Exploratory Study on Size-Selective Production of Gold Nanospheres in Aqueous Solution

摘要

By applying high pressures well above the critical pressure of water (22.1 MPa), we prepared gold nanoparticles (Au NPs) using a nanosecond pulsed laser-induced size-reduction technique. The Au NPs thus obtained exhibited a remarkably narrow size distribution and size-selectivity dependent on the applied laser energy density. This is significant because previous attempts under ambient pressure failed to achieve such size-selective generation. Very spherical Au NPs of diameters, 46 nm and 33 nm with a standard deviation of only 2-3 nm, were obtained at the expense of original faceted 58-nm Au NPs (Fig. 1). We ascribed our results to the formation of a supercritical water layer surrounding the liquid droplet NP transformed by laser heating. The supercritical layer originates from heat transfer from the particle, leading to water temperatures above the critical point of 647 K, which acts as an effective heat sink for photothermal size reduction.