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 5 wt% 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)63− 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)63−, 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 Cr2O72− and Fe(CN)63− 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)63− by the composite were 96.84, 94, and 89.84%, respectively.