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.