Effect of energy band alignments in carbon doped ZnO/TiO2 hybrid heterojunction photocatalyst on the photodegradation of ofloxacin

Abstract

The present study highlights the influence and efficacy of a self-doped carbon (C)–ZnO/TiO2 hybrid heterojunction for the photocatalytic degradation of ofloxacin (OFX) in aqueous media. The flower-like hybrid heterojunction was prepared via hydrothermal treatment at varying concentrations of ZnO and TiO2. C doping was internally introduced to the ZnO lattice by the decomposition of polyvinylpyrrolidone as a source to achieve better band alignment. A systematic investigation was performed to elucidate the mechanism of photodegradation by the heterojunction via analyzing the parameters such as composition, dosage, and pH of the system. The optimized sample 1:2 (Zn: Ti) ratio exhibited a photodegradation efficiency of 99.9% for OFX within 60 min, demonstrating a reaction rate 1.6 times higher than that of C–ZnO. Moreover, the involvement of charge carriers was analyzed through scavenging experiments. The results showed that trapping superoxide anions resulted in a 57.8% reduction in photoactivity, confirming their significant involvement in the process. The n-doping of C and subsequent defects level formation in the heterojunction hybrid was supported by X-ray photoelectron spectroscopy. The mechanism for the effective and extended photodegradation of hybrid heterojunctions was proposed by investigating band-gap using Tauc plot and valence band spectra using ultraviolet photoelectron spectroscopy. The valence band spectra verified the uplift of energy bands via doping, confirming the strong reducing power of the heterojunction hybrids. Additionally, liquid chromatography-mass spectroscopy was employed to perform the identification of the degradation pathway and intermediates.

Keywords

• Photocatalysis
• Ofloxacin
• Hybrid heterojunction
• Band alignment
• Degradation pathway