Preparation Of Novel Bi₄MO₈X(M=V,Nb,Ta;X=Cl,I)and Photodegradation Of Organic Pollutants

Photocatalysis is one of the most promising advanced oxidation techniques, and has great potential forenvironment remediation purposes and especially for wastewater purification due to itsenvironment-friendly, high-efficiency and low-cost. In the past decade, the remarkable progress in this fieldhas been mainly focused on the high activity heterogeneous photocatalysts. It is shown that suchphotocatalysts can degrade most kinds of organic compounds under ultraviolet light irradiation. However,the fast recombination rate of the photogenerated electron-hole pairs hinders the commercialization of thistechnology. Therefore, it is of great interest to improve the catalytic activity of photocatalysts for thedegradation of organic contaminants. From the viewpoint of environment protection and energyconservation, development of visible-light induced photocatalysts with high activity is indispensable.In this work, Bi4NbxTa(1-x)O8I photocatalysts have been synthesized by solid state reaction method andcharacterized by powder X-ray diffraction (XRD), Scanning electron microscope (SEM) and UV-Visdiffuse reflectance spectroscopy (UV-Vis DRS). The photocatalytic activity of these photocatalysts wasevaluated by the degradation of methyl orange (MO) in aqueous solutions under visible light, ultravioletlight and solar irradiation. The effects of catalyst dosage, initial pH and MO concentration on the removalefficiency were studied, and the photocatalytic reaction kinetics of MO degradation as well. The resultsindicated that Bi4NbxTa(1-x)O8I exhibited high photocatalytic activity for the removal of MO in aqueoussolutions. For example, the removal efficiency of MO by Bi₄Nb_0.1Ta_0.9O₈I was as high as92%within12hvisible light irradiation under the optimal conditions: initial MO concentration of5-10mg/L, catalystdosage of6g/L and natural pH (6-8), the MO molecules could be completely degradated byBi₄Nb_0.1Ta_0.9O₈I within40min under ultraviolet light irradiation, and the photodegradation efficiencyreaches to60%after7h solar irradiation. Five main degradation products were observed by HPLC/MS andtheir chemical structures were suggested. Furthermore, the photocatalytic degradation of Bisphenol A (BPA)was also investigated under visible light irradiation. It is found that99%BPA could be removed byBi₄Nb_0.1Ta_0.9O₈I after16h visible light irradiation, and the possibility for the photosensitization effect inthe degradation process of MO under visible light irradiation has been excluded. Therefore, it is expectedthat Bi4NbxTa(1-x)O8I would be promising photocatalysts for the removal of azo dyes under visible light,ultraviolet light and solar irradiation. Novel nanoscale photocatalyst Bi₄VO₈Cl was applied to degradation of six pharmaceuticals such asmetronidazole (MTZ), aciclovir, levofloxacin hydrochloride, sulfonamide, adrenaline hydrochloride,ribavirin under visible light irradiation. The catalyst were synthesized with a hydrothermal method bycontrolling the pH of the reaction solution and characterized by XRD, SEM, UV-Vis DRS, XPS (X-rayPhotoelectron Spectroscopy). Metronidazole was selected as a typical sample to evaluate the photocatalyticsystem in details. Its removal efficiency by Bi₄VO₈Cl was as high as100%within9h visible lightirradiation under the optimal conditions. The MTZ could be completely degradated by Bi₄VO₈Cl within10min under ultraviolet light or6h solar irradiation. Simultaneously, it was found that the crystallinity of thecatalysts played an important role in their degradation efficiency on MTZ. Bi₄VO₈Cl catalyst prepared atpH3(pH3-Bi₄VO₈Cl) displayed the best crystallinity and showed the highest photocatalytic activity.Furthermore, the removal of total organic carbon (TOC) of six drugs after10h visible light irradiationpreliminarily indicated that in the photocatalytic system we studied, aciclovir, levofloxacin hydrochloride,sulfonamide, adrenaline hydrochloride, ribavirin are easily-degrading PPCPs. Metronidazole isslowly-degrading PPCPs. PPCPs with imidazole ring was resistant against visible light irradiation. ByHPLC/MS, four main products were observed in MTZ degradation process and a suggested pathway ofdegradation was proposed. Therefore, it is expected that Bi₄VO₈Cl would be promising photocatalysts forthe removal of pharmaceuticals and personal care products under visible light, ultraviolet light and solarirradiation.