Boosted Activity for Toluene Selective Photooxidation over Fe-Doped Bi2WO6

Magnetic recyclable visible light-driven Bi2WO6/Fe3O4/RGO for photocatalytic degradation of Microcystin-LR: Mechanism, pathway, and influencing factors

Photocatalysis was an attractive strategy that had potential to tackle the Microcystin-LR (MC-LR) contamination of aquatic ecosystems. Herein, magnetic photocatalyst Fe3O4/Bi2WO6/Reduced graphene oxide composites (Bi2WO6/Fe3O4/RGO) were employed to degrade MC-LR. The removal efficiency and kinetic constant of the optimized Bi2WO6/Fe3O4/RGO (Bi2WO6/Fe3O4-40%/RGO) was 1.8 and 2.3 times stronger than the pure Bi2WO6. The improved activity of Bi2WO6/Fe3O4-40%/RGO was corresponded to the expanded visible light adsorption ability and reduction of photogenerated carrier recombination efficiency through the integration of Bi2WO6 and Fe3O4-40%/RGO. The MC-LR removal efficiency exhibited a positive tendency to the initial density of algae cells, fulvic acid, and the concentration of MC-LR decreased. The existed anions (Cl-, CO3-2, NO3-, H2PO4-) reduced MC-LR removal efficiency of Bi2WO6/Fe3O4-40%/RGO. The Bi2WO6/Fe3O4-40%/RGO could degrade 79.3% of MC-LR at pH = 7 after 180 min reaction process. The trapping experiments and ESR tests confirmed that the h+, ∙OH, and ∙O2- played a significant role in MC-LR degradation. The LC-MS/MS result revealed the intermediates and possible degradation pathways.

Toluene Oxidation: CO2 vs Benzaldehyde: Current Status and Future Perspectives

Toluene is a common and significant volatile organic compound (VOC). Although it finds extensive application in various industrial processes (chemical manufacturing, paint and adhesive production, and as a solvent), it creates a huge environmental impact when emitted freely into the atmosphere. Two solutions were found to mitigate the emission of this pollutant: the total oxidation to CO2 and H2O and the selective oxidation into benzaldehyde. This review discusses the two main alternatives for tackling this problem: converting the toluene into carbon dioxide by total oxidation or into benzaldehyde by selective oxidation. It presents new catalytic advances, new trends, and the advantages and disadvantages of both methods.

Preparation of a Nanosheeted Uranyl-Organic Framework for Enhanced Photocatalytic Oxidation of Toluene

Preparation of ultrathin metal-organic framework (MOF) nanosheets is an effective way to improve the catalytic efficiency of MOF photocatalysts owing to their superiority in reducing the recombination rate of photogenerated electrons and holes and enhancing charge transfer. Herein, a light-sensitive two-dimensional uranyl-organic framework named HNU-68 was synthesized. Due to its interlayer stacking structure, the corresponding ultrathin nanosheets with a thickness of 4.4 nm (HNU-68-N) can be obtained through ultrasonic exfoliation. HNU-68-N exhibited an enhanced ability to selectively oxidize toluene to benzaldehyde, with the value of turnover frequency being approximately three times higher than that of the bulk HNU-68. This enhancement is attributed to the smaller size and interface resistance of the layered HNU-68-N nanosheets, which facilitate more thorough substrate contact and faster charge transfer, leading to an improvement in the photocatalytic efficiency. This work provides a potential candidate for the application of ultrathin uranyl-based nanosheets.

Regulating the Active Sites of Cs2 AgBiCl6 by Doping for Efficient Coupling of Photocatalytic CO2 Reduction and Benzyl Alcohol Oxidation

Halide perovskites exhibit outstanding optoelectronic properties, which make them an ideal choice for photocatalytic CO2 reduction and benzyl alcohol (BA) oxidation. Nevertheless, the simultaneous realization of the above redox coupling reactions on halide perovskites remains a great challenge, as it requires distinct catalytic sites for different target reactions. Herein, the catalytic sites of Cs2 AgBiCl6 (CABC) are regulated by doping Fe for efficient coupling of photocatalytic CO2 reduction and BA oxidation. The Fe-doped CABC (Fe: CABC) exhibits an enhanced visible-light response and effective charge separation. Experimental results and theoretical calculations reveal a synergistic interplay between Bi and Fe sites, where the Bi and Fe sites have lower activation energies toward CO2 reduction and BA oxidation. Further investigations demonstrate that electrons and holes prefer to accumulate at the Bi site and Fe site under light irradiation, respectively, which creates favorable conditions for facilitating CO2 reduction and BA oxidation. The resultant Fe: CABC achieves a high photocatalytic performance toward CO (18.5 µmol g-1  h-1 ) and BD (1.1 mmol g-1  h-1 ) generation, which surpasses most of the state-of-the-art halide photocatalysts. This work demonstrates a facile strategy for regulating the catalytic site for redox coupling reactions, which will pave a new way for designing halide perovskites for photocatalysis.

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.

Visible light-driven photocatalytic degradation of Microcystin-LR by Bi2WO6/Reduced graphene oxide heterojunctions: Mechanistic insight, DFT calculation and degradation pathways

Developing heterostructure photocatalysts for removing Microcystin-LR (MC-LR) under visible light was of positive significance to control the risk of Microcystins and ensure the safety of water quality. Herein, the Bi₂WO₆/Reduced graphene oxide (RGO) nanocomposites were prepared via a simple one-spot hydrothermal method for the first time to degrade MC-LR. The optimized Bi₂WO₆/RGO (Bi₂WO₆/RGO_3%) achieved a removal efficiency of 82.3% toward MC-LR, with 1.9-fold higher efficiencies than Bi₂WO₆, and it showed superior reusability and high stability after 5 cycles. The degradation efficiency of MC-LR demonstrated a negative trend with the initial concentration of MC-LR, fulvic acid, and initial algal density increased, while MC-LR removal rate for the presence of anions was in the order of Cl^- > CO₃^-2 > NO₃^- > H₂PO₄^-. The degradation efficiency of MC-LR could reach up to 82.3% within 180 min in the neutral condition. The active species detection experiments and EPR measurements demonstrated that the holes (h⁺), hydroxide radicals (∙OH), and superoxide radicals (∙O₂^-) participated in the degradation of MC-LR. The DFT calculations showed that 0.56 of electron transferred from Bi₂WO₆ to RGO, indicating RGO introduction could prevent the recombination of photoelectrons and holes and was beneficial for MC-LR degradation. Finally, the possible intermediate products and degradation pathways were also proposed by the LC-MS/MS analysis.

Controlling the Photocatalytic Activity and Benzylamine Photooxidation Selectivity of Bi2WO6 via Ion Substitution: Effects of Electronegativity

Doping or ion substitution is often used as an effective strategy to improve photocatalytic activities of several semiconductors. Most frequently, the dopants provide extra states to increase light absorption, alter the electronic structure, or lower the carrier recombination. This work focuses on ion substitution in Bi₂WO₆, where the dopants modify band-edge potentials of the catalysts. Specifically, we investigate how the electronegativity (EN) of the dopant could be used to tune the band-edge potentials and how such changes influence the photocatalytic mechanism. Compared to Te that has a lower EN, I lowers the band-edge potentials. While substitutions with both ions enhance Rh B photodegradation and benzylamine photooxidation, the modified band potentials of I-doped Bi₂WO₆ influence the benzylamine photooxidation pathway, resulting in higher selectivity. Additionally, substitution of I⁷⁺ in the Bi₂WO₆ lattice improves the morphologies, decreases the band-gap energy, and reduces the carrier recombination. As a result, I-doped Bi₂WO₆ shows almost 3 times higher %conversion while maintaining 100% selectivity in the oxidative coupling of benzylamine. The findings here signify the importance of the choices of dopants on the photocatalytic reactions and would benefit the design of other related materials for such applications.

Fabrication of hydrangea-shaped Bi2WO6/ZIF-8 visible-light responsive photocatalysts for degradation of methylene blue

In this paper, the hydrangea-shaped Bi₂WO₆/ZIF-8 (BWOZ) visible light photocatalysts have been prepared via a facile synthetic strategy for the first time. The constructed BWOZ composites were systematically studied by a series of characterization techniques. The SEM results manifested the octahedral ZIF-8 coated the flower-like Bi₂WO₆ uniformly and the composition of BWOZ composites had been confirmed by XPS measurement. And the photocatalytic activity was evaluated by eliminating methylene blue with the help of visible light. The results showed that 7%-BWOZ (7.0 wt% Bi₂WO₆) exhibited better photodegradation capability than pure Bi₂WO₆ and ZIF-8. Compared with Bi₂WO₆, the photocatalytic degradation of methylene blue by 7%-BWOZ could reach 85.7%. In addition, the pseudo-first-order kinetic constant of 7%-BWOZ was 23.00 and 1.61 times that of pristine Bi₂WO₆ and ZIF-8, respectively. The improved photocatalytic ability of BWOZ systems may be due to the construction of heterojunctions between Bi₂WO₆ and ZIF-8, which resulted in the rapid separation of photogenerated carriers. Additionally, the specific surface area of the formed BWOZ system was also improved in comparison with the flower-shaped Bi₂WO₆, and thus more active sites could be provided to contact with methylene blue molecules, thereby achieving better removal capacity. Moreover, trapping experiments and electron spin resonance results further illustrated that the coexistence of multiple free radicals realized efficient degradation of methylene blue. More importantly, the photocatalytic property of the 7%-BWOZ composite remained even after three cycles. Furthermore, a feasible photodegradation mechanism was also explored in depth.

Piezotronic Effect-Assisted Photoelectrochemical Exosomal MicroRNA Monitoring Based on an Electron Donor Self-Supplying Strategy

Exosomal microRNAs (miRNAs) as newly emerging reliable and noninvasive biomarkers have demonstrated a significant function in early cancer diagnosis. Photoelectrochemical (PEC) biosensing has attracted unprecedented attention in exosomal miRNA monitoring due to its inherent advantages of both electrochemical and optical techniques; however, the severe charge carrier recombination greatly restricts the PEC assay performance. Herein, a high-sensitive PEC strategy assisted by the piezoelectric effect is designed based on Bi₂WO₆/Cu₂S heterojunctions and implemented for the monitoring of exosomal miRNAs. The introduction of the piezoelectric effect enables promoted electron-hole transfer and separation, thereby improving the analytical sensitivity. In addition, a target reprogramming metal-organic framework-capped CaO₂ (MOF@CaO₂) hybrids is prepared, in which MOF@CaO₂ being responsive to exosomal miRNAs induces exposure of the capped CaO₂ to H₂O and then triggers self-supplying of H₂O₂, which effectively suppresses the electron-hole recombination, giving rise to an amplified photocurrent and a decrease in the cost of the reaction. Benefiting from the coupled sensitization strategy, the as-fabricated PEC strategy exhibits high sensitivity, specificity, low cost, and ease of use for real-time analysis of exosomal miRNAs within the effectiveness linear range of 0.1 fM-1 μM. The present work demonstrates promising external field coupling-enhanced PEC bioassay and offers innovative thoughts for applying this strategy in other fields.

Enhanced Photocatalytic Activity of Hierarchical Bi2WO6 Microballs by Modification with Noble Metals

Visible-responsive photocatalysts for environmental purification and fuel generation are, currently, highly sought after. Among the possible candidates, Bi2WO6 (BWO) has been considered due to its efficient light harvesting, stability, and promising activities. Here, hierarchical BWO microballs have been prepared using a hydrothermal method, and additionally modified with deposits of noble metals (gold, silver, copper, palladium and platinum) by the photodeposition method. The structure, morphology, photoabsorption properties, and surface composition of bare and metal-modified BWO samples were investigated by XRD, SEM, DRS and XPS analyses. The photocatalytic activity was evaluated by the oxidative degradation of model dye (methyl orange (MO)) under UV/vis, and hydrogen generation under vis and/or UV irradiation. It was found that hierarchical morphology is detrimental for high photocatalytic activity in both tested systems, resulting in the improved degradation of MO (ca. 65% during 90 min of UV/vis irradiation), and hydrogen evolution (0.1 and 0.4 μmol h−1 under vis and UV/vis irradiation, respectively). Moreover, the type of noble metal and its properties influence the overall photocatalytic performance. It was found that, under UV/vis irradiation, only platinum accelerates hydrogen evolution, whereas under vis irradiation the activity follows the order: BWO < BWO/Cu < BWO/Ag < BWO/Pt < BWO/Pd < BWO/Au. It was concluded that zero-valent metal is recommended for high vis response, probably due to plasmonic photocatalysis, efficient light harvesting ability, and co-catalytic role.

In situ decomposition of bromine-substituted catechol to increase the activity of titanium dioxide catalyst for visible-light-induced aerobic conversion of toluene to benzaldehyde

Surface-modified TiO2 generated by the photolysis of tetrabromocatechol showed higher activity than bare TiO2 in visible-light-induced photocatalytic toluene oxidation.

Defect-Induced Ce-Doped Bi2WO6 for Efficient Electrocatalytic N2 Reduction

Electrochemical nitrogen reduction reaction (NRR) is a promising method for synthesizing ammonia (NH₃). However, due to the extremely strong N≡N bond and the competing hydrogen evolution reaction (HER), the electrochemical NRR process remains a great challenge in achieving a high NH₃ yielding rate and a high Faradaic efficiency (FE). Recently, either Bi-based or W-based catalysts have been used in N₂ fixation due to lower HER activity. To further promote N₂ activation, we develop a simple protocol to introduce and adjust the crystal defects in the host lattice of Bi₂WO₆ nanoflowers via adjusting the amount of Ce dopant (denoted as xCe-Bi₂WO₆, where x represents the designed mole percentage of Ce). At -0.20 V versus the reversible hydrogen electrode (RHE), 10%Ce-Bi₂WO₆ manifests a high NH₃ yielding rate (22.5 μg h^-1 mg^-1_cat.), a high FE (15.9%), and excellent electrochemical and structure durability. Its performance is better than most previously reported Bi-based and W-based electrocatalysts for NRR in aqueous solutions. According to density functional theory (DFT) calculations, the introduction of crystal defects into Bi₂WO₆ can strengthen the adsorption and activation of N₂, thus leading to a significant increase in NRR activity.

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.

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.