Research on adsorption of hexavalent chromium onto chitosan cross-linked modified litchi pericarp

A new type metal adsorbent was successfully prepared by chitosan and litchi pericarp modified with NaOH，by the method of dropping into sphericity under the conditions of appropriate stirring time，stirring rate and suitable pH. Batch adsorption experiments were carried out to evaluate the effects of initial concentration of Cr（Ⅵ）， initial pH，adsorption time and dosage of chitosan cross-linked modified litchi pericarp on the adsorption of Cr（Ⅵ）. The adsorption kinetics，adsorption isotherm，scanning electron microscopy and infrared spectroscopy were analyzed. The results showed that the optimum of adsorption Cr（Ⅵ） on chitosan cross-linked modified litchi pericarp occurred at initial Cr（Ⅵ） solution concentration of 120 mg/L，initial pH at 1 and per 100 mL adsorption solution with 0.2 g chitosan cross-linked modified litchi pericarp for 240 mimutes. The kinetics of adsorption exhibited quasisecond- order behavior and basically coincided quasi-first-order model. The adsorption date was well described by Langmuir isotherm model. The adsorption was identified as monomolecular layer. The maximum adsorption capacity of Cr（Ⅵ） was 108.7 mg/g at indoor temperature. And scanning electron microcopy indicated that the chitosan cross-linked modified litchi pericarp had rougher surface and more porosities after adsorption. Besides，chitosan crosslinked modified litchi pericarp contained the vast majority of functional groups. Especially，hydroxyl and amide play an irreplaceable roles in adsorption of Cr（Ⅵ）.