Preparation and Characterization of Amphoteric Cellulose Hydrogels as Adsorbents for the Anionic Dyes in Aqueous Solutions

A series of cellulose ampholytes (CAms), with substitution degrees of cationic groups (DSC) of 0.41, 0.79, and 1.08, and with a substitution degree of anionic groups of 0.68, was prepared from sodium carboxymethylcellulose by a cationization reaction with 2,3-epoxypropyltrimethylammonium chloride. The obtained CAms were crosslinked by ethyleneglycoldiglycidylether (EGDE) to obtain cellulose polyampholyte hydrogels (CAmGs). The CAmGs adsorbed three anionic dyes, viz. AR9, AR13, and AB92, and the absorption depended on the DSC of the hydrogels and the pH of the adsorption medium: the maximum adsorption of anionic dyes occurred using CAmGs with higher DSC values, and under lower pH (less than 3) conditions. The adsorption of these dyes can be fitted by the Langmuir adsorption isotherm model, which revealed the maximum flocculation capacity of CAmGs for each dye. These encouraging results indicate that CAmGs may be applicable for use as novel adsorbents for wastewater treatment.