Designing a sulphonic acid functionalized benzimidazolium based poly(ionic liquid) for efficient adsorption of hexavalent chromium

Abstract

Herein, the facile synthesis of sulphonic acid functioned benzimidazolium based poly(ionic liquid) (SBPIL) is reported for the first time and we investigated its efficacy towards the removal of Cr(VI). SBPIL was synthesized by co-polymerization of styrene and 1-(4-vinylbenzyl)-1H-benzimidazole, followed by reaction with 1,4-butane sultone and subsequent functionalization with sulphonic acid. The prepared SBPIL was characterized by elemental analysis, FT-IR and NMR spectra, SEM-EDAX, TGA and X-ray diffraction techniques. The batch adsorption method was applied for examining the Cr(VI) removal and also to investigate the kinetics and thermodynamics of adsorption. The adsorption process was correlated with the Langmuir and Freundlich adsorption isotherm models and the Langmuir adsorption capacity was estimated to be 40.81 mg g⁻¹. The thermodynamic study concluded that the adsorption process is exothermic and spontaneous and the adsorption kinetics were well fitted by a pseudo-second order kinetic model. Investigation on the effect of counter ions on the adsorption process revealed that Cl⁻ ions had no influence on the adsorption, whereas SO₄²⁻ and NO₃⁻ were found to affect the Cr(VI) adsorption by 3.6% and 19.5% respectively. SBPIL exhibited excellent stability and recyclability and the adsorbent could be easily regenerated using 1 M H₂SO₄ and examined for Cr(VI) removal from successive batches.