Abstract
Exploring efficient photocatalysts for eliminating coexisting organic pollutants and heavy metal ions is important for sustainable and green environmental purification. Herein, in-situ precipitation-deposition of AgBr onto COF TzDa feasibly fabricated a new heterojunction composite COF TzDa/AgBr, which readily transformed to COF TzDa/Ag/AgBr under exposure to light. The structure, morphology, composition, optical and electrochemical properties of this composite were characterized through various techniques. The activities of COF TzDa/Ag/AgBr in degrading antibiotics tetracycline (TC) and reducing Cr(VI) under simulated visible-light were extensively improved compared with bare COF TzDa, AgBr and their physical mixture. Credited to the synergism among TC, Cr(VI) and the photocatalyst, COF TzDa/Ag/AgBr demonstrated even higher efficiency in simultaneously removing TC/Cr(VI) mixture than for the single pollutant. Furthermore, plausible TC degradation intermediates and pathways were postulated by HPLC-MS analysis. Investigations on band structure, radicals quenching and ESR spectra concluded a Z-scheme charge transfer mechanism with Ag NPs as electron mediator in COF TzDa/Ag/AgBr, which revealed that O2− and h+ were responsible for degrading TC, while photo-generated electrons reduced toxic Cr(VI) to non-toxic Cr(III). The enhanced performance of COF TzDa/Ag/AgBr should stem from the reinforced visible-light adsorption, increased surface areas, accelerated charge transfer and separation, and inhibited Ag/AgBr aggregation. COF TzDa/Ag/AgBr also displayed good stability during the recycled treatment of TC and Cr(VI), while TC degradation under COF TzDa/Ag/AgBr was not obviously influenced by common environmental factors. Thus, this work might offer a promising strategy for the treatment and purification of wastewater containing organic pollutants and heavy metal ions.
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