Flexible structural regulation of montmorillonite through intercalation by zwitterionic surfactants for effective removal of methylene blue

Herein, the structural evolution of organo-montmorillonite (organo-Mt) after the intercalation of zwitterionic surfactants with different alkyl chains was investigated and linked the adsorption behavior of cationic dye (methylene blue, MB). The zeta potential of Mt before and after intercalation showed very small change. While the modification had a significant effect on hydrophilicity of Mt owing to introducing the alkyl chains. The interlayer spacing of Mt was determined by X-ray diffraction, which was used to analyze the arrangement patterns of zwitterionic surfactants in the interlayer according to the molecules size. The relationship between the structural characteristic of organo-Mt and adsorption changes indicated that the paraffin-type arrangement of zwitterionic surfactants and overlong alkyl chain were unfavorable to adsorption. The introduction of appropriate hydrophobic structure endowed high dye adsorption capacity, evidencing the importance of structure regulation of Mt in adsorption. The adsorption of MB by organo-Mt was a spontaneous exothermic process, in which MB molecules were covered on organo-Mt in a monolayer. Compared with Na-Mt, the adsorption capacity of 0.6CEC BS-10/Mt (lateral monolayer arrangement of BS-10 in the interlayer of Mt) could be increased by about 20%. Overall, this work provided valuable guidance for the modification (more types of modifiers) and utilization (adsorbents, nanomaterials, etc.) of Mt in different fields.