Adsorption and intercalation of low and medium molar mass chitosans on/in the sodium montmorillonite

•Only one layer of chitosan was adsorbed in the interlayer of montmorillonite.•Electrostatic interaction in the adsorption might be due to the protonated amino groups.•The molecular weight of chitosan had minimal effect on the intercalation. Chitosan-montmorillonite composites can provide hydrophobicity and amino groups to enhance the performances of montmorillonite in wastewater treatment. In this paper, low molar mass chitosan (LC) and medium molar mass chitosan (MC) were selected to intercalate a sodium montmorillonite (Mt). The adsorption isotherm of LC and MC on the Mt and the pH dependency were measured. Thermo X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the chitosan-Mt composites. Results showed that with hydrochloric acid as the solvent of chitosans, increasing pH from 3 to 5.5 enhanced the adsorption of both LC and MC on the Mt, and when the equilibrium concentration of chitosans approached 300mg/L at pH 5.5, the amount of adsorbed chitosan reached the highest level of 0.203mg/mg for LC and 0.190mg/mg for MC, respectively. When the Mt was saturated with the chitosan, the amino groups on the chitosan were bonded with the Mt through electrostatic interaction and there was monolayer of the chitosan in the interlayer space of Mt, which were confirmed by FTIR spectra and XRD patterns, respectively.