UiO-66 Derivatives Research Articles

Insight into the efficient loading and enhanced activity of enzymes immobilized on functionalized UiO-66

Enzyme immobilization is an effective strategy for achieving efficient and sustainable enzyme catalysis. As a kind of promising enzyme-loading materials, the systematic research on zirconium based metal organic frameworks (Zr-MOFs) about immobilization performance at molecular level is still in its initial stage. In this work, UiO-66 was functionalized with various groups (-H, -NH2, -COOH, -OH, -2OH) for the immobilization of cytochrome c (Cyt c) and antioxidant enzyme catalase (CAT). Then the effects of surface-functionalized UiO-66 derivatives on the loading efficiency, enzyme stability and catalysis kinetics were systematically investigated. In addition, the affinity constants of Cyt c and CAT towards UiO-66-series MOFs carriers were also compared. The results have shown that hydroxyl group functionalized UiO-66 represents the highest enzyme loading capacity, enhanced activity and improved stability for Cyt c and CAT possibly due to high surface area and suitable microenvironments as well as enhanced affinity towards the enzymes provided by the introduction of a single hydroxyl group. Our research would foresee immense potential of MOFs in engineering biocatalysts.

Acyl chloride-mediated synthesis of rhodanine-modified UiO-66 for high-efficiency silver recovery

Silver (Ag) recovery is essential for ecological protection, human health and economic benefits. Effective capture of Ag(I) from wastewater is still challenging due to insufficient accessible sites of adsorbents. Herein, an acyl chloride-mediated strategy is developed to synthesize rhodanine (Rd) modified UiO-66 derivatives for Ag(I) adsorption. Benefitting from the high grafting density of Rd, the optimal Rd-modified UiO-66-NH2 (UiO-66-NH2@20Rd) features an ultra-high uptake capacity (maximum capacity of 923.9 mg·g−1) and selectivity (maximum selectivity coefficient of 1665.52) for Ag(I). Almost 90 % of Ag(I) could be captured in one minute over UiO-66-NH2@20Rd and maintained a removal rate of 98.9 % even after six cycles. Moreover, a fixed-bed column test demonstrates that approximately 21,780 bed volumes of Ag(I) simulated wastewater can be effectively treated, indicating great promise for practical application. Mechanism investigation illustrates that outstanding performance can be attributed to the synergistic effect of Ag(I) adsorption and reduction on dense rhodanine sites. This study highlights that such a general strategy can provide a valuable avenue toward various functional adsorption materials.

Adsorption properties of M-UiO-66 (M = Zr(IV); Hf(IV) or Ce(IV)) with BDC or PDC linker.

The increasing CO2 emissions and their direct impact on climate change due to the greenhouse effect are environmental issues that must be solved as soon as possible. Metal-organic frameworks (MOFs) are one class of crystalline adsorbent materials that are thought to have enormous potential in CO2 capture applications. In this research, the effect of changing the metal center between Zr(IV), Ce(IV), and Hf(IV), and the linker between BDC and PDC has been fully studied. Thus, the six UiO-66 isoreticular derivatives have been synthesized and characterized by FTIR, PXRD, TGA, and N2 adsorption. We also report the BET surface area, CO2 adsorption capacities, kinetics, and the adsorption isosteric heat (Qst) of the UiO-66 derivatives mentioned family. The CO2 adsorption kinetics were evaluated using pseudo-first order, pseudo-second order, Avrami's kinetic models, and the rate-limiting step with Boyd's film diffusion, interparticle diffusion, and intraparticle diffusion models. The isosteric heats of CO2 adsorption using various MOFs are in the range 20-65 kJ mol-1 observing differences in adsorption capacities between 1.15 and 4.72 mmol g-1 at different temperatures due to the electrostatic interactions between CO2 and extra-framework metal ions. The isosteric heat of adsorption calculation in this report, which accounts for the unexpectedly high heat released from Zr-UiO-66-PDC, is finally represented as an increase in the interaction of CO2 with the PDC linker and an increase in Qst with defects.

Facile preparation of UiO-66 derivatives for the removal of Co(II) from aqueous solution: study on adsorption properties and irradiation stability

Facile preparation of UiO-66 derivatives for the removal of Co(II) from aqueous solution: study on adsorption properties and irradiation stability

Acidic Properties of Known and New COOH-Functionalized M(IV) Metal-Organic Frameworks.

Herein, we report two new COOH-functionalized metal-organic frameworks (MOFs) of composition [M6 O4 (OH)6 (PMA)2 (H2 PMA)]×H2 O, M=Zr, Hf), denoted CAU-61, synthesized by using pyromellitic acid (H4 PMA), a tetracarboxylic acid, as the linker and acetic acid as the solvent. The structure was determined from powder X-ray diffraction data and one-dimensional inorganic building units are connected through tetracarboxylate as well as dicarboxylate linker molecules, resulting in highly stable microporous framework structures with limiting and maximum pore diameter of ∼3.6 and ∼5.0 Å, respectively, lined with -COOH groups. Thermal stabilities of up to 400 °C in air, chemical stability in water at pH 1 to 12 and water uptake of 17 mol/mol prompted us to study the proton exchange of the μ2 -OH, μ3 -OH of the IBU and -COOH groups of the linker by titration with LiOH. Comparison of the pKa values with three UiO-66 derivatives confirms distinct pKa value ranges and trends for the different acidic protons. Furthermore, the preparation of Zr-CAU-61 membranes and first results on permeation of dyes and ions in aqueous solutions are presented.

Development of high refractive index UiO-66 framework derivatives via ligand halogenation.

UiO-66 is a Zr-based metal-organic framework (MOF) with exceptional chemical and thermal stability. The modular design of a MOF allows the tuning of its electronic and optical properties to obtain tailored materials for optical applications. Making use of the halogenation of the 1,4-benzenedicarboxylate (bdc) linker, the well-known monohalogenated UiO-66 derivatives were examined. In addition, a novel diiodo bdc based UiO-66 analogue is introduced. The novel UiO-66-I2 MOF is fully characterized experimentally. By applying density functional theory (DFT), fully relaxed periodic structures of the halogenated UiO-66 derivatives are generated. Subsequently, the HSE06 hybrid DFT functional is used to calculate the electronic structures and optical properties. The obtained band gap energies are validated with UV-Vis measurements to assure a precise description of the optical properties. Finally, the calculated refractive index dispersion curves are evaluated underlining the capabilities to tailor the optical properties of MOFs by linker functionalization.

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.

Effect of Synthesis Temperature on Water Adsorption in UiO-66 Derivatives: Experiment, DFT+D Modeling, and Monte Carlo Simulations

In this work, density functional theory (DFT) and Monte Carlo calculations were combined with standard volumetric adsorption as well as quasi-equilibrated temperature-programmed desorption and adsorption measurements to study water adsorption in UiO-66 derivatives containing −NH2, −NO2, and −Br substituents. Based on DFT modeling, both the position and geometry of the substituents were determined and one model was selected for each structure. By using Monte Carlo simulations and the force field developed in our previous work for the adsorption of water in metal–organic frameworks, we reproduced experimental adsorption isotherms and isobars. The results allow us to explain the water adsorption process in UiO-66 derivatives. Detailed physicochemical characterization by means of elemental analysis, powder X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis enabled us to determine the influence of the synthesis temperature on the structure and properties of the materials.

Potassium Storage Performance of UiO-66 Derivatives from First Principles Calculations

Potassium Storage Performance of UiO-66 Derivatives from First Principles Calculations

The chemistry behind room temperature synthesis of hafnium and cerium UiO-66 derivatives

RT formation of Hf and Ce UiO-66 derivatives is investigated using a one-step method where the linker and metal salt are simply combined, and a two-step method where the inorganic component is pre-heated to form metal clusters.

The joint effect of naphthalene-system and defects on dye removal by UiO-66 derivatives

We report the results of the application of UiO-66 derivates for dye removal. This complex process includes two parallel mechanisms. The first one is the adsorption of the dye into the pores of MOF. The second one is photocatalytic degradation. We used two linkers for MOF synthesis: 1,4-benzene dicarboxylate and 1,4-naphthalene dicarboxylate. The introduction of these molecules in various ratios into the UiO-66-type structure allowed us to trace the effect of naphthalene species on the methylene blue removal. It was shown that a conjugated π-system of naphthalene rings led to charge transfer from linker to zirconium ions. It reduces the bandgap of the material and, therefore, results in higher photocatalytic performance. We also traced the effect of defects in the MOF structure on methylene blue degradation. It was shown that unsaturated zirconium ions in defect pores effectively catalyze dye cleavage and direct this process to the oxidative demethylation pathway. Obtained results could be applied to improve the photocatalytic properties of UiO-66 derivates. • We report UiO-66 derivates for dye removal. • This process could be considered as adsorption and photocatalytic degradation. • The introduction of naphthalene rings into the UiO-66 reduces the bandgap and enhanced photocatalytic performance. • Unsaturated zirconium ions in defect pores effectively catalyze dye cleavage as well. • Proposed catalysts work under visible light.

Recoverable and recyclable gas hydrate inhibitors based on magnetic nanoparticle-decorated metal–organic frameworks

In the oil and gas industries, the development of gas hydrate inhibitors is one of the most critical issues to prevent hydrate formation for flow assurance in pipelines. Low-dosage and recoverable/recyclable hydrate inhibitors are very important environmentally and economically. Herein, we propose a new class of kinetic hydrate inhibitors (KHIs) based on magnetic nanoparticle (NP)-decorated metal–organic frameworks (MOFs). As a KHI candidate, UiO-66 derivatives bearing different functional groups were examined, and UiO-66-NH2 showed superior performance with low dosage (1 wt%) in terms of the onset temperature of CH4 hydrate formation. To realize recoverability, magnetic Fe3O4 NPs were adopted to produce a core–shell-type composite, Fe3O4@UiO-66-NH2. This core–shell inhibitor was successfully recovered and reused, exhibiting a comparable performance to fresh UiO-66-NH2. This first example of a MOF as a KHI will contribute toward a new era of recoverable gas hydrate inhibitors.

High-Throughput Screening of MOFs for Breakdown of V-Series Nerve Agents.

Metal-organic frameworks (MOFs) have shown promise for the catalytic decomposition of chemical weapons. Finding the best materials for the degradation of nerve agents requires the ability to screen a high number of samples and elucidate the key parameters of effective catalysis. In this work, a high-throughput screening (HTS) method has been developed to evaluate MOFs as catalysts, specifically against the V-class of nerve agents. Over 100 MOFs have been tested using the V-class simulant, O,O-diethyl S-phenyl phosphorothioate (DEPPT), revealing good activity for some UiO-66 derivatives. A medium-throughput hydrolysis assay for the nerve agent O-ethyl S-[2-(diisopropylamino)ethyl]methylphosphonothioate (VX) was also performed using six MOFs selected from HTS and was validated by 31P NMR. The results demonstrated that the DEPPT-based assay is a good indicator of V-series agent reactivity and should be considered in addition to the common (4-nitrophenyl)phosphate (DMNP) assay that is used for G-series agents.

UiO-66 derivatives and their composite membranes for effective proton conduction.

As newly emerging proton-conducting materials, metal-organic frameworks (MOFs) have been attracting wide attention in the field of proton exchange membrane fuel cells. However, for most of the MOF materials, long-term stability is a huge obstacle for practical applications. So, the structural stability of MOFs is the critical prerequisite for the design and development of modified materials with excellent proton conductivity. In this review, stable UiO-66 derivatives were chosen as the research object, and modification methods including post-synthesis modification and hybridization were mainly summarized. Based on the reported typical functionalization strategies, we found that the modified UiO-66 derivatives and their composite membranes demonstrate ultra-high proton conductivity similar to that of commercial Nafion, indicating their great application potential in fuel cells. This Frontier article focuses on the recent development in the modification of UiO-66 type frameworks and their composite membranes and the tuning of proton conductivity with structural factors.

Room temperature aqueous synthesis of UiO-66 derivatives via postsynthetic exchange.

Herein, we report the room temperature aqueous synthesis of the Zr(iv)-based metal-organic framework UiO-66 and a series of functionalized derivatives through postsynthetic exchange from a perfluorinated UiO-66-F4 precursor. All synthesized MOFs in this study were thoroughly characterized to verify formation of the desired MOF, porosity, crystallinity, and exchanged ligand content. This report represents a green, aqueous, room temperature synthesis of a highly valued series of Zr(iv)-based MOFs.

Encapsulation of β-alanine model amino-acid in zirconium(IV) metal organic frameworks: Defect engineering to improve host guest interactions

Metal-Organic Frameworks (MOFs) are porous coordination networks assembled through metal complexes with organic linkers. Due to their chemical versatility, these materials are being investigated for various applications including gas storage and separation, biomedicine and catalysis. The aim of this work is the encapsulation of the model β-alanine amino-acid in the nanostructured zirconium-based MOF (UiO-66) which contains the ligand H2BDC (1,4-benzenedicaboxylic acid). Additionally, ligand functionalization (by using H2doBDC (2,5-dihydroxy-1,4-benzenedicarboxylic acid) and defect engineering have been carried out to produce UiO-66 derivatives, in order to modify the host-guest interactions, and hence study their influence on the β-alanine loading capacity and release kinetics. The as-obtained materials have been characterized by X-ray diffraction (XRD), X-ray thermo diffraction (TDX), infrared (IR) spectroscopy, thermogravimetric analysis-differential scanning calorimetry (TG-DSC) and elemental analysis (EA). Morphology of nanoscale MOFs has been explored by transition electron microscopy (TEM). Adsorption isotherms have been constructed, and the concentration of β-alanine in the post-adsorption solution (supernatant) has been quantified by high performance liquid chromatography coupled with mass spectroscopy (HPLC-MS) and EA. Adsorption capacity values indicate that the presence of hydroxyl groups at the organic linker H2doBDC enhances the host-guess affinity between the framework and the adsorbate β-alanine. The influence of defect engineering, on the adsorption however, is not that obvious. On the other hand, desorption experiments show similar behaviour for H2doBDC-based derivatives. An adsorption mechanism has been proposed consisting of a combination of host-guest interaction at low concentrations, and covalent anchoring/ligand displacement by β-alanine at the inorganic clusters.

Functionalization of UiO-66-NH2 with rhodanine via amidation: Towarding a robust adsorbent with dual coordination sites for selective capture of Ag(I) from wastewater

Selective capture and maximum recovery of Ag(I) from wastewater is of great significance for a sustainable future. In this work, novel rhodanine (Rd)-functionalized UiO-66 adsorbents (i.e., UiO-66-Rd and UiO-66-NH2-Rd) were designed and synthesized. Different from previously reported UiO-66 derivatives with single metal coordination sites, the as-synthesized UiO-66-Rd and UiO-66-NH2-Rd have dual coordination sites, resulting in higher capacity and outstanding selectivity. The maximum capacities of UiO-66-Rd and UiO-66-NH2-Rd are 112 and 163 mg·g−1, nearly 5.6 and 8.2 times higher than that of UiO-66, respectively. Impressively, the maximum selectivity coefficient of UiO-66-NH2-Rd is approximately 1795 and 1173 folds higher than that of UiO-66 and UiO-66-NH2. The experimental characterizations and theoretical calculations indicate that the Rd-induced enhancement in the adsorptivity and selectivity are mainly attributed to the dual coordination sites (i.e., CS and CS bonds), which collectively coordinate with Ag(I) in the form of Ag mono-coordinated with S. Compared with the UiO-66-Rd, UiO-66-NH2-Rd possesses excellent recyclability and durability due to the vital role of amide bonds generated from NH2 group in the functionalization of UiO-66 with Rd. Furthermore, UiO-66-NH2-Rd can almost completely remove Ag(I) from the actual wastewater with complex matrix, satisfying the national integrated wastewater discharge standard and industrial wastewater emission standard, highlighting a great potential of practical application.

Protective Coating on Aluminum Alloy Created By Combined Solvothermal and Chemical Methods: Corrosion Test

This work demonstrate an in-situ solvothermal deposition of zirconium based metal-organic framework (MOF), UiO-66 derivatives on aluminum alloy. Such protection remarkably enhance the corrosion resistance and hydrophobic properties of the aluminum alloy. The observed corrosion resistance of the fabricated film was attributed to the resistant nature of the UiO-66 coating created on the alloy surface. SEM, FTIR, and XRD techniques were used to understand the microstructure and crystal structure of the designed composite materials. Electrochemical impedance spectroscopy (EIS) was used to assess the surface impedance.

Halogen bonding in UiO-66 frameworks promotes superior chemical warfare agent simulant degradation

Herein, a series of halogenated UiO-66 derivatives was synthesized and analyzed for the breakdown of the chemical warfare agent simulant dimethyl-4-nitrophenyl phosphate (DMNP) to analyze ligand effects. UiO-66-I degrades DMNP at a rate four times faster than the most active previously reported MOFs. MOF defects were quantified and ruled out as a cause for increased activity. Theoretical calculations suggest the enhanced activity of UiO-66-I originates from halogen bonding of the iodine atom to the phosphoester linkage allowing for more rapid hydrolysis of the P-O bond.

Scalable, room temperature, and water-based synthesis of functionalized zirconium-based metal–organic frameworks for toxic chemical removal

An inexpensive, environmentally benign and scalable strategy was developed to synthesize UiO-66 derivatives in water at room temperature.