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