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We report a one-pot synthesis method for a production of a stable Ag-Au bimetal colloidal solutions (Ag-Au hydrosols) by simply mixing disodium salt of ethylenediaminetetraacetic acid (Na 2 EDTA) with AgNO 3 and HAuCl 4 in aqueous alkaline medium at 80 °C. We found that Na 2 EDTA act not only as a reductant of metal ions and a potent stabilizer of metal nanoparticle size, but also as an effective agent for controlling the composition of the formed nanoparticles, owing to the high complexing affinity of Na 2 EDTA to silver ions. It was found that by controlling Na 2 EDTA concentration in the reaction mixture it is possible to control not only size and size distribution of a synthesized colloidal bimetallic Ag-Au nanoparticles, but bimetallic Ag-Au nanoparticles composition (Ag/Au ratio) as well.

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The possibility of  Na2EDTA applying as a reducing and stabilizing reagent in aqueous medium to obtain gold hydrosols from hydrogen tetrachloroaurate was studied. It was found that, depending on the pH of the reaction medium, both nanosized precipitates (~60 nm) and gold hydrosols, consisting of spherical nanoparticles of uniform size (12–15 nm), can be obtained. Stable gold sols are formed at pH ≥ 10.5. Sol formation process rate depends on the temperature and concentration of  Na2EDTA and increases with their increase. An electrochemical study of processes of  HAuCl4 reduction and Na2EDTA oxidation showed that the possibility of gold hydrosols formation in an alkaline medium is due to the kinetic inhibition of the reduction process of gold hydroxo complexes formed during this process.