Enhanced CO2 capture by PEHA-functionalized sepiolite via in-situ Mg pillaring: A synergistic effect of structure and chemistry.

Sepiolite (SEP)-based solid amine is considered as a low-cost adsorbent for CO2 capture. However, the inferior physical structure and constrained chemical properties impede its further development. Herein, by utilizing magnesium-containing waste liquid from acid-treatment sepiolite as a precursor, MgO nanostructures that act as pillars, permanently propping open the sepiolite layers and creating a Mg pillared sepiolite support (SEPMgO) with a high surface area (279 m2/g) and large pore volume (0.75 cm3/g), achieving the resource utilization of waste. Pentaethylenehexamine (PEHA) was impregnated onto SEPMgO to synthesize an adsorbent. The SEPMgO-PEHA0.9 adsorbent achieved the optimal CO2 adsorption capacity of 3.2 mmol/g at 60 °C. The adsorption capacity only decreased by 10 % after ten cycles. In-situ DRIFTS analysis reveals the capture process of SEPMgO-PEHA0.9 follows zwitterion and base-catalyzed hydration mechanism, with the latter being significantly promoted by the alkaline environment provided by magnesium oxide. Life cycle assessment validated a low carbon footprint of 0.136 t of CO2 emissions per tonne captured, marking a 25% reduction compared to SBA-15-based sorbents. The SEPMgO-PEHA0.9 adsorbent is a promising candidate for the application of mineral materials in CO2 capture and sustainable development.