Influence of Zn incorporation on the structural and gas adsorption properties of CdIF-1 metal-organic frameworks

Abstract Precise control of pore structure in metal-organic frameworks (MOF) is crucial for optimizing gas adsorption and separation performance. By introducing a second metal Zn into the CdIF-1 MOF, we confirmed the preservation of its long-range topology, indicating a single-phase structure in bimetallic Cd1−xZnxIF-1 (x = 0 to 0.5) MOF. XRD analysis reveals a unit cell contraction with increasing Zn content, which simultaneously modifies the surface area and pore structure. To investigate the influence of Zn incorporation on the local structure of the metal centers, as well as metal distribution throughout the framework, we employed X-ray absorption spectroscopy (XAS) and solid-state NMR (SSNMR) spectroscopy. Cd L3-edge and Zn K-edge XAS spectra indicate that Cd and Zn share a very similar local coordination environment in Cd1−xZnxIF-1, whereas 111Cd SSNMR results suggest a random replacement of Cd by Zn. Gas adsorption experiments for CO2, C2H2, C2H4, C2H6, and C3H8 reveal that these subtle structural modifications have an impact on the adsorption performance. Interestingly, as the kinetic diameter of the gas molecules approaches or even slightly surpasses the MOF aperture size, the adsorption capacity increases.