3. Results
Metal nanoparticles formed by irradiating a synthesis solution containing Pt2+, Ni2+, and diethylene glycol with microwaves are shown in Fig. 1. As the number of irradiation cycles increases from N = 1 to 4 (1 cycle = 50 s on and 30 s off), the colour of the synthesis solution becomes darker (Fig. 1a), indicating a continuous increase of the total volume of metal nanoparticles. Indeed, the ICP-OES analysis shows increasing amounts of Pt and Ni found in the nanoparticles from cycle 1 to 4 after they are completely digested using aqua regia (Fig. 1b). Interestingly, nanoparticles formed by a single cycle of microwave irradiation (N = 1) contain only Pt and Pt is always favored over Ni by the polyol reduction reaction during synthesis. The further increase of N above 4 exhausts the supply of Pt with the additional reduction of Ni alone.