Electron transfer mechanism that Ti3C2 regulates Cl-doped carbon nitride nanotube: Realizing efficient photocatalytic decarbonization and denitrification in wastewater

Abstract

In this work, we prepared Cl-doped g-C3N4 nanotube composite Ti3C2 (Cl-TCN@TC) photocatalyst for the first time by electrostatic self-assembly method, which has great advantages in decarbonization and denitrification of wastewater. Cl-TCN@TC-2 showed good removal effect on tetracycline (TC, 91.08 %) and p-nitrophenol (p-NP, 70.92 %). The degradation kinetic constants of TC in pre-20 min and p-NP in 120 min by Cl-TCN@TC-2 were 28.8 and 29.0 times higher than those of CN. The COD removal rates of domestic sewage and oilfield produced water by Cl-TCN@TC-2 reached 54.2 % and 64.8 %. After adding 2 mM HCOOH, the nitrate (NO3–) degradation rate of Cl-TCN@TC-2 reached 50.24 %, which is 12.62 times that of CN, and the N2 selectivity was 92.46 %. The addition of HCOOH will produce •CO2– to assisted the photocatalytic denitrification. DFT calculations show that under visible light irradiation, the electrons (e-) on Ti3C2 will transfer to the valence band (VB) of Cl-TCN and combine with photoinduced-holes (h+), while the photoinduced-e- in the VB will be transferred to its conduction band (CB), realizing the separation of photogenerated e--h+ pairs. This kind of e- transfer pathway has been rarely reported in previous studies. With this e- transfer property of Cl-TCN@TC, a large amount of •O2– is generated on the surface of Cl-TCN, which determines that Cl-TCN@TC has higher photocatalytic activity. In the process of denitrification, the e- in the Cl-TCN CB transfers to the O atom and break the NO bond of NO3–, which greatly improves the denitrification performance of Cl-TCN@TC.