Gold Nanotriangle Formation through Strong-Field Laser Processing of Aqueous KAuCl4 and Postirradiation Reduction by Hydrogen Peroxide.

Femtosecond laser irradiation of aqueous KAuCl4 followed by postirradiation reduction with hydrogen peroxide (H2O2) is investigated as a new approach for the synthesis of gold nanotriangles (AuNTs) without any added surfactant molecules. Laser irradiation was applied for times ranging from 5 to 240 s, and postirradiation reduction of the solutions was monitored by UV-vis spectroscopy. Laser processing of aqueous KAuCl4 for 240 s, where the full reduction of Au(III) occurred during irradiation, produced spherical gold nanoparticles (AuNPs) with an average size of 11.4 ± 3.4 nm. Irradiation for shorter times (i.e., 15 s) resulted in the formation of laser-generated AuNP seeds (5.7 ± 1.8 nm) in equilibrium with unreacted KAuCl4 after termination of laser irradiation. The postirradiation reduction of these solutions by H2O2 produced a mixture of spherical and triangular AuNPs. Decreasing the laser irradiation time from 45 to 5 s significantly reduced the number of laser-generated Au seeds, the amount of H2O2 produced, and the rate of postirradiation reduction, resulting in the formation of a large number of AuNTs with sizes increasing from 29.5 ± 10.2 to 125 ± 43.2 nm. Postirradiation reduction is kinetically inhibited in the absence of laser-generated AuNP seeds.