A comparative study of different routes for the modification of montmorillonite with ammonium and phosphonium salts

The objective of this work was to use a statistical tool to study and evaluate the main parameters in the preparation of organo-montmorillonite (O-Mt) by using different compounds and reactional routes (aqueous, semi-solid and supercritical CO2 medium) aiming a better relationship between efficiency and environmental impact. For this, ammonium-modified montmorillonite (AmMt) and phosphonium-modified montmorillonite (PhMt) were prepared according to design of experiments. The samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) and contact angle. XRD and TGA analysis showed that the compounds were incorporated in the montmorillonite providing an efficient modification by all the reactional routes employed. The clay interlayer spacing was expanded and AmMt showed the largest d001 while PhMt showed better thermal stability. Statistical analysis indicated that the process parameters had low or no significance in the organo-montmorillonite characteristics. XRD, TGA and FTIR showed that the d001, yield and chemical environment of the O-Mt changed with the amount of organic compound and washing process. The contact angle test showed that the surface tension of montmorillonite was reduced with organophilization. It was concluded that semi-solid method could be a good, efficient and environmentally friendly alternative to prepare O-Mt.