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Aqueous reduction of hydrogen tetrachloroaurate(III) with alkaline tetrakis(hydroxymethyl)phosphonium chloride yields gold in an ultrafinely divided form as a stable colloidal hydrosol, with mean metal-cluster diameter between 1 and 2 nm, without the need for large organic stabilizing molecules. The ultraviolet-visible extinction spectrum is very similar to those of other gold colloids of similar dimensions and includes a weak plasmon feature. Dispersions with characteristics of yet finer clusters are prepared using lower initial concentrations of Au3+ ions. Boiling the sols in the presence of appropriate colloidal stabilizers (ionic and/or polymeric) is a route to coarser (3-10 nm particle diameter) gold hydrosols.
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Duff et al. (1993) studied this question.
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