(449ca) Preparation of Amine Modified Bimodal Mesoporous Silica Particles for CO2 Separation

Mesoporous silica has been extensively studied for many applications such as CO₂ adsorbents, drug delivery, catalysis, and so on. Among them, bimodal mesoporous silica (BMS), which had two different sizes of mesopores, have drawn much attention recently because it exhibited unique diffusion properties in the pores. For this reason, when BMS was modified to have affinity with CO₂, it was expected that both of high CO₂ adsorption capacity and fast adsorption rate would be achieved by small and large pores, respectively. Therefore, we prepared various kinds of amine modified BMS, and the effects of pore structure of BMS samples and the type of introduced amine on CO₂ adsorption/desorption properties were examined in this study. In the experiments, BMS were prepared by co-condensation of two different silica precursors. Tetraethylorthosilicate (TEOS) and triblock copolymer Purulonic 123 (P123) were used as silica precursors and templating agent, respectively. Polymethylhydrosiloxane (PMHS) was not only used as silica precursors but also as template for large pores. First, various BMS samples were prepared with different PMHS concentration, and the pore structures of the resulting samples were investigated. Bimodal mesoporous silicas were successfully synthesized and it was found that the pore diameter and the pore volume could be controlled by changing PMHS concentrations. After that, amines such as polyethyleneimine (PEI) or aminopropyl residue were introduced in the pores of BMS samples and CO₂ adsorption/desorption properties were measured. In addition, MCM-48 was also prepared as samples of monomodal mesoporous silica and then amine modification was carried out in the same way for comparison. The results showed that by optimizing the pore structures, the PEI modified BMS showed improved CO₂ adsorption/desorption properties.