The effect of pH on the bonding of Cu2+ and chitosan-montmorillonite composite

•Bonding with amino in chitosan contribute main adsorption capacity.•Amino bond with copper ion near pH 5.0.•Hydroxyl was more active at pH 3 than at pH 5.

Based on the contradict statements on the mechanisms of the bonding between metal ions and chitosan based adsorbent, this paper present studies on the Cu2+ adsorption by the chitosan-montmorillonite composite. The in situ attenuated total reflectance Fourier transform infrared spectroscopy and two dimensional correlation analysis were used to record the spectra during the adsorption and the pH perturbation, and analyze the interaction sequence of the groups related to the adsorption, respectively. The results showed that the bonding with −NH3+ might attribute the adsorption capacity greater than that with hydroxyl. The hydroxyl of chitosan (or composite) take part in the Cu2+ adsorption at pH 3.0-5.0 and were more active at lower pH. The amino replaced hydroxyl as the bonding sites with the change of −NH3+ to −NH2 by proton exchange when pH was near 5.0.