Kinetics and mechanism analysis for the photodegradation of PFOA on different solid particles

Perfluorooctanoic acid (PFOA) has attracted considerable attention due to its worldwide distribution, bioaccumulation potential, environmental persistence, and possible toxic effects. In this work, the photodegradation kinetics and mechanisms of PFOA on six different solid particles were investigated. After 24 h of Hg lamp irradiation, significant degradation of PFOA was observed on paddy soil (PS), black soil (BS), yellow soil (YS), red soil (RS), Jiuxiang river soil (JXR) and 400 mesh quartz sand (QS). The photodegradation of PFOA on solid matrixes all followed pseudo-first-order kinetics, and the order of PFOA loss was QS > RS > JXR > YS > BS > PS. The intrinsic properties of solid particles, including light-shielding effect, organic carbon contents, particle size distribution and fractal dimension, and silica contents all have some correlations with PFOA photodegradation. In addition, trifluoroacetic acid (TFA) on solid particles can be effectively photodegraded, while it was hardly degraded in aqueous solution. Mass spectrometry results showed that decarboxylation and elimination were the two main reactions for PFOA photodegradation, leading to the formation of various products. This study may help deepen our understanding on the photochemical behaviors of PFOA on solid particles, which are important to evaluate the environmental fate of PFOA in the air.