Controllable Pyridine N-Oxidation–Nucleophilic Dechlorination Process for Enhanced Dechlorination of Chloropyridines: The Cooperation of HCO4– and HO2–

Dechlorination of chloropyridines can eliminate their detrimental environmental effects. However, traditional dechlorination technology cannot efficiently break the C–Cl bond of chloropyridines, which is restricted by the uncontrollable nonselective species. Hence, we propose the carbonate species-activated hydrogen peroxide (carbonate species/H2O2) process wherein the selective oxidant (peroxymonocarbonate ion, HCO4–) and selective reductant (hydroperoxide anion, HO2–) controllably coexist by manipulation of reaction pH. Taking 2-chloropyridine (Cl–Py) as an example, HCO4– first induces Cl–Py into pyridine N-oxidation intermediates, which then suffer from the nucleophilic dechlorination by HO2–. The obtained dechlorination efficiencies in the carbonate species/H2O2 process (32.5–84.5%) based on the cooperation of HCO4– and HO2– are significantly higher than those in the HO2–-mediated sodium hydroxide/hydrogen peroxide process (0–43.8%). Theoretical calculations confirm that pyridine N-oxidation of Cl–Py can effectively lower the energy barrier of the dechlorination process. Moreover, the carbonate species/H2O2 process exhibits superior anti-interference performance and low electric energy consumption. Furthermore, Cl–Py is completely detoxified via the carbonate species/H2O2 process. More importantly, the carbonate species/H2O2 process is applicable for efficient dehalogenation of halogenated pyridines and pyrazines. This work offers a simple and useful strategy to enhance the dehalogenation efficiency of halogenated organics and sheds new insights into the application of the carbonate species/H2O2 process in practical environmental remediation.