Electroless Deposition of Platinum Nanoparticles in Room-Temperature Ionic Liquids

The electroless deposition of Pt nanoparticles (Pt-NPs) could be carried out by dissolving potassium tetrachloroplatinate­(II) (K₂[PtCl₄]) in 1-ethyl-3-methylimidazolium (EMI⁺) room-temperature ionic liquids (RTILs) containing bis­(trifluoromethylsulfonyl) imide (NTf₂^–) or tetrafluoroborate (BF₄^–) anion and small cations, such as H⁺, K⁺, and Li⁺. In this case, no deposition of Pt-NPs occurred in RTILs without such small cations. The formation of Pt-NPs was only observed in RTILs containing trifluoromethanesulfonimide (HNTf₂) and protons at high temperature (≥80 °C) when potassium hexachloroplatinate­(IV) (K₂[PtCl₆]) was dissolved in the RTILs. The obtained Pt-NPs gave a characteristic absorption spectrum of ultrasmall Pt-NPs. The ultrasmall and uniform Pt-NPs of ca. 1–4 nm in diameter were produced and the Pt-NPs/EMI⁺NTf₂^– dispersion was kept stably for several months without adding any additional stabilizers or capping molecules. The identified Fourier-transform patterns along the [0 1 1] zone axis were observed for the TEM images of Pt-NPs. On the basis of the results obtained, a probable mechanism of the electroless formation of Pt-NPs is discussed