COF TzDa/Ag/AgBr Z-scheme heterojunction photocatalyst for efficient visible light driven elimination of antibiotics tetracycline and heavy metal ion Cr(VI)

• A new Z-scheme photocatalyst COF TzDa/Ag/AgBr is successfully fabricated. • Enhanced TC oxidation and Cr(VI) reduction are realized under visible light. • COF TzDa/Ag/AgBr simultaneously removes TC/Cr(VI) mixture with synergistic effect. • Mechanisms for TC degradation and Cr(VI) reduction are proposed. • COF TzDa/Ag/AgBr exhibits good stability in cyclic use on TC and Cr(VI) removal. 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 O 2 − 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.