Prolonged HKUST-1 functionality under extreme hydrothermal conditions by electrospinning polystyrene fibers as a new coating method

The metal-organic framework (MOF) HKUST-1 (CuBTC) has been regarded as a promising adsorbent due to its open metal sites, easy synthesis method, and lower synthesis cost. However, a big challenge related to its practical application is its poor hydrostability. The porosity of as-synthesized HKUST-1powder may drop 50% in less than one month and it can decompose within days at high humid and hot atmosphere. In this work, we demonstrate that the hydrothermal stability of HKUST-1 is greatly improved after coating it with a thin hydrophobic polymer. The HKUST-1 particles may be directly impregnated in polystyrene fibers during the electrospinning process by suspending sonochemically synthesized HKUST-1 powder in the polystyrene dope solution. It was confirmed that the final HKUST-1 loading was 5% by TGA. Nitrogen isotherms do not show the expected nitrogen uptake in these fibers; however, the carbon dioxide isotherms do. This suggests that the particles are embedded under a layer of polystyrene in agreement with SEM images, and that the nitrogen is unable to penetrate this layer over the length of a nitrogen adsorption experiment. HKUST-1 powder and 5 wt% HKUST-1 fibers are exposed to extreme hydrothermal conditions, and CO₂ uptake is measured at varying time steps. Nearly complete hydrolytic degradation of pure HKUST-1 powder is observed at 6 h, but the rate of degradation in the 5 wt% HKUST-1 impregnated fibers is slowed, and 20% CO₂ uptake capacity is still observed at 48 h.