Synthesis of cross‐linked homopolymers and copolymers of 1‐vinylimidazole in supercritical carbon dioxide for removal of Cr(VI) from aqueous solution

In this work, cross‐linked poly(1‐vinylimidazole) (PVIm) and poly(1‐vinylimidazole‐co‐acrylic acid) poly(VIm‐co‐AA)] polyampholytes microgel were synthesized by precipitation polymerization in supercritical carbon dioxide at 14 and 20 MPa. The obtained products were characterized by Fourier transform infrared spectroscopy and Energy‐dispersive X‐ray spectroscopy. The results indicate that the functional monomers including 1‐VIm and AA were cross‐linked in polymers successfully. Aggregate particles with diameters of approximately 200 nm were observed by scanning electron microscopy and particle size distribution. Surface area analysis showed that the surface area of microgel prepared at a pressure of 14 MPa are 40.28 m²/g. The swelling behavior of polyampholytes microgel was studied. The cross‐linking degrees of PVIm and copolymers can reach 92.6% and 98.1%. The effect of pH values of solution, contact time, adsorbent dosage, initial Cr(VI) concentration on adsorption capacity were also investigated. The results revealed that cross‐linked polymer has a high adsorption capacity of 306.0 mg/g for Cr(VI) in 130 mg/l solution at pH 2 and cross‐linker ratio of 27.3%. Copyright © 2013 John Wiley & Sons, Ltd.