Removal of the neonicotinoid insecticide acetamiprid from wastewater using heterogeneous photocatalysis

Top-down versus bottom-up oxidation of a neonicotinoid pesticide by OH radicals

Emerging contaminants (EC) distributed on surfaces in the environment can be oxidized by gas phase species (top-down) or by oxidants generated by the underlying substrate (bottom-up). One class of EC is the neonicotinoid (NN) pesticides that are widely distributed in air, water, and on plant and soil surfaces as well as on airborne dust and building materials. This study investigates the OH oxidation of the systemic NN pesticide acetamiprid (ACM) at room temperature. ACM on particles and as thin films on solid substrates were oxidized by OH radicals either from the gas phase or from an underlying TiO2 or NaNO2 substrate, and for comparison, in the aqueous phase. The site of OH attack is both the secondary >CH2 group as well as the primary -CH3 group attached to the tertiary amine nitrogen, with the latter dominating. In the case of top-down oxidation of ACM by gas phase OH radicals, addition to the -CN group also occurs. Major products are carbonyls and alcohols, but in the presence of sufficient water, their hydrolyzed products dominate. Kinetics measurements show ACM is more reactive toward gas phase OH radicals than other NN nitroguanidines, with an atmospheric lifetime of a few days. Bottom-up oxidation of ACM on TiO2 exposed to sunlight outdoors (temperatures were above 30 °C) was also shown to occur and is likely to be competitive with top-down oxidation. These findings highlight the different potential oxidation processes for EC and provide key data for assessing their environmental fates and toxicologies.

Reducing the risk of exposure of airborne antibiotic resistant bacteria and antibiotic resistance genes by dynamic continuous flow photocatalytic reactor

In this study, based on the dynamic photocatalytic reactor constructed by the new photocatalyst TiO₂/MXene, the purification process of different biological particles in aerosol was systematically studied. Multidrug resistant bacteria were easier to inactivate than common bacteria of the same kind, whether under UV conditions or photocatalysis. Photocatalyst was loaded on porous polyurethane sponge filler so that the combined effect of adsorption and advanced oxidation significantly improved the antibiotic resistant bacteria (ARB) disinfection effect. The inactivation efficiency of two ARBs under UV254 increased by 1.2 lg and 2.1 lg. In addition, it was found that the microorganisms treated by UV had slight self-repair phenomenon in a short time, while the microbial activity decreased continuously after photocatalysis. With the addition of photocatalyst, the particle size distribution of airborne Escherichia coli decreased and the micro morphology of cells was more seriously damaged. Antibiotic resistance genes (ARGs) carried by ARB can be dissociated into the environment after cell destruction, but it can be removed at a high level (sul2 can achieve 2.11 lg) in the continuous reactor at the same time. While avoiding secondary pollution, it also provides a powerful solution for airborne ARGs control.