Adsorption and Mechanism of Cr(Ⅵ) and Cu(Ⅱ) by Polyethyleneimine Modified Chitosan Aerogel

A polyethylenimide modified chitosan aerogel adsorbent (CS/PEI) was fabricated by freeze-drying using chitosan (CS) as the base material, glutaraldehyde (GA) as the crosslinking agent and polyethylenimide (PEI) as the grafting material. The structure of the aerogels were characterized, and the adsorption properties, model and mechanism for aqueous Cr(Ⅵ) and Cu(Ⅱ) were further revealed. The optimum pH of CS/PEI-1 adsorbing Cr(Ⅵ) and Cu(Ⅱ) was 3 and 6. Adsorption kinetics and isotherm were more consistent with pseudo-second-order model and Langmuir model, and the maximum adsorption capacities for Cr(Ⅵ) and Cu(Ⅱ) were 88.69 and 93.51 mg/g, respectively. The adsorption thermodynamics showed that the adsorption of Cr(Ⅵ) and Cu(Ⅱ) by CS/PEI-1 was a spontaneous, endothermic and entropy increasing process. The adsorption mechanism showed that the adsorption of CS/PEI-1 on Cr(Ⅵ) and Cu(Ⅱ) mainly included electrostatic attraction, chelation, complexation, redox, pore diffusion, pore filling, etc.