Surfactant- and reducer-free synthesis of gold nanoparticles in aqueous solutions

Abstract

We report here the surfactant-and reducer-free synthesis of gold nanoparticles from an aqueous hydrogen tetrachloroaurate (III) tetrahydrate (HAuCl 4 ·4H 2 O) solution using a high-frequency (950 kHz) ultrasound (in the absence of any stabilizing, capping and reducing agents). In particular, size, shape and stability of gold nanoparticles prepared by the 950 kHz ultrasound irradiation (sonication) for 8 min in the surfactant-free aqueous solutions were examined in terms of AuCl 4 -concentration (in the range of 0.01-0.1 mM), additional salts (NaCl, HCl and NaOH) and temperature (in the range of 4-60 ˚C). We found that higher AuCl 4 -concentration promoted particle growth (size increase) and plate formation.In addition, the plate formation was enhanced with the addition of NaCl or HCl (but not NaOH). This is most likely due to the AuCl 4 -reduction on a certain crystal facets (e.g., (110) facets) caused by the adsorption of Cl -ions on specific crystal facets (e.g., (111) facets).Furthermore, we revealed that the temperature elevated above 50 ˚C led to the formation of spherical gold nanoparticles with the diameter of 20-60 nm from a 0.1 mM AuCl 4 -aqueous solution while triangular plates formed coexisting with spherical nanoparticles below 50 ˚C.

Hydrogen-assisted fabrication of spherical gold nanoparticles through sonochemical reduction of tetrachloride gold(III) ions in water

“…Since Cl -ions prefer to adsorb onto gold surface [37,38], Cl -ions should affect strongly the crystal growth and stabilization. Indeed, we confirmed that plate-like particles were preferably formed rather than spherical AuNPs with the addition of HCl or NaCl in the sonochemical synthesis of AuNPs [27]. This means that Cl -ions adsorb a certain crystal facet, and thereby [AuCl4] -reduction occurs on other crystal facets [39,40].…”

“…Numerous reports have described the size-and shape-control of metal nanoparticles in terms of molecular characteristics of capping agents and kinetics of metal ion reduction by reducing agents [13][14][15][16][17][18][19][20][21][22][23][24]. On the other hand, we have recently investigated the synthesis of gold nanoparticles (AuNPs) through the sonochemical reduction of tetrachloride gold(III) ions ([AuCl4] -) in aqueous solutions in the absence of any additional reducing and capping agents [27]. The AuNPs are formed through the reduction of [AuCl4] -by hydrogen radicals (H•) generated from sonolysis of water (H2O → H• + •OH) as follows [28][29][30] Figure 1a).…”

Effect of Experimental Parameters on the Fabrication of Gold Nanoparticles via Laser Ablation

“…Advantages of this method include the relative simplicity of the procedure and the absence of chemical reagents in the final preparation, but the size distributions of the GNPs prepared by this technique tend to be broadened due to the agglomeration and ejection of large fragments during laser ablation. To achieve the particlesize reducetion, different surfactants can be used [39][40][41]. Another important advantages gold nanoparticles prepared by PLAL process were stable for a period of months.…”

Elucidation of Activity Enhancement Factors for the Oxygen Reduction Reaction on Platinum and Palladium Single Crystal Electrodes

“…The nanoparticles were synthesized from 0.5 mM hydrogen tetrachloraurate (III) tetrahydrate (HAuCl 4 ·4H 2 O) aqueous solution by surfactant-and reducer-free synthesis with high-frequency ultrasonic (950 kHz). 45 Colloidal solution of the nanoparticles was dropped uniformly on a single crystal surface in Ar atmosphere. The solution was dried in Ar atmosphere so that the nanoparticles were fixed on the surfaces.…”