Visible-Light Activation of a Dissolved Organic Matter-TiO 2 Complex Mediated via Ligand-to-Metal Charge Transfer.
Hoang Tran BuiHyeon Yeong ParkPedro J J AlvarezJaesang LeeWooyul KimEun-Ju KimPublished in: Environmental science & technology (2022)
Given the widespread use of TiO 2 , its release into aquatic systems and complexation with dissolved organic matter (DOM) are highly possible, making it important to understand how such interactions affect photocatalytic activity under visible light. Here, we show that humic acid/TiO 2 complexes (HA/TiO 2 ) exhibit photoactivity (without significant electron-hole activation) under visible light through ligand-to-metal charge transfer (LMCT). The observed visible-light activities for pollutant removal and bacterial inactivation are primarily linked to the generation of H 2 O 2 via the conduction band. By systematically considering molecular-scale interactions between TiO 2 and organic functional groups in HA, we find a key role of phenolic groups in visible-light absorption and H 2 O 2 photogeneration. The photochemical formation of H 2 O 2 in river waters spiked with TiO 2 is notably elevated above naturally occurring H 2 O 2 generated from background organic constituents due to LMCT contribution. Our findings suggest that H 2 O 2 generation by HA/TiO 2 is related to the quantity and functional group chemistry of DOM, which provides chemical insights into photocatalytic activity and potential ecotoxicity of TiO 2 in environmental and engineered systems.