Imprinting of the surface of mesoporous silicates using organic structure directing agents

摘要

A new protocol has been developed for incorporating the tetrapropylammonium cation (TPA~+) into the walls of the mesoporous material SBA-15 with subsequent calcination to form a novel porous material. This modified material has been extensively characterized using powder x-ray diffraction (PXRD), nitrogen sorption studies, NMR spectroscopy, thermogravimetric analyses (TGA), SEM and TEM. As a result of this treatment, the original mesoporous structure of SBA-15 is retained with a slight decrease in the unit cell dimension from 107 to 105 A. The average pore diameter is increased from 48 to 68 A although the total pore volume remains the same. ~(29) Si MAS NMR spectra indicate that the silica phase is further condensed and densified. As a result a concomitant loss in BET surface area from 770 to 390 m~2/g is observed. The incorporation of TPA~+ into the amorphous siliceous walls of SBA-15 is confirmed by ~(13)C-{~1H} CP MAS NMR spectroscopy and by TGA.