Chitosan-poly(vinyl alcohol)/attapulgite nanocomposites for copper(II) ions removal: pH dependence and adsorption mechanisms

Abstract

Abstract A novel adsorbent, chitosan-poly(vinyl alcohol)/attapulgite (CTS-PVA/APT) nanocomposite, was prepared and used to remove Cu(II) ions from aqueous solutions. Batch adsorption experiments show that the adsorption capacity of the nanocomposite for Cu(II) ions are greatly influenced by the pH value of solutions. The adsorption capacity increased from 0 to 35.79 mg/g with increasing the pH value of solutions from 2.00 to 6.50. The adsorption mechanism of the nanocomposite for Cu(II) ions in various pH solutions were analyzed by XPS and FTIR measurements. Results show that, in strong acidic solutions, because of the protonation of NH 2 groups and OH groups, the Cu(II) adsorption on the nanocomposite is mainly through a non-specific interaction (physical adsorption, electrostatic attraction, etc.) or a very weak chemical interaction. In weak acidic solutions, the Cu(II) adsorption on the nanocomposite mainly depends on the chelation between NH 2 groups and Cu 2+ ions. In nearly neutral solutions, Cu(OH) + and Cu(OH) 2 coexist simultaneously. They are adsorbed on the surface of the nanocomposite by chelating with NH 2 groups and OH groups or physical adsorption. The adsorption process of Cu(II) ions on the nanocomposite fits well with the pseudo-first order kinetic equation in the initial 7 min, while the whole adsorption process can be better explained by the pseudo-second order kinetic model and the Freundlich model better.