Oxidation of amines and their derivatives with persulfate without activation: Impact of mineral oxides and stoichiometric efficiency

Abstract Persulfate (PS; peroxydisulfate and peroxymonosulfate) activation on aquifer materials via a single-electron chain reaction can generate various reactive oxygen species (ROS) for aqueous contaminant degradation by in situ chemical oxidation (ISCO). However, this process may be altered when amino compounds (AMCs) are present in the groundwater due to their rapid reaction with PS without activation. In this study, we investigate these reaction processes by employing a series of probe AMCs. The nucleophilic displacement and polymerization reactions of AMCs with PS in water are enhanced by deprotonation or electron-donating substitutions on the AMCs, and the obtained rate constants are 2–4 orders of magnitude higher than those of phenolic or nitro compounds. In addition, the presence of mineral oxides changes both the oxidation rates and stoichiometric efficiency (η) of the AMCs because the oxides compete with AMCs to interact with PS in a low-efficiency and heterogeneous manner. Unlike electrophilic pollutants such as nitrobenzene, the higher reactivity of PS with nucleophilic AMCs compared with mineral oxides results in the dominance of heterolytic PS decomposition via two-electron oxidation. On this basis, we can predict the value of η for PS in this complicated heterogeneous system using the property-related parameters (RM) of mineral oxides and Hammett constants (σ+) of AMCs. This study highlights the overestimation of η for AMCs as the specific contaminants in persulfate-based ISCO. Moreover, the coexistence of AMCs as nucleophilic agents contributes to natural oxidant demand, which may impact the remediation of contaminated groundwater and oxidant stoichiometry.