Synthesis of cetylpyridinium chloride/Keggin-Al30 modified montmorillonite: experimental and molecular simulation investigation

Inorganic-organic modification of montmorillonite was carried out by the polymerized hydroxyaluminum cation (Keggin-Al-30, [Al30O8(OH)(56)(H2O)(24)](18+)) and hexadecylpyridinium chloride (cetylpyridinium chloride, CPC). The loading characteristics of CPC on montmorillonite and structural changes of montmorillonite before and after the modification were studied. The results demonstrated that Al-30 could enter into interlayers of montmorillonite, and CPC can enter into the interlayers or be adsorbed on the surface of Al-30 modified montmorillonite (Al-30 PMT) through hydrophobic interaction of alkyl chains. After the inorganic-organic modification, montmorillonite still can maintain stratified structures. With the increase of CPC dosage and solid-liquid ratio, the loading capacity of CPC on Al-30 PMT increased gradually. However, the loading capacity of CPC decreased firstly and then increased with the increase of pH. The CPC modification process of Al-30 PMT conforms to the Freundlich model and pseudo-second-order kinetic model, and thermodynamic studies showed that it is a spontaneous entropy increase and endothermic process. In addition, the model of Al-30 PMT modification by different CPC dosages was constructed through molecular simulation. The results demonstrated that arrangement of CPC in interlayers of Al-30 PMT includes lateral double-layer, inclined double-layer, and pseudo-three-layer. The simulated value of d(001) is close to the experimental value, which proves the compatibility of experiment and simulation. This research further enriches the basic theory of montmorillonite modification technology, which provides application potential for the development of montmorillonite as a low-cost and high-efficiency adsorbent.