Nanofibrous carbon microspheres with hierarchical porosity for deep eutectic solvent loading and highly efficient SO2 adsorption

Abstract

Deep eutectic solvents (DESs) are promising absorbents for SO2 capture. However, the high viscosity of DESs limits their applications in the SO2 separation industry. In this study, nanofibrous and porous carbon microspheres (NCMs) with a large surface area (344.5 m2·g−1) were prepared from chitin and used to load [emim]Cl + imidazole DESs for the first time using a physical dispersion process. The DESs were uniformly adsorbed onto the nanofibrous carbon surfaces, and a novel adsorbent (NCMs-xDESs) was formed with a three-dimensional hierarchical porous structure. NCMs showed high loading capacity for DESs (the ideal load ratio was 5:1) and exhibited an appropriate solid-state with significantly decreased DESs viscosity. NCMs-xDESs were used to capture SO2, and the results showed that NCMs-5DESs had the highest adsorption capability for SO2 compared with other NCMs-xDESs. The adsorption capacity of NCMs-5DESs for pure SO2 reached up to 14.66 mol/kg under 25 ℃ and 1 bar conditions. The adsorption capacity remained at 2.89 mol/kg even at low-content SO2 (1,700 ppm) in the mixed gas, which was higher than most solid adsorbents reported in the literature. The excellent adsorption capability was due to the porous structure of the NCMs and the multiple interactions between DESs and SO2. The DESs contained the strong electron-donating ability of Cl−1 and weakly basic tertiary N that can interact with SO2 via electron deficiency and Lewis acids. H-bonding interactions also formed between the DESs and SO2. Additionally, the NCMs-DESs absorbent exhibited excellent reversibility and selectivity for SO2 adsorption after ten cycles. Therefore, the NCMs-DESs absorbent may be a promising candidate for SO2 capture in polluted gas.