Chloroauric acid sodium borohydride

Add five 1-ml aliquots of the sodium borohydride solution to the chloroauric acid/ carbonate suspension with rapid stirring. A color change from bluish-purple to reddish-orange will be noted as the additions take place. 

The preparation of colloidal gold is generally accomplished by reduction of chloroauric acid (HAUCI4) solution with sodium citrate [19-23], which is known to be influenced by several factors such as temperature and reactant concentrations [22]. Alternatively, other reducing agents can be used such as tetrakis(hydroxymethyl)phosphonium chloride (THPC) [24], borohydride [20,25] and toluene [26]. 

Colloids of alloys have been made by the chemical reduction of the appropriate salt mixture in the solution phase. Thus, Ag-Pd and Cu-Pd colloids of varying composition have been prepared by alcohol reduction of mixtures of silver nitrate or copper oxide with palladium oxide (Vasan and Rao 1995). Fe-Pt alloy nanocrystals have been made by thermal decomposition of the Fe and Pt acetylac-etonates in high-boiling organic solvents (Sun et al. 2000). Au-Ag alloy nanocrystals have been made by co-reduction of silver nitrate and chloroauric acid with sodium borohydride (Sandhyarani et al. 2000 He et al. 2002). 

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