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

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 2019-10, Vol.383, p.111994, Article 111994
• Main Authors: Nakanishi, Ryuzo, Saeki, Morihisa, Taguchi, Tomitsugu, Ohba, Hironori
• Format: Article
• Language: English
• Subjects: Acidity; Aqueous solutions; Ethanol; Gold; Gold nanoparticle; Gold(III) ion; Hydrochloric acid; Hydrogen chloride; Isopolymolybdate; Laser-induced particle formation; Molybdate; Molybdenum; Molybdenum blue; Nanoparticles; Photoreduction; Precursors; Sodium chloride; Species; Spectroscopy
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2019.111994

[Display omitted] •Laser-induced formation of Au nanoparticles from a mixture of AuCl4− and molybdate in hydrochloric acid solutions.•Direct photoreduction of Au(III) is significantly inhibited by a large excess of Cl−.•Photoirradiation generates molybdenum blue species from isopolymolybdate.•The nascent molybdenum blue species reduce Au(III), promoting the formation of Au nanoparticles. 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.