Polyamine functionalized cage hollow mesoporous SiO2 microspheres for CO2 capture over a wide temperature range

Hollow SiO2 microspheres have become attractive materials for nanotechnology applications owing to their biological inertness and high functionality. In this study, hydrophobic spherical hollow cages were formed using the soft stencil method with Pluronic F127 and cetyltrimethylammonium bromide (CTAB) as the structure-directing agent, and hollow nanoporous SiO2 microspheres (FHMS) were prepared using the soft template method. Various of amine functionalization modes were further employed to demonstrate the complexity of the relationship between pore structure/amidation mode/amine content and adsorption capacity. The hollow morphology of the porous silica was revealed using field-emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and its porous properties were revealed using nitrogen adsorption-desorption isotherm measurements. Experiments on the fixed-bed dynamic adsorption process at 15% CO2 showed that the high specific surface area, high pore volume and amine content of the carriers had a positive effect on the adsorption performance. However, the accessibility of the adsorption centre was affected at high loadings, and the amine efficiency and adsorption capacity were reduced. The dual amine functionalized FHMS-G-I60 maintained the integrity and order of the hollow mesoporous carrier structure, and overcame the dilemma of easy loss in the cycle process of the impregnation method and the low adsorption capacity of the grafting method. It possessed an adsorption capacity of 3.62 mmol/g, high adsorption cycling stability (more than 99.5% adsorption maintained after 10 cycles) and high amine efficiency (0.2852 mmol CO2/mmol N). CO2-TPD analysis (Thermal Programmed Desorption) further showed that FHMS-G-I60 had a faster desorption rate and lower regeneration energy consumption. In general, such structure-directed prepared matrices and functionalized with different amines are promising and low-cost adsorbents that can be used to capture CO2 from ambient air and flue gases under different demands.