Improving Oxidation Resistance of CO2-Adsorbents Modified with Dual Amino Silanes in the Presence of Air

Amine-containing materials have been explored as potential CO2 capture adsorbents, but their low oxidative stability has been the most significant barrier to their practical implementation. In this work, adsorbents were prepared by two types of amino silanes, one contained tertiary amine and hydroxy groups (BHAPS), whereas the other had primary amine (APTMS), at different ratios ranging from 10% to 50% through 2-steps and single-step procedures. The combination of these amino silanes resulted in synergy, with the best oxidation stability obtained at a ratio of 20%BHAPS for 2-step and 50%BHAPS for single-step synthesis. The resulting sorbents exhibit a loss of CO2 capacity of around 70% after 190 h and 240 h aging in the air at 110 oC for 20%BHAPS (2-step) and 50%BHAPS (single-step), respectively. The results showed a slower deactivation rate than a typical APTMS/silica, which exhibits a total loss of 90% and 98% of CO2 uptake capability following the same treatment of 190 and 240 h. The stability of silica-grafted amino silanes showed that the oxidative stability of sorbents depended on the amino silane loading and oxidation duration. The results suggested that the hydroxyl groups of BHAPS help protect APTMS from oxidation. The surface characteristics of sorbents have a significant influence on O2 diffusion, regulating the oxidation rate. Attenuated total reflection-Fourier transform infrared spectroscopy, solid and liquid carbon and proton NMR, and thermogravimetric analysis were applied to characterize adsorbent properties.