PREPARATION AND CHARACTERIZATION OF COLLOIDAL SILVER PLATINUM ALLOYS

Colloidal silver-platinum alloys have been prepared by NaBH4 reduction of silver(I) bis(oxalato)platinate(II) (Ag2[Pt(C2O4)2]) in ethylene glycol and characterized by means of EDX, HRTEM, XRD, and optical absorption spectra. The HRTEM micrographs show that the metal particles thus prepared have homogeneous {111} lattice spacing of 2.31 +/- 0.02 angstrom, which is an intermediate value between those of monometallic Ag and Pt colloids, indicating that they are Ag-Pt alloys. The same trend is found in the XRD profiles. Optical spectra of the Ag-Pt alloy colloid show a plasma resonance band at 354 nm. The peak wavelength shifts in the range of 330-410 nm by varying the Ag/Pt ratio. The alloy formation has been studied by step-by-step reduction of Ag2[Pt(C2O4)2]. It is suggested that the reduction of [Pt(C2O4)2]2- takes place by the catalytic action of the Ag particles to form the Ag-Pt alloy.