Calcium Alginate Aerogel-MIL160 Nanocomposites for CO₂ Removal

Using MOFs in powder form leads to mass transfer limitations and large pressure drops in packed bed adsorbers. Use of MOF/aerogel composites (called MOFACs) in bead form could overcome these challenges without compromising the MOF's adsorption performance, as observed with other shaping methods, such as the use of polymeric binders. In this study, Ca-alginate-aerogel-MIL-160(Al) MOFACs (AlgMIL160) were prepared via sol/gel-assisted direct mixing methods, followed by supercritical drying. The gas sorption, powder X-ray diffraction, FTIR, and scanning electron microscopy characterization results showed that the MOF was successfully incorporated into the aerogel, while the MOF structure was preserved. Adsorption measurements were carried out in both static single-component and dynamic binary gas mixture modes. Obtained isotherms were successfully fitted to the Langmuir model followed by ideal adsorbed solution theory (IAST). The single-component gas adsorption isotherms of CO₂ on MOFACs with MIL-160(Al) loadings of 25, 50, and 75 wt % revealed a CO₂ uptake of 0.43, 0.70, and 0.98 mmol/g at 150 mbar and 25 °C which were higher than that of pure MOF (1.23 mmol/g) based on the MOF loading in the composites, showing the synergistic effect of aerogel and MOF composites. Incorporation of MIL-160(Al) into the aerogel network which is comprised of 75% MIL-160(Al) and 25% Ca-alginate aerogel enhanced MIL-160(Al)'s CO₂/N₂ IAST selectivity from 53 to 70 at 25 °C and 1000 mbar. Both experimental and simulated CO₂ adsorption isotherms showed good agreement. The dynamic adsorption performance of the MOFACs studied by using a binary mixture of 15% CO₂/85% N₂ was close to the single-component CO₂ adsorption with slightly decreased uptake showing the competitive adsorptions between CO₂ and N₂ molecules. This novel nanocomposite with remarkable CO₂ capture performance can be used in gas adsorbers without causing large pressure drops.