Synthesis of ordered mesoporous silica from biomass ash and its application in CO₂ adsorption

It is possible to achieve high-value utilization of solid wastes and lower the cost of mesoporous silica synthesis by synthesizing mesoporous silica from solid wastes. In this study, silica was extracted using the alkali fusion method using biomass ash as the starting material. Biomass ash based mesoporous silica was successfully prepared by hydrothermal method with silicon extract solution as silicon source. The optimum conditions for preparation were determined as follows: addition of cetyltrimethylammonium bromide was 0.45g, hydrothermal temperature was 120 °C, hydrothermal time was 24h. The prepared mesoporous silicon was systematically characterized, and the results showed that high surface area (495 m²/g) and ordered pore structure appeared in the synthesized mesoporous silica materials. The synthesized mesoporous silica showed excellent CO₂ adsorption performance (0.749 mmol/g) at 25 °C and 1 bar. According to the calculation of adsorption isotherm and thermodynamics, non-linear Freundlich model can fit the adsorption isotherm better and the adsorption heat of mesoporous silica is less than 20 kJ/mol, which belongs to physical adsorption. After five cycles of CO₂ adsorption, the adsorption property was still above 90%, and the CO₂/N₂ adsorption selectivity reached 396.6, showing good regeneration performance and adsorption selectivity. This research can provide a new possibility for the high-value exploitation of biomass ash and reducing the cost of synthetic mesoporous silica.