Role of brush-like additives in CO₂ adsorbents for the enhancement of amine efficiency

Amine adsorbents have been widely investigated for direct CO₂ capture from air. However, the low amine efficiency of the widely-studied amine sorbents is the critical factor to hinder the practical application under dry conditions. Herein, we developed the brush-like cetyltrimethylammonium chloride (CTAC) templating strategy to prepare micro-mesoporous silica nanoparticles (MMSN-X) and TEPA-functionalized adsorbents (MMSN-X/TEPA-Y). The character of samples was investigated by transmission electron microscopy, N₂ adsorption-desorption, Fourier transform infrared spectroscopy, thermal gravimetric analyzer and X-ray photoelectron spectroscopy. The adsorbent (MMSN-30/TEPA-50) with appropriate amount of brush-like CTAC exhibited higher CO₂ adsorption capacities (3.68 mmol/g_adsorbent under simulated dry air conditions) than that of the adsorbents with none or less additives. The kinetic and thermodynamic model were applied to investigate the adsorption rate control factors and adsorption behavior of CO₂ adsorbents with brush-like CTAC. Moreover, with the effect of brush-like CTAC, the significant variation of adsorption product (conversion from carbamate (CO₂/N = 0.5) to carbamic acid (CO₂/N = 1)) was detected by in situ Fourier transform infrared spectroscopy. These results demonstrated that the combination of CO₂ and amine was altered in the presence of brush-like CTAC and thereby the amine efficiency was enhanced, which could be expected to be an efficient adsorbent for CO₂ from air in practical applications.