Switching the free radical based peroxydisulfate activation to the nonradical pathway by a chrome shaving–derived biochar for the efficient degradation of tetracycline

Abstract

The nonradical pathway in peroxydisulfate (PDS) activation for refractory contaminant removal has attracted increasing attention due to its inherent advantages. Hence, a new bimetallic biochar (Cr–Fe/BC) was synthesized via pyrolysis by using chrome shaving and ferric sulfate as the raw materials. Results illustrated that tetracycline (TC) could been completely removed in a small amount of Cr–Fe/BC (0.03 g/L) and PDS (2 mM) within 60 min with a high mineralization rate (82%). Besides, the Cr–Fe/BC/PDS system exhibited a strong anti–interference capability for coexisting organics and inorganics in water. Based on the results of various spectroscopic evidences and DFT calculations, iron introduction successfully transformed the free radical degradation process that was dominated by sulfate radicals (SO4–) into the nonradical degradation process that was dominated by electron transfer. The tunning mechanism of the free radical/nonradical pathway was connected to the increased π–electrons flow in sp2–carbon by conjugation after the iron introduction. Meanwhile, ecotoxicological safety of TC intermediates identified to validate the superiority of the nonradical process. In this work, a new method for inducing nonradical pathway was provided in the process of PDS activation, which effectively avoided harmful intermediates generation in the process of organic contaminants degradation.