Compound specific isotope analysis to characterize degradation mechanisms of p-chloroaniline by persulfate at ambient temperature

Abstract

Compound-specific isotope analysis (CSIA) is a useful technique that has received an increasing attention for studying the degradation mechanisms of organic contaminants based on stable isotope fractionation concepts. This study reports the degradation mechanisms of p-chloroaniline (PCA) at different pH values (3, 5, 7 and 9) induced by persulfate (PS) based on 13C isotope fractionation during its preferential oxidation with SO4− and OH. The results showed that the degradation of PCA followed first-order kinetics (rate constants, 0.026, 0.0362, 0.0754 and 0.0497 h−1 at pH = 3, 5, 7 and 9, respectively), with the fastest degradation under neutral conditions (pH 7). The degradation rate was found to be higher under alkaline conditions (pH 9) compared to acidic conditions (pH 3 and 5). A normal carbon isotope fractionation of PAC was observed under neutral and alkaline conditions (eg., εC = −0.8‰ ±0.10 at pH 7 and εC = −1.0‰ ±0.17 at pH 9). However, a reverse carbon isotope effect at pH 3 (εC = 0.6‰ ±0.07) and pH 5 (εC = 1.1‰ ±0.06) was observed, respectively. Based on the identified transformation products and the insights revealed by CSIA, the degradation pathways were proposed. The current findings are crucial in understanding the PCA degradation mechanisms with SO4− and OH in aqueous systems.