Insight into the photodegradation of o,p'-dichlorodiphenyltrichloroethane in a broad spectrum of irradiation light

Abstract

Photolysis is the main pathway for the degradation of persistent organic pollutants (POPs). Most investigations, however, have been limited to the ultraviolet or visible region, and the reaction mechanism of infrared (IR) light is still unclear. In this study, the photodegradation of o,p'-dichlorodiphenyltrichloroethanes (o,p'-DDT) on the silica (SiO2)/air interface under different irradiation light sources was systematically investigated. Interestingly, for the first time, effective degradation of o,p'-DDT under IR light irradiation was observed, which was ascribed to the anti-Stokes Raman scattering process of SiO2. Moreover, desert sands could also serve as a vector for the photodegradation of o,p'-DDT. The lower removal efficiency of desert sands compared to pure SiO2 was a combined effect of differences in Fe3+ component and SiO2 content. It is worth noting that direct photodegradation plays a dominant role in the photodegradation of o,p'-DDT on SiO2. Besides, indirect photodegradation resulted mainly from •OH (25.0%), O2•− (6.9%), and 1O2 (5.6%) generated in the reaction system. In addition to hydroxylation and dechlorination products, the formation of four novel silicon-based products was observed, which resulted from the direct reaction of silyl radicals with o,p'-DDT. This study revealed that the specific Raman scattering effect of SiO2 played a vital role in the self-purification process of POPs upon SiO2-based environmental matrices. The light-mediated decontamination system upon SiO2 constructed in this study could provide critical information for addressing POPs contamination on sands.