The synthesis of gold nanoparticles by a citrate-radiolytical method

• Gold nanoparticles were synthesised by classical and citrate-radiolytical methods.
• The size of gold nanoparticles was controlled by different saturated gases.
• Radiolytically intensified citrate oxidation is advantageous for Au(III) reduction.
• A comparison of particle sizes between classical and radiolytical methods was made.

The classical citrate method is based on the reduction of an Au(III) precursor with sodium citrate in an aqueous solution near the boiling point. In this work gold nanoparticles (GNPs) were synthesised via a citrate method using reduction by gamma-irradiation at room temperature. The Au(III)–citrate aqueous precursor solution was gamma-irradiated to doses of up to 30 kGy. The dose rate of gamma-irradiation was ~8 kGy h−1. The GNP size was controlled by the adsorbed dose as well as by different saturated gases (air or nitrogen) present in precursor solutions. The results showed that gamma-irradiation produced smaller GNPs in the presence of precursor solutions saturated with nitrogen compared with the ones saturated with air. By increasing both the gold(III) and citrate concentrations in precursor solutions, stable and highly concentrated colloidal gold/citrate suspensions were synthesised using classical and citrate-radiolytical reduction methods. Gamma-irradiation thus produced well-dispersed and highly concentrated GNPs in an aqueous citrate solution in the presence of dissolved oxygen and without adding any reducing or stabilising agents. Radiolytically intensified citrate oxidation and decarboxylation to acetone and other products by dissolved oxygen was advantageous for Au(III) reduction and subsequent formation of gold nanoparticles. Since the completely same precursor solutions were used both in the classical and citrate-radiolytical reduction methods, a real comparison of GNP sizes between these two methods was given.