Preparation of chitin composite hydrogel for dye-contaminated water treatment

Abstract

Chitin is the most abundant natural amino polysaccharide. In this study, chitin was dissolved in 8% NaOH/6% urea solution by freezing/thawing method and then was blended with sodium alginate solution, attapulgite powder and epichlorohydrin. This mixture was set aside for 12 hours at 25ºC without agitation. By this simple blending and setting aside method, a novel chitin composite hydrogel for dye-contaminated water treatment was prepared. A cross-linked structure was proved by Fourier transform infrared spectroscopy (FTIR). Freeze-dried composite hydrogel exhibited a porous structure and rod-like attapulgite was distributed on the wall of pores, which was observed by scanning electron microscopy (SEM) images. Swelling test showed that sodium alginate significantly enhanced the swelling of chitin-sodium alginate hydrogel compared to the pure chitin hydrogel. Adsorption test to methylene blue solution showed that adsorption capacity of composite hydrogel changed with the content of attapulgite and increased with the increase of initial concentration of methylene blue. The maximum adsorption capacity was 116.6 mg g-1. Adsorption kinetic is best described by pseudo-second order model. Adsorption isotherm agrees well with Fraundlinch model. Chitin composite hydrogel is a promising adsorption material for dye-contaminated water treatment.