Metallacarborane-functionalized graphene oxide as a recyclable UVC/UVA photocatalyst for micropollutant removal

This study reports the application of a metallacarborane-based photocatalyst for the removal of organic micropollutants in water. The anionic θ-cobaltacarborane salt H[3,3’-Co(1,2-C 2 B 9 H 11 ) 2 ] (abbreviated as H[1]) was non-covalently linked onto amine-functionalized graphene oxide (GO@NH 2 ) to create a hybrid, recyclable photocatalyst (GO@NH 2 -H[1]). Both the homogeneous and heterogeneous systems were evaluated under UVC and UVA irradiation for the degradation of four representative micropollutants galaxolide (HHCB), tonalide (AHTN), chlorpyrifos (CPS), and triclosan (TCS)- in ultrapure water, drinking water (DW), and wastewater effluent (WW). The homogeneous protonated θ-cobaltacarborane photocatalyst, H[1] alone, exhibited high activity under UVC even at low catalyst loading, while UVA-driven degradation required aeration to reach high efficiencies. The heterogeneous system, GO@NH 2 -H[1], showed excellent activity under both light sources, and effective performance across all matrices. While CPS and TCS were more persistent, aeration notably enhanced their degradation under UVA. Transformation products were characterized by UHPLC-QTOF, confirming limited formation of toxic intermediates. A mechanistic pathway involving photoexcited Co(III) species, superoxide, and hydroxyl radicals was proposed. The catalyst retained its activity over six reuse cycles, with low leaching and good reusability, demonstrating high stability and photochemical robustness. These findings introduce metallacarborane-based photocatalysis as a green, oxidant-free, and reusable approach for emerging contaminant removal, supporting its potential integration in advanced water treatment technologies.