Moisture-tolerant diamine-appended metal–organic framework composites for effective indoor CO₂ capture through facile spray coating

Reducing the concentration of indoor carbon dioxide (CO₂) to an acceptable safe level of 1,000 ppm is an important issue because a high level of CO₂ in closed spaces causes lethargy and fatigue. Although diamine-functionalized metal–organic framework (MOF) adsorbents with high CO₂ capacities under indoor air conditions are available, the moisture-induced degradation of MOFs and their shaping remains a challenge for practical applications. Herein, we report the fabrication of epn-functionalized Mg₂(dobpdc) composites, which proceeded by mixing with a polystyrene-block-polybutadiene-block-polystyrene (SBS) hydrophobic polymer (epn = 1-ethylpropane-1,3-diamine; dobpdc⁴⁻ = 4,4′-dioxido-3,3′-biphenyldicarboxylate). The composites were successfully shaped in the form of membranes with different amounts of MOF (epn-MOFX@SBS; X = 60–80 wt%). Specifically, epn-MOF80@SBS exhibited a significant CO₂ adsorption of 2.8 mmol g⁻¹ at 1,000 ppm with recyclable working capacity. The composites were further coated on the surfaces of different supports, such as a Ti mesh, an air filter, and granular activated carbon via a facile and simple spraying method. The experimental conditions were 1,000 ppm CO₂ and 60% relative humidity in a 50-L chamber; the coated materials displayed invariant CO₂ removal performances over 10 cycles and even after 7 days of exposure. The recyclable and long-term CO₂ adsorption capacities demonstrate that the MOF-polymer composites and their coating on various supports provide a useful and effective route for indoor CO₂ capture under realistic conditions.