Synthesis of Single-Nanometer-Sized Gold Nanoparticles in Liquid–Liquid Dispersion System by Femtosecond Laser Irradiation

Abstract

Gold nanoparticles (AuNPs) show unique optical properties and catalytic activities, and their synthesis from gold ions has been widely studied. One of the additive-reagent-free and noncontact production procedures is the reduction of gold ions in solution by femtosecond laser pulses; however, the aggregation of AuNPs is unavoidable in homogeneous solution. Here, we report the synthesis of single-nanometer-sized AuNPs in a mixture of aqueous HAuCl 4 solution and n-hexane (the mixture) and in aqueous HAuCl 4 solution (the aqueous solution) by femtosecond laser irradiation in the absence of any additive reagents. Transmission electron microscopy revealed that circlelike colonies consisting of well-separated AuNPs were obtained from the mixture, while highly stacked and agglomerated AuNPs were obtained from the aqueous solution. The mean size of AuNPs in the mixture was nearly independent of the laser irradiation time, whereas that obtained in aqueous solution was gradually shifted to smaller size by laser irradiation period. We propose that the adsorption of primary AuNPs on the surface of hexane microdroplets and the fragmentation of large AuNPs in water by successive laser pulses retain single-nanometer-sized AuNPs in the mixture. The use of liquid−liquid interface on hexane microdroplets in aqueous solution provides a simple and useful environment to synthesize small AuNPs without the aid of surfactants or capping agents.

On-demand Plasmon Nanoparticle-Embedded Laser-Induced Periodic Surface Structures (LIPSSs) on Silicon for Optical Nanosensing

“…Metallic NP formation under action of intense laser irradiation is commonly attributed to the generation of solvated electrons and hydrogen radicals produced during optical breakdown of water-based systems 39,[44][45][46] or another active radical species depending on the composition of the solution 47,48 . However many precursors used for synthesis of NPs have the ability to be directly decomposed by laser even in relatively mild conditions far from the plasma formation as a result of photo- [49][50][51] or thermo-induced processes 52 .…”

Synthesis of iron-based nanoparticles from ferrocene by femtosecond laser irradiation: Suppression of the particle growth in a mixture of water and hexane

“…We recently succeeded synthesizing gold NPs with the diameter less than 10 nm from gold ions in a mixture of water and n-hexane in a short-time laser irradiation. We proposed that the adsorption of charged primary gold NPs on the surface of hexane microdroplets prevented NPs from growing [27]. The fs-laser induced nucleation is powerful method; however, the success is dependent on the reduction potential of metal ions: the more positive the reduction potential of metal ion, the more the metal ion tends to be reduced.…”

“…The second role of liquid-liquid interface, namely adsorption effect, was demonstrated for the synthesis of single-nanometer-sized gold NPs: the aggregation of charged primary gold nanoparticles was suppressed by the adsorption of them on the surface of hexane microdroplets dispersed in water [27]. The proper use of liquid-liquid interface between water and organic solvent would be useful to produce desired NPs…”

An electron-capture efficiency in femtosecond filamentation

“…Hence, chemical products starting from hydrogen, oxygen, and hydrogen peroxide [8,9], as well as reduction of metal ion [10,11] have been reported. This is also followed by the formation of nanoparticles (the most studied example): gold, Aun [12][13][14][15][16][17][18]; carbon nanoparticles [19]; diamond formation [20]; and DNA base modification [21], and ultimately, cancer therapy [22]. Femtosecond filamentation is accompanied by white light laser.…”

“…Although Aun formation mechanisms have been extensively studied in a filament, they involve multistep reactions. To reach the final products Aun, the reactions involve at least three electron reduction steps followed by mediation with H2O2 [12][13][14][15][16][17][18]. On the other hand, carbon nanoparticle formation and application to biological systems are promising [18,[20][21][22], and would also be composed of multistep reactions.…”