抄録
Gold nanoparticles (AuNPs) were spontaneously formed through the reduction of tetrachloride gold(III) ions ([AuCl_4]^-) after mixing of an aqueous [AuCl_4]^- solution with an argon (Ar)-purged ultrapure water sonicated with 950 kHz bath-type ultrasonicator at 20 ℃ for 8 min in the absence of any added reducing agents. This indicates that some chemical species which can reduce [AuCl_4]^- exist in the sonicated water. In this work, in particular, we examine the contribution of nitrogen radical (N・), oxygen radical (O・) and recombination products (e.g., ・O_2^- and ^1O_2) generated from sonolysis of water to the [AuCl_4]^- reduction and AuNP formation in sonicated water. In order to evaluate the contribution of N・, O・, ・O_2- and ^1O_2 to the [AuCl_4]^- reduction in sonicated water, we checked the [AuCl_4]^- reduction in N_2-purged sonicated water and O_2-purged sonicated water. We found that [AuCl_4]^- was hardly reduced in the N_2-purged sonicated water and O_2-purged sonicated water. This suggests that the reduction of [AuCl_4]^- is not attributed to the N・, O・, ・O_2^- and ^1O_2 generated from the sonolysis of water. On the other hand, the [AuCl_4]^- was significantly reduced in air-saturated sonicated water. This implies that nitrogen oxide compounds generated from sonolysis of water contribute to the [AuCl_4]^- reduction and the AuNP formation in sonicated water.
