Preparation of colloidal silver-palladium alloys by UV-irradiation in mixtures of acetone and 2-propanol

Ultrafine silver, palladium, and silver-palladium alloy particles have been prepared by UV photolysis (253.7 nn wavelength) of silver perchlorate and/or palladium acetate in mixture solutions of acetone and 2-propanol in the presence of poly(vinylpyrrolidone). The colloids obtained have been characterized by means of TEM, XRD, and optical absorption spectra. The average particle sizes of the Pd colloids are 2-3 nm, and are independent of palladium acetate concentration, whereas those of Ag colloids increase from 3 to 9 nm with increasing concentration of silver perchlorate. Irradiation of mixtures of two salts in mixtures of acetone and 2-propanol in the presence of poly(vinylpyrrolidone) shows that the optical absorption bands become sharp and shift to longer wavelengths with increasing molar ratio of Ag. The observed spectra are in good agreement with the calculated spectra of alloy colloids. Further, formation of alloy colloids having average size of about 1-4 nm is strongly suggested by the XRD result. The particle size distributions of alloy colloids are very narrow. In addition, the maximum absorption bands and particle sizes of alloy colloids are altered with the solvent compositions.