Invited feature articleModification of ZnIn2S4 by anthraquinone-2-sulfonate doped polypyrrole as acceptor-donor system for enhanced photocatalytic degradation of tetracycline

•AQS/PPy-ZnIn2S4 composite photocatalyst showed better photocatalytic activity.•The O2− played a major role with AQS/PPy-ZnIn2S4 composite photocatalyst.•The AQS behaved as electron acceptor-donor mediator and PPy served as holes acceptor-donor mediator.•Photocatalytic reactions mainly occurred in the solution by free diffusion of reactive species.

Visible-light photocatalytic degradation of tetracycline was investigated by functional modified ZnIn2S4 via anthraquinone-2-sulfonate (AQS) doped polypyrrole (PPy). The best photocatalytic activity of AQS/PPy-ZnIn2S4 composite photocatalyst was obtained when the weight ratio of AQS/PPy versus ZnIn2S4 was 1.0% and the molar ratio of PPy to AQS was 40. After 3.0 h photocatalytic reaction, more than 98% tetracycline was removed and almost 2.0 times higher of NPOC (non-purgeable organic carbon) removal rate was obtained compared with pure ZnIn2S4. Active species trapping experiments demonstrated that O2− played a major role rather than the OH and photogenerated holes. The AQS doped in PPy matrix behaved as electron acceptor-donor mediator which facilitated the formation of O2−. Two kinds of solid phase extraction (SPE) methods were developed before gas chromatography mass spectroscopy (GC-MS) analysis and eight intermediates were detected. The degradation of tetracycline originated from the photogenerated holes via loss of some functional groups and then aromatic ring was destroyed by the oxidation of active species O2− and OH via hydroxylation reaction.

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