Effects of cation exchange on the pore and surface structure and adsorption characteristics of montmorillonite

Ca-montmorillonite was exchanged with the metal cations, titanium, iron, and copper and the ion-exchange effects on the surface area, pore structure and adsorption property of the montmorillonite were studied. The changes in the pore structure and the surface roughness of the montmorillonite were first characterized based on the classical and fractal analyses of the nitrogen adsorption isotherms as well as the XRD and TGA/DSC patterns. Then, the adsorption isotherms of benzene, hexane, and cyclohexane were measured to identify how exchange process affected the adsorption characteristics of the montmorillonite. It was found that the ion-exchange processes could induce enormous changes in the surface and pore structure of montmorillonite and these changes could be interpreted with the coverture of the surface roughness (surface screening effect), the inhibition of the movement of nitrogen molecule into pores (pore blocking effect), and the interlamellar expansion of the montmorillonite (pore opening effect). The effect of alterations of the surface area and the pore structure on the adsorption characteristics of montmorillonite was discussed.