The Roles of Sono-induced Nitrosation and Nitration in the Sono-degradation of Diphenylamine in Water: Mechanisms, Kinetics and Impact Factors

Abstract

The potential risks of sono-induced nitrosation and nitration side reactions and consequent toxic nitrogenous byproducts were first investigated via sono-degradation of diphenylamine (DPhA) in this study. The kinetic models for overall DPhA degradation and the formation of nitrosation byproduct (N-nitrosodiphenylamine, NDPhA) and nitration byproducts (2-nitro-DPhA and 4-nitro-DPhA) were well established and fitted (R2 > 0.98). Nitrosation contributed much more than nitration (namely, 43.3 – 47.3 times) to the sono-degradation of DPhA. The contribution of sono-induced nitrosation ranged from 0.4 to 56.6% at different conditions. The maximum NDPhA formation rate and the contribution of sono-induced nitrosation were obtained at 600 and 200 kHz, respectively, as ultrasonic frequencies at 200 to 800 kHz. Both NDPhA formation rate and the contribution of sono-induced nitrosation increased with increasing power density, while decreased with increasing initial pH and DPhA concentration. PO43–, HCO3–, NH4+ and Fe2+ presented negative impacts on sono-induced nitrosation in order of HCO3– >> Fe2+ > PO43– > NH4+, while Br– exhibited a promoting effect. The mechanism of NDPhA formation via sono-induced nitrosation was first proposed.