Microstructural and physical properties of silica aerogels based on oil shale ash

The silica aerogels based on oil shale ash were successfully synthesized in the presence of different surface modification agents via ambient pressure drying. The organic modification of hydrogels was a crucial step during the processing which preserved mesopores in ambient pressure drying. It was found that the textural properties of silica aerogels dependent on the type of surface modification agents. The hexamethyldisilazane (HMDZ) modified aerogels had much lower tapping density (0.084 cm3), higher specific surface area (980 m2/g) and larger cumulative pore volume (2.42 cm3/g) and higher porosity (96.16%) than those of dimethyldichlorosilane (DMDC) and trimethylchlorosilane (TMCS) modified aerogels. The HMDZ modified aerogel exhibited a narrow pore size distribution and small average pore size, while DMDC and TMCS modified aerogels had relatively wider pore size distributions, bigger average pore sizes and lower porosity. The FT-IR analysis indicated that as the number of alkyl groups present in surface modification agents increased, the intensity of the peaks related to –OH at 3500 and 1600 cm− 1 decreased (HMDZ < TMCS < DMDC).The TG–DTA analysis revealed that all the surface-modified aerogels were found to be thermally stable up to a temperature of 350 °C, the HMDZ and TMCS modified aerogels showed higher thermal stability (∼ 400 °C).