Simultaneous photocatalytic Cr(VI) reduction and ciprofloxacin oxidation over TiO2/Fe0 composite under aerobic conditions: Performance, durability, pathway and mechanism

•Photocatalytic activity of TiO2/Fe0 composite was superior to bare TiO2.•CIP oxidation could be accelerated under acidic and aerobic conditions.•A low Pb(II) concentration could induce an enhancement of CIP oxidation.•A low EDTA concentration did positively affect the removals of Cr(VI) and CIP.•A reaction mechanism for Cr(VI) reduction and CIP oxidation was proposed.

Coexistence of organic compounds and heavy metals in aquaculture waters is a widespread problem. In this study, a rapid reduction of Cr(VI) and oxidation of ciprofloxacin (CIP) in a simultaneous manner was firstly reported through the photocatalysis of TiO2/Fe0 composite under aerobic conditions. The significantly enhanced removals of Cr(VI) and CIP by TiO2/Fe0 composite due to a synergetic effect between oxidation and reduction processes. Within 60 min UV light irradiation, the simultaneous removals of Cr(VI) and CIP by TiO2/Fe0 composite were 97.7 and 94.6%, respectively, whereas the corresponding values by TiO2 were 57.9 and 68.7%. CIP oxidation process could be significantly accelerated under acidic and aerobic conditions. Intriguingly, a low Pb(II) concentration could induce an enhancement of CIP oxidation, whereas a negative effect on both Cr(VI) reduction and CIP oxidation was observed at a relatively high concentration. A low concentration of ethylene diamine tetra-acetic acid (EDTA) did positively affect both Cr(VI) reduction and CIP oxidation processes, whereas a negative effect on CIP oxidation was found at a relatively high concentration. A possible reaction pathway and mechanism between CIP oxidation and Cr(VI) reduction was proposed. CIP was attacked by HO produced from the decomposition of water and photo-excited holes through substitution and hydroxylation processes, leading to the production of a series of intermediates, whereas the Cr(VI) was converted into Cr(III) through the capture of photo-excited electrons and Fe0 reduction.

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