Releasing Si--O tetrahedron and Al--O octahedron from montmorillonite to enhance the adsorption performance of carbon@chitosan@ montmorillonite nanosheet for cationic dyes: Coupling quantum chemistry simulations with experiments

A novel adsorbent of carbon@chitosan@montmorillonite nanosheet (C@CS@ MTN) was successfully fabricated layer -by-layer assembly method to deal with cationic dye wastewater. Batch adsorption experiments showed that the ad-sorption capacities of MB and RhB were higher than 325 mg & BULL;g-1 and 236 mg & BULL;g-1, respectively, indicating that C@ CS@MTN exhibited an excellent adsorption performance. Through quantum chemistry simulations, the molecular electrostatic potential, electron density, differential charge density, molecular orbital distribution and adsorption bind-ing energy were analyzed to reveal the adsorption reaction mechanism between C@CS@MTN and cationic dyes. The results indicated that Si--O tetrahedron ring and Al--O octahedron ring released from montmorillonite with inherent periodic structure was beneficial to electrostatic attraction, while cation-pi interaction benefitted from the interaction between Al atoms of Al--O octahedron ring and benzene ring. It was noteworthy that the electron transfer direction of electrostatic attraction was from O atoms of Si--O tetrahedron ring to the benzene ring of dye molecules, but the elec-tron transfer direction of cation-pi interaction was from benzene ring of dye molecules to Al atoms of Al--O octahedron ring. These results provide fundamental theoretical support for the functional design of mineral-based adsorbents and the efficient removal of cationic dyes.