Multifunctional Cl-S double-doped carbon nitride nanotube unit in catalytic ozone oxidation synergistic photocatalytic system: Generation of ROS-rich region and effective treatment of organic wastewater

Abstract Catalytic ozone oxidation synergistic photocatalysis (COP) can effectively overcome the shortcomings of incomplete mineralization and strong pH dependence of O3 and slow reaction rate of photocatalytic. Cl, S double-doped carbon nitride nanotube unit (Cl/S-CN) with the ability of catalyzing O3 and visible light photocatalysis was synthesized by hydrothermal self-repairing method to improve the applicability of the COP system in actual organic wastewater. Characterization and density functional theory (DFT) calculations found that Cl/S-CN has a stable and ordered nanotube (tube diameter: 56 nm) arrangement, a good energy band structure, and excellent e- delivery efficiency. It can generate reactive oxygen species (ROS)-rich region in the unit to promote the ROS chain cycle reaction, thereby generating more numbers and types of (non–)free radicals to participate in the degradation of organic pollution. For tetracycline (100 mg/L), the degradation rate in O3/vis/Cl/S-CN system was 90.1% at 10 min, and the degradation rate of TOC was 78% at 30 min. For P-nitrophenol (20 mg/L), the degradation rate was 91.6% at 20 min, and the degradation rate of TOC was 66% at 30 min. The COD degradation rates of influent water, secondary effluent water and oilfield produced water in COP system at 30 min were 70.5%, 83.4% and 76.5%, respectively. Cl/S-CN can catalyze the production of high activity ROS-rich region in COP system, effectively promote the production of ·OH, 1O2 and other active substances, and improve the applicability of COP system in actual organic wastewater.