Competitive Adsorption removal of Congo red and Rhodamine B over alkaline membrane from in situ polymerization of Gemini cationic molecule

An alkaline membrane with full interpenetrating network (Full-IPN) with positive charge groups of uniform distribution was prepared as adsorbent for removal of Rhodamine B (RB) and Congo red (CR) in single and binary dye systems. Compared with single dye system, in binary dye systems a synergistic effect is due to the interaction between RB (cationic dyes) and CR (anionic dyes), which will impede the adsorption of CR or RB. Moreover, under the same experimental conditions, the magnitude of CR removal is better than that of RB in binary dye systems and that in the single system. The aforementioned phenomenon has resulted from one CR molecule bound to one RB molecule; the RB-CR binding occurred spontaneously, and the main binding forces between CR and RB were hydrogen bond and van der Waals interactions. Pseudo-second-order rate equation and Freundlich adsorption isotherm are with the better fit in single and binary dye systems for fitting the kinetic data. The results of Delta G, Delta H and Delta S revealed that the adsorption process for single and binary systems is endothermic and spontaneous. The electrostatic interaction between the dye and the quaternized ammonium groups present in membrane was identified as a major mechanism of the adsorption process.