Property variation of ionic liquid [Bmim][AuCl4] immobilized on carboxylated polystyrene submicrospheres with a small surface area

In order to understand the effect of surface chemical groups on the immobilized species, Au-containing imidazolium-based ionic liquid (IL) Bmim]AuCl₄] was intentionally immobilized on polystyrene (PS) submicrospheres (d ～300 nm) with a very small surface area (4–10 m²/g), which possess carboxyl-moiety (COONa or COOH) on the surface. The behavior of immobilized Bmim]AuCl₄] on the two types of submicrospheres was investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and powder X-ray diffraction (XRD). It was revealed that the melting points (T _m) of Bmim]AuCl₄] that had been immobilized on PS-COONa and PS-COOH submicrospheres were decreased by 2.7 and 4.1°C, respectively. The interaction mechanism between the IL and submicrosphere surface moieties was further analyzed by X-ray absorption fine structure (XAFS) analysis. The data indicated that the coordination environment of Au species changed markedly when Bmim] AuCl₄] was immobilized on the surfaces of PS-COONa and PS-COOH submicrospheres, as illustrated by the decrease in white line peak intensity. The effect of surface COOH groups on T _m depression and the white line peak intensity of the XANES spectrum is more pronounced than that of COONa groups, most likely due to the possible hydrogen bond formation between the COOH group and Bmim]⁺.