Photon localization-assisted visible light photocatalysis of photonic crystal CdS-N/ZnO heterojunction for efficient photodegradation tetracycline hydrochloride

Abstract

Herein, ZnO based materials are modified to narrow the photonic band gap, improved utilization rate of visible light and recombination efficiency of photoexcited carriers for the photocatalytic degradation of tetracycline hydrochloride (TCH). For this purpose, a photonic crystal (PC) heterojunction was constructed comprising of nitrogen (N) doped cadmium sulfide (CdS) coupled with ZnO (CdS-N/ZnO) via sacrificial template and multilayer in-situ deposition methods. The constructed PC junction acted as photocatalyst for the effective degradation of TCH under visible light by synergistically promoting the separation efficiency of electron-hole pairs, narrowing the band gap and broadening the light absorption spectrum of ZnO. Moreover, a slow light effect was achieved by adjusting the band gap of the PC overlapped with the wavelength of incident light, which finally enhanced the light harvesting performance of the CdS-N/ZnO photocatalyst. The optimized PC CdS-N/ZnO composites exhibited efficient TCH removal rate of 97.0 % in 90 min and kb as 4.00–15.17 times that of other reported catalysts. Moreover, PC CdS-N/ZnO catalyst achieved 45.2 % mineralization rates reached in 120 min with high stability and reusability for six cycles. HPLC-MS method was used for monitoring the intermediates of TCH degradation, and also analyzing the possible pathways of products. In addition, the toxicity of TCH and its intermediates were also investigated, which showed that the toxicity has effectively been alleviated. The photocatalytic mechanism endowed that ·O2– and h+ are the major active free radicals in the photocatalytic degradation process, and the electron transport path is type Ⅱ heterostructure. This work will thus envisage a novel vision of designing ZnO photocatalysts for the antibiotic degradation in the practical application of wastewater treatment.