One-step synthesis of floatable BiOCl/BiOBr@FACs enriched in oxygen vacancies for improved photocatalytic activity via peroxymonosulfate activation

In this study, we developed a highly active floatable photocatalyst by incorporating BiOCl/BiOBr heterojunctions with abundant oxygen vacancies (OVs) onto fly ash cenospheres (FACs) composites, aiming to enhance the efficiency of tetracycline (TC) removal. The physicochemical properties of resulting composites were analyzed using various characterization techniques. The findings demonstrated the uniform anchoring of nanosheet-array-like BiOCl, BiOBr, or BiOCl/BiOBr heterojunctions on the surface of FACs. Intriguingly, the BiOCl/BiOBr heterojunctions exhibited an increased content of OVs compared to BiOCl and BiOBr alone. The degradation experiments of TC revealed that the BiOCl/BiOBr@FACs composites displayed optimal photodegradability, which was further enhanced by the assistance of peroxymonosulfate (PMS). Furthermore, through active species capture experiments and ESR analysis, we proposed a synergistic reactive mechanism that differed from single photocatalytic processes and traditional PMS activation. Active species such as h+, 1O2, ·O2-, ·OH and ·SO4- were found to participate in the synergistic process of TC degradation, in which the presence of PMS promoted the production of ·O2- via OVs active sites instead of inhibition. Importantly, the immobilized BiOCl/BiOBr@FACs composites exhibited floatability on the water surface and were readily excited by visible light, making them suitable for reuse and practical applications. This study presents an innovative approach for designing recyclable photocatalysts and achieving efficient wastewater treatment with the assistance of PMS.