Combination of Optimization and Metalated‐Ligand Exchange: An Effective Approach to Functionalize UiO‐66(Zr) MOFs for CO2 Separation

The strategy to functionalize water‐stable metal–organic frameworks (MOFs) in order to improve their CO₂ uptake capacities for efficient CO₂ separation remains limited and challenging. We herein present an effective approach to functionalize a prominent water‐stable MOF, UiO‐66(Zr), by a combination of optimization and metalated‐ligand exchange. In particular, by systematic optimization, we have successfully obtained UiO‐66(Zr) of the highest BET surface area reported so far (1730 m² g^?1). Moreover, it shows a hybrid Type I/IV N₂ isotherm at 77 K and a mesopore size of 3.9 nm for the first time. The UiO‐66 MOF underwent a metalated‐ligand‐exchange (MLE) process to yield a series of new UiO‐66‐type MOFs, among which UiO‐66‐(COONa)₂‐EX and UiO‐66‐(COOLi)₄‐EX MOFs have both enhanced CO₂ working capacity and IAST CO₂/N₂ selectivity. Our approach has thus suggested an alternative design to achieve water‐stable MOFs with high crystallinity and gas uptake for efficient CO₂ separation.     

Spray‐Coating of Catalytically Active MOF–Polythiourea through Postsynthetic Polymerization

A UiO‐66‐NCS MOF was formed by postsynthetic modification of UiO‐66‐NH₂. The UiO‐66‐NCS MOFs displays a circa 20‐fold increase in activity against the chemical warfare agent simulant dimethyl‐4‐nitrophenyl phosphate (DMNP) compared to UiO‐66‐NH₂, making it the most active MOF materials using a validated high‐throughput screening. The ?NCS functional groups provide reactive handles for postsynthetic polymerization of the MOFs into functional materials. These MOFs can be tethered to amine‐terminated polypropylene polymers (Jeffamines) through a facile room‐temperature synthesis with no byproducts. The MOFs are then crosslinked into a MOF–polythiourea (MOF–PTU) composite material, maintaining the catalytic properties of the MOF and the flexibility of the polymer. This MOF–PTU hybrid material was spray‐coated onto Nyco textile fibers, displaying excellent adhesion to the fiber surface. The spray‐coated fibers were screened for the degradation of DMNP and showed durable catalytic reactivity.     

Metal–Organic Gel Material Based on UiO‐66‐NH2 Nanoparticles for Improved Adsorption and Conversion of Carbon Dioxide

Metal–organic frameworks (MOFs) including the UiO‐66 series show potential application in the adsorption and conversion of CO₂. Herein, we report the first tetravalent metal‐based metal–organic gels constructed from Zr^IV and 2‐aminoterephthalic acid (H₂BDC‐NH₂). The ZrBDC‐NH₂ gel materials are based on UiO‐66‐NH₂ nanoparticles and were easily prepared under mild conditions (80 °C for 4.5 h). The ZrBDC‐NH₂‐1:1‐0.2 gel material has a high surface area (up to 1040 m² g^?1) and showed outstanding performance in CO₂ adsorption (by using the dried material) and conversion (by using the wet gel) arising from the combined advantages of the gel and the UiO‐66‐NH₂ MOF. The ZrBDC‐NH₂‐1:1‐0.2 dried material showed 38 % higher capture capacity for CO₂ at 298 K than microcrystalline UiO‐66‐NH₂. It showed high ideal adsorbed solution theory selectivity (71.6 at 298 K) for a CO₂/N₂ gas mixture (molar ratio 15:85). Furthermore, the ZrBDC‐NH₂‐1:1‐0.2 gel showed activity as a heterogeneous catalyst in the chemical fixation of CO₂ and an excellent catalytic performance was achieved for the cycloaddition of atmospheric pressure of CO₂ to epoxides at 373 K. In addition, the gel catalyst could be reused over multiple cycles with no considerable loss of catalytic activity.     

Highly Sensitive and Selective Detection of Pb(II) by NH2−SiO2/Ru(bpy)32+−UiO66 based Solid‐state ECL Sensor

In this study, a novel electrochemiluminescence (ECL) sensor for highly sensitive and selective detection of Pb(II) was developed based on Ru(bpy)₃²⁺ encapsulated UiO66 metal‐organic‐framework (Ru(bpy)₃²⁺?UiO66 MOF) and ?NH₂ group functionalized silica (NH₂?SiO₂). The NH₂?SiO₂ with large surface area provided an excellent platform for the ECL sensor. As numerous exposed carboxyl groups were present on UiO66 backbone, the Ru(bpy)₃²⁺?UiO66 could be steadily immobilized to NH₂?SiO₂ by forming amide bonds. Meanwhile, the introduced UiO66 MOF which used for the encapsulation of Ru(bpy)₃²⁺, significantly enhanced the ECL efficiency of the proposed sensor, as it possessed a large specific surface area and porosity for the loading of Ru(bpy)₃²⁺. Moreover, a high quenching effect on ECL intensity was obtained in the presence of Pb(II) in the electrolyte. Under the optimal conditions, the quenched ECL intensity showed a good linear relationship within Pb(II) concentration in the range from 1.0×10^?6 to 1.0×10² μM, with a detection limit of 1.0×10^?7 μM (S/N=3). The proposed sensor for Pb(II) detection was simple in operation, rapid in testing, stable in signal, and showed a good anti‐interference ability to some other metal ions. Besides, its application for detecting Pb(II) in a real sample was also investigated here. This work provides a potential platform for metal ions detection in environmental monitoring field.     

Ultra‐Fast Degradation of Chemical Warfare Agents Using MOF–Nanofiber Kebabs

The threat associated with chemical warfare agents (CWAs) motivates the development of new materials to provide enhanced protection with a reduced burden. Metal–organic frame‐works (MOFs) have recently been shown as highly effective catalysts for detoxifying CWAs, but challenges still remain for integrating MOFs into functional filter media and/or protective garments. Herein, we report a series of MOF–nanofiber kebab structures for fast degradation of CWAs. We found TiO₂ coatings deposited via atomic layer deposition (ALD) onto polyamide‐6 nanofibers enable the formation of conformal Zr‐based MOF thin films including UiO‐66, UiO‐66‐NH₂, and UiO‐67. Cross‐sectional TEM images show that these MOF crystals nucleate and grow directly on and around the nanofibers, with strong attachment to the substrates. These MOF‐functionalized nanofibers exhibit excellent reactivity for detoxifying CWAs. The half‐lives of a CWA simulant compound and nerve agent soman (GD) are as short as 7.3 min and 2.3 min, respectively. These results therefore provide the earliest report of MOF–nanofiber textile composites capable of ultra‐fast degradation of CWAs.     

Fluorocarbon Separation in a Thermally Robust Zirconium Carboxylate Metal–Organic Framework

Fluorocarbons have important applications in industry, but are environmentally unfriendly, and can cause ozone depletion and contribute to the global warming with long atmospheric lifetimes and high global warming potential. In this work, the metal–organic framework UiO‐66(Zr) is demonstrated to have excellent performance characteristics to separate fluorocarbon mixtures at room temperature. Adsorption isotherm measurements of UiO‐66(Zr) display high fluorocarbon sorption uptakes of 5.0 mmol g^?1 for R22 (CHClF₂), 4.6 mmol g^?1 for R125 (CHF₂CF₃), and 2.9 mmol g^?1 for R32 (CH₂F₂) at 298 K and 1 bar. Breakthrough data obtained for binary (R22/R32 and R32/R125) and ternary (R32/R125/R134a) mixtures reveal high selectivities and capacities of UiO‐66(Zr) for the separation and recycling of these fluorocarbon mixtures. Furthermore, the UiO‐66(Zr) saturated with R22 and R125 can be regenerated at temperatures as low as 120 °C with excellent desorption–adsorption cycling stabilities.     

Enhancing CO2 Separation Ability of a Metal–Organic Framework by Post‐Synthetic Ligand Exchange with Flexible Aliphatic Carboxylates

A series of porous metal–organic frameworks having flexible carboxylic acid pendants in their pores (UiO‐66‐ADn: n=4, 6, 8, and 10, where n denotes the number of carbons in a pendant) has been synthesized by post‐synthetic ligand exchange of terephthalate in UiO‐66 with a series of alkanedioic acids (HO₂C(CH₂)_n?2CO₂H). NMR, IR, PXRD, TEM, and mass spectral data have suggested that a terephthalate linker in UiO‐66 was substituted by two alkanedioate moieties, resulting in free carboxyl pendants in the pores. When post‐synthetically modified UiO‐66 was partially digested by adjusting the amount of added HF/sample, NMR spectra indicated that the ratio of alkanedioic acid/terephthalic acid was increased with smaller amounts of acid, implying that the ligand substitution proceeded from the outer layer of the particles. Gas sorption studies indicated that the surface areas and the pore volumes of all UiO‐66‐ADns were decreased compared to those of UiO‐66, and that the CO₂ adsorption capacities of UiO‐66‐ADn (n=4, 8) were similar to that of UiO‐66. In the case of UiO‐66‐AD6, the CO₂ uptake capacity was 34 % higher at 298 K and 58 % higher at 323 K compared to those of UiO‐66. It was elucidated by thermodynamic calculations that the introduction of flexible carboxyl pendants of appropriate length has two effects: 1) it increases the interaction enthalpy between the host framework and CO₂ molecules, and 2) it mitigates the entropy loss upon CO₂ adsorption due to the formation of multiple configurations for the interactions between carboxyl groups and CO₂ molecules. The ideal adsorption solution theory (IAST) selectivity for CO₂ adsorption over that of CH₄ was enhanced for all of the UiO‐66‐ADns compared to that of UiO‐66 at 298 K. In particular, UiO‐66‐AD6 showed the most strongly enhanced CO₂ uptake capacity and significantly increased selectivity for CO₂ adsorption over that of CH₄ at ambient temperature, suggesting that it is a promising material for sequestering CO₂ from landfill gas.     

The First Study on the Reactivity of Water Vapor in Metal–Organic Frameworks with Platinum Nanocrystals

We first studied the reactivity of H₂O vapor in metal–organic frameworks (MOFs) with Pt nanocrystals (NCs) through the water–gas shift (WGS) reaction. A water‐stable MOF, UiO‐66, serves as a highly effective support material for the WGS reaction compared with ZrO₂. The origin of the high catalytic performance was investigated using in situ IR spectroscopy. In addition, from a comparison of the catalytic activities of Pt on UiO‐66, where Pt NCs are located on the surface of UiO‐66 and Pt@UiO‐66, where Pt NCs are coated with UiO‐66, we found that the competitive effects of H₂O condensation and diffusion in the UiO‐66 play important roles in the catalytic activity of Pt NCs. A thinner UiO‐66 coating further enhanced the WGS reaction activity of Pt NCs by minimizing the negative effect of slow H₂O diffusion in UiO‐66.     

Boosting Photocatalytic Hydrogen Production of a Metal–Organic Framework Decorated with Platinum Nanoparticles: The Platinum Location Matters

Improving the efficiency of electron–hole separation and charge‐carrier utilization plays a central role in photocatalysis. Herein, Pt nanoparticles of ca. 3 nm are incorporated inside or supported on a representative metal–organic framework (MOF), UiO‐66‐NH₂, denoted as Pt@UiO‐66‐NH₂ and Pt/UiO‐66‐NH₂, respectively, for photocatalytic hydrogen production via water splitting. Compared with the pristine MOF, both Pt‐decorated MOF nanocomposites exhibit significantly improved yet distinctly different hydrogen‐production activities, highlighting that the photocatalytic efficiency strongly correlates with the Pt location relative to the MOF. The Pt@UiO‐66‐NH₂ greatly shortens the electron‐transport distance, which favors the electron–hole separation and thereby yields much higher efficiency than Pt/UiO‐66‐NH₂. The involved mechanism has been further unveiled by means of ultrafast transient absorption and photoluminescence spectroscopy.     

Cooperative Multifunctional Catalysts for Nitrone Synthesis: Platinum Nanoclusters in Amine‐Functionalized Metal–Organic Frameworks

Nitrones are key intermediates in organic synthesis and the pharmaceutical industry. The heterogeneous synthesis of nitrones with multifunctional catalysts is extremely attractive but rarely explored. Herein, we report ultrasmall platinum nanoclusters (PtNCs) encapsulated in amine‐functionalized Zr metal–organic framework (MOF), UiO‐66‐NH₂ (Pt@UiO‐66‐NH₂) as a multifunctional catalyst in the one‐pot tandem synthesis of nitrones. By virtue of the cooperative interplay among the selective hydrogenation activity provided by the ultrasmall PtNCs and Lewis acidity/basicity/nanoconfinement endowed by UiO‐66‐NH₂, Pt@UiO‐66‐NH₂ exhibits remarkable activity and selectivity, in comparison to Pt/carbon, Pt@UiO‐66, and Pd@UiO‐66‐NH₂. Pt@UiO‐66‐NH₂ also outperforms Pt nanoparticles supported on the external surface of the same MOF (Pt/UiO‐66‐NH₂). To our knowledge, this work demonstrates the first examples of one‐pot synthesis of nitrones using recyclable multifunctional heterogeneous catalysts.     

An Evaluation of UiO‐66 for Gas‐Based Applications

In addition to its high thermal stability, repetitive hydration/dehydration tests have revealed that the porous zirconium terephthalate UiO‐66 switches reversibly between its dehydroxylated and hydroxylated versions. The structure of its dehydroxylated form has thus been elucidated by coupling molecular simulations and X‐ray powder diffraction data. Infrared measurements have shown that relatively weak acid sites are available while microcalorimetry combined with Monte Carlo simulations emphasize moderate interactions between the UiO‐66 surface and a wide range of guest molecules including CH₄, CO, and CO₂. These properties, in conjunction with its significant adsorption capacity, make UiO‐66 of interest for its further evaluation for CO₂ recovery in industrial applications. This global approach suggests a strategy for the evaluation of metal–organic frameworks for gas‐based applications.     

Water Stable Zr–Benzenedicarboxylate Metal–Organic Frameworks as Photocatalysts for Hydrogen Generation

The Zr‐containing metal–organic frameworks (MOFs) formed by terephthalate (UiO‐66) and 2‐aminoterephthalate ligands [UiO‐66(NH₂)] are two notably water‐resistant MOFs that exhibit photocatalytic activity for hydrogen generation in methanol or water/methanol upon irradiation at wavelength longer than 300 nm. The apparent quantum yield for H₂ generation using monochromatic light at 370 nm in water/methanol 3:1 was of 3.5 % for UiO‐66(NH₂). Laser‐flash photolysis has allowed detecting for UiO‐66 and UiO‐66(NH₂) the photochemical generation of a long lived charge separated state whose decay is not complete 300 μs after the laser flash. Our finding and particularly the influence of the amino group producing a bathochromic shift in the optical spectrum without altering the photochemistry shows promises for the development of more efficient MOFs for water splitting.     

Hierarchical Pore Development by Plasma Etching of Zr‐Based Metal–Organic Frameworks

The typically stable Zr‐based metal–organic frameworks (MOFs) UiO‐66 and UiO‐66‐NH₂ were treated with tetrafluoromethane (CF₄) and hexafluoroethane (C₂F₆) plasmas. Through interactions between fluoride radicals from the perfluoroalkane plasma and the zirconium–oxygen bonds of the MOF, the resulting materials showed the development of mesoporosity, creating a hierarchical pore structure. It is anticipated that this strategy can be used as a post‐synthetic technique for developing hierarchical networks in a variety of MOFs.     

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(SO₃H)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.     

Evaluation of UiO‐66 metal organic framework as an effective sorbent for Curcumin's overdose

Metal organic frameworks (MOFs) UiO‐66 (UiO stands for University of Oslo) and NH₂‐UiO‐66 were prepared and characterized as sorbent (antidotal agents) for curcumin (CUR) adsorption. The structure of products were characterized by X‐ray powder diffraction (XRD), Field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), Attenuated Total Reflectance‐Fourier transform infrared spectroscopy (ATR‐FTIR), and N₂ adsorption–desorption measurements. FESEM showed NH₂‐UiO‐66 displayed symmetrical crystals with triangular base pyramid morphology, with the particle size around 100 nm and uniform size distribution. Adsorption capacities of CUR/MOFs with different mass ratios in the feed were investigated in the present study, and this investigation revealed that when the CUR/MOFs with mass ratio was around 0.4, the absorption capacity of NH₂‐UiO‐66 had tended to maximum. Although, functionalization reduced the specific surface area and free volume, introducing polar amine groups could improve the affinity of NH₂‐UiO‐66 respect to CUR. Kinetic studies showed that the kinetic data are well fitted with the pseudo‐ second‐order model. MTT assay revealed that MOFs at the concentration range of 0–560 μg/ml had no cytotoxic effect on the Human Foreskin Fibroblast normal cell line (HFF‐2). These results suggest that these MOFs could be safe as sorbent for adsorb CUR from the body.     

Gated Channels and Selectivity Tuning of CO2 over N2 Sorption by Post‐Synthetic Modification of a UiO‐66‐Type Metal–Organic Framework

The highly porous and stable metal–organic framework (MOF) UiO‐66 was altered using post‐synthetic modifications (PSMs). Prefunctionalization allowed the introduction of carbon double bonds into the framework through a four‐step synthesis from 2‐bromo‐1,4‐benzenedicarboxylic acid; the organic linker 2‐allyl‐1,4‐benzenedicarboxylic acid was obtained. The corresponding functionalized MOF (UiO‐66‐allyl) served as a platform for further PSMs. From UiO‐66‐allyl, epoxy, dibromide, thioether, diamine, and amino alcohol functionalities were synthesized. The abilities of these compounds to adsorb CO₂ and N₂ were compared, which revealed the structure–selectivity correlations. All synthesized MOFs showed profound thermal stability together with an increased ability for selective CO₂ uptake and molecular gate functionalities at low temperatures.     

Oxidation reactions catalysed by molybdenum(VI) complexes grafted on UiO‐66 metal–organic framework as an elegant nanoreactor

A heterogeneous catalyst was synthesized by immobilizing Mo(CO)₃ in a UiO‐66 metal–organic framework. The benzene ring of the organic linker in UiO‐66 was modified via liquid‐phase deposition of molybdenum hexacarbonyl, Mo(CO)₆, as starting precursor to form the (arene)Mo(CO)₃ species inside the framework. The structure of this catalyst was characterized using X‐ray diffraction, and chemical integrity was confirmed using Fourier transform infrared and diffuse reflectance UV–visible spectroscopic methods. The metal content was analysed with inductively coupled plasma. Field emission scanning electron microscopy was used to measure particle size and N₂ adsorption measurements to characterize the specific surface area. This catalytic system was efficiently applied for epoxidation of alkenes and oxidation of sulfides. The Mo‐containing metal–organic framework was reused several times without any appreciable loss of its efficiency.     

Impact of the Nature of the Organic Spacer on the Crystallization Kinetics of UiO‐66(Zr)‐Type MOFs

The influence of the constitutive dicarboxylate linkers (size, functional group) over the crystallization kinetics of a series of porous Zr metal–organic frameworks with the UiO‐66 topology has been investigated by in situ time‐resolved energy dispersive X‐ray diffraction (EDXRD). Both large aromatic spacers (2,6‐naphthalene‐, 4,4′‐biphenyl‐ and 3,3′‐dichloro‐4,4′‐azobenzene‐dicarboxylates) and a series of X‐functionalized terephthalates (X=NH₂, NO₂, Br, CH₃) were investigated in dimethylformamide (DMF) at different temperatures and compared with the parent UiO‐66. Using different crystallization models, rate constants and further kinetic parameters (such as activation energy) have been extracted. Finally, the impact of the replacement of the toxic DMF by water on the crystallization kinetics was studied through the synthesis of the functionalized UiO‐66‐NO₂ solid.     

Single‐Site Copper(II) Water Oxidation Electrocatalysis: Rate Enhancements with HPO42− as a Proton Acceptor at pH 8

The complex Cu^II(Py₃P) ( 1 ) is an electrocatalyst for water oxidation to dioxygen in H₂PO₄^?/HPO₄^2? buffered aqueous solutions. Controlled potential electrolysis experiments with 1 at pH 8.0 at an applied potential of 1.40 V versus the normal hydrogen electrode resulted in the formation of dioxygen (84 % Faradaic yield) through multiple catalyst turnovers with minimal catalyst deactivation. The results of an electrochemical kinetics study point to a single‐site mechanism for water oxidation catalysis with involvement of phosphate buffer anions either through atom–proton transfer in a rate‐limiting O? O bond‐forming step with HPO₄^2? as the acceptor base or by concerted electron–proton transfer with electron transfer to the electrode and proton transfer to the HPO₄^2? base.     

Facile preparation of stainless steel microextraction fiber via in situ growth of metal–organic framework UiO‐66 and its application to sensitive analysis of polycyclic musks

A functional stainless steel microextraction fiber easily prepared by in situ growing metal–organic framework UiO‐66 was presented and used for high‐performance analysis of polycyclic musks. Via the robust Ag‐SH bonding reaction, mercaptoacetic acid was easily anchored on Ag film to provide carboxyl group on the stainless steel fiber, then in situ grown UiO‐66 was fulfilled via the coordination reaction between Zr⁴⁺ and carboxyl group. Good characteristics including large surface area, high thermal stability, and good adsorption property were achieved. Sensitive detection limits (0.015–0.040 ng/L) were achieved for polycyclic musks by coupling with gas chromatography with mass spectrometry, and it could be stable enough for 150 extraction cycles without a significant loss of extraction efficiency. Compared with the classical commercial fibers, 2.2–11.4 times higher enhancement factors were shown. Applied to the analysis of fortified river water samples, five typical polycyclic musks were well detected with the recoveries of 90.2–101.8%, respectively. It showed a facile approach for preparing stainless steel microextraction fiber via chemically bonding in situ grown metal–organic framework for high‐performance enrichment.