Swelling-agent-free synthesis of rice husk derived silica materials with large mesopores for efficient CO₂ capture

Swelling-agent-free synthesis of silica materials with large mesopores were developed using silicate from rice husk ash (RHA) as an alternative silica precursor in this study. Unlike the conventional methods for preparing large-pore silica materials in which toxic and expensive additives were employed as swelling agents, the obtained silica materials with large mesopores could be facilely prepared via a simple temperature-controlled approach without adding pore expanders. The fusion and hydrothermal temperature effects on the structural properties of obtained mesoporous silicas were investigated by the XRD, nitrogen adsorption-desorption, SEM and TEM analyses. The obtained mesoporous MS-400(25), which was fabricated using rice husk fused at 400°C and treated with sodium hydroxide at 25°C, exhibited bimodal meso-porosities (2.7 and 24nm) and large pore volume (1.92cm³/g). The bi-porosities mainly originated from the intra-particle mesostructure within silica particles and the inter-particle porosity between the aggregated nano-sized silica particles, respectively. The synthesized silicas were applied as the supports of adsorbents for CO₂ capture. The adsorption tests clearly revealed that the tetraethylenepentamine (TEPA) impregnated MS-400(25) material could achieve CO₂ adsorption capacity of 173mg/g under 10% CO₂ at 75°C, which was the best sorbents among all samples due to its relatively large pore volume.