Metal particles dispersed on supports are important to improve the catalytic activity of metals. Herein, ultrasmall platinum nanoparticles (Pt NPs) immobilized in viologen micelles have been prepared by reducing chloroplatinic acid with DMF in the presence of a viologen-based surfactant, which not only acts as the nucleation site of metal particle formation, but also is responsible for protecting the Pt NPs from further growth or aggregation. The viologen-templated Pt NPs remain stable for several months without any noticeable aggregation. The obtained Pt NPs–viologen micelles show higher catalytic activity and stability in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol by NaBH4 as compared with unprotected Pt NPs. The high catalytic activity is due to the viologen shell around the Pt NPs, which results in the formation of ultrasmall Pt NPs and, more importantly, provides a high concentration of 4-NP near the Pt NPs–viologen micelles. Notably, viologen, as an electron transfer mediator, plays a key role in the high catalytic activity.
