Mechanism of carboxymethyl chitosan hybrid montmorillonite and adsorption of Pb(II) and Congo red by CMC-MMT organic-inorganic hybrid composite

Abstract

The carboxymethyl-chitosan-montmorillonite (CMC-MMT) organic-inorganic hybrid material was applied to adsorb Pb(II) and Congo red (CR) anionic dye from aqueous solution. Molecular dynamics(MD) simulation was carried out to reveal the mechanism of CMC hybrid MMT. The results suggested that CMC has been adsorbed on the interlayer space and surface of MMT, hydrogen bonds had been formed between hydroxyl & carboxyl groups of CMC with the surface of MMT, Van der Waals interaction was also existed, while amino groups of CMC hadn't obvious interaction with the surface of MMT. Batch experiments were executed to investigate the adsorption effect of CMC-MMT was compared with Na-MMT and CMC. The results showed that CMC-MMT exhibited the higher adsorption capacity than Na-MMT and CMC, The OH and COOH or NH₂ groups of CMC chains may serve as electrostatic interaction active sites and coordination sites, which improved the adsorption performance of CMC-MMT on Pb(II)，and the insertion of CMC enlarged the inter-layer space of MMT, resulting in more surface active sites in the CMC-MMT hybrid composite, which increased the adsorption of organic pollutant CR. The kinetic and isotherm studies indicated that the pseudo-second-order and the Langmuir model well described the adsorption equilibrium of Pb(II) and CR on CMC-MMT.

Keywords: Carboxymethyl chitosan-montmorillonite; Molecular dynamics simulation; Organic-inorganic hybrid.