Kinetic Control of [AuCl] Photochemical Reduction and Gold Nanoparticle Size with Hydroxyl Radical Scavengers.

Laser-induced photochemical reduction of aqueous [AuCl] is a green synthesis approach requiring no chemical reducing agents or stabilizers; but size control over the resulting gold nanoparticles remains a challenge. Under optical breakdown conditions producing hydrated electrons (e) and hydroxyl radicals (OH) through decomposition of water, [AuCl] reduction kinetics follow an autocatalytic rate law, which is governed by rate constants: nucleation rate , dependent on e; and growth rate , dependent on the OH recombination product, HO. In this work, we add the hydroxyl radical scavengers isopropyl alcohol and sodium acetate to limit HO formation.

Radical Chemistry in a Femtosecond Laser Plasma: Photochemical Reduction of Ag⁺ in Liquid Ammonia Solution.

Plasmas with dense concentrations of reactive species such as hydrated electrons and hydroxyl radicals are generated from focusing intense femtosecond laser pulses into aqueous media. These radical species can reduce metal ions such as Au to form metal nanoparticles (NPs). However, the formation of H₂O₂ by the recombination of hydroxyl radicals inhibits the reduction of Ag⁺ through back-oxidation.

Roles of Free Electrons and HO in the Optical Breakdown-Induced Photochemical Reduction of Aqueous [AuCl].

Free electrons and HO formed in an optical breakdown plasma are found to directly control the kinetics of [AuCl] reduction to form Au nanoparticles (AuNPs) during femtosecond laser-assisted synthesis of AuNPs. The formation rates of both free electrons and HO strongly depend on the energy and duration of the 800 nm laser pulses over the ranges of 10-2400 μJ and 30-1500 fs. By monitoring the conversion of [AuCl] to AuNPs using in situ UV-vis spectroscopy during laser irradiation, the first- and second-order rate constants in the autocatalytic rate law, k and k, were extracted and compared to the computed free electron densities and experimentally measured HO formation rates.