause of enhanced photoactivity. In addition, the Cu-Bi₂MoO₆ catalyst exhibited higher capability in the adsorption and activation of N₂. Under the combined effects of the aforementioned changes, Cu-Bi₂MoO₆ demonstrated considerably higher photocatalytic efficiency than Bi₂MoO₆. The optimized NH₃ generation rate reached 302 μmol/L g^-1h^-1 and 157 μmol/L g^-1h^-1 under simulated solar light and visible light, respectively, both achieving about 2.2 times higher than that of Bi₂MoO₆. This work provides a successful example of improving photocatalytic N₂ fixation, and it may show some light on the design and preparation of heteroatom-doped semiconductor photocatalysts for N₂-to-NH₃ conversion.

Effective Nanocomposite Based on Bi2MoO6/MoS2/AuNRs for NIR-II Light-Boosted Photodynamic/Chemodynamic Therapy

Bi₂MoO₆ (BMO) nanoparticles (NPs) have been widely used as a photocatalyst to decompose organic pollutants, but their potential for photodynamic therapy (PDT) is yet to be explored. Normally, the UV absorption property of BMO NPs is not suitable for clinical application because the penetration depth of the UV light is too small. To overcome this limitation, we rationally designed a novel nanocomposite based on Bi₂MoO₆/MoS₂/AuNRs (BMO-MSA), which simultaneously possesses both the high photodynamic ability and POD-like activity under NIR-II light irradiation. Additionally, it has excellent photothermal stability with good photothermal conversion efficiency. The as-prepared BMO-MSA nanocomposite could induce the germline apoptosis of Caenorhabditis elegans (C. elegans) via the cep-1/p53 pathway after being illuminated by light with a wavelength of 1064 nm. The in vivo investigations confirmed the ability of the BMO-MSA nanocomposite for the induction of DNA damage in the worms, and the mechanism was approved by determining the egl-1 fold induction in the mutants that have a loss of function in the genes involved in DNA damage response mutants. Thus, this work has not only provided a novel PDT agent, which may be used for PDT in the NIR-II region, but also introduced a new approach to therapy, taking advantage of both PDT and CDT effects.

TiO2@COF Nanowire Arrays: A "Filter Amplifier" Heterojunction Strategy to Reverse the Redox Nature

Surface modification is a promising method to change the surface properties of nanomaterials, but it is limited in enhancing their intrinsic redox nature. In this work, a "filter amplifier" strategy is proposed for the first time to reverse the intrinsic redox nature of materials. This is demonstrated by coating a COF-316 layer with controlled thickness on TiO₂ to form core-sheath nanowire arrays. This unique structure forms a Z-scheme heterojunction to function as "a filter amplifier" which can conceal the intrinsic oxidative sites and increase the extrinsic reductive sites. Consequently, the selective response of TiO₂ is dramatically reversed from reductive ethanol and methanol to oxidative NO₂. Moreover, TiO₂@COF-316 provides remarkably improved sensitivity, response, and recovery speed, as well as unusual anti-humidity properties as compared with TiO₂. This work not only provides a new strategy to rationally modulate the surface chemistry properties of nanomaterials but also opens an avenue to design high-performance electronic devices with a Z-scheme heterojunction.

Improved Performance of g-C3N4 for Optoelectronic Detection of NO2 Gas by Coupling Metal-Organic Framework Nanosheets with Coordinatively Unsaturated Ni(II) Sites

Sensitive and selective optoelectronic detection of NO₂ with g-C₃N₄ (CN) is critical, but it remains challenging to achieve ultralow concentration (ppb-level) detection. Herein, Ni metal-organic frameworks/CN nanosheet heterojunctions were successfully fabricated by the electrostatic induced assembly strategy and then treated by a post-alkali etching process for creating coordinatively unsaturated Ni(II) sites. The optimized heterojunction exhibits a record detection limitation of 1 ppb for NO₂, well below that observed on pristine CN, and an outstanding selectivity over other gases, along with long-time stability (120 days) at room temperature. The resulting superior detection performance benefits from the enhanced charge transfer and separation of the closely contacted heterojunction interface and the favorable adsorption of NO₂ by unsaturated Ni(II) as selective adsorption sites mainly by means of the time-resolved photoluminescence spectra and in situ X-ray photoelectron spectra. Moreover, the in situ Fourier transform infrared spectra and temperature-programmed desorption disclose that the promotion adsorption of NO₂ depends on the strengthened interaction between NO₂ and Ni(II) node sites at the aid of OH groups from unsaturated coordination. This work offers a versatile solution to develop promising CN-based optoelectronic sensors at room temperature.

Nb, Se-codoped ZnIn2S4/NbSe2composites with enhanced catalytic activity and photodegradation performance towards tetracycline

Low quantum efficiency and serious photogenerated carrier recombination have been urgent bottleneck problems for photocatalytic materials. Herein, we prepared Nb, Se-codoped ZnIn₂S₄/NbSe₂composites through a facile solvothermal method. The synergetic effect of codoping and cocatalyst was investigated on the photodegradation performance towards tetracycline under visible-light irradiation. By adjusting the final composition, the comprehensive characterization revealed that the optimum degradation efficiency of NS/ZIS-1.6 catalyst arrived at 75% in 70 min, which was 5.8 times higher than that of pure ZnIn₂S₄. Deep analysis indicated that the enhanced photocatalytic performance could be attributed to higher light absorption, more efficient electron/hole separation, faster charge transport, and lower carrier recombination. This work may offer novel viewpoint for design of high-performance catalysts towards the visible-light-driven photodegradation system.

Construction of activated biochar/Bi2WO6 and /Bi2MoO6 composites to enhance adsorption and photocatalysis performance for efficient application in the removal of pollutants and disinfection

To synergistically enhance the adsorption and photocatalytic performance of Bi2WO6 and Bi2MoO6, using activated biochar (ACB) as substrate, ACB-Bi2WO6 and ACB-Bi2MoO6 composites were facilely prepared by hydrothermal synthesis. Their adsorption-photocatalytic degradation effects on rhodamine B (RhB), tetracycline (TC), and norfloxacin (NOR) were comparatively investigated. Additionally, the effects of environmental factors, wastewater treatment tests, and disinfection were systematically studied, and the enhancement mechanisms and reasons for the degradation differences were highlighted. The results showed that ACB-Bi2WO6 and ACB-Bi2MoO6 were confirmed to form intimately contacted heterojunctions by various advanced characterization techniques. The introduction of ACB narrowed the band-gap energy of Bi2WO6 and Bi2MoO6, and improved the visible light absorption range and specific surface area. The optimal loading ratios of ACB-Bi2WO6 and ACB-Bi2MoO6 were 1:1.06 and 1:0.58, respectively. The removal rate of ACB-Bi2WO6 for high concentrations of RhB (200 mg·L-1), TC and NOR (50 mg·L-1) were 89.15%, 87.27%, and 72.17%, respectively, which were higher than those of ACB-Bi2MoO6 and significantly stronger than those of Bi2WO6 and Bi2MoO6. This was attributed to the more effective inhibition of photogenerated carrier recombination, higher absorbance, and uniform morphology via ACB-Bi2WO6. ·OH and holes were dominant active species in photocatalysis, and the possible photogenerated carrier transfer path is type II heterojunction. Furthermore, ACB-Bi2WO6 possessed good reusability, and the removal of RhB and TC from the actual wastewater exceeded 80.63% and 58.54%, respectively. The sterilization rates of ACB-Bi2WO6 reached 99% and 95% for E. coli and S. aureus within 24 h, respectively. Therefore, ACB-Bi2WO6 was more recommended for environmental applications.

Bismuth-Based Multi-Component Heterostructured Nanocatalysts for Hydrogen Generation

Developing a unique catalytic system with enhanced activity is the topmost priority in the science of H2 energy to reduce costs in large-scale applications, such as automobiles and domestic sectors. Researchers are striving to design an effective catalytic system capable of significantly accelerating H2 production efficiency through green pathways, such as photochemical, electrochemical, and photoelectrochemical routes. Bi-based nanocatalysts are relatively cost-effective and environmentally benign materials which possess advanced optoelectronic properties. However, these nanocatalysts suffer back recombination reactions during photochemical and photoelectrochemical operations which impede their catalytic efficiency. However, heterojunction formation allows the separation of electron–hole pairs to avoid recombination via interfacial charge transfer. Thus, synergetic effects between the Bi-based heterostructured nanocatalysts largely improves the course of H2 generation. Here, we propose the systematic review of Bi-based heterostructured nanocatalysts, highlighting an in-depth discussion of various exceptional heterostructures, such as TiO2/BiWO6, BiWO6/Bi2S3, Bi2WO6/BiVO4, Bi2O3/Bi2WO6, ZnIn2S4/BiVO4, Bi2O3/Bi2MoO6, etc. The reviewed heterostructures exhibit excellent H2 evolution efficiency, ascribed to their higher stability, more exposed active sites, controlled morphology, and remarkable band-gap tunability. We adopted a slightly different approach for reviewing Bi-based heterostructures, compiling them according to their applicability in H2 energy and discussing challenges, prospects, and guidance to develop better and more efficient nanocatalytic systems.

Constructing 3D magnetic flower-like Fe3O4@SiO2@Co3O4@BiOCl heterojunction photocatalyst for degrading rhodamine B

In this work, the 3D magnetic flower-like Fe₃O₄@SiO₂@Co₃O₄@BiOCl heterojunction photocatalyst was successfully prepared. The combination of BiOCl with Co₃O₄ favored to increase specific surface area and separate photo-generated carriers of the resulting composite, resulting in the improvement of catalytic efficiency. The photocatalytic activities of Fe₃O₄@SiO₂@Co₃O₄@BiOCl were researched in details. In 50 min of visible light, the degradation efficiency for rhodamine B (RhB) of Fe₃O₄@SiO₂@Co₃O₄@BiOCl was 98.41%. It still maintained 94.22% even after three tests. Furthermore, the photodegradation mechanisms were also investigated, indicating that the improved efficiency was ascribed to the superior separation of photo-induced electron-hole pairs. This study supplies a new perception to fabricate photocatalysts for actual uses.

Recent trends in Bi-based nanomaterials: challenges, fabrication, enhancement techniques, and environmental applications

One of the most enticing approaches to environmental restoration and energy conversion is photocatalysis powered by solar light. Traditional photocatalysts have limited practical uses due to inadequate light absorption, charge separation, and unknown reaction mechanisms. Discovering new visible-light photocatalysts and investigating their modification is crucial in photocatalysis. Bi-based photocatalytic nanomaterials have gotten much interest as they exhibit distinctive geometric shapes, flexible electronic structures, and good photocatalytic performance under visible light. They can be employed as stand-alone photocatalysts for pollution control and energy production, but they do not have optimum efficacy. As a result, their photocatalytic effectiveness has been significantly improved in the recent decades. Numerous newly created concepts and methodologies have brought significant progress in defining the fundamental features of photocatalysts, upgrading the photocatalytic ability, and understanding essential reactions of the photocatalytic process. This paper provides insights into the characteristics of Bi-based photocatalysts, making them a promising future nanomaterial for environmental remediation. The current review discusses the fabrication techniques and enhancement in Bi-based semiconductor photocatalysts. Various environmental applications, such as H₂ generation and elimination of water pollutants, are also discussed in terms of semiconductor photocatalysis. Future developments will be guided by the uses, issues, and possibilities of Bi-based photocatalysts.

Rapid fabrication of MgO@g-C3N4 heterojunctions for photocatalytic nitric oxide removal

Nitric oxide (NO) is an air pollutant impacting the environment, human health, and other biotas. Among the technologies to treat NO pollution, photocatalytic oxidation under visible light is considered an effective means. This study describes photocatalytic oxidation to degrade NO under visible light with the support of a photocatalyst. MgO@g-C₃N₄ heterojunction photocatalysts were synthesized by one-step pyrolysis of MgO and urea at 550 °C for two hours. The photocatalytic NO removal efficiency of the MgO@g-C₃N₄ heterojunctions was significantly improved and reached a maximum value of 75.4% under visible light irradiation. Differential reflectance spectroscopy (DRS) was used to determine the optical properties and bandgap energies of the material. The bandgap of the material decreases with increasing amounts of MgO. The photoluminescence spectra indicate that the recombination of electron-hole pairs is hindered by doping MgO onto g-C₃N₄. Also, NO conversion, DeNOx index, apparent quantum efficiency, trapping tests, and electron spin resonance measurements were carried out to understand the photocatalytic mechanism of the materials. The high reusability of the MgO@g-C₃N₄ heterojunction was shown by a five-cycle recycling test. This study provides a simple way to synthesize photocatalytic heterojunction materials with high reusability and the potential of heterojunction photocatalysts in the field of environmental remediation.

Ferroelectric-assisted charge carrier separation over Bi2MoO6 nanosheets for photocatalytic dye degradation

Low energy conversion efficiency from the absorbed photon to the catalytic species remains a major obstacle for the real application of photocatalysis. In recent years, the introduction of a built-in electric field has proved to be impactful in facilitating the photoinduced charge separation, among which, ferroelectric polarization is highly recommended by getting rid of mechanical stresses. Developing ferroelectrics directly as photoactive semiconductors is promising in view of the synergistic catalytic enhancement. Therefore, Bi₂MoO₆ nanosheets with ultrathin layered structure (<10 nm) and abundant oxygen vacancies were synthesized through the hydrothermal method. The two-dimensional nanostructure created more active sites and a convenient polarization condition. Subsequently, corona poling was applied on the Bi₂MoO₆ nanosheets, which can significantly accelerate the 100% degradation rate of RhB from 50 to 20 min, surpassing that of metal-free photocatalysts. The combined effect of semiconductor, ferroelectric polarization, oxygen vacancies, and nano-layered structure offers new strategies for designing multifield coupling catalysts, providing insights into the regulation of charge carrier dynamics.

Efficient Oxygen Vacancy Defect Engineering for Enhancing Visible-Light Photocatalytic Performance over SnO2-x Ultrafine Nanocrystals

Regardless of its good electron-transfer ability and chemical stability, pure Zn₂SnO₄ (ZSO) still has intrinsic deficiencies of a narrow spectral response region, poor absorption ability, and high photo-activated carrier recombination rate. Aiming to overcome the deficiencies above-mentioned, we designed a facile hydrothermal route for etching ZSO nanoparticles in a dilute acetic acid solution, through which efficient oxygen vacancy defect engineering was accomplished and SnO_2-x nanocrystals were obtained with an ultrafine particle size. In comparison with the untreated ZSO nanoparticles, the specific surface area of SnO_2-x nanocrystals was substantially enlarged, subsequently leading to the notable augmentation of active sites for the photo-degradation reaction. Aside from the above, it is worth noting that SnO_2-x nanocrystals were endowed with a broad spectral response, enhancing light absorption capacity and the photo-activated carrier transfer rate with the aid of oxygen vacancy defect engineering. Accordingly, SnO_2-x nanocrystals exhibited significantly enhanced photoactivity toward the degradation of the organic dye rhodamine B (RhB), which could be imputed to the synergistic effect of increasing active sites, intensified visible-light harvesting, and the separation rate of the photo-activated charge carrier caused by the oxygen vacancy defect engineering. In addition, these findings will inspire us to open up a novel pathway to design and prepare oxide compound photocatalysts modified by oxygen vacancy defects in pursuing excellent visible-light photoactivity.

Fast Cross-Linked Hydrogel as a Green Light-Activated Photocatalyst for Localized Biofilm Disruption and Brush-Free Tooth Whitening

Biofilm-driven caries and tooth discoloration are two major problems in oral health care. The current methods have the disadvantages of insufficient biofilm targeting and irreversible enamel damage. Herein, an injectable sodium alginate hydrogel membrane doped with bismuth oxychloride (Bi₁₂O₁₇Cl₂) and cubic cuprous oxide (Cu₂O) nanoparticles was designed to simultaneously achieve local tooth whitening and biofilm removal through a photodynamic dental therapy process. This fast cross-linked hydrogel could form a biofilm removal coating on the target tooth surface precisely. Afterward, reactive oxygen species was effectively released on demand under green light, which could not only eradicate the biofilm but also whiten the tooth non-destructively in a facile manner without significant damage to both the enamel and biological cells. After the usage, the removal of this hydrogel can also enhance the effect of biofilm destruction and caries prevention.

Efficient Prevention of Aspergillus flavus Spores Spread in Air Using Plasmonic Ag-AgCl/α-Fe2O3 under Visible Light Irradiation

Aspergillus flavus is a kind of widespread fungi that can produce carcinogenic, teratogenic, and mutagenic secondary metabolites known as aflatoxins. Aspergillus flavus mainly spread through the means of fungal spores in air, thus preventing the spores spread is an effective strategy to control aflatoxins contamination from source. Herein, a rapid and efficient control way to prevent the spread of Aspergillus flavus spores in air was demonstrated. Ag-AgCl nanoparticles were combined with tetrahedral α-Fe₂O₃ to form plasmonic composites that presented 93.65 ± 1.53% prevention rate of Aspergillus flavus spores under 50 min visible light irradiation. The efficient activity was attributed to the synergy effect of Ag including intrinsic disinfection, electron sink, and localized surface plasmon resonance effect, which were proven by photoelectric characterization, density functional theory, and finite difference time domain methods. The calculated work functions of α-Fe₂O₃, Ag, and AgCl were 3.71, 4.52, and 5.38 eV, respectively, which could accelerate photoinduced carrier transfer through Ag during photoreaction. Moreover, it was found that the intrinsic disinfection of Ag and hydroxyl radical from photocatalytic reaction were the main factors to the prevention of Aspergillus flavus spores, which resulted in the destruction of spore structure and the leakage of intracellular protein with 62.15 ± 2.63 μg mL^-1. Most important, it was proven that the composites also showed high activity (90.52 ± 1.26%) to prevent Aspergillus flavus spore spread in the storage process of peanuts. These findings not only provided useful information for an efficient and potential strategy to prevent Aspergillus flavus contamination but also could be as a reference in toxic fungi control.

Tin bisulfide nanoplates anchored onto flower-like bismuth tungstate nanosheets for enhancement in the photocatalytic degradation of organic pollutant

The development of efficient heterojunctions through a simple and facile method is an effective way to enhance the photocatalytic performance of bismuth-based oxide semiconductors for industrial applications. Here, the novel flower-like type II SnS₂/Bi₂WO₆ heterostructure consisting of bismuth tungstate (Bi₂WO₆) nanosheets and tin bisulfide (SnS₂) nanoplates was successfully designed and synthesized. The crystal structure, composition, morphology, and photoelectric properties of the heterostructure were systematically characterized. In addition, the photocatalytic activity of SnS₂/Bi₂WO₆ was analyzed and compared with Bi₂WO₆ or SnS₂ alone or physical mixture of SnS₂ and Bi₂WO₆. 2%SnS₂/Bi₂WO₆ presents a 3.1 times greater degradation rate constant (0.0065 min^-1) than that of Bi₂WO₆ (0.0021 min^-1) under low visible light irradiation (5.3 mW·cm^-2, a 44 W LED), while SnS₂ alone exhibits no photocatalytic effect toward glyphosate. Furthermore, 2%SnS₂/Bi₂WO₆ maintains 93% of its original photocatalytic activity even after four cycles. The possible photocatalytic degradation pathway of glyphosate and photocatalytic mechanism are also proposed. The excellent photocatalytic performance of SnS₂/Bi₂WO₆ is attributed to the decoration of SnS₂ nanoplates on the surface of Bi₂WO₆, appropriate (113)/(020) ratio, increased visible-light absorption, and effective separation of photoinduced carriers. This paper reports a new methodology that can act as a reference basis to design and develop visible-light responsive photocatalysts with outstanding photocatalytic performance for carbon dioxide reduction, water splitting, and pollutant degradation.

Activating oxygen deficient TiO2 in the visible region by Bi2MoO6 for CO2 photoreduction to methanol

Fast photogenerated charge recombination and inappropriate bandgap for visible light driven charge generation hinders the performance of TiO₂. In this study, TiO₂ was activated for visible light driven CO₂ reduction in the presence of Bi₂MoO₆ as an electron donor. Furthermore, the introduction of oxygen vacancies resulted in enhanced CO₂ adsorption and conversion. The best catalyst gives 27.1 μmol g^-1 h^-1 methanol formation. DRIFTS was used to explain the methanol formation mechanism on oxygen deficient TiO₂.

Graphene-based photocatalytic nanocomposites used to treat pharmaceutical and personal care product wastewater: A review

Photocatalytic technology has been widely studied by researchers in the field of environmental purification. This technology can not only completely convert organic pollutants into small molecules of CO₂ and H₂O through redox reactions but also remove metal ions and other inorganic substances from water. This article reviews the research progress of graphene-based photocatalytic nanocomposites in the treatment of wastewater. First, we elucidate the basic principles of photocatalysis, the types of graphene-based nanocomposites, and the role of graphene in photocatalysis (e.g., graphene can accelerate the separation of photon-hole pairs and increase the intensity and range of light absorption). Second, the preparation, characterization, and application of composites in wastewater are introduced. We also discuss the kinetic model of the photocatalytic degradation of pollutants. Finally, the enhancement mechanism of graphene in terms of photocatalysis is not completely clear, and graphene-based photocatalysts with high catalytic efficiency, low cost, and large-scale production have not yet appeared, so there is an urgent need for more extensive and in-depth research.

Oxygen Vacancy-Mediated Growth of Amorphous Discharge Products toward an Ultrawide Band Light-Assisted Li-O2 Batteries

Photoassisted electrochemical reaction is regarded as an effective approach to reduce the overpotential of lithium-oxygen (Li-O₂ ) batteries. However, the achievement of both broadband absorption and long term battery cycling stability are still a formidable challenge. Herein, an oxygen vacancy-mediated fast kinetics for a photoassisted Li-O₂ system is developed with a silver/bismuth molybdate (Ag/Bi₂ MoO₆ ) hybrid cathode. The cathode can offer both double advantages for light absorption covering UV to visible region and excellent electrochemical activity for O₂ . Upon discharging, the photoexcited electrons from Ag nanoplate based on the localized surface plasmon resonance (LSPR) are injected into the oxygen vacancy in Bi₂ MoO₆ . The fast oxygen reaction kinetics generate the amorphous Li₂ O₂ , and the discharge plateau is improved to 3.05 V. Upon charging, the photoexcited holes are capable to decompose amorphous Li₂ O₂ promptly, yielding a very low charge plateau of 3.25 V. A first cycle round-trip efficiency is 93.8% and retention of 70% over 500 h, which is the longest cycle life ever reported in photoassisted Li-O₂ batteries. This work offers a general and reliable strategy for boosting the electrochemical kinetics by tailoring the crystalline of Li₂ O₂ with wide-band light.

Designing and fabricating a CdS QDs/Bi2MoO6 monolayer S-scheme heterojunction for highly efficient photocatalytic C2H4 degradation under visible light

Achieving efficient photocatalytic degradation of atmospheric volatile organic compounds (VOCs) under sun-light is still a significant challenge for environmental protection. The S-scheme heterojunction with its unique charge migration route, high charge separation rate and strong redox ability, has great potential. However, how to regulate interfacial charge transfer of the S-scheme heterojunction is of significant importance. Here, density functional theory (DFT) calculations were first conducted and predicted that an S-scheme heterojunction could be formed in the CdS quantum dots/Bi₂MoO₆ monolayer system. Subsequently, this novel heterojunction is constructed by in-situ hydrothermal synthesis of CdS quantum dots on monolayer Bi₂MoO₆. Under visible-light, this novel S-scheme system gives a high-efficiency photocatalytic degradation rate (6.04 × 10^-2 min^-1) towards C₂H₄, which is 30.3 times higher than that of pure CdS (1.99 × 10^-3 min^-1) and 41.7 times higher than pure Bi₂MoO₆ (1.45 × 10^-3 min^-1). Strong evidence for the S-scheme charge transfer path is provided by in-situ XPS, PL, TRPL and EPR.

Fabrication of Bi2MoO6 Nanosheets/TiO2 Nanorod Arrays Heterostructures for Enhanced Photocatalytic Performance under Visible-Light Irradiation

Bi₂MoO₆/TiO₂ heterostructures (HSs) were synthesized in the present study by growing Bi₂MoO₆ nanosheets on vertically aligned TiO₂ nanorod arrays using a two-step solvothermal method. Their morphology and structure were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Excellent visible-light absorption was observed by UV–Vis absorption spectroscopy, which was attributed to the presence of the Bi₂MoO₆ nanosheets with a narrow-band-gap. The specific surface area and pore volume of the photocatalysts were significantly increased due to the hierarchical structure composed of Bi₂MoO₆ nanosheets and TiO₂ nanorods. The photoluminescence and photoelectrochemical characterizations showed improved separation and collection efficiency of the Bi₂MoO₆/TiO₂ HSs towards the interface charge carrier. The photocatalytic analysis of the Bi₂MoO₆/TiO₂ HSs demonstrated a significantly better methylene blue (MB) degradation efficiency of 95% within 3 h than pristine TiO₂ nanorod arrays under visible-light irradiation. After three photocatalytic cycles, the degradation rate remained at ~90%. The improved performance of the Bi₂MoO₆/TiO₂ HSs was attributed to the synergy among the extended absorption of visible light; the large, specific surface area of the hierarchical structure; and the enhanced separation efficiency of the photogenerated electron-hole pairs. Finally, we also established the Bi₂MoO₆/TiO₂ HSs band structure and described the photocatalytic dye degradation mechanism. The related electrochemical analysis and free-radical trapping experiments indicated that h⁺, ·O₂⁻ and ·OH have significant effects on the degradation process.

Bi2S3-decorated three-dimensional BiOCl as a Z-scheme heterojunction with highly exposed {001} facets of BiOCl for enhanced visible-light photocatalytic performance

In BOC-BS-x, the highly exposed {001} facets of BiOCl have more oxygen vacancies, which can facilitate the migration of carriers.

A review on hierarchical Bi2MoO6 nanostructures for photocatalysis applications

This overview provides comprehensive understanding and development trends of hierarchical Bi2MoO6 nanostructures as photocatalysts for efficient photocatalysis applications.

Nanosheets loaded on tetrahedral surfaces form a Z-type Bi2MoO6/γ-Bi2O3 heterojunction to enhance the photocatalytic degradation activity of lomefloxacin and Rhodamine B

Nanosheets loading on tetrahedral surfaces of a Bi2MoO6/γ-Bi2O3 heterojunction forming a Z-type energy band to enhance the photocatalytic degradation activity.

Developing sustainable, high-performance perovskites in photocatalysis: design strategies and applications

Solar energy is attractive because it is free, renewable, abundant and sustainable. Photocatalysis is one of the feasible routes to utilize solar energy for the degradation of pollutants and the production of fuel. Perovskites and their derivatives have received substantial attention in both photocatalytic wastewater treatment and energy production because of their highly tailorable structural and physicochemical properties. This review illustrates the basic principles of photocatalytic reactions and the application of these principles to the design of robust and sustainable perovskite photocatalysts. It details the structures of the perovskites and the physics and chemistry behind photocatalytic reactions and describes the advantages and limitations of popular strategies for the design of photoactive perovskites. This is followed by examples of how these strategies are applied to enhance the photocatalytic efficiency of oxide, halide and oxyhalide perovskites, with a focus on materials with potential for practical application, that is, not containing scarce or toxic elements. It is expected that this overview of the development of photocatalysts and deeper understanding of photocatalytic principles will accelerate the exploitation of efficient perovskite photocatalysts and bring about effective solutions to the energy and environmental crisis.

2D Piezoelectric Bi2 MoO6 Nanoribbons for GSH-Enhanced Sonodynamic Therapy

Reducing the scavenging capacity of reactive oxygen species (ROS) and elevating ROS production are two primary goals of developing novel sonosensitizers for sonodynamic therapy (SDT). Hence, ultrathin 2D Bi₂ MoO₆ -poly(ethylene glycol) nanoribbons (BMO NRs) are designed as piezoelectric sonosensitizers for glutathione (GSH)-enhanced SDT. In cancer cells, BMO NRs can consume endogenous GSH to disrupt redox homeostasis, and the GSH-activated BMO NRs (GBMO) exhibit an oxygen-deficient structure, which can promote the separation of electron-hole pairs, thereby enhancing the efficiency of ROS production in SDT. The ultrathin GBMO NRs are piezoelectric, in which ultrasonic waves introduce mechanical strain to the nanoribbons, resulting in piezoelectric polarization and band tilting, thus accelerating toxic ROS production. The as-synthesized BMO NRs enable excellent computed tomography imaging of tumors and significant tumor suppression in vitro and in vivo. A piezoelectric Bi₂ MoO₆ sonosensitizer-mediated two-step enhancement SDT process, which is activated by endogenous GSH and amplified by exogenous ultrasound, is proposed. This process not only provides new options for improving SDT but also broadens the application of 2D piezoelectric materials as sonosensitizers in SDT.

Symmetry and the Role of the Anion Sublattice in Aurivillius Oxyfluoride Bi2TiO4F2

The photocatalytic and dielectric behaviors of Aurivillius oxyfluorides such as Bi₂TiO₄F₂ depend sensitively on their crystal structure and symmetry but these are not fully understood. Our experimental work combined with symmetry analysis demonstrates the factors that influence anion order and how this might be tuned to break inversion symmetry. We explore an experimental approach to explore anion order, which combines Rietveld analysis with strain analysis.

Aurivillius oxyfluoride Bi₂TiO₄F₂ shows a promising photocatalytic behavior, which has been related to its polar structure, but polar properties have been difficult to reproduce in bulk samples. We explore a possible anion order and how this could give polar structures when combined with other distortions. We highlight the influence of strain on anion order and therefore the properties in these systems.

Rationally designed f-MWCNT-coated bismuth molybdate (f-MWCNT@BMO) nanocomposites for the voltammetric detection of biomolecule dopamine in biological samples

Selective and sensitive dopamine (DPA) sensor was developed using hydrothermally prepared functionalized multi-walled carbon nanotube-coated bismuth molybdate (f-MWCNT@BMO). The f-MWCNT@BMO-reinforced electrode exhibited an outstanding electrocatalytic activity towards DPA oxidation. The nanocomposite-reinforced electrode displayed a rapid response towards DPA sensing and possessed the minimized potential of (E_pa + 0.285 V vs Ag/AgCl) in 0.1 M phosphate buffer (PB). The electrochemical results of prepared sensors were analyzed using the differential pulse voltammetry method (DPV). As a result, the f-MWCNT@BMO-reinforced electrode exhibited a widelinear range of 10 nM - 814 μM with a very low detection limit of 3.4 nM towards DPA oxidation. The developed sensor shows excellent selectivity in presence of similar functional group biomolecules. The detection of DPA in real samples was evaluated in human serum, as the results of the proposed sensor possessed good recoveries.

Synergism of carbon quantum dots and Au nanoparticles with Bi2MoO6 for activity enhanced photocatalytic oxidative degradation of phenol

Localized surface plasmon resonance (LSPR) offers an opportunity to enhance the efficiency of photocatalysis. However, the photocatalysts's plasmonic enhancement is still limited, as most metals/semiconductors depend on LSPR contribution of isolated metal nanoparticles. In the present work, carbon quantum dots (CQDs) and Au nanoparticles (NPs) were simultaneously assembled on the surface of a three-dimensional (3D) spherical Bi₂MoO₆ (BMO) nanostructure with surface oxygen vacancies (SOVs). The collective excitation of CQDs and Au NPs demonstrated an effective strategy to improve the utilization of up-conversion emission and plasmonic energy. The contribution of CQDs and Au NPs assembled on the surface of BMO (7 wt% CQDs/Au/BMO) realized a photocatalytic phenol degradation enhancement (apparent rate constants, k _app/min^-1) of 56.5, 9.5 and 3.9, and 2.2-fold increase compared to BMO, BMO-SOVs, Au/BMO and CQDs/BMO, respectively. The as-fabricated 7 wt% CQDs/Au/BMO exhibited the highest mineralization rate for phenol degradation with 72.4% TOC removal rate in 120 min. The excellent photocatalytic performance of CQDs/Au/BMO was attributed to the synergistic effect of CQDs, Au NPs and SOVs. The CQD up-conversion emission synergetically boosts Au NPs' LSPR significantly promoting the separation and migration of photogenerated electron (e^-)/hole (h⁺) pairs, which could improve the oxygen molecule activation process and thereby their ability to generate reactive oxygen species (ROS). The present work is a step forward to understand and construct similar photocatalysts using an entirely reasonable hypothesis of activity enhancement mechanism according to the active species capture experiments and band structure analysis.

Achieving High-Quality Freshwater from a Self-Sustainable Integrated Solar Redox-Flow Desalination Device

Solar-assisted electrochemical desalination has offered a new energy-water nexus technology for sustainable development in recent studies. However, only a few reports have demonstrated insufficient photocurrent, a low salt removal rate, and poor stability. In this study, a high-quality freshwater level of 5-10 ppm (from an initial feed of 10 000 ppm), an enhanced salt removal rate (217.8 µg cm^-2 min^-1 of NaCl), and improved cycling and long-term stability are achieved by integrating dye-sensitized solar cells (DSSCs) and redox-flow desalination (RFD) under light irradiation without additional electrical energy consumption. The DSSC redox electrolyte (I^- /I₃^- ) is circulated between the photoanode (N719/TiO₂ ) and intermediate electrode (graphite paper). Two DSSCs in parallel or series connections are directly coupled to the RFD device. Overall, this hybrid system can be used to boost photo electrochemical desalination technology. The energy-water nexus technology will open a new route for dual-role devices with photodesalination functions without energy consumption and solar-to-electricity generation.

Modulating oxygen vacancies on bismuth-molybdate hierarchical hollow microspheres for photocatalytic selective alcohol oxidation with hydrogen peroxide production

Photocatalytic selective oxidation of alcohols into high value-added carbonyl compounds accompanied by producing hydrogen peroxide (H₂O₂) is undoubtedly a more efficient solar energy conversion strategy with high atom economy. Herein, we have developed an efficient photocatalyst of bismuth-molybdate (Bi₂MoO₆) hierarchical hollow microspheres with tunable surface oxygen vacancies (OVs) for promoting the photocatalytic selective alcohol oxidation with H₂O₂ production. The effect of surface OVs on the photocatalytic efficiency is studied systematically by comparing the performance of different photocatalysts. The benzaldehyde and H₂O₂ production rates over the OV-rich Bi₂MoO₆ photocatalyst reach up to 1310 and 67.2 μmol g^-1 h^-1, respectively, which are 2.3 and 4.0 times those generated from the OV-poor Bi₂MoO₆ hollow microspheres. The roles of various active radicals in the photocatalytic reaction are probed by a series of controlled experiments and in situ ESR measurements, revealing that both superoxide radical (•O₂^-) and carbon-centered radical are the key active intermediates. The introduction of surface OVs on Bi₂MoO₆ hollow microspheres accelerates the separation and transfer of photo-generated charge carriers as well as enhances the adsorption and activation of reactant molecules, thereby greatly promoting the photocatalytic selective oxidation of alcohols along with H₂O₂ production. This work not only demonstrates a facile strategy for the preparation of high-efficiency photocatalysts by simultaneous modulations of morphology and surface defects, but also offers insight into developing the dual-functional photocatalytic reactions for the full utilizations of photoinduced electrons and holes.

The origins of charge separation in anisotropic facet photocatalysts investigated through first-principles calculations

It was recently discovered that the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) can be completed on the {110} and {001} facets, respectively, of a 18-facet SrTiO₃ mono-crystal. The effective charge separation is attributed to the facet junction at the interface between two arbitrary anisotropic crystal planes. Theoretical estimation of the built-in potential at the facet junction can greatly improve understanding of the mechanism. This work employs density functional theory (DFT) calculations to investigate such potential at the (110)/(100) facet junction in SrTiO₃ crystals. The formation of the facet junction is verified by a calculated work function difference between the (110) and (100) planes, which form p-type and n-type segments of the junction, respectively. The built-in potential is estimated at about 2.9 V. As a result, with the ultra high built-in potential, electrons and holes can effectively transfer to different anisotropic planes to complete both photo-oxidative and photo-reductive reactions.