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.