Low-dose bicarbonate promoting hydrogen peroxide conversion to hydroxyl radicals for heterogeneous photo-Fenton degradation of neonicotinoids through copper hydroxyphosphate.

Activating peroxymonocarbonate (HCO4-), generated in-situ by the reaction between H2O2 and HCO3-, is a promising remediation technology for pollutants treatment. However, the utilization of HCO3- with concentration higher than surface water and the generation of weakly oxidizing reactive oxygen species face the bottleneck challenges of high treatment cost and refractory pollutants inefficient degradation. The present work has been confirmed an attractive result that the •OH formation was significantly promoted with broad-spectrum responsive Cu2(OH)PO4 catalyst in sunlight-driven heterogeneous photo-Fenton system with the environmental relevant concentration (2 mM) of HCO3- (SH-PF + HC system), thereby effectively degrading refractory imidacloprid. The conversion of H2O2 to HCO4- in the presence of HCO3- inhibited the occurrence of H2O2 unsatisfactory decomposition to O2/H2O/•O2-. The HCO4- was more prone to electron transfer with Cu2(OH)PO4 and reduced reaction energy barrier for generating •OH based on the results of electrochemical measurements and theoretical calculation, causing a 2-fold increase in the utilization efficiency (74.6%) of H2O2 for yielding •OH. The effective mineralization and detoxification of imidacloprid were realized in SH-PF + HC system, which existed robust anti-interference against coexisting substances and universality for various pollutants degradation. The HCO3- in natural waters can be effectively utilized to accelerate imidacloprid degradation using Cu2(OH)PO4 catalyst in SH-PF system. The study has provided an effective strategy to promote •OH formation by using low-dose HCO3- in sunlit natural waters for the practical treatment of refractory pollutants.