5 research outputs found
Modeling of metal-organic frameworks for optical applications
Metal-organic frameworks (MOFs) are an important class of porous hybrid materials. They
consist of metal ions or metal-oxo clusters forming the so-called inorganic building units
connected by organic ligands acting as linker molecules leading to an intrinsic porosity of
the framework. MOFs have been discussed intensively with regard to classical applications of
porous materials like catalysis and gas separation. In this work, a different aspect is focused,
namely the use of MOFs as optical materials. One fundamental property in this respect is the
refractive index (RI).
To ensure the reliable and precise calculation of the RI of MOFs a novel ab initio simulation
protocol was developed in this work. By applying density functional theory (DFT), accurate
models of MOF crystal structures were prepared and the optical properties were calculated
precisely. Starting with the well-known UiO-66 MOF and its established nitro- and aminofunctionalized
derivatives UiO-66-NO2 and UiO-66-NH2, this simulation protocol was used to
calculate the electronic structures and the corresponding optical properties. Furthermore, the
incorporation of âpushâpullâ linkers into the UiO-66 framework was studied to allow a further
tuning of the RI of the parent UiO-66 MOF. In this context, a novel UiO-66 analogue denoted
as UiO-66-(NH2,NO2) was presented. In addition, the use of halogenated linkers yielding the
well-known monohalogenated UiO-66 derivatives denoted as UiO-66-X ( = F, Cl, Br, I) was
studied. To obtain high RI values while preserving the transparency in the visible spectral
region, a novel dihalogenated UiO-66 derivative denoted as UiO-66-I2 was introduced.
The simulation protocol developed in the first part of this work allows a detailed study of
the electronic structure of MOFs and a better understanding how the the various modular
components of a MOF influence its RI. This protocol is computationally demanding. As a consequence,
a second, more efficient simulation protocol was presented allowing the screening of
MOFs with regard to their RI. This simulation protocol is based on a fragmentation scheme
for MOFs allowing the separate calculation of the polarizability of the modular components of
MOFs using DFT. These polarizabilities were used to compute the total polarizability of a MOF
and subsequently the corresponding RI by applying the Lorenz-Lorentz equation.Metall-organische GerĂŒste (engl. metal-organic frameworks, MOFs) stellen eine bedeutende
Gruppe innerhalb der porösen Hybridmaterialien dar. Sie bestehen aus Metallionen oder Metall-
Oxo-Clustern, die als anorganische Baueinheiten bezeichnet werden und durch organische
Liganden verknĂŒpft sind, die als Linker bezeichnet werden. MOFs wurden intensiv im Hinblick
auf klassische Anwendungsgebiete fĂŒr poröse Materialien wie beispielsweise Katalyse und
Gastrennung betrachtet. Im Gegensatz dazu werden in dieser Arbeit MOFs fĂŒr die Verwendung
als Materialien fĂŒr optische Anwendungen untersucht. Hierbei ist insbesondere der
Brechungsindex (refraktiver Index, RI) von besonderer Relevanz.
In dieser Arbeit wurde ein ab initio Simulationsprotokoll entwickelt, das eine verlÀssliche
und prÀzise Berechnung der elektronischen Struktur und des RIs von MOFs ermöglicht. Hierzu
wird die Dichtefunktionaltheorie (DFT) verwendet, um ausgehend von Einkristallstrukturdaten
Modelle von MOFs zu erstellen und die optischen Eigenschaften zu berechnen. Beginnend
mit dem bekannten MOF UiO-66 und dessen etablierten nitro- und aminofunktionalisierten
Derivaten UiO-66-NO2 und UiO-66-NH2 wurde dieses Simulationsprotokoll angewendet. AnschlieĂend
wurde die Verwendung von âpush-pullâ-LinkermolekĂŒlen zum Aufbau des UiO-66
GerĂŒsts untersucht und das neue UiO-66-(NH2,NO2) Derivat computer-chemisch charakterisiert.
Weiterhin wurde die Verwendung von monohalogenierten LinkermolekĂŒlen untersucht, mit
welchen die UiO-66-X ( = F, Cl, Br, I) Derivate erhalten werden können. ZusÀtzlich wurde
das neue UiO-66-I2 Derivat vorgestellt, um im sichtbaren Spektralbereich einen hohen RI bei
gleichzeitiger Transparenz zu erhalten.
Das im ersten Teil dieser Arbeit vorgestellte Simulationsprotokoll erlaubt ein tieferes VerstÀndnis
des Einflusses der modularen Komponenten eines MOFs auf den RI, aber ist mit einem
hohen Rechenaufwand verbunden. Daher wurde ein weiteres effizienteres Simulationsprotokoll
zur Berechnung des RIs von MOFs entwickelt. Dieses Protokoll basiert auf der Fragmentierung
von MOFs, so dass die Polarisierbarkeiten der modularen Komponenten eines MOFs separat
mittels DFT berechnet werden konnten. AnschlieĂend wurde die Polarisierbarkeit des MOFs
und der entsprechende RI unter der Verwendung der Lorenz-Lorentz-Gleichung berechnet
Tuning the optical properties of the metal-organic framework UiO-66 via ligand functionalization
Metal-organic frameworks (MOFs) are a promising class of materials for optical applications, especially due to their modular design which allows fine-tuning of the relevant properties. The present theoretical study examines the Zr-based UiO-66-MOF and derivatives of it with respect to their optical properties. Starting from the well-known monofunctional amino- and nitro-functionalized UiO-66 derivatives, we introduce novel UiO-66-type MOFs containing bifunctional push-pull 1,4-benzenedicarboxylate (bdc) linkers. The successful synthesis of such a novel UiO-66 derivative is also reported. It was carried out using a para-nitroaniline (PNA)-based bdc-analogue linker. Applying density functional theory (DFT), suitable models for all UiO-66-MOF analogues were generated by assessing different exchange-correlation functionals. Afterwards, HSE06 hybrid functional calculations were performed to obtain the electronic structures and optical properties. The detailed HSE06 electronic structure calculations were validated with UV-Vis measurements to ensure reliable results. Finally, the refractive index dispersion of the seven UiO-66-type materials is compared, showing the possibility to tailor the optical properties by the use of functionalized linker molecules. Specifically, the refractive index can be varied over a wide range from 1.37 to 1.78
Correction: Tuning the optical properties of the metal-organic framework UiO-66 via ligand functionalization
The authors apologise that the comparison of calculated (HSE06) and experimental band gaps shown in Fig. 3 were incorrect, the experimental values did not match the presented UV-Vis spectra and Tauc plots. The figure is corrected as follows: The corrections shown here do not affect the conclusions in the paper. (Figure Presented).The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers
MetalâOrganic Framework Co-MOF-74-Based HostâGuest Composites for Resistive Gas Sensing
Increasing demands in thefield of sensing, especially for gas detectionapplications, require new approaches to chemical sensors. Metalâorganic frameworks (MOFs) can play a decisive role owing to their outstanding performances regardinggas selectivity and sensitivity. The tetrathiafulvalene (TTF)-infiltrated MOF, Co-MOF-74, has been prepared following the hostâguest concept and evaluated inresistive gas sensing. The Co-MOF-74-TTF crystal morphology has beencharacterized via X-ray diffraction and scanning electron microscopy, while thesuccessful incorporation of TTF into the MOF has been validated via X-rayphotoemission spectroscopy, thermogravimetric analysis, UV/vis, infrared (IR), andRaman investigations. We demonstrate a reduced yet ample uptake of CO2in thepores of the new material by IR imaging and adsorption isotherms. Thenanocomposite Co-MOF-74-TTF exhibits an increased electrical conductivity incomparison to Co-MOF-74 which can be influenced by gas adsorption from asurrounding atmosphere. This effect could be used for gas sensing