Aqueous photoproduction of Au nanoparticles by natural organic matter: effect of NaBH4 reduction

Abstract

Treatment of seven types of natural organic matter (NOM) with sodium borohydride (NaBH₄), a selective reductant of carbonyl-containing functional groups, results in significantly decreased photoproduction of Au nanoparticles (Au⁰) from Au³⁺. Comparison of these results with those obtained from a series of model aromatic ketones and quinones demonstrates that these reaction rate changes after NaBH₄ treatment can be largely assigned to the aromatic ketone moieties in NOM. Moreover, these results are consistent with the charge-transfer model in which charge-transfer transitions arise among hydroxy-aromatic donors and carbonyl-containing acceptors. Electron paramagnetic resonance (EPR) analysis also uniformly indicates the important role of carbonyl-containing moieties in superoxide radical (O₂˙⁻) generation and denies that of phenolic moieties.