Interlayer modification of a layered H-octosilicate (H-RUB-18) with methanol: Formation of a highly ordered organosilicate nanohybrid

Highly ordered silicate-organic nanohybrids were prepared by the modification of interlayer silanol groups of a layered polysilicic acid (H-octosilicate, H-RUB-18) with methanol. The grafting reaction was performed in a Teflon-lined stainless steel autoclave at 120°C for various reaction periods. The grafting of methoxy groups onto the interlayer surface was evidenced by the downfield chemical shifts of the methyl groups in the solid state ¹³C NMR spectra and the exothermic DTA peaks with substantial weight losses due to combustion of methyl groups. The degree of modification with the methoxy groups was variable in the range between 0.42 and 0.95, depending on the reaction time. The retention of the layered silicate structure was proved by XRD and ²⁹Si HD/MAS NMR. The structure was also analyzed by molecular mechanics force field calculation and Rietveld analysis, indicating the expansion of the silicate plane composed of the 5⁴ cage with six-membered rings in the structure. This small structural distortion, caused by repulsion between the grafted methoxy groups, resulted in transformation of the crystal system from tetragonal to monoclinic. Hydrogen molecules were sorbed into the grafted products.