Abstract
We report the generation of gold nanoparticles (AuNPs) from the aqueous solution of chloro(2,2′,2″-terpyridine)gold(III) ion ([Au(tpy)Cl]2+) through X-ray radiolysis and optical excitation at a synchrotron. The original purpose of the experiment was to investigate the photoinduced structural changes of [Au(tpy)Cl]2+ upon 400 nm excitation using time-resolved X-ray liquidography (TRXL). Initially, the TRXL data did not show any signal that would suggest structural changes of the solute molecule, but after an induction time, the TRXL data started to show sharp peaks and valleys. In the early phase, AuNPs with two types of morphology, dendrites, and spheres, were formed by the reducing action of hydrated electrons generated by the X-ray radiolysis of water, thereby allowing the detection of TRXL data due to the laser-induced lattice expansion and relaxation of AuNPs. Along with the lattice expansion, the dendritic and spherical AuNPs were transformed into smaller, raspberry-shaped AuNPs of a relatively uniform size via ablation by the optical femtosecond laser pulse used for the TRXL experiment. Density functional theory calculations confirm that the reduction potential of the metal complex relative to the hydration potential of X-ray-generated electrons determines the facile AuNP formation observed for [Au(tpy)Cl]2+.
Highlights
Information on the structural dynamics of a chemical reaction is crucial for determining its reaction mechanism
In a typical Time-resolved X-ray liquidograpy (TRXL) experiment [16,17,18], with X-ray facilities such as synchrotrons and X-ray free-electron lasers (XFELs), a liquid solution containing the solute molecule of interest is exposed to a femtosecond laser pulse to initiate a photochemical reaction of the solute molecule, and the structural changes associated with the subsequent reactions of the solute molecule are probed by an X-ray scattering of the solution sample as a function of time delays between the laser pulse and the X-ray pulse
In our effort to investigate the structural dynamics of chloro(2,2,2 -terpyridine)gold(III) ion ([Au(tpy)Cl]2+, tpy = 2,2 :6,2 -terpyridine) in water, we accidentally observed that the [Au(tpy)Cl]2+ undergoes a nanoparticle formation—in this case, the formation of gold nanoparticles (AuNPs)
Summary
Information on the structural dynamics of a chemical reaction is crucial for determining its reaction mechanism. In our effort to investigate the structural dynamics of chloro(2,2 ,2 -terpyridine)gold(III) ion ([Au(tpy)Cl]2+, tpy = 2,2 :6 ,2 -terpyridine) in water, we accidentally observed that the [Au(tpy)Cl]2+ undergoes a nanoparticle formation—in this case, the formation of gold nanoparticles (AuNPs) This observation provides useful information for studying nanoparticle formation induced by X-ray radiolysis and exploring the determining factor for the X-ray-induced generation of nanoparticles. AuNPs are synthesized by the reduction of HAuCl4 via solvated electrons generated by gamma rays, X-rays, or intense optical to near-infrared femtosecond pulses This method has relevance with our observation of AuNPs formation in the TRXL experiment. The RPs of all metal-containing molecules in water studied by TRXL as well as HAuCl4 and [Au(tpy)Cl]Cl2 confirm this conclusion
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