Photodeposition synthesis of CdS QDs-decorated TiO2 for efficient photocatalytic degradation of metronidazole under visible light

Photocatalysis technology has received much attention on the treatment of antibiotics residues. In this paper, CdS quantum dots (QDs)-decorated TiO2 (CDS-T for short) have been prepared successfully through a photodeposition method and utilized as photocatalysts for degradation of metronidazole (MTZ). Under visible light irradiation for 60 min, the degradation ratio of MTZ over CDS-T-3 that was prepared by 3 h of photodeposition reached up to 90.9%, which was 1.5 times than that reached over commercial CdS. The decoration of CdS QDs onto TiO2 can enlarge light absorption range to visible region. Furthermore, greatly improved separation efficiency of photogenerated carriers is realized through forming heterojunction. Activity control experiments demonstrate that O2·− serve as the main active species, while ·OH and holes (h+) play secondary roles on the MTZ degradation. Moreover, electron spin resonance (ESR) technique, terephthalic acid photoluminescence (TA-PL) technique and N,N-diethyl-p-phenylenediamine (DPD) method confirm that larger amounts of active species are generated from CDS-T-3 than that from commercial CdS under visible light. This study can not only offer an easy method to prepare CdS quantum dots-decorated TiO2 but also enlarge its application in solving the problem of metronidazole contamination.