Browsing by Author "Speed, Daniel"

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    The Effects of Functional Groups and Missing Linkers on the Adsorption Capacity of Aromatic Hydrocarbons in UiO-66 Thin Films
    (MDPI, 2020) Shankwitz, Jennifer; Speed, Daniel; Sinanan, Dillon; Szulczewski, Greg; University of Alabama Tuscaloosa
    The adsorption of benzene, toluene, ethylbenzene, and xylene isomers, also known as BTEX, from the gas phase into porous thin films of the metal-organic framework UiO-66-X, where X = H, NH2, and NO2, was measured to quantify adsorption capacity. The thin films were grown by a vapor-conversion method onto Au-coated quartz microbalance crystals. The MOF thin films were characterized by IR and Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The thin films were activated by heating under high vacuum and exposed to each gas to calculate the Henry's constant. The results demonstrate that the functional groups in the organic linker and missing-linkers both play important roles in the adsorption capacity. Several trends can be observed in the data. First, all the compounds in the BTEX family have lower Henry's constants in the UiO-66-H films compared to the UiO-66-NH2 and UiO-66-NO2 films, which can largely be attributed to the absence of a functional group on the linker. Second, at 25 degrees C, the Henry's constants for all the BTEX compounds in UiO-66-NO2 films are larger than UiO-66-NH2 films. Third, the role of missing linkers is addressed by comparing the measured adsorption capacity to ideal pore filling. The results show that the UiO-66-H films are the most defect-free and the UiO-66-NO2 films have the most missing linker defects.
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    Surface Deposition and Characterization of Metal-Organic Frameworks As Thin Films
    (University of Alabama Libraries, 2024) Speed, Daniel; Szulczewski, Gregory J
    Metal-organic frameworks (MOFs) are a premier candidate material for next-generation functional materials in basic science and industry. These porous crystalline materials can be designed around the coordination geometry of metal ions or clusters and organic linker molecules to yield materials with controlled pore size and chemical functional groups. Surface deposited MOFs are of particular interest to applications in gas sensors. However, relatively little work has been done to understand the growth mechanism of surface deposited MOFs and how best to measure their adsorption properties relative to bulk materials. MOF thin films were deposited by a vapor-assisted conversion (VAC) technique onto a variety of substrates. Specifically, MOF thin films of UiO-67-X where X is H and NH2 and M- MOF-74 where M is Co and Ni were growth on quartz crystal microbalance (QCM) surfaces, which allowed for gravimetric measurements to determine adsorption capacity. In addition, the films were characterized by powder X-ray diffraction, vibrational spectroscopy and scanning electron microscopy (SEM). The influence of the synthesis conditions (precursor concentration, temperature, and time) on the growth mechanism of UiO-67 was studied in detail. SEM studies were able to identify a preference for solvent phase or surface growth modes by quenching the VAC process over time. The precursor concentration and modulator were found to influence the growth mode most significantly.Vapor phase adsorption experiments were conducted on compounds from the BTEX family, namely, benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p- xylene isomers. Adsorption experiments on UiO-67-H films at 30 °C yielded saturation adsorption capacities from 22.4 – 26.9 % by mass, for the BTEX compounds.Similar adsorption experiments were conducted on the BTEX compounds, except toluene, at 25 °C on M-MOF-74 films. The maximum adsorption capacity was ≈17 – 20% by mass and 36 – 42 % by mass for Ni-MOF-74 and Co-MOF-74 films, respectively. These saturation values measured in thin film materials closely match the values measured on bulk materials. The difference in adsorption capacity between Ni-MOF-74 and Co-MOF-74 has been attributed to missing linker defects caused by the decomposition of the DMF solvent.