Synthesis and characterization of imidazole-bearing polymer-modified montmorillonite for adsorption of perchlorate

Abstract

Poly (4-vinylbenzyl methylimidazolium chloride) (PIm) in different stoichiometric amounts were applied for the modification of montmorillonite (Mt). The distribution of the distinguished Im+ (vinylbenzyl methylimidazolium cation) species attached to Mt. layer and the vinylbenzyl methylimidazolium chloride (Im-Cl) species with the counter ion was investigated through a meticulous calculation based on TG-DTA, CHN analysis, and the measurements of released Cl− during modification. The constructions of the PIm as the modifier on Mt. were illustrated at a molecular level. Two configurations of intercalated PIm were proposed based on the XRD results, and the morphologies of PIm arrangement on the composites were characterized by FTIR, SEM, and N2 adsorption/desorption measurements. The construction and arrangement of PIm had a significant effect on the migration of ClO4− in the channels or on the surface of the PIm-Mt composites as suggested by the kinetics modeling. The previously calculated Im-Cl amount on PIm-Mt was comparatively discussed with the calculated theoretical adsorption capacity obtained by isotherms modeling and the experimental adsorption amount in practice. The combined analysis of the chemical interaction and theoretical statistics helped to elicit the dominant ion-exchange mechanism assisted by the dynamic re-distribution of anionic and cationic species in the aqueous phase during adsorption. Using the strategy to increase the hydrophobicity of the quaternary ammonium site, a remarkable selectivity of ClO4−on PIm-Mt was achieved over NO3−, Cl− and SO42− with 50 times higher concentrations and low dosage of the adsorbents. Moreover, the significant reduction of the organo-modifier release was observed on the multiply charged macromolecule which was attributed to the constraint among the repeated units throws chemical bonds. Both the improved selectivity and the reduced organic release enable the PIm-Mt to become a more suitable adsorbent for water treatment of ClO4−.