PREPARATION OF COLLOIDAL SILVER-PALLADIUM ALLOYS BY UV-IRRADIATION INMIXTURES 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 perchl orate and/or palladium acetate in mixture solutions of acetone and 2-p ropanol in the presence of poly(vinylpyrrolidone). The colloids obtain ed have been characterized by means of TEM, XRD, and optical absorptio n spectra. The average particle sizes of the Pd colloids are 2-3 nm, a nd are independent of palladium acetate concentration, whereas those o f 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) sh ows that the optical absorption bands become sharp and shift to longer wavelengths with increasing molar ratio of Ag. The observed spectra a re in good agreement with the calculated spectra of alloy colloids. Fu rther, formation of alloy colloids having average size of about 1-4 nm is strongly suggested by the XRD result. The particle size distributi ons of alloy colloids are very narrow. In addition, the maximum absorp tion bands and particle sizes of alloy colloids are altered with the s olvent compositions.