Framework UiO-66 Research Articles

Modified UiO-66 frameworks with methylthio, thiol and sulfonic acid function groups: The structure and visible-light-driven photocatalytic property study

Isostructural UiO-66-(SO3H)2, UiO-66-(SH)2 and UiO-66-(SCH3)2 were obtained through systemic synthesis by decorating the sulfur-containing groups (X = –SCH3, –SH, –SO3H) on the terephthalate linkers of UiO-66 (a metal-organic framework constructed with terephthalate linkers and Zr(IV)-oxo clusters). These UiO-66-X2 derivates exhibited as n-type semiconductors, wherein the electronic properties and molecule dimensions of the function groups –X played key roles in determining their band gap (Eg) and photoactive properties. The –SCH3 is shown as the most efficient functional group and is responsible for that dramatically narrowed Eg of the UiO-66-(SCH3)2 and photocatalytic property. In sharp contrast to that state-of-the-art UiO-66-NH2 (constructed with 2-aminoterephthalate linkers) having no visible-light induced photocatalytic activity to split water into H2 even with Pt as co-catalyst, Pt/UiO-66-(SCH3)2 showed a high efficient H2 generation (3871 μmol/g) from water with sacrificial ascorbic acid (0.2 M) under λ > 400 nm irradiation. The structure-property relationship of UiO-66-X2 was studied through experimental and theoretical methods.

An insight into the effect of azobenzene functionalities studied in UiO-66 frameworks for low energy CO2 capture and CO2/N2 membrane separation

Tailoring the content of the light-responsive ligand in UiO-66 topology through a mixed-linker approach for CO2 adsorbent and mixed matrix membrane application.

Ab Initio Evaluation of Henry Coefficients Using Importance Sampling.

We present a new algorithm that allows for an efficient evaluation of the Henry coefficient of a guest molecule inside a porous material, which permits to use ab initio energy calculations. The Widom insertion method, which is currently used to compute these Henry coefficients, typically requires millions of energy evaluations. Our new methodology reduces this number by more than 1 order of magnitude, enabling the use of an ab initio potential energy surface. The methodology we propose is reminiscent of the well-known importance sampling technique which is frequently used in Monte Carlo integrations. First, a conventional Widom insertion simulation is performed using a force field. In the second step, the Widom results are used to select a limited number of configurations and only for these configurations the ab initio evaluation of the energy is required. Finally, by appropriately reweighting the latter energies, an accurate estimation of the ab initio Henry coefficient is possible at a moderate computational cost. We apply our methodology to the adsorption of CO2 in Mg-MOF-74, a prototypical case where interactions of a polar guest molecule with unsaturated metal sites dominate the adsorption mechanism. In this case generic force fields such as UFF or Dreiding are inappropriate and the use of ab initio methods is indispensable. In a second case study, we compute Henry coefficients of methane in UiO-66 using different levels of theory. We pay particular attention to the influence of the dispersion corrections and the role of many-body effects. For the final example, we qualitatively investigate adsorption features for a series of functionalized UiO-66 frameworks. Overall the cases we present show that accurate computations of Henry coefficients is extremely challenging, as different levels of theory provide strongly varying results. At the same time ab initio calculations have added value compared to force fields, as they provide a physically more sound description of the adsorption mechanism and in some cases clearly improve correspondence with experiment.

Probing Metal-Organic Framework Design for Adsorptive Natural Gas Purification.

Parent and amine-functionalized analogues of metal-organic frameworks (MOFs), UiO-66(Zr), MIL-125(Ti), and MIL-101(Cr), were evaluated for their hydrogen sulfide (H2S) adsorption efficacy and post-exposure acid gas stability. Adsorption experiments were conducted through fixed-bed breakthrough studies utilizing multicomponent 1% H2S/99% CH4 and 1% H2S/10% CO2/89% CH4 natural gas simulant mixtures. Instability of MIL-101(Cr) materials after H2S exposure was discovered through powderX-ray diffraction and porosity measurements following adsorbent pelletization, whereas other materials retained their characteristic properties. Linker-based amine functionalities increased H2S breakthrough times and saturation capacities from their parent MOF analogues. Competitive CO2 adsorption effects were mitigated in mesoporous MIL-101(Cr) and MIL-101-NH2(Cr), in comparison to microporous UiO-66(Zr) and MIL-125(Ti) frameworks. This result suggests that the installation of H2S binding sites in large-pore MOFs could potentially enhance H2S selectivity. In situ Fourier transform infrared measurements in 10% CO2 and 5000 ppm H2S environments suggest that framework hydroxyl and amine moieties serve as H2S physisorption sites. Results from this study elucidate design strategies and stability considerations for engineering MOFs in sour gas purification applications.

Decoration of Cotton Fibers with a Water-Stable Metal-Organic Framework (UiO-66) for the Decomposition and Enhanced Adsorption of Micropollutants in Water.

We report on the successful functionalization of cotton fabrics with a water-stable metal–organic framework (MOF), UiO-66, under mild solvothermal conditions (80 °C) and its ability to adsorb and degrade water micropollutants. The functionalized cotton samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). UiO-66 crystals grew in a uniform and conformal manner over the surface of the cotton fibers. The cotton fabrics functionalized with UiO-66 frameworks exhibited an enhanced uptake capacity for methylchlorophenoxypropionic acid (MCPP), a commonly used herbicide. The functionalized fabrics also showed photocatalytic activity, demonstrated by the degradation of acetaminophen, a common pharmaceutical compound, under simulated sunlight irradiation. These results indicate that UiO-66 can be supported on textile substrates for filtration and photocatalytic purposes and that these substrates can find applications in wastewater decontamination and micropollutant degradation.

New UiO-66/CuxS Heterostructures: Surface Functionalization Synthesis and Their Application in Photocatalytic Degradation of RhB

Abstract Metal-organic frameworks (MOFs) and their heterostructures have been considered as suitable materials for photodegradation of organic pollutants in water treatment. In this work, a series of UiO-66/CuxS composites with different CuxS contents were prepared by using 3-mercaptopropionic acid as a surface-functionalizing agent to anchor CuxS nanoparticles onto UiO-66 surface. The as-synthesized UiO-66/CuxS composites were characterized by using XRD, SEM, TEM, XPS, UV-Vis, PL and the possible growth mechanism of the heterostructure composites was proposed. The UiO-66/CuxS composites were successfully used as photocatalysts for the degradation of Rhodamine B (RhB) under visible-light irradiation. Noticeably, the photocatalytic efficiency of UiO-66/CuxS composites could be tuned by changing Cu/Zr molar ratios. The enhanced photocatalytic activity could be attributed to the synergistic effect between CuxS nanoparticles and UiO-66 frameworks materials. This study provided useful information for the preparation of MOF/semiconductor heterostructure photocatalysts via the surface functionalization method.

Preparation of highly-hydrophobic novel N-coordinated UiO-66(Zr) with dopamine via fast mechano-chemical method for (CHO-/Cl-)-VOCs competitive adsorption in humid environment

A novel mechano-chemical strategy using dopamine to modify UiO-66(Zr) by N-coordination was proposed to enhance its competitive adsorption for acetaldehyde, chlorobenzene/H2O, both thermodynamically and kinetically. The newly synthesized material was characterized by SEM, EDX, XPS, PXRD, FT-IR, TGA/DTG and BET techniques. Results showed that N was successfully grafted into UiO-66(Zr) frameworks through coordination interaction with Zr-O clusters resulting in M-UiO-66(Zr-N3.0). The obtained M-UiO-66(Zr-N3.0) exhibited a significant increase in adsorption of chlorobenzene (4.94mmol/g) and acetaldehyde (9.42mmol/g) compared to parent UiO-66(Zr) and UiO-66(Zr)-NH2. The H2O adsorption uptake of M-UiO-66(Zr-N3.0) decreased by 20% that of UiO-66(Zr) and 47% of UiO-66(Zr)-NH2 indicating higher hydrophobicity of the modified material. Kinetic performance indicated that diffusivity of chlorobenzene on M-UiO-66(Zr-N3.0) was about 7.8 and 40times higher than that of the parent UiO-66(Zr) and UiO-66(Zr)-NH2 respectively and 15.4times higher than that of H2O on itself. Based on the results, the current N-modification strategy can be deemed as an efficient way to improve MOFs competitive adsorption towards VOCs under humid conditions and it might play active role in industries involving adsorbent applications.

Cerium-based azide- and nitro-functionalized UiO-66 frameworks as turn-on fluorescent probes for the sensing of hydrogen sulphide

A new and an existing Ce-based metal–organic framework (MOF) having a UiO-66 framework topology and incorporating azide and nitro functional groups in their frameworks have been successfully used as turn-on fluorescent probes for the sensing of H2S under physiological conditions. The azide (1-N3) and nitro (2-NO2) functionalized Ce MOFs have been synthesized under similar solvothermal conditions (100 °C, 15 min) using ammonium cerium(IV) nitrate and H2BDC-X (BDC = 1,4-benzenedicarboxylate; X = –N3 for 1-N3 and –NO2 for 2-NO2) linkers in DMF/H2O (DMF = N,N-dimethylformamide) mixtures. The phase purity of both compounds has been confirmed by X-ray powder diffraction (XRPD) analyses, infrared spectroscopy and thermogravimetric (TG) analyses. The thermally activated forms of both compounds (1′-N3 and 2′-NO2) show fast response time, excellent selectivity and sensitivity for the detection of H2S under physiological conditions (HEPES buffer, pH 7.4) through the fluorescence ‘turn-on’ mechanism. The detection limits (12.2 μM for 1′-N3 and 34.8 μM for 2′-NO2) of both materials lie within the range of the H2S concentration observed in biological systems. The materials can selectively detect H2S even in the presence of other competing biomolecules. Apart from the sensing of H2S, both compounds exhibit high uptake of CO2 (2.6 mmol g−1 for 1′-N3 and 3.7 mmol g−1 for 2′-NO2) at 0 °C and 1 bar. Thus, the materials are promising candidates in the fields of H2S sensing and CO2 capture.

Defect engineering of UiO-66 for CO2 and H2O uptake – a combined experimental and simulation study

Defect concentrations and their compensating groups have been systematically tuned within UiO-66 frameworks by using modified microwave-assisted solvothermal methods. Both of these factors have a pronounced effect on CO2 and H2O adsorption at low and high pressure.

Understanding Intrinsic Light Absorption Properties of UiO-66 Frameworks: A Combined Theoretical and Experimental Study.

A combined theoretical and experimental study is performed in order to elucidate the effects of linker functional groups on the photoabsorption properties of UiO-66-X materials. This study, in which both mono- and difunctionalized linkers (with X = OH, NH2, or SH) are investigated, aims to obtain a more complete picture of the choice of functionalization. Static time-dependent density functional theory calculations combined with molecular dynamics simulations are performed on the linkers, and the results are compared to experimental UV/vis spectra in order to understand the electronic effects governing the absorption spectra. The disubstituted linkers show larger shifts than the monosubstituted variants, making them promising candidates for further study as photocatalysts. Next, the interaction between the linker and the inorganic part of the framework is theoretically investigated using a cluster model. The proposed ligand-to-metal-charge transfer is theoretically observed and is influenced by the differences in functionalization. Finally, the computed electronic properties of the periodic UiO-66 materials reveal that the band gap can be altered by linker functionalization and ranges from 4.0 down to 2.2 eV. Study of the periodic density of states allows the band gap modulations of the framework to be explained in terms of a functionalization-induced band in the band gap of the original UiO-66 host.

Pt@UiO-66 Heterostructures for Highly Selective Detection of Hydrogen Peroxide with an Extended Linear Range

In this study, a good core-shell heterostructure of Pt NPs@UiO-66 was fabricated by encapsulating presynthesized platinum nanoparticles (Pt NPs) into the host matrix of UiO-66 which possesses the slender triangular windows with a diameter of 6 Å. The transmission electron microscopy images exhibited that the number of the encapsulated Pt NPs and the crystalline morphology of as-synthesized core-shell heterostructure samples had a series of changes with increasing the volume of the injected Pt NPs precursor solution. Among these samples, the Pt NPs@UiO-66-2 sample had a good crystalline morphology with several well-dispersed Pt NPs encapsulated in UiO-66 frameworks. But there were no obvious Pt NPs observed in the Pt NPs@UiO-66-1 sample, and for the Pt NPs@UiO-66-3 sample, the number of Pt NPs encapsulated in UiO-66 matrix notably reduced and the metal organic framework (MOF) crystals became small and aggregated. The electrochemical measurements showed that the Pt NPs@UiO-66-2 sample modified glass carbon electrode (GCE) presented a remarkable electrocatalytic activity toward hydrogen peroxide (H2O2) oxidation, including an excellent anti-interference performance even if the concentration of the interference species was the same as the H2O2, an extended linear range from 5 μM to 14.75 mM, a low detection limit, as well as good stability and reproducibility. The results indicate the superiority of MOFs in H2O2 detection. And more importantly, it will provide a new opportunity to promote the anti-interference performance of the nonenzyme electrochemical sensors.

Superprotonic conductivity of a UiO-66 framework functionalized with sulfonic acid groups by facile postsynthetic oxidation.

Facile postsynthetic oxidation of the thiol-laced UiO-66-type framework UiO-66(SH)2 enabled the generation of UiO-66(SO3 H)2 with sulfonic acid groups covalently linked to the backbone of the system. The oxidized material exhibited a superprotonic conductivity of 8.4×10(-2) S cm(-1) at 80 °C and 90 % relative humidity, and long-term stability of the conductivity was observed. This level of conductivity exceeds that of any proton-conducting MOF reported to date and is equivalent to the conductivity of the most effective known electrolyte, Nafion.

Enhanced selectivity of CO2 over CH4 in sulphonate-, carboxylate- and iodo-functionalized UiO-66 frameworks

Three new functionalized UiO-66-X (X = -SO(3)H, 1; -CO(2)H, 2; -I; 3) frameworks incorporating BDC-X (BDC: 1,4-benzenedicarboxylate) linkers have been synthesized by a solvothermal method using conventional electric heating. The as-synthesized (AS) as well as the thermally activated compounds were characterized by X-ray powder diffraction (XRPD), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, thermogravimetric (TG), and elemental analysis. The occluded H(2)BDC-X molecules can be removed by exchange with polar solvent molecules followed by thermal treatment under vacuum leading to the empty-pore forms of the title compounds. Thermogravimetric analysis (TGA) and temperature-dependent XRPD (TDXRPD) experiments indicate that 1, 2 and 3 are stable up to 260, 340 and 360 °C, respectively. The compounds maintain their structural integrity in water, acetic acid and 1 M HCl, as verified by XRPD analysis of the samples recovered after suspending them in the respective liquids. As confirmed by N(2), CO(2) and CH(4) sorption analyses, all of the thermally activated compounds exhibit significant microporosity (S(Langmuir): 769-842 m(2) g(-1)), which are comparable to that of the parent UiO-66 compound. Compared to the unfunctionalized UiO-66 compound, all the three functionalized solids possess higher ideal selectivity in adsorption of CO(2) over CH(4) at 33 °C.