Tuning the textural properties of HMS mesoporous silica. Functionalization towards CO2 adsorption

HMS mesoporous silica materials were prepared using different amines as structure directing agents. Textural properties showed a clear dependence on the molecule used, with too long and too short amines yielding significantly distorted structures. CO2 adsorbents were obtained by loading additional amino groups on supports before (as made) or after removing the structure directing agent (extracted and calcined). Organic loading was performed by grafting with diethylenetriamine-trimethoxysilane (DT) and by impregnation with polyethyleneimine (PEI). CO2 adsorption analyses showed a higher CO2 uptake and amine efficiency (defined as the molar ratio CO2/N) for uniformly structured adsorbents. Besides, as-made materials showed the best CO2 adsorption properties due to a synergistic effect between loaded amines and those already present in the support. The influence of adsorption temperature, operation cycles and CO2 concentration was also studied. A maximum CO2 uptake of 4.19 mmol CO2/g (184 mg CO2/g) was registered in pure CO2 (90 degrees C, 1 bar), while a value of 1.80 mmol CO2/g was found in direct air capture conditions (400 ppm CO2, 45 degrees C, 1 bar).