Insights into peroxymonosulfate activation for carbofuran degradation under visible LED via a double-component photocatalyst of Fe (III) impregnated N-doped TiO2

Abstract A hybrid process was proposed for carbofuran (CBF) degradation, a carbamate pesticide with a special refractory property, through peroxymonosulfate (PMS) activation under visible LED (Vis LED) by FeIII impregnated N-doped TiO2 photocatalyst (FeNT). An in-depth investigation was conducted to examine the synergistic effect of the FeNT/PMS/Vis LED process under various reaction conditions. An increase in the rate constant was observed with the increment of pH from 2.4 to 7.4, implying the feasibility of the process at neutral pH. A further increase in pH from 8.9 to 11 showed a sudden drop in the rate constant (if the role of base activation is ignored). The efficiency of CBF degradation is still more than 70% after adding NO3−, SO42−, HCO3−, and Cl−. Interestingly, the efficiency was not influenced even after the further increment of nitrate concentration. Furthermore, the high chloride concentrations caused an enhanced efficiency due to the generation of reactive halogens through two-electron transfer. Sixteen major intermediates were recognized and eight of them were never reported in the previous studies. Surprisingly, a new degradation pathway was noted in this study via H-abstractions and cyclization mechanisms. The FeNT/PMS/Vis LED process exhibited a dual functionality in terms of mineralization efficiency and about 90% TOC reduction can be achieved. Therefore, these findings provide new insights into the mechanism of PMS activation under Vis LED after coupling non-metal doped TiO2 photocatalyst with a metal component, and its implications for degradation of refractory and non-biodegradable pollutants in wastewater.