Preparation Of Bismuth Oxychloride Photocatalyst And Its Degradation Of Organic Pollutants

Water pollution is a major problem accompanying the development of human production.Semiconductor photocatalysis technology has become an emerging research technology for water pollution treatment because of the use of clean and renewable solar energy.In recent years,the exploration of semiconductor photocatalysts has intensified,and bismuth-based photocatalysts have attracted the attention of many scholars due to their suitable band gap,low toxicity,and excellent physical and chemical properties.In this paper,Bi₃O₄Cl and Bi₄NbO₈Cl were prepared by solid-phase method,and on this basis,the photodegradation performance of the catalysts was improved by constructing heterojunction.The formation of heterojunctions was demonstrated by various characterization methods,and the formation process was discussed.The photocatalytic performance of the catalysts was evaluated by degrading ciprofloxacin（CIP）and rhodamine B（Rh B）solutions.The photoelectric properties of photocatalyst and the mechanism of photocatalytic process were discussed in detail.The main research contents are as follows:（1）A Bi₂S₃/Bi₂O₂CO₃/Bi₃O₄Cl ternary heterojunction was constructed in situ using a one-step hydrothermal method,and the performance of the catalysts for photocatalytic degradation of ciprofloxacin（CIP）and rhodamine B（Rh B）solutions was investigated.For the formation of Bi₂S₃/Bi₂O₂CO₃/Bi₃O₄Cl,Bi₃O₄Cl provided the Bi source to generate tightly bonded heterojunctions in situ;thiourea and CO₂ in air provided C source for Bi₂O₂CO₃;thiourea provided S source for Bi₂S₃.Compared with pure Bi₃O₄Cl,Bi₂S₃/Bi₂O₂CO₃/Bi₃O₄Cl（BBS-0.2）which was prepared by adding 0.2 mol thiourea and 0.3 g Bi₃O₄Cl to 60 m L deionized water,showed a better photocatalytic performance.The degradation efficiencies of 87.2%CIP in 80 min and 64.8%Rh B in 180 min under light irradiation,are 2.4 times and2.0 times of Bi₃O₄Cl,respectively.In the photocatalytic degradation process,the h⁺plays a major role and·O₂^-plays an auxiliary role.The improved photodegradation performance of Bi₂S₃/Bi₂O₂CO₃/Bi₃O₄Cl is due to:Bi₂O₂CO₃ can act as a trap for photogenerated electrons of Bi₃O₄Cl and Bi₂S₃,which is beneficial to separate photogenerated hole-electron pairs;Bi₂S₃ can improve the optical properties of the catalyst;and the specific surface area of the catalyst is increased.（2）After Bi₄NbO₈Cl was prepared by solid phase method,a certain amount of anhydrous ethanol and acetic acid were added and placed at room temperature for different reaction time to prepare BiOCl/Bi₄NbO₈Cl heterojunction in situ.By XRD and HRTEM analysis,BiOCl was transformed from impurities such as Bi₂₄O₃₁Cl₁₀contained in Bi₄NbO₈Cl prepared by solid-phase method.Comparative experiments showed that Bi₄NbO₈Cl did not participate in the reaction in the experimental system of this paper.Among them,the BiOCl/Bi₄NbO₈Cl heterojunction（BBN-96）with a reaction time of 96 h exhibited excellent degradation ability in the degradation of ciprofloxacin（CIP）and rhodamine B（Rh B）solutions.Under full light conditions,the degradation rate of CIP（10 mg/L）solution by BBN-96 within 100 min was0.01354/min,which was 21.5 times and 5.5 times that of BiOCl and Bi₄NbO₈Cl,respectively;99.3%of Rh B（10 mg/L）could be degraded within 20 min,which was3.0 times that of BiOCl and 6.0 times that of Bi₄NbO₈Cl;84.1%Rh B（20 mg/L）could be degraded within 120 min,which was 18.7 times that of Bi₄NbO₈Cl.Capture agent experiments and electron spin resonance spectroscopy（ESR）demonstrated that the main active species during the photodegradation of BBN-96 were·O₂^-and h⁺.The performance improvement of BiOCl/Bi₄NbO₈Cl heterojunction is mainly due to:It has the photoresponse range of Bi₄NbO₈Cl;the type II heterojunction promotes the separation of photogenerated electrons and holes,resulting in an increase in the number of active species that can be effectively utilized in the photocatalytic process;the specific surface area of the catalyst is increased.