Facile prepared ball-like TiO2 at GO composites for oxytetracycline removal under solar and visible lights.

With the widespread use of oxytetracycline (OTC), residual OTCs have been detected in natural surface waters, as well as in water and wastewater treatment systems. Semiconductor photocatalysis has been proven to be a green and high-performing method for the removal of organic contaminants. However, most photocatalysts are only effective when irradiated by UV light. This study explores the efficiency of a new semiconductor photocatalysis method for OTC removal under solar and visible light. To expand the spectral range from the UV to the visible region, a facile prepared ball-like TiO2 at graphene oxide (TiO2@GO) composite, a TiO2-associated catalyst, was synthesized. Chemical characterization indicated that the TiO2@GO has the features of both TiO2 and GO, with the regular TiO2 fiber balls cladded by GO nanosheets. The photocatalytic activity of TiO2@GO composites under solar and visible light was evaluated in terms of OTC degradation. Values of 100% and 90% OTC removal efficiencies were achieved with TiO2@GO at 6 mg/L under solar and visible light irradiation, respectively. The band structure of TiO2@GO expanded the spectral range to full light wavelengths, facilitating formation of a light-induced electron hole (h+), which was identified in this study as the major cause of OTC degradation. The pH and TSS levels (>100 mg/L) were found to have high and low impacts, respectively, on the removal efficiency of OTC, while natural organic matter (NOM) was found to have an insignificant impact. Furthermore, the degradation of OTC with catalysis by TiO2@GO was verified using two real water samples, and averages of 90% and 75% OTC removal efficiencies were achieved under solar and visible light respectively. The results indicate that the synthesized TiO2@GO composites can provide an effective way of removing toxic organic compounds, including OTC, from the water system.