Tunable Generation of Reactive Oxygen Species in SnO2/SnS2 Nanostructures: Mechanistic Insights into Indigo Carmine Photodegradation

In semiconductor-based photocatalysis, one of the most significant directions in future research is designing materials with improved activity for the targeted photodegradation of organic contaminants. However, obtaining such photocatalysts requires an in-depth mechanistic understanding of the involved interfacial processes. In this framework, a comprehensive knowledge of photocatalysts' ability to produce particular reactive oxygen species (ROS) and their interaction with contaminants is particularly crucial. This work aims to examine how the phase composition of SnO2/SnS2-based nanomaterials (from bare SnO2 to SnS2) affects their ability to generate various ROS and propose the corresponding photodegradation mechanism. To this end, we combined three methods: scavenger tests, electron paramagnetic resonance (EPR) spin trapping techniques, and UV–vis nitro blue tetrazolium (NBT) assay. To demonstrate the implications of different ROS involved in the photodegradation of a particular substance, indigo carmine (IC) dye was chosen as a model contaminant. The second purpose of this study was to reveal and explain side effects that appear during tests with commonly applied scavengers. The results demonstrate the possibility of tunable ROS generation (from •OH through 1O2 to O2•–) in SnO2/SnS2-based photocatalysts and the crucial role of superoxide radicals in the IC photodegradation. These findings were correlated with the band diagrams to rationalize the mechanisms of ROS formation and IC degradation. The applied experimental approach demonstrated the importance of using multiple techniques to examine ROS generation processes and elucidate their mechanistic roles.