Adsorption and diffusion in thin films of nanoporous metal–organic frameworks: ferrocene in SURMOF Cu2(ndc)2(dabco)

Abstract

The adsorption and diffusion of ferrocene (FC) in thin MOF films of type Cu₂(ndc)₂(dabco) were studied by X-ray diffraction and using a quartz-crystal microbalance (QCM) at different temperatures. A quantitative analysis of the uptake curves in the QCM during loading with FC from the gas phase yields 0.19 FC compounds per pore at a temperature of 305 K and of 0.06 at 335 K, respectively. From an analysis of this temperature dependence we obtain an adsorption enthalpy of −30 kJ mol⁻¹. A quantitative analysis of the time dependence of the QCM uptake curves yields very small diffusivities on the order of 10⁻¹⁹ to 10⁻¹⁷ m² s⁻¹, while the activation energy for diffusion amounts to +90 kJ mol⁻¹. These results show that using a quartz crystal microbalance for uptake studies in SURMOFs is a valuable tool for investigating very slowly diffusing compounds in nanoporous materials.