Kinetic Regularities of Nanogold Synthesis. Auto-Catalytic Mechanism of the Process

The work is devoted to the study of the kinetics of colloidal gold formation. On the basis of experimental data, a kinetic model including the stages of Au³⁺ and Au¹⁺ reduction with the formation of metallic gold nanoparticles was developed. A kinetic feature of the process is the presence of a long induction period (several hours), while an increase in the induction period is observed with increasing concentration of the initial reagent (Au³⁺). Kinetic modeling shows that the induction period is determined by the process of reverse oxidation of Au⁰ with intermediate formation of one-electron oxidized gold. The principal result is the demonstration of the fact of acceleration of the process gold nanoparticles formation (reduction of the induction period) when the final product (Au⁰) is introduced into the system, which is an unambiguous sign of the autocatalytic process. Estimates of rate constants of all elementary stages of the reaction have been made, the slowest process being the first stage of Au³⁺ reduction.