Cl/S co-doped carbon nitride nanotube clusters effectively drive the metal-free photo-Fenton reaction under visible light: A new ROS conversion mechanism

In this work, we used Cl/S co-doped carbon nitride nanotube clusters (Cl/S-TCN) photocatalyst to effectively drive the metal-free photo-Fenton (MF-PF) reaction. The synergistic effect of Cl/S-TCN and H2O2 made MF-PF(Cl/S-TCN) system have excellent degradation performance for organic wastewater in a wide pH range (3-9). The optimal amount of H2O2 was only 10 mM, the degradation rate of p-nitro-phenol (p-NP) by MF-PF(Cl/S-TCN) system under neutral conditions can be increased from 50.3% to 98.2%, the degradation rate of tetracycline (TC) reached more than 90% within 20 min, and the COD removal rates of domestic sewage and oilfield produced water reached 70.3% and 82.6% accordingly. MF-PF(Cl/S-TCN) system had excellent stability, and the performance loss was less than 0.7% after four cycles of ex-periments. Density functional theory calculations showed that Cl and S dopants accelerated the sepa-ration of photogenerated electrons and holes on the surface of Cl/S-TCN. These photogenerated electrons and holes, were used as electron donors and electron acceptors for reacting with H2O2, destroyed the O-O bond and O-H bond of H2O2, and finally converted H2O2 to center dot OH and center dot O-2(-) with strong oxidation, which is the key to enhance the performance of MF-PF(Cl/S-TCN) system. Such reaction pathway was rarely reported in previous studies. (C) 2022 Elsevier Ltd. All rights reserved.