Optimized reduction conditions for the microfluidic synthesis of 1.3 ± 0.3 nm Pt clusters

Recently, small (<2 nm) and monodispersed Pt clusters has gained much attention due to their high catalytic activity in the aerobic oxidations. However, the chemical synthesis of small Pt clusters is not trivial; high temperature is often required to completely reduce the Pt4+/2+ions to Pt0, which accelerates the growth of the Pt clusters. Here, we discussed a very simple microfluidic reduction of Pt4+to Pt0by NaBH4in the presence of PVP that produces <2 nm Pt clusters in any variable reduction conditions. The microfluidic reduction conditions were optimized for the synthesis of possible smallest Pt clusters in terms of five reaction parameters: (1) temperature, (2) concentration of H2PtCl6, (3) molar ratio of NaBH4to Pt4+ions, (4) molar ratio of PVP-monomer to Pt4+ions, and (5) molecular weight/chain length of PVP. We found that possible smallest particles with average diameter 1.3 ± 0.3 nm were produced when aqueous solutions of H2PtCl6(4 mM) and NaBH4(40 mM) containing PVP (160 mM) were injected into the micromixer placed in an icebath at a flow rate of 200 mL/h. The produced particles were characterized by UV–visible absorption spectrophotometry, powder X-ray diffractometry and transmission electron microscopy.