Preparation and Utilization of New Carboxyl Group Containing Cation Exchangers Based on Starch Using a Dry Reaction Method

Abstract

New cation exchange resins are prepared through reaction of starch — as an inexpensive and biodegradable backbone — and citric acid (CA), as a crosslinking and carboxyl groups bearing agent, in the presence of sodium hypophosphite (SHP) as catalyst at elevated temperature. In this way insoluble crosslinked networks are produced with pendent carboxyl groups. Factors affecting the resin formation, such as reactants concentration, reaction temperature, reaction time, and starch type, are studied. Proper conditions are selected to prepare two cation exchangers based on maize starch and rice starch having capacities of 188 meq/100 g, and 192 meq/100 g, respectively. Potentiometric titration showed that these resins were weakly basic cation exchangers with pKa values of 7.21 and 6.32, respectively. These resins were used in the removal of some basic dyes from aqueous solutions. Adsorption kinetics and isotherms of methylene blue on both resins were investigated.