Semiconductor-based solar photocatalytic degradation of surrogate naphthenic acids: Insights on degradation mechanism and the effects of pH, water matrix, and compound structure on the degradation kinetics

Semiconductor-based photocatalysis is emerging as a potent oxidation for degrading Naphthenic acids (NAs) in oil sands process water (OSPW). Here, the impacts of some of the OSPW-relevant parameters and properties were investigated to address some questions about the previously observed varied performance of a given catalyst in different OSPW samples and the differences of some catalysts in OSPW that could not be explained by their intrinsic electrophysical properties. To examine the individual impacts of the selected factors, model NAs were used with ultra-performance liquid chromatography (UPLC) for the analyses. The photocatalytic degradation kinetics was enhanced by the presence of Cl − and SO 4 2− in the water while HCO 3 − dampened the kinetics. The impact of a significant change in water pH appeared to be dependent on the direction of the change relative to the isoelectric points (IEP) of the catalyst. The reactivity of NAs in the photocatalysis was strongly structure-dependent with the alkyl branching and substituent being influential factors. The study of the reaction mechanism indicated that both O 2 − and OH mediated in the reactions. The study provides more understanding of the potentially varied dynamics of the photocatalytic process in treating different streams and can help make better-informed process designs. • Water pH and the catalyst's isoelectric point influenced the photocatalytic degradation of NAs. • CO 3 2− inhibited the photodegradation kinetics of cyclohexane carboxylic acid. • SO 4 2− enhanced the photodegradation of cyclohexane carboxylic acid. • Alkyl branching and the type of substituent on structures influenced their degradation.