Silylation of saponite with 3-aminopropyltriethoxysilane

A series of saponites (Sap) with a fixed Si/Mg ratio and varied Al contents were synthesized by using hydrothermal methods. The spectral, structural and morphology characters of the obtained products were characterized by a combination of XRD, FTIR, TG-DTG, TEM, ²⁹Si MAS NMR, ¹³C NMR etc. before and after 3-aminopropyltriethoxysilane (APTES) grafting. XRD patterns showed that well-ordered Sap were obtained with starting Si/Al ratios of 5.43 and 7.89. Silylation reactions have little or no effect on the layered structure of Sap at the used dosage of APTES. The existence of the –CH₂ stretching bands at around 2937 cm^− 1 in IR spectra clearly showed the incorporation of silane in the grafted samples. TG–DTG curves revealed that the samples with higher crystallinity displayed higher dehydroxylation temperature, as expected. A new mass loss located at around 420 °C in silylated Sap was ascribed to the volatilization of the alkyl group in silane. The ²⁹Si NMR spectroscopy showed a series of signals of T structures, ascribed to the different silylation modes between silane and Sap. Furthermore, silylation procedures led to a decrease of the intensity of the signals at ca. − 84 ppm along with an increase of the intensity of Q³ signals. A further increase in the silane concentration did not decrease the resonance at − 84 ppm any further. This phenomenon confirmed the coexistence of Q² structure with Q³Si(2Al) structure, which resulted from the broken bonds at the edge surfaces of the synthesized Sap.