Facile Synthesis and Optimization of Graphitic Carbon Nitride Nanoparticles to Effectively Photodegrade Tetracycline under Visible Light in Water

Abstract

The rapid development of industry and medicine in modern society has produced a group of emerging contaminants (ECs) that are harmful to the ecosystem and difficult to remove from the environment. In this study, several graphitic carbon nitrides (GCNs) have been successfully synthesized by the calcination method, and their efficiency in the photocatalytic degradation of tetracyclines (TCs) was evaluated under the irradiation of visible light (λ = 420 nm). CNU achieved the highest TC degradation efficiency by completely degrading tetracycline within 90 min. The best degradation rate constant of 18.9 × 10^–3 min^–1 was obtained at pH 7, which is 17-fold and 1.5-fold than that at pH 3 and pH 5, respectively. Above pH 7, the degradation rate sharply rose due to the alkaline hydrolysis of TCs. The addition of common electrolytes has been shown to reduce the photocatalytic degradation rate as a result of photocatalyst aggregation. The results of EPR, scavenging tests, and LC-QTOF/MS analysis showed that the photogenerated holes and •O₂^– produced by CNU upon photoirradiation degrade TC into small organic molecules such as 1-tetralone and 3-formyl propanoic acid. This study demonstrated the ease of environmentally friendly GCN preparation and their potential for the removal of ECs from the environment.