Novel Amine-Functionalized Magnesium Oxide Adsorbents for CO₂Capture at Ambient Conditions

In this study, we synthesized novel magnesium oxide-based adsorbents and utilized them for CO₂capture at ambient conditions (1atm, 30°C). Magnesium oxide (MgO) was synthesized using a facile sol-gel technique starting from magnesium nitrate and ammonium hydroxide, sodium hydroxide or oxalic acid. MgO adsorbent synthesized in the presence of ammonium hydroxide (labeled as MgO-A) showed the highest surface area (350 m²/g), which has been correlated with the highest CO₂adsorption capacity (30mg/g) relative to those synthesized in the presence of sodium hydroxide (MgO-N) or oxalic acid (MgO-O). The characterization of the MgO samples (MgO-A, MgO-N and MgO-O) using XRD, FTIR, SEM, BET, and elemental analysis revealed that the synthesis route has a significant impact not only on surface area but also on the crystallinity, morphology, and textural properties (surface area, porosity and pore size distribution) of these MgO adsorbents. Nonetheless, the key novelty of the work reported herein is the functionalization of MgO with 3-aminopropyl-triethoxysilane (APTES), diethylenetriamine (DETA) and polyethylenimine (PEI) and their utilization for CO₂capture at ambient conditions. The functionalization of MgO-A with the three amines significantly altered its characteristics (i.e., crystallinity, morphology, and textural properties). More importantly, the functionalization of MgO-A with APTES and DETA resulted in an increase in CO₂adsorption from 30 (in the case of the unmodified MgO-A) to 65 and 47.6mg/g, respectively. These values correspond, respectively, to 0.81 and 1.13mol CO₂captured/mol amine loaded on MgO-A. However, the functionalization of MgO-A with the polymeric amine (PEI) caused a significant reduction in the adsorbent surface area, leading to a decrease in CO₂adsorption. Regeneration studies (using APTES-MgO-A as an example) demonstrated that contacting the spent adsorbent with N₂gas at 120°C for a short time can fully restore its original adsorption capacity, suggesting the potential commercial use of APTES-MgO-A for CO₂capture with a minimal energy requirement.