Liquid- and Gas-Phase Diffusion of Ferrocene in Thin Films of Metal-Organic Frameworks

Wencai Zhou,Christof Wöll,Lars Heinke

doi:10.3390/ma8063767

Wencai Zhou, Christof Wöll + Show 1 more

Open Access

https://doi.org/10.3390/ma8063767

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Journal: Materials	Publication Date: Jun 19, 2015
Citations: 69	License type: CC BY 4.0

Affiliation: Karlsruhe Institute of Technology

Abstract

The mass transfer of the guest molecules in nanoporous host materials, in particular in metal-organic frameworks (MOFs), is among the crucial features of their applications. By using thin surface-mounted MOF films in combination with a quartz crystal microbalance (QCM), the diffusion of ferrocene vapor and of ethanolic and hexanic ferrocene solution in HKUST-1 was investigated. For the first time, liquid- and gas-phase diffusion in MOFs was compared directly in the identical sample. The diffusion coefficients are in the same order of magnitude (~10−16 m2·s−1), whereas the diffusion coefficient of ferrocene in the empty framework is roughly 3-times smaller than in the MOF which is filled with ethanol or n-hexane.

Highlights

Metal-organic frameworks (MOFs) are crystalline, nanoporous hybrid materials, which attract a considerable amount of attention due to their unique properties, such as their very large specific surface area and their enormous variety [1,2]
The uptake curves recorded by quartz crystal microbalance (QCM) enable an analysis of the equilibrium concentration and of the mass transfer parameter, i.e., the diffusion coefficient
Since the surface-mounted metal-organic framework (SURMOF) pores which are activated in argon can be considered as empty, the QCM experiments allow a straightforward quantification of the uptake amount, as demonstrated in references [34,35,36]

Summary

Introduction

Metal-organic frameworks (MOFs) are crystalline, nanoporous hybrid materials, which attract a considerable amount of attention due to their unique properties, such as their very large specific surface area and their enormous variety [1,2]. MOF properties can be varied over wide ranges in a rational manner, resulting in tunable structures This enables many interesting applications, such as the storage and separation of gases, as sensors as well as in catalysis [3,4,5]. The MOF films are prepared on a QCM sensor in a layer-by-layer fashion employing liquid-phase epitaxy These thin MOF films are referred to as surface-mounted MOFs, SURMOFs [14,15,16]. SURMOF films in combination with QCM were used to investigate the diffusion of vapor molecules such as pyridine [24], cyclohexane [25] or ferrocene [26] in MOFs. On the other hand, the QCM was used to investigate the SURMOF growth in the (alternating) synthesis solutions, i.e., in the liquid phase [27].

Experimental Section

Results and Discussions

Conclusions