Three dimensional resolution of the spatial, chemical, and physical properties of materials is driving the material science and is one of the great challenges of present research worldwide. In fact an accurate material characterization has become a rate-limiting step, hindering the development and prosperity of functional materials. We wish to addresses this challenge by systematically studying porous materials based on their molecular building blocks, size, hierarchy, and macroscopic performance.
In one of our works, we tried to overcome the challenge of size determination of MOF NPs. The chemical and physical properties of NPs in general and MOF NPs in particular are size-dependent. However, although the “size” of NPs plays a key role on their behavior, its definition is not trivial, as one has to distinguish between different “sizes” from different physical characterization techniques. We highlight and define some reasonable recommendations of how the MOF NP size should be explored in hopes of standardizing MOF NP properties.
We are also interested in the spatial distribution of the functional groups throughout MOF crystals (Figure), and how this arrangement affects the scaffold. We used fluorescent dyes to represent functionalizations, allowing us to visualize their position in/on the MOFs. Using advanced fluorescence techniques like the fluorescence lifetime imaging (FLIM) and Förster resonance energy transfer (FRET) analysis, we can measure the distribution of the dyes and probe their local environment well below the resolution limit of a light microscope. This research revealed an unexpected relationship between the MOF functionalization method and the formation of nanoscale defects in the framework, whose spatial distribution cannot be investigated with standard bulk characterization techniques.
M. Modena, P. Hirschle, S. Wuttke,* T. Burg,* Mass Measurements Reveal Preferential Sorption of Mixed Solvent Components in Porous Nanoparticles, Small 2018, 14, 1800826. (DOI: 10.1002/smll.201800826)
W. Schrimpf, J. Jiang, Z. Ji, P. Hirschle, D. C. Lamb, O. M. Yaghi,* S. Wuttke,* Chemical Diversity in a Metal-Organic Framework, Nature Commun. 2018, 9:1647. (DOI: 10.1038/s41467-018-04050-w)
W. Schrimpf, G. Ossato, P. Hirschle, S. Wuttke,* D. C. Lamb,* Investigation of the co- dependence of morphology and fluorescence lifetime in a metal-organic framework, Small 2016, 27, 3651-3657. (DOI: 10.1002/smll.201600619)
P. Hirschle, T. Preiß, F. Auras, A. Pick, J. Völkner, D. Valdeperez, G. Witte, W. J. Parak, J. O. Rädler, S. Wuttke,* Exploration of MOF nanoparticles sizes using various physical characterization methods – Is what you measure what you get?, CrystEngComm. 2016, 18, 4359-4368. (DOI : 10.1039/C6CE00198J)