A robust and flexible Cu-based metal–organic framework for gas separation and volatile organic compounds detection

Abstract

In the continuous search for new materials able to interact with CO₂ and Volatile Organic Compounds (VOCs), metal–organic frameworks (MOFs) have emerged as an outstanding class in CO₂ adsorption and VOCs detection. Particularly, Cu-based MOFs with coordinatively unsaturated sites (CUS) are considered one of the most appealing class of MOFs due to their ability to interact with these gases. In this work, a novel MOF named GR-MOF-26, based on copper and the combination of the 5-amino-2,4,6-triiodoisophthalic acid (H₂atiip) and 4,4′-bipyridyl (bipy) ligands, is reported. This material presents Cu CUS with a square-planar pyramid geometry and exhibits permanent porosity (specific Dubinin–Radushkevich surface area of 150 m² g⁻¹) combined with a strong light absorption in almost the entire UV-Vis spectrum range (with a reflectance maximum at 510 nm), excellent chemical stability in different organic solvents and in a broad range of pH (from 3 to 10), and moderate selectivity for CO₂ adsorption (0.98 mmol g⁻¹ at 1 bar and 2.1 mmol g⁻¹ at 24 bar) over CH₄. Further, single-crystal X-ray diffraction studies demonstrated that GR-MOF-26 is able to reversibly change its structure and colour upon exposure to different hydrophilic VOCs, and the driving force for these changes is a combination of different parameters (such as pore content, modification of the Cu coordination sphere and/or the structural flexibility).