Cetyltrimethylammonium bromide – Oleic acid (CTAB-OA) bilayer coated iron oxide nanocrystals for enhanced chromium (VI) photoreduction via ligand-to-metal charge transfer mechanism

Photoactive cetyltrimethylammonium bromide-oleic acid (CTAB-OA) bilayer coated iron oxide nanocrystals (IONCs) were precisely synthesized and demonstrated for photo-enhanced hexavalent chromium (Cr(VI)) treatment. For these materials, an outward facing, CTAB layer offers specific affinity Cr(VI), while the core IONC (8–25 nm, as Fe3O4 single domain) surface participates in Fe(II)/Fe(III) redox cycling. Further, at coating-particle interface, OA alters material photoactive dynamics (near UV visible light) via a ligand-to-metal charge transfer (LMCT) mechanism, significantly enhancing Cr(VI) reduction. To delineate process variables, we first quantified photo-catalytic reduction rates under UVA irradiation (sunlight mimic intensities) function of size, which correlates with amount available ferrous ion (Fe(II)). It was observed that 25 nm functionalized showed outstanding sorption photoreduction performance compared other explored controls ( e.g. TiO2 nanocrystals). We systematically mechanism(s) through matrix control experiments, considering solution pH, dissolved gas (air, O2, CO2), along hydroxyl superoxide radicals. Results indicate Fe(II) (at interface) acts primary reductant Fe(III) (oxidized from Fe(II)) (re)cycles photocatalyzed pathway. Taken together, this work presents clear physical mechanistic description CTAB-OA IONCs which, when optimized, are highly effective treatment irradiation. In addition to potential broad application contaminant targets reactive Fe(II), many, also highlights need precise interfacial understanding nano composite materials towards optimization.