Visible light degradation of tetracycline using oxygen-rich titanium dioxide nanosheets decorated by carbon quantum dots

Tetracycline (TC) is widely applied as a broad-spectrum bacteriostat and has been detected in various water environments with its metabolites, thus posing a serious threat to the aquatic ecosystem and human health. In this work, a novel composite of carbon quantum dot oxygen-rich titanium dioxide nanosheets (CQD-OTNs) was successfully constructed and prepared by an improved two-step hydrothermal method and was applied in the photo-degradation of TC. The CQD-OTNs could increase the degradation ratio of TC to 94.1% with 120 min visible light irradiation, and the degradation rate was about 2.3 times higher than that of pure titanium dioxide nanosheets. The improved photocatalytic activity of CQD-OTNs was attributed to the constructed oxygen enriched structure and CQDs, by widening the longest absorption wavelength (from 375 of TNs to 420 nm), facilitating the separation of generated electron-holes (e--h+), and suppressing the recombination of the electron-hole pairs. The generated holes, hydroxyl radical (•OH), and superoxide radical (•O2–) participated in the catalytic reaction, and the h+ dominated the degradation of TC. The toxicity of the degradation solution increased firstly in 10 min and then gradually decreased to that as ultrapure water. Furthermore, the possible degradation pathways of TC were proposed and discussed.