Influence of dextran hydrogel characteristics on adsorption capacity for anionic dyes

A series of cationic amphiphilic dextran hydrogels with pendent N, N-dimethyl-N-alkyl-N-(2-hydroxypropyl) ammonium chloride pendent groups was obtained with various molar ratios hydrophilic (alkyl = C₂)/hydrophobic groups (alkyl = C₁₂ or C₁₆), total content in amino groups (50-68 mol%) and water swelling capacity (3-15 g water/g dry gel). Adsorption capacity for anionic dyes (Methyl Orange and Rose Bengal) was studied as a function of hydrogel characteristics. Adsorption kinetics was mainly influenced by swelling porosity and dye molecular weight. Equilibrium data showed that the maximum sorption capacity was strongly dependent on hydrophobic segment content, which enhanced the affinity dye-gel (increased Langmuir constant K_L) and contribution of ion-exchange to adsorption mechanism, and significantly decreased the maximum uptake of Rose Bengal. The hydrophilic highly swollen hydrogel had the best adsorption capacity for Rose Bengal (1700 mg/g) at 25 °C, and more hydrophobic gels could adsorb 830-900 mg Methyl Orange/g, irrespective of the medium temperature.