Different water matrixes leading to noticeable differences of tetracycline removal by ZnO

Abstract

Differential photocatalytic degradation of antibiotics in experimentally pure water and natural waters is essential to study the transport transformation and elimination of antibiotics in the environment. In this study, a typical photocatalyst zinc oxide nanoparticles (ZnO NPs) was used to degrade the antibiotic tetracycline (TC) in pure water, river water and seawater. The differences in the photocatalytic degradation characteristics of TC in different aqueous matrices were systematically analyzed by environmental factors investigation, product degradation pathways study, toxicity evaluation and theoretical calculations. Humic acids (HA) and acetone exhibited shielding effect and photosensitization on TC degradation. Metal ions (Cu(II), Zn(II), Pb(II) and Cd(II)) with concentrations in the range of 0–1.0 mg∙L-1 inhibited TC degradation in three water matrices. With increasing metal concentration, the inhibitory effect was slightly enhanced in pure water, significantly enhanced in river water, enhanced first and then weakened in seawater. Density functional theory (DFT) calculation confirmed that metal ions competed with ZnO for TC adsorption. Furthermore, TC in pure water was degraded into small molecules with m/z less than 100, while the m/z of the products in both river water and seawater was more than 400 under the same condition. Toxicity evaluation showed that the toxicity of the intermediates in river water and seawater was significantly higher than that in pure water. Thus, the degradation pattern of TC in laboratory pure water was significantly different from that in the actual water. This study provides obvious reference to degradation elimination and ecotoxicity study of antibiotics in real water.