Effect of degree of substitution on adsorption behavior of Basic Green 4 by highly crosslinked amphoteric starch with quaternary ammonium and carboxyl groups

A series of crosslinked amphoteric starches with different degrees of substitution (DS) of carboxymethyl groups synthesized by a semi-dry process are investigated as an absorbent for removal of basic dye. Basic Green 4 is used to study the absorption behavior under various conditions, including initial pH of solution, dose of amphoteric starches, and dye initial concentration, adsorption time, adsorption temperature, and DS of carboxymethyl groups. The results show that adsorption amount of amphoteric starch is dependent of initial pH of dye solution, dose of absorbents and adsorption time. The adsorption capacity is affected strongly by the DS of carboxymethyl groups in the absorbents. The adsorption isotherm is discussed by modeling Langmuir and Freundlich isotherm. The kinetic study shows that the pseudo-second-order model fits the experimental data better. Also, the thermodynamic parameters are shown.