Synergistic effect between montmorillonite and imidazolium-functionalized carboxylate-based polyelectrolyte for enhancing the removal of methylene blue

Abstract

The composite of montmorillonite (Mt) and novel imidazolium-functionalized carboxylate-based polyelectrolyte (P(NaAA/VIC)) was formed through the bridging interaction of zwitterionic groups, enabling efficient and rapid removal of industrial cationic dye methylene blue (MB) from aqueous solution. The removal rate of pure P(NaAA/VIC) was difficult to reach 90%, while P(NaAA/VIC)/Mt composites achieved the removal rate of more than 95%. The substantial improvements of removal rate were attributed to the formation of larger adsorbed aggregates, facilitating easy separation. Importantly, Mt laminae, as a rigid structure, could effectively prevent molecular chain of polyelectrolyte curling due to electrostatic shielding after adsorption, which made the adsorption sites play a full role, thus enhancing the adsorption efficiency. The maximum adsorption capacity of composite (80 wt% P(NaAA/VIC) and 20 wt% Mt) was increased by about 20% compared with pure P(NaAA/VIC). And the excessive zwitterionic groups in polyelectrolyte would lead to a decrease in adsorption capacity. The systematic investigation revealed that the adsorption was a spontaneous exothermic process driven by electrostatic interactions, conforming to the pseudo-second-order kinetic model, in which the adsorption was monolayer coverage. The composite can achieve an high adsorption capacity of 1381.7 mg/g at 20 °C, demonstrating enormous potential in the treatment of cationic dye wastewater.