Efficient visible-light photocatalytic degradation of imidacloprid and acetamiprid using a modified carbon nitride/tungstophosphoric acid composite induced by a nucleophilic addition reaction

Abstract

This study proposed a novel method to combine modified carbon nitride (MCN) and tungstophosphoric acid (HPW). First, carbon nitride (CN), containing more uncondensed amino and carbonyl groups, was prepared by thermal condensation from urea at a low temperature. Then, in the presence of formic acid, a reversible nucleophilic addition reaction was performed between the carbonyl groups of formaldehyde (or CN) and amino groups of CN. Subsequently, during the HPW impregnation, the reverse reaction occurred, which increased the HPW loading. The results of the XPS and FTIR analyses verified the occurrence of a nucleophilic addition reaction during the formaldehyde treatment, as well as the formation of hydroxyl functional groups in the intermediate products. After impregnation with HPW, the disappearance of the hydroxyl groups and the recovery of the carbonyl groups were observed in the XPS C1s spectra. The as-prepared MCN450/HPW, obtained by modifying CN450 (CN calcined at 450 °C) with formaldehyde and loading with HPW, exhibited excellent visible-light (λ > 400 nm) photocatalytic degradation of imidacloprid and acetamiprid. The degradation rate constant (0.70 h−1) of imidacloprid was 6.4 times that of CN450, while the degradation rate of acetamiprid by MCN450/HPW was 11 times that of CN450. The results of the active species capture experiments showed that OH and h+ were the main active species in the visible-light photocatalytic degradation process.