Preparation and evaluation of adipic acid dihydrazide cross-linked carboxymethyl chitosan microspheres for copper ion adsorption

Adipic acid dihydrazide (ADH) was used to cross-link carboxymethyl chitosan (CMCS) microspheres for Cu2+ removal from aqueous solution. SEM, FTIR, XPS and BET techniques were performed to characterize the ADH cross-linked CMCS (ADH-CMCS) microspheres. The effects on adsorption capacities of pH value, adsorption time, and initial Cu2+ concentration were investigated. The adsorption experiments demonstrated ADH-CMCS microspheres had high adsorption capacity for Cu2+ removal. Furthermore, in order to investigate the effect of ADH in ADH-CMCS microspheres on Cu2+ adsorption, cross-linking experiments and XPS tests were carried out to reveal the adsorption mechanism. The results suggested that ADH in ADH-CMCS microspheres had a compensation action on its consumption of binding sites for Cu2+ adsorption. The XPS etching results showed cross-linking reaction occurred mainly on the surfaces of the microspheres. The kinetics of Cu2+ adsorption on ADH-CMCS microspheres complied with the pseudo-second-order model, indicating a chemical reaction process. The adsorption data analysis using three different adsorption isotherm models indicated that ADH-CMCS microspheres were of heterogeneity surfaces. Moreover, the ADH-CMCS microspheres still exhibited good adsorption performances after the fifth adsorption-desorption cycle. (C) 2016 Elsevier B.V. All rights reserved.