CO2/H2O adsorption and co-adsorption on functionalized and modified mesoporous silicas

Abstract

A challenging current objective in the world is the decrease of the CO2 emissions in the air. Adsorption is an economically and environmentally favorable process but, it requires performant adsorbents meaning porous materials with high CO2 adsorption capacities and good affinity even in presence of water. In this study, we propose to measure not only the CO2 adsorption capacities and affinities but also the water adsorption capacities independently and the co-adsorption of these molecules on type SBA mesoporous silicas.Two different approaches have been explored to improve the CO2 adsorption on such materials: one relies on the silica structure modification by using the BTESE (1,2-Bis(triethoxysilyl)ethane) as silicon source to increase the material hydrophobicity. The other one is based on the grafted SBA silica with amine groups (3-(triethoxysilyl) propylamine called APTES) to significantly improve the CO2 affinity.Then CO2 adsorption capacities, affinities, and enthalpies, have been measured by coupling manometry and calorimetry at 303K and compared to H2O adsorption. In the case of the modified materials, the CO2 affinity and capacity decrease as the ethyl groups amount increases, relevant of the fact that for both H2O and CO2 adsorption the same adsorption sites (silanols) are involved. In the case of the grafted materials, CO2 adsorption affinity and capacity are increased, nevertheless it is less efficient when the grafted groups amount increase.Competitive breakthrough adsorption experiments have confirmed these trends. In humid conditions at 10%RH, 20%RH and 50%RH, H2O enhances CO2 adsorption for modified and grafted materials contrary to the dry sample.