Preparation of cationic functional starch/Na+-MMT composite and its application for effective removal of three hazardous metal anionic ions with different valence

The design of cost-effective biopolymers-based adsorbents is of particular interest. In our work, a cationic functional starch (CFS)/Na+-montmorillonite (Na+-MMT) composite was prepared by combining 5wt% modified starch containing quaternary ammonium cationic functional groups and 0.5% w/v Na+-MMT dispersed solution together. Its microstructure was characterized by FTIR and XRD. Removal of three metal anionic ions with different valence like: MnO4-, Cr2O72-, and Fe(CN)(6)(3-) by the composite was compared. Adsorption equilibrium, kinetics, and thermodynamic models were also investigated. The adsorption capacity was very high and followed the sequence of MnO4- > Cr2O72- > Fe (CN)(6)(3-), which could be demonstrated with strong electrostatic interaction between active cationic functional groups and metal anionic ions. The Langmuir isotherm gave satisfying fits to equilibrium data of MnO4- ions indicating monolayer adsorption to monovalent anionic ion, while the Freundlich equation fitting equilibrium data of Cr(2)O(7)(2-)and Fe(CN)(6)(3-) ions better predicated multilayer adsorption to polyvalent anionic ion. There was a better matching accuracy between the experimental data and the pseudo second order model. The removal percentages for the three ions of MnO4, Cr2O72-, Fe(CN)(6)(3-)by the composite were 96.84, 94, and 89.84%, respectively.