Amine/vermiculite composite aerogels fabricated by polyethyleneimine-induced vermiculite nanosheet gelation for efficient direct air capture

Abstract

Direct air capture (DAC), being able to remove the accumulated CO2 in atmosphere and CO2 carbon emission from discrete sources, is a promising technology for mitigating the global greenhouse effect and achieving carbon neutrality. However, achieving high-capacity, low-cost DAC of CO2 through simple methods remains a significant challenge. In this study, a simple, cost-effective, and environmentally friendly method for fabricating amine/vermiculite composite aerogels is proposed for capturing CO2 from ambient air. Natural two-dimensional material, vermiculite nanosheets with exposed surface and intrinsic negative charge, was utilized as the the building blocks for fabricating aerogel as solid amine adsorbents, via the fast gelatin between vermiculite and amine, significantly reducing the cost of adsorbent preparation while achieving promising CO2 capture capability. The effects of amine loading, amine molecular weight, and porosity on CO2 capture capacity and amine efficiency were investigated. It is found that the amine with larger molecular weights endows more stable amine anchoring in the composite aerogel, the aerogels using amine with higher molecular weights demonstrated higher residual amine ratios under vacuum conditions during the aerogel adsorbent synthesis, consequently enhancing the CO2 capture capacity of the adsorbents. By optimizing synthesis strategy and the amine loading of the composite aerogels, the highest CO2 capture capacity (0.72 mmol/g) and amine efficiency (0.29) were achieved. The monolithic structure of the aerogels ensures low pressure drop of 0.35 hPa during gas flow-through, enhancing their integration and applicability in adsorption devices. The vermiculite-based adsorbents exhibit unique advantages in practical DAC processes, including lower cost, higher amine efficiency, and stable cyclic performance. These findings hold significant promise for the application and advancement of DAC technologies.