Carboxymethyl Inulin Modified Chitosan Composites for Cu (II) Removal in Aqueous Solution: Synthesis, Influencing Factors and Adsorption Mechanism

A new biomass-based carboxymethyl inulin modified chitosan material was designed and synthesized as an adsorbent for the Cu (II) removal from aqueous solutions, in which carboxymethyl inulin (CMI) with specific degree of substitution (DS) was prepared by optimal three steps alkalization-etherification processes, and then moderately crosslinked with chitosan by DMTMM. The structure and morphology of CMI-CS were characterized using fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), brunauer–emmett–teller (BET) and thermogravimetric analysis (TGA) analyses. The effects of CMI dosage, adsorption time, adsorption temperature, pH and initial Cu (II) concentration on the adsorption capability of CMI-CS to Cu (II) were investigated. The adsorption capacity of the adsorbent for Cu (II) was 49.4 mg/g under the conditions of CMI and CS mass ratio 3:2, pH 6, and adsorption time for 90 min. Its adsorption kinetics fitted the pseudo-second-order model, and adsorption isotherms followed by the Freundlich and the Temkin models well. XPS, FTIR, and SEM were used to explore the adsorption mechanism. The results demonstrated chemisorption and physisorption coexist in the adsorption process. The nitrogen-containing groups and oxygen-containing functional groups of CMI-CS adsorbent participated in the adsorption of Cu (II) through electrostatic interaction and chelation. Based on the above traits, the biomass-based adsorbent shows promising application in wastewater treatment. Graphical Abstract: (Figure presented.)