Bifunctional mesoporous hybrid sol-gel prepared silicas for CO2 adsorption

Bifunctionalized mesoporous silica materials were prepared by sol–gel method applying newly proposed sequence of addition of the used silanols in the systems tetraethylortosilicate (TEOS): Tris[3-(trimethoxysilyl)propyl] isocyanurate (ISC): bis[(3- trimethoxysilyl)propyl]amine (BTPA), TEOS: ISC: (3-mercaptopropyl)trimethoxysilane (MPTMS) (TEOS: ISC: MPTMS) and TEOS: BTPA: MPTMS. The bi-functionalized hybrid silicas were synthesized by co-condensation reaction between TEOS and silsesquioxane precursors in acidic media. Soft template approach for pore formation was applied with structural directing agent Pluronic P123. Mesitylene and KCl were used for improving the materials' texture. New sequences of addition of the silanol precursors into the reaction mixture were applied in order to achieve better distribution of the functional groups on the materials surface and for prevention of entrapment of the functional groups in the pore walls. The synthesized bi-functional hybrid mesoporous silicas were investigated by FTIR, N2-physisorption, DTA/TG-MS, SEM, XPS and XRD techniques. CO2 adsorption properties of the synthesized bi-functionalized hybrids were investigated. I was found that the sequence of addition of silanol precursors, the type of the silsesquioxane precursors and the presence of isocyanurate groups have significant influence on the materials texture, morphology and CO2 sorption properties. The presence of isocyanurate groups in the hybrid silica framework significantly improves the textural characteristics and CO2 sorption capacities. The determined heats of adsorption evidenced CO2 physisorption on the active sites of the hybrid materials.