The preparation of Pt nanoparticles by methanol and citrate.

Platinum nanoparticles of 2-3 nm average size and ca. +/-2 nm distribution can be successfully prepared by methanol reduction while using sodium citrate as the stabilizer. Sol formation was investigated by UV-visible spectroscopy and EXAFS (extended X-ray absorption fine structure spectroscopy). The formation of Pt nanoparticles was confirmed by the presence of Pt-Pt bonding in the solution after a certain induction period in methanol-reduced sol with or without citrate. The possible two-step reduction of Pt(IV) was revealed by correlating EXAFS, UV-visible spectra and pH data. The presence of citrate resulted in a smaller Pt-Pt coordination number and a slower sol formation process. All these results prove that citrate acted as the stabilizer in this synthesis.