(693g) Aqueous in Situ Synthesis of PEI-Uio-66-NH2 Composites for CO2 Capture

Polyethyleneimine (PEI)-based solid sorbents are promising alternatives to conventional monoethanolamine (MEA) scrubbing for carbon capture, offering lower regeneration energy, and operating costs while avoiding MEA’s high energy demand. Metal-organic frameworks (MOFs), particularly UiO-66-NH₂, serve as excellent solid supports for PEI due to their high surface area, tunable pore structure, and chemical stability, while the amino groups in UiO-66-NH₂ can enhance CO₂ affinity and facilitate better PEI dispersion within the framework. However, most reported PEI-UiO-66-NH₂ composites are synthesized via physical mixing using toxic organic solvents like dimethylformamide (DMF), often requiring lengthy synthesis time for formation, and resulting in poor PEI distribution or MOF pore blockage. In contrast, aqueous in situ synthesis offers a greener, scalable alternative that may promote more uniform integration of PEI into the MOF structure.

In this work, we employed a rapid, aqueous phase in situ synthesis of UiO-66-NH₂ in the presence of PEI for carbon capture application. Polymer-MOF composites of PEI-UiO-66-NH₂ with varying PEI loadings were synthesized and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). While XRD confirmed the synthesis of UiO-66-NH₂ crystals, SEM showed the formation of spherical-shaped crystals of UiO-66-NH₂. Furthermore, FTIR and TGA confirmed the presence of PEI in the composite. We then evaluated the CO₂ adsorption performance of these composites, observing capacities comparable to pristine UiO-66-NH₂, with values around 3-4 mmol/g at 1 bar and 0 ^oC. Notably, the composites maintained this CO₂ adsorption capacity over multiple adsorption-desorption cycles where the composites were washed in between cycles for CO₂ regeneration. Our findings indicate that aqueous-phase synthesis of UiO-66-NH₂ in the presence of PEI can yield composites with stable CO₂ capture performance and this approach offers a promising avenue for developing efficient and sustainable CO₂ capture materials.