Nano-scale structure control of mesoporous silica

Structure change during a process from a layered sodium silicate, kanemite, to a noble mesoporous silica, folding sheet mesoporous materials (FSM), was studied by 29Si-MAS-NMR and X-ray powder diffraction. Cation exchange of Na+ in the kanemite for hexadecyltrimethylammonium (HDTMA) ion folded unit silica sheets to form an HDTMA/silica intermediate with nano-scale hexagonal symmetry. Following pH adjustment at 8.5 promoted condensation reactions between adjacent silica sheets to form an HDTMA/silica complex, which caused local rearrangement of SiO4-tetrahedra in the sheets. Removing the organic component from the HDTMA/silica complex by calcination at 550 °C gave a porous silica where uniform nano-scale pores were arranged regularly. XRD patterns suggested a characteristic SiO4-tetrahedra arrangement in the walls of the porous materials.