Photoinduced gold recovery mediated by isopolymolybdate in strongly acidic HCl/NaCl solutions

Abstract

The laser-induced formation of gold nanoparticles (AuNPs) was studied in hydrochloric acid solutions containing isopolymolybdate. Aqueous solutions of HAuCl4 (0.5 mM) in HCl (0.1–1.0 M)/NaCl media containing ethanol (0.5% v/v) were irradiated with 355 nm laser pulses in the absence or presence of molybdate. The reaction progress was probed by UV–vis spectroscopy. Without molybdate, the formation of AuNPs is significantly hindered because a large excess of Cl− renders the AuCl4− precursor resistant to direct photoreduction with ethanol. The incorporation of molybdate into solution effectively mediates the photoinduced formation of AuNPs in 0.1–0.5 M HCl. For this range of acidity, photoirradiation generates the molybdenum blue (MB) species from the reaction of photoexcited Mo36O1128− (polyoxoanions) with ethanol, followed by the reduction of AuCl4− with the MB species. At a higher acidity, the formation of AuNPs is virtually undetectable because the MB species are no longer generated due to the absence of anionic molybdate precursors.