Activation of sodium percarbonate by cysteine complexation of Fe(ii) for the degradation of acetaminophen in water

Abstract

To overcome the limitations of the Fe(II)-activated percarbonate process for ACT removal, this study introduced cysteine as a complexing agent into the Fe(II)/SPC system and enhanced the degradation efficiency of ACT. Investigations were conducted on the effects of pH, temperature, common anions (Cl⁻, HCO₃⁻ and NO₃⁻) in the water column, and humic acid (HA) on the degrading efficiency of the Cys/Fe(II)/SPC system. The results showed that under ideal conditions, 99.9% removal of ACT at 0.05 mM could be achieved. Alkaline environments inhibited ACT degradation, whereas acidic environments promoted it. Electron paramagnetic resonance (EPR) successfully detected ˙OH and O₂˙⁻, but no ¹O₂ radical signal was detected. Further research was carried out to determine how much ˙OH and O₂˙⁻ contributed to the oxidation process. The results showed that both ˙OH and O₂˙⁻ contributed to the degradation of the ACT, with ˙OH's contribution being particularly significant. Mass spectrometry analysis was used to determine the structure of the oxidation products. Vulnerable sites in ACT were predicted using density functional theory. Using LC-MS/MS analysis, seven intermediates of the Cys/Fe(II)/SPC degradation of ACT were individually identified. The results showed that the acetylamino group on ACT and the C–N bond on the benzene ring are susceptible to attack by ˙OH. The T.E.S.T. toxicity prediction model was used to predict the toxicity of ACT and its intermediates. The results showed a trend towards reduced acute toxicity and overall developmental toxicity.