We report on the time evolution of the sodium tetrachloroaurate (NaAuCl(4)) chemical properties as a function of soft X-ray exposure in a dried sample on a silicon surface using X-ray photoelectron spectroscopy (XPS). Our investigations provide mechanistic insight into the photoreduction kinetics from Au(III) to Au(I) and then Au(I) to Au(0). We unambiguously show that XPS photoreduction occurs in stepwise fashion via the Au(I) state. Both photoreduction steps undergo first-order kinetics.

We report on the time evolution of gold nanoparticle (AuNP) optical properties and size distributions as a function of laser irradiation in pure water samples and at sodium dodecylsulphate (SDS) surfactant concentrations above and below the SDS critical micelle concentration in water. Our investigations provide a mechanistic insight into the laser-induced formation kinetics involved in AuNP production via 1064 nm laser irradiation in aqueous solution, as well as the relative stabilities of different AuNP size regimes. Following preparation via laser ablation at 1064 nm, we show that 532 nm laser irradiation in the absence of surfactant generates AuNP that are both small in size and possess a narrow particle size distribution. This distribution remains narrow and shifts to smaller average particle size with increasing surfactant concentration.

We report on the time evolution of gold nanoparticles produced by laser ablation in the presence of the cationic surfactants cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC) in aqueous solution. The broader applicability of a laser-induced nanoparticle formation kinetic model previously developed by us for the case of anionic surfactants in aqueous solution [ J. Phys. Chem. C 2010 , 114 , 15931 - 15940 ] is shown to also apply in the presence of cationic surfactants. We explore the surface properties of the nanoparticles produced in the presence of the cationic surfactants via synchrotron X-ray photoelectron spectroscopy (XPS). The XPS data indicate that at CTA(+) concentrations approximating the aqueous critical micelle concentration Au(III) is present on the nanoparticle surface. Such oxidation is not observed at (i) lower CTA(+) concentrations, (ii) in the presence of an anionic surfactant, or (iii) in the case of pure water as a solvent.

The time evolution of gold nanoparticle (AuNP) yields by in-situ laser irradiation from bulk gold in aqueous solutions containing the surfactant sodium dodecylsulfate (SDS) at concentrations above and below the critical micelle concentration in water is reported. These studies are augmented by transmission electron microscopy images of AuNP samples at each SDS concentration recorded after 90 min of laser irradiation. The results show that while a low concentration of SDS plays a role in the formation kinetics, there is no apparent influence of the SDS concentration around the surfactant critical micelle concentration on particle size during AuNP production.