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The Boost of Toluene Capture in UiO-66 Triggered by Structural Defects or Air Humidity.

ABSTRACT: This work aimed to investigate the adsorption of toluene in UiO-66 materials. Toluene is a volatile, aromatic organic molecule that is recognized as the main component of VOCs. These compounds are harmful to the environment as well as to living organisms. One of the materials that allows the capture of toluene is the UiO-66. A satisfactory representation of the calculated isotherm steep front and sorption capacity compared to the experiment was obtained by reducing the force field σ parameter by 5% and increasing ε by 5%. Average occupation profiles, which are projections of the positions of molecules during pressure increase, as well as RDFs, which are designed to determine the distance of the center of mass of the toluene molecule from organic linkers and metal clusters, respectively, made it possible to explain the mechanism of toluene adsorption on the UiO-66 material.

SUBMITTER: Jajko G

PROVIDER: S-EPMC10291636 | biostudies-literature | 2023 Jun

REPOSITORIES: biostudies-literature

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The Boost of Toluene Capture in UiO-66 Triggered by Structural Defects or Air Humidity.

Jajko Gabriela G Sevillano Juan José Gutiérrez JJG Calero Sofia S Makowski Wacław W Kozyra Paweł P

The journal of physical chemistry letters 20230613 24

This work aimed to investigate the adsorption of toluene in UiO-66 materials. Toluene is a volatile, aromatic organic molecule that is recognized as the main component of VOCs. These compounds are harmful to the environment as well as to living organisms. One of the materials that allows the capture of toluene is the UiO-66. A satisfactory representation of the calculated isotherm steep front and sorption capacity compared to the experiment was obtained by reducing the force field σ parameter by ...[more]

PMID: 37310235

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Vibrational spectroscopy investigation of defects in Zr- and Hf-UiO-66.

Project description:Defect engineering in metal-organic framework compounds has allowed for improvements in catalysis-based functionalities, gas sensing, and gas storage. Metal-organic framework UiO-66 compounds with Zr- and Hf-based metal secondary building units were studied with Raman and infrared vibrational spectroscopy. Missing linker and missing cluster defects were engineered into the crystal structure via a modulated synthesis technique. Missing cluster defects in Hf-UiO-66 are first characterized by powder X-ray diffraction (PXRD) whereby two low-angle peaks were fit to extract the relative quantity of reo topology in four defective samples. A monotonic red-shift of the Raman-active Hf-O coordination bond vibration is interpreted as a signature of missing cluster defects, resulting from less-rigid charge-balancing monocarboxylate formate ions replacing the dicarboxylate linker molecule. This signature is hypothesized to be independent of the topology in which the defects appear. Missing linker defects in Zr-UiO-66 are characterized by infrared absorption spectroscopy by the quenching of C-C and C-H vibrational modes confined to the linker molecule. Together, Raman and infrared vibrational spectroscopies coupled with standard characterization techniques are employed to directly probe the nature of defects as well as offer new characterization tools for missing cluster defects in UiO-66.

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Project description:Thermal transport in metal-organic frameworks (MOFs) is an essential but frequently overlooked property. Among the small number of existing studies on thermal transport in MOFs, even fewer have considered explicitly the influence of defects. However, defects naturally exist in MOF crystals and are known to influence many of their material properties. In this work, we investigate the influence of both randomly and symmetrically distributed defects on the thermal conductivity of the MOF UiO-66. Two types of defects were examined: missing linker and missing cluster defects. For symmetrically distributed (i.e., spatially correlated) defects, we considered three experimentally resolved defect nanodomains of UiO-66 with underlying topologies of bcu, reo, and scu. We observed that both randomly distributed missing linker and missing cluster defects typically decrease thermal conductivity, as expected. However, we found that the spatial arrangement of defects can significantly impact thermal conductivity. In particular, the spatially correlated missing linker defect nanodomain (bcu topology) displayed an intriguing anisotropy, with the thermal conductivity along a particular direction being higher than that of the defect-free UiO-66. We attribute this unusual defect-induced increase in thermal conductivity to the removal of the linkers perpendicular to the primary direction of heat transport. These perpendicular linkers act as phonon scattering sources such that removing them increases thermal conductivity in that direction. Moreover, we also observed an increase in phonon group velocity, which might also contribute to the unusual increase. Overall, we show that structural defects could be an additional lever to tune the thermal conductivity of MOFs.

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PANI@UiO-66 and PANI@UiO-66-NH2 Polymer-MOF Hybrid Composites as Tunable Semiconducting Materials.

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Dynamic acidity in defective UiO-66.

Project description:The metal-organic framework (MOF) material UiO-66 has emerged as one of the most promising MOF materials due to its thermal and chemical stability and its potential for catalytic applications. Typically, as-synthesised UiO-66 has a relatively high concentration of missing linker defects. The presence of these defects has been correlated with catalytic activity but characterisation of defect structure has proved elusive. We refine a recent experimental determination of defect structure using static and dynamic first principles approaches, which reveals a dynamic and labile acid centre that could be tailored for functional applications in catalysis.

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Preparation of a Series of Pd@UIO-66 by a Double-Solvent Method and Its Catalytic Performance for Toluene Oxidation.

Project description:This paper reports on the preparation, characterization, and catalytic properties of the Pd@UIO-66 for toluene oxidation. The samples are prepared by the double-solvent method to form catalysts with large specific surface area, highly dispersed Pd0 (Elemental palladium) and abundant adsorbed oxygen, which are characterized by X-ray Photoelectron Spectroscopy (XPS), Brunauer-Emmett-Teller (BET) and Transmission Electron Microscopy (TEM). The results show that as the Pd content increases, the adsorbed oxygen content further increases, but at the same time Pd0 will agglomerate and lose some active sites, which will affect its catalytic performance. While 0.2%Pd@UIO-66 has the highest concentration of Pd0, the result shows it has the best catalytic activity and the T90 temperature is 210 °C.

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Hydrogenative Ring-Rearrangement of Furfural to Cyclopentanone over Pd/UiO-66-NO2 with Tunable Missing-Linker Defects.

Project description:Upgrading furfural (FAL) to cyclopentanone (CPO) is of great importance for the synthesis of high-value chemicals and biomass utilization. The hydrogenative ring-rearrangement of FAL is catalyzed by metal-acid bifunctional catalysts. The Lewis acidity is a key factor in promoting the rearrangement of furan rings and achieving a high selectivity to CPO. In this work, highly dispersed Pd nanoparticles were successfully encapsulated into the cavities of a Zr based MOF, UiO-66-NO2, by impregnation using a double-solvent method (DSM) followed by H2 reduction. The obtained Pd/UiO-66-NO2 catalyst showed a significantly better catalytic performance in the aforementioned reaction than the Pd/UiO-66 catalyst due to the higher Lewis acidity of the support. Moreover, by using a thermal treatment. The Lewis acidity can be further increased through the creating of missing-linker defects. The resulting defective Pd/UiO-66-NO2 exhibited the highest CPO selectivity and FAL conversion of 96.6% and 98.9%, respectively. In addition, the catalyst was able to maintain a high activity and stability after four consecutive runs. The current study not only provides an efficient catalytic reaction system for the hydrogenative ring-rearrangement of furfural to cyclopentanone but also emphasizes the importance of defect sites.

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Engineering the defects of UiO-66 MOF for an improved catalytic detoxification of CWA simulant: methyl paraoxon.

Project description:Exigency in search of an ideal candidate for an effective detoxification of chemical warfare agents is still continuing. Zirconium-based Metal-organic Framework (MOF) UiO-66 has shown a significant detoxification of such toxic chemicals owing to its tunable physio-chemical properties and profuse catalytic sites. In this context, a series of UiO-66 MOFs synthesized by tuning the acidity constant (pK a) and concentration of the modulator, synthesis temperature and water molecules was tested for their detoxification efficiency against the simulant 'methyl-paraoxon' at room temperature. Amongst, HCl modulated UiO-66 across the considered synthesis temperature have shown competent catalytic performance in virtue of defects generation within its structure. In addition, the role of catalytic features of UiO-66 obtained by tailoring its defects in enhancing the degradation efficiency has been systematically investigated. The detoxification efficiency of 98.5% with a half-life time of 0.23 min has confirmed the effectiveness of engineered defects in enhancing the catalytic activity of UiO-66 in detoxifying the identified simulant.

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