Synthesis of high yield mesoporous silica for efficient CO2 adsorption using coal gasification fine slag

The coal gasification fine slag (FS) is a solid waste rich in Si components. The preparation of high-performance mesoporous silica for CO 2 capture using FS as raw materials will alleviate environmental pollution. The alkali-fusion method was used to obtain the high activated Si-containing precursor which could be completely dissolved in NaOH solution with low alkalinity concentration (3 %). The mesoporous silica with highly ordered hexagonal phase was prepared which had high surface area of 1629 m 2 /g and pore volume of 0.8 cm 3 /g. The Si concentration had the great effect on the yield of mesoporous silica and the mechanism for the formation and growth of mesoporous silica between high and low Si-precursor concentration was different. In the preparation process for high yield of mesoporous silica, the silicate ions primarily tended to adsorb around the cetyltrimethylammonium bromide micelles to form nuclei and then the silicate reacted preferentially with the surface silanol groups on the existing particles rather than generating new nuclei. The condensation of the silicate at the external surface of the surfactant micelles occurred to grow into large particles. However, the mesoporous silica particles formation in the lower concentration of silicate species in the alkali solutions was mainly contributed to the interactions between silicate species and CTAB rather than the deposition of silica species. The mesoporous silica showed high CO 2 adsorption performance. The breakthrough time of MS-8 occurred at 22 min and CO 2 adsorption capacity was 2.3 mmol/g at 25 °C. All these results suggest that the silica in fine slag could be fully utilized to prepare mesoporous silica which had a great potential to be used for practical and industrial CO 2 adsorption applications.