Reaction Dynamics for Gold Nanoparticles Synthesis in Solution Plasma

We describe the dynamics of the synthesis of gold nanoparticles by glow discharge in aqueous solutions. Initial [AuCl₄]^- concentration and the voltage applied between the electrodes were varied. Reduction rates were calculated from changes in concentration of [AuCl ₄]^- vs. discharge time. A pulsed power supply was used to generate discharges in the aqueous solutions. The morphology of the nanoparticles obtained was observed by transmission electron microscopy (TEM). [AuCl₄]^- was reduced by H radicals or electrons generated by the discharge. Dendrite-shaped nanoparticles -150 nm in size were formed after discharge for 1 mm. The pH of the solution decreased gradually with increasing discharge time. The decrease in pH led to dissolution of gold nanoparticles. The reduction and dissolution rates increased proportionately with the applied voltage. The size of gold nanoparticles decreased during discharge and was 20 nm after discharge for 45 mm. When the reduction rate lowered as a result of dissolution, anisotropic nanoparticles were formed and continued to grow in the solution.