AbstractPoly(1-vinylimidazole) (PVIm)/silica nanocomposite particles were prepared via free radical polymerization of VIm in the presence of unmodified silica and crosslinker N,N′-methylenebisacrylamide without any surfactant by a one-pot route in supercritical carbon dioxide. The strong acid-base interaction between the hydroxyl groups (acidic) of silica surfaces and the imidazole groups (basic) of 1-VIm was strong enough to promote the formation of long-stable PVIm/silica nanocomposite particles. Transmission electron microscopy and scanning electron microscopy results showed that the silica nanoparticles were encapsulated into the polymer and with a specific pore structure. Fourier transform infrared spectroscopy results suggested the strong interaction between PVIm and silica. The nanocomposites were shown to possess higher thermal stability than PVIm. A maximum surface area of 60.76 m2/g was obtained via standard nitrogen adsorption analysis. The property of the composite materials in terms of heavy metal ion removal was investigated. The maximum adsorption capacity of Cr (VI) is 331.5 mg/g in the experimental range.