Photochemical Production of Hydroxyl Radicals from Lake Natural Colloidal Particles: Microheterogeneous Distribution and Formation Mechanism

Natural colloidal particles (NCPs) are ubiquitous in lake ecosystems, whereas information on the photochemical production, distribution, and formation mechanism for hydroxyl radicals ( • OH) from NCPs remains unknown. Herein, NCPs from different lake waters were extracted, with source- and concentration-dependent heterogeneities in formation potential, microheterogeneous distribution, and mechanism for • OH being explored. NCPs were composed of inorganic colloidal particles (ICPs) and organic colloidal particles (OCPs), and NCPs-mediated • OH was divided into free • OH and bound • OH. Results showed that, regardless of NCP sources and concentrations, apparent quantum yields of free • OH were 1.22–5.24 times lower than those of bound • OH, indicating high production potential and microheterogeneous distribution. It was indicated that ICPs primarily contributed to the production of bound • OH, while OCPs were the main components responsible for free • OH generation. Furthermore, water oxidation by valence band holes in ICPs acted as the primary pathway for bound • OH formation, while oxygen-mediated chain reactions driven by excited triplet states and superoxide anions contributed to free • OH formation. The microheterogeneous distribution of • OH exhibited distinct attenuation rates toward aquatic contaminants. This study highlights NCPs as important photochemical • OH sources that significantly influence the behaviors and fate of nutrients and contaminants in aquatic ecosystems.