Pseudomorphic transformation and post synthetic modification of amorphous silica for CO₂ sorption applications

Template directed porous silica has shown significant promise in numerous applications such as gas sorption, catalysis and pharmaceutical drug delivery. Mesoporous silicas such as MCM-41, SBA-15 and KIT-6 have been widely reported; however, thus far these materials require long synthesis processes and expensive starting materials. As an alternative, pseudomorphic transformations can convert low-grade amorphous silica into more useful materials. Herein, we demonstrate the effect of pseudomorphic transformations upon the properties of non-porous silica spheres. Surface area can be increased from < 2 m² g⁻¹, for non-porous silica spheres, to 724 m² g⁻¹ for the resulting pseudomorphic species. Silica species were subsequently functionalised with aminopropyltriethoxysilane (APTES) and tetraethylenepentamine (TEPA) via post-synthetic modification. Post-synthetic modification was found to significantly enhance the CO₂ sorption performance of the silica species with CO₂ sorption capacities of up to ca. 92 mg CO₂ g⁻¹ achieved, compared to a maximum uptake of 18 mg CO₂ g⁻¹ for the non-porous silica variants.