Amine-impregnated nanoarchitectonics of mesoporous silica for capturing dry and humid 400 ppm carbon dioxide: A comparative study

Various amine-impregnated mesoporous silica adsorbents were prepared for a comparative study of 400 ppm CO2 adsorption at room temperature (25 or 30 °C) under dry and 60% relative humidity conditions. Five types of amines–polyethylenimine (PEI), tetraethylenepentamine (TEPA), triethylenetetramine (TETA), diethylenetriamine (DETA), and ethylenediamine (EDA)–and three types of mesoporous silica with different pore structures (SBA-15, MCM-41, and MCM-48) were used. The amine loading amount was also optimized according to the CO2 adsorption results obtained using a thermogravimetric analyzer under dry conditions. SBA-15 samples with 50–60 wt% loadings of TEPA and TETA showed a relatively high adsorption capacity of approximately 2 mmol g−1. The adsorption capacities of EDA and DETA loaded samples were less than 0.5 mmol g−1. The PEI impregnated SBA-15 exhibited relatively high CO2 adsorption rate (0.058 mmol g−1 min−1). X-ray diffraction, Fourier transform infrared spectroscopy, N2 adsorption/desorption, and scanning electron microscopy revealed that the amines filled the mesopores of the sample. The amines also covered the outer surface of the mesoporous silica with narrow pore sizes (MCM-41 and MCM48). In humid conditions, SBA-15 with 50 wt% loading of PEI, TEPA, and TETA showed an adsorption capacity of 2.16 mmol g−1, 2.12 mmol g−1, and 1.80 mmol g−1, respectively. An enhanced capacity was observed under humid conditions, especially for the PEI-loaded samples. During the cyclic adsorption test, PEI-and TEPA-impregnated SBA-15 exhibited superior cycling stability compared to the sample with TETA, where the material retained a capacity of approximately 2 mmol g−1 over 10 cycles.