Persulfate activation by nano zero-valent iron for the degradation of metoprolol in water: influencing factors, degradation pathways and toxicity analysis

Abstract

In this study, nano zero-valent iron (nZVI) was utilized to activate persulfate (PS) for the degradation of metoprolol (MTP), a commonly used drug for curing cardiovascular diseases, in water. Quenching tests indicated that both the sulfate radical (SO₄˙⁻) and hydroxyl radical (˙OH) contributed to the degradation of MTP, while SO₄˙⁻ seemed to play a large role under natural pH conditions. Batch tests were conducted to investigate the effects of several influencing factors, such as PS concentration, initial MTP concentration, pH, temperature and common anions, on the degradation performance of MTP. Generally, lower MTP concentration and pH values, and higher PS concentration and temperature favoured MTP degradation. HCO₃⁻, NO₃⁻ and SO₄²⁻ were found to inhibit MTP degradation, while Cl⁻ enhanced MTP degradation. Several corrosion products of nZVI, including Fe₃O₄, Fe₂O₃ and FeSO₄, were formed during the reaction, which was reflected by the combined XRD and XPS analysis. Degradation pathways of MTP were proposed according to the identified transformation products, and the peak areas of the major products along with the time were also monitored. Finally, the toxicity of the reaction solution was assessed by experiments using Aliivibrio fischeri. Overall, it could be concluded that nZVI/PS might be a promising method for the rapid treatment of MTP-caused water pollution.