Tunable amine loading of amine grafted mesoporous silica grafted at room temperature: Applications for CO2 capture

Development of Amino-Functionalized Silica by Co-condensation and Alkylation for Direct Air Capture

CO2 chemisorption using amine-based sorbents is one of the most effective techniques for carbon capture and storage. Solid CO2 sorbents with amines immobilized on their surface have been attracting attention due to the easy collection of sorbents and reusability. In this study, we developed a solid CO2 adsorbent by co-condensation of a silanizing reagent having a chloroalkyl group and tetraethyl ethoxysilane, followed by alkylation of the chloroalkyl group with diamine. The fabricated amine-immobilized silica with a high density of amino groups on its surface achieved the chemical adsorption of 400 ppm of CO2 with 4.3 wtCO2 % loading, CO2 release upon heating at 80 °C, and reusability for adsorption and desorption cycles with high amine utilization efficiency (0.20 molCO2 /mol-N). This surface modification method is applicable to various amines bearing more than two amino functional groups, enabling the development of solid CO2 sorbents for the selective capture of low-concentration CO2 directly from the air.

High-Efficiency Silane Utilization in Amine-Modified Adsorbents for Direct Air Capture through Interconnected Three-Dimensional Pores

Economic synthesis of amine-modified solid adsorbents is pivotal for the global-scale direct air capture (DAC) technologies required to realize net-zero emissions. To address the problems of the traditional reflux method using excessively costly amino silane, we propose introducing silane by impregnation into mesoporous silica with interconnected three-dimensional pores. X-ray diffraction, Fourier transform infrared spectroscopy, N2 adsorption-desorption, transmission electron and scanning electron microscopies, magic-angle spinning nuclear magnetic resonance, and elemental analysis identified the spatial distribution of amino silane in the materials with different loading levels. The results of structure characterization and a comparison with a reference experiment (using a porous support with one-dimensional pores and/or the conventional reflux method) revealed that the proposed strategy provided a uniform amine distribution, together with a high utilization efficiency of the amino silane. We also demonstrate that the obtained material has a high adsorption capacity and good recycling stability comparable to those of the previously reported amino silane modified adsorbents under simulated DAC conditions.

Effect of Temperature on CO2 Adsorption onto Amine-Functionalized KIT-6 Adsorbents

The mesoporous silica KIT-6 was synthesized and functionalized with 3-aminopropyltriethoxysilane (APTES) by grafting at 110 °C. The composites were prepared with three different concentrations of APTES: 20, 30 and 40 wt.%. The as-prepared samples were characterized by thermal gravimetric analysis in air and nitrogen atmosphere (TG/DTA), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction and nitrogen adsorption-desorption. In this study, CO2 adsorption-desorption was investigated using temperature programmed desorption mass spectrometry (TPD-MS) at different temperatures. The adsorption capacity of the prepared composites is 2.23 mmol CO2/g at 40 °C and decreases to 0.95 mmol/g at 70 °C. Regarding the efficiency of the amino groups, the best result was obtained for APTES-grafted KIT-6 at 40 °C, with 0.512 mmol CO2/mmol NH2. The results showed good cyclical stability in adsorption capacities even after nine adsorption-desorption cycles.