Tuning of BixOyCl formation with sonication time during ultrasound-hydrothermal preparation

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

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

Sonochemically assisted the synthesis and catalytic application of bismuth-based photocatalyst: A mini review

Recently, bismuth (Bi)-based photocatalysts have been a well-deserved hotspot in the field of photocatalysis owning to their photoelectrochemical properties driven by the distortion of the Bi 6 s orbital, while their narrow band gap and poor quantum efficiency still restrict their application. With the development of ultrasonic technology, it is expected to become a broom to clear the application obstacles of Bi-based photocatalysts. The special forces and environmental conditions brought by ultrasonic irradiation play beneficial roles in the preparation, modification and performance releasement of Bi-based photocatalysts. In this review, the role and influencing factors of ultrasound in the preparation and modification of Bi-based photocatalysts were introduced. Crucially, the mechanism of the improving the performance for various types of Bi-based photocatalysts by ultrasound in the whole process of photocatalysis was deeply analyzed. Then, the application of ultrasonic synergistic Bi-based photocatalysts in contaminants treatment and energy conversion was briefly introduced. Finally, based on an unambiguous understanding of ultrasonic technology in assisting Bi-based photocatalysts, the future directions and possibilities for ultrasonic synergistic Bi-based photocatalysts are explored.

Self-assembled micro and nano rod-shaped porphyrin@Bi12O17Cl2 composite as an efficient photocatalyst for degradation of organic contaminants

Bi12O17Cl2 is a potential photocatalyst in practical applications due to its excellent photostability, visible light activity, and competitive bandgap energy. However, the fast recombination of photogenerated charge carriers makes it impractical for pollution mitigation. Recently, aggregated porphyrins have emerged as photosensitizers in light-dependent applications such as photocatalysis. Although Bi12O17Cl2 and porphyrin can function as separate photocatalysts, their photocatalytic properties in terms of visible light adsorption, charge separation and transport, can be improved when they are combined to form heterostructure. In this study, rod-shaped aggregated 5,10,15, 20-Tetrakis (4-carboxyphenyl) porphyrin was synthesized by CTAB-assisted, self-assembly strategy and Bi12O17Cl2 by a facile microwave method. The porphyrin and Bi12O17Cl2 were combined to generate a series of x%Porphyrin@Bi12O17Cl2 having 0.02% wt., 0.1% wt., 0.4% wt., 1% wt. and 10% wt. as compositions of porphyrin. The materials' photocatalytic degradation efficiency was tested on Rhodamine B dye as a representative pollutant. The best and worst performances were reported for 1%Porphyrin@Bi12O17Cl2 and 10%Porphyrin@Bi12O17Cl2, respectively, which are 3.1 and 0.5 times increases in efficiency compared to pure Bi12O17Cl2. From the radical trapping experiment, electrons and superoxide were the dominant reactive species in the degradation process. The enhanced photocatalytic capability of the materials was attributed to the photosensitizing property of porphyrin and the heterojunction formation, which promotes the separation of photogenerated charge carriers. A plausible step-scheme (S-scheme) was proposed for the photocatalytic degradation mechanism. The S-scheme provided the high redox potential of the photogenerated charge carriers. The findings herein offer a new option for improving the photocatalytic performance of Bi12O17Cl2 for environmental applications through the photosensitization strategy.

Preparation and application of Ag plasmon Bi3O4Cl photocatalyst for removal of emerging contaminants under visible light

Photocatalytic degradation has been extensively investigated toward the removal emerging contaminants (ECs) from water. In this study, a series of Ag-Bi₃O₄Cl plasmon photocatalysts were synthesized through the photo-deposition of metallic Ag on the Bi₃O₄Cl surface. The effects of plasmon modification on the catalytic performance of bismuth oxychlorides were analyzed. Ag addition did not alter the morphology of Bi₃O₄Cl. With the increasing Ag content, the number of oxygen defects on the catalyst surface first increased and then decreased. Moreover, the surface plasmon resonance effect of Ag suppressed the recombination of electron-hole pairs, promoting the migration and separation of photocarriers and improving the light absorption efficiency. However, the addition of excessive Ag reduced the number of active sites on the Bi₃O₄Cl surface, hindering the catalytic degradation of pollutants. The optimal Ag-Bi₃O₄Cl photocatalyst (Ag ratio: 0.025; solution pH: 9; dosage: 0.8 g/L) achieved 93.8 and 94.9% removal of ciprofloxacin and tetrabromobisphenol A, respectively. The physicochemical and photoelectric properties of Ag-Bi₃O₄Cl were determined through various characterization techniques. This study demonstrates that introducing metallic Ag alters the electron transfer path of the catalyst, reduces the recombination rate of electron-hole pairs, and effectively improves the catalytic efficiency of Bi₃O₄Cl. Furthermore, the pathways of ciprofloxacin degradation products and their biotoxicity were revealed.

Fabrication of Bi-Bi3O4Cl plasmon photocatalysts for removal of aqueous emerging contaminants under visible light

Photocatalytic oxidation of emerging contaminants (ECs) in water has recently gained extensive attentions. In this study, bismuth oxychloride-based plasmon photocatalysts (Bi-Bi₃O₄Cl) exhibiting high performance were successfully developed by reducing Bi³⁺ on the surface of Bi₃O₄Cl. Consequently, the photocatalysts were used to remove ECs from water. The effects of developmental process and Bi metal plasmon resonance on the photoelectric performances of Bi-Bi₃O₄Cl were investigated through a series of characterizations. The UV-vis diffuse reflection and photoluminescence spectra revealed that the light absorption range of the photocatalyst gradually increased and the electron recombination rate gradually decreased with the introduction of Bi metals. The optimal removal rates of ciprofloxacin and tetrabromobisphenol A by Bi-Bi₃O₄Cl were 93.8% and 96.4%; the respective reaction rate constants were 5.48 and 4.93 times higher than that of Bi₃O₄Cl. The mechanism study indicated that main reactants in the photocatalytic system were •O₂^- radicals and photogenerated holes, and the existence of oxygen vacancies and Bi metals promoted electron transfer in photocatalyst. In conclusion, this research produces a novel, green, highly efficient, and stable visible light photocatalyst for the removal of ECs from water.

Ultrasonic treatment enhances the formation of oxygen vacancies and trivalent manganese on α-MnO2 surfaces: Mechanism and application

Catalytic activity is the main obstacle limiting the application of peroxymonosulfate (PMS) activation on transition metal oxide catalysts in organic pollutant removal. Herein, ultrasonic treatment was applied to α-MnO₂ to fabricate a new u-α-MnO₂ catalyst for PMS activation. Dimethyl phthalate (DMP, 10 mg/L) was almost completely degraded within 90 min, and the pseudofirst-order rate constant for DMP degradation in the u-α-MnO₂/PMS system was ∼7 times that in the initial α-MnO₂/PMS system. The ultrasonic treatment altered the crystalline and pore structures of α-MnO₂ and produced defects on the u-α-MnO₂ catalyst. According to the XPS, TG, and EPR results, higher contents of trivalent Mn and oxygen vacancies (OVs) were produced on the catalyst surfaces. The OVs induced the decomposition of PMS to produce ¹O₂, which was identified as the main reactive oxygen species (ROS) responsible for DMP degradation. The u-α-MnO₂ catalyst presented great reusability, especially by ultrasonic regeneration of OVs toward the used catalyst. This study provides new insights into regulating OVs generation and strengthening catalyst activity in the PMS activation process for its application in water purification.

Di-functional Cu2+-doped BiOCl photocatalyst for degradation of organic pollutant and inhibition of cyanobacterial growth

Photocatalytic oxidation of contaminants in water has recently gained extensive attentions. In this study, Cu²⁺-doped BiOCl microsphere photocatalysts were prepared using solvothermal method. The effects of Cu²⁺ doping ratio on the morphological structures and photoelectric and photocatalytic properties of BiOCl were studied in detail. Results showed that Cu²⁺ doping affected the particle size of BiOCl microspheres. The introduction of Cu²⁺ ions gradually increased the light absorption range and decreased the electron recombination rate of photocatalysts as shown by ultraviolet-visible diffuse reflection and photoluminescence spectra. The best doping ratio was 0.25 Cu²⁺-BiOCl, showing the highest photocatalytic activity for rhodamine B (14.25 time higher than BiOCl) and a good inhibition of algal growth. The main reactants in the photocatalytic system were·OH and h⁺ (electron holes). Density functional theory (DFT) calculations further demonstrated that the doping of Cu²⁺ ions made the photogenerated carriers in BiOCl easier to generate and ensured the charge was transferred more rapidly. In conclusion, a novel high-efficiency multifunctional photocatalyst is proposed for the efficient organic pollutants removal and algae growth inhibition from water.

Preparation and application of BiOBr-Bi2S3 heterojunctions for efficient photocatalytic removal of Cr(VI)

Recently, the photocatalytic reduction of Cr(VI) has been extensively studied. Herein, we successfully prepared the BiOBr-Bi₂S₃ heterojunctions with high photocatalytic Cr(VI) reduction performance using an ion exchange method. The optimal BiOBr-Bi₂S₃ heterojunction (prepared with BiOBr, pH of 6.0, 2 mmol Na₂S₂O₃·5H₂O,) achieved 100% removal of Cr(VI) within 12 min. The performance of photo-reduced Cr(VI) was about 28.9 and 184.6 times higher than that of pure Bi₂S₃ and BiOBr, respectively. Besides, BiOBr-Bi₂S₃ heterojunctions had a good adsorption efficiency for Cr(III), suggesting that they could be applied as bifunctional photocatalyst. The formation process and photoelectric properties of the BiOBr-Bi₂S₃ heterojunctions were revealed by a series of characterizations. In conclusion, this work reported the synergistic effect of adsorption and photocatalysis of the BiOBr-Bi₂S₃ heterojunctions for Cr removal for the first time, suggesting that the BiOBr-Bi₂S₃ heterojunctions could act as a novel photocatalytic adsorbent to treat the Cr(VI)-containing wastewater.

Bismuth oxychloride-based materials for the removal of organic pollutants in wastewater

Various kind of organics are toxic and detrimental, resulting in eutrophication, black, odorous water and so on. Photocatalysis has been deemed to be a promising technology which can decompose different kinds of organic pollutants under visible light irradiation, finally achieving non-poisonous, harmless CO2, water and other inorganic materials. Bismuth oxychloride (BiOCl) is considered as a promising photocatalyst for the efficient degradation of organic pollutants due to its high chemical stability, unique layered structure, resistance to corrosion and favorable photocatalytic property. However, BiOCl can only absorb UV irradiation because of its wide band gap of 3.2 eV-3.5 eV that limits its photocatalytic performance. Herein, a lot of methods have been reviewed to improve its photocatalytic activity. We introduced the unique and special layered structure of BiOCl, the typical and common synthesis methods that can control the morphology, and the most important part is varies of modification routes of BiOCl and the application of BiOCl-based materials for photocatalytic degradation of organic pollutants. Besides, we summarized the crucial issues and perspectives about the application of BiOCl in pollution management.