Preparation of Ultrafine Particles of Gold Utilizing Emulsion-type Liquid Membrane Technique

A novel preparation method of ultrafine particles of precious metals using an emulsion-type liquid membrane technique has been developed by the present authors. In this method, water-in-oil emulsion, consisting of an organic phase of MIBK-Span 80-kerosene solution and an internal aqueous phase containing a suitable reductant, is contacted with an external aqueous solution containing precious metal salts. Various factors, which affect the particle size of gold, including the concentrations of MIBK, Span 80 and Au (III), identity of reductant and its concentration, etc, were examined. An increase in the concentration of Au (III) and a decrease in the concentrations of Span 80 and reductant result in an increase in particle size of gold powders. The value of pH of internal solution is another important factor to control the particle size. Gold particles can also be prepared by contacting external aqueous solution containing reductant with emulsion where Au (III) is contained in the internal aqueous phase.