The role of layer charge on saponite functionalization with a cationic alcoxysilane investigated by physicochemical and electrochemical characterization

Abstract

The influence of layer charges of synthetic saponite on its functionalization by a cationic organosilane was investigated for the first time to the best of our knowledge. Saponites of varying layer charges (M^z + _x/z [Mg₆][Si_8-xAl_x]O₂₀(OH)₄nH₂O, with x = 0.25, 0.5, 1.0 and 2.0) were successfully synthesized by controlled substitution of Si by Al and functionalized by the cationic organosilane (Trimethyl [3-(trimethoxysilyl)propyl] ammonium chloride). The organic compound was mainly located in the interlayer space as indicated by the increase of the d₀₀₁-values of saponite samples after modification. The process was certainly driven by the replacement of the interlayer cations by the cationic alcoxysilane. The optimal grafted amount was obtained with the layer charge 1.0, representing the best compromise between the amount of exchangeable cation and layers’ swelling. The layer charge was also found to structure the alcoxysilane orientation in the interlayer space. Electrochemical characterizations revealed the significant capacity of unmodified saponites to accumulate cations as the layers charge increased. The modified saponites showed poor accumulation of cations and thus suggested that the immobilized alcoxysilanes were not exchangeable. This result demonstrated the effective grafting of the organic compound and highlighted the determinant role of layer charges in the functionalization process.