Cr-based Metal-organic Framework Research Articles

Co(BO2)2 supported on MIL-101 as high-performance anode material for Li-ion battery

In this work, via a simple liquid impregnation method, Co(BO2)2 nanoparticles are successfully loaded on the surface of Cr-based metal organic frameworks MIL-101 without destroying the three-dimensional organic frameworks. As received Co(BO2)2@MIL-101 composite shows the improved cyclability when serves as anode for rechargeable Li-ion batteries. The obtained Co(BO2)2@MIL-101 electrode demonstrates high reversible capacity of 810 mA h g−1 after 100 cycles at a current density of 200 mA g−1 and shows stable cycle performance (coulombic efficiency remains above 95%). The improvement could be attributed to MIL-101, which provides effective barrier spaces for Co(BO2)2 to relax the volumetric variation and maintains superior conductivity during the charge and discharge process.

Pyridine-grafted Cr-based metal–organic frameworks for adsorption and removal of microcystin-LR from aqueous solution

A Cr-based metal–organic framework grafted with pyridine was named MIL-101(Cr)-Py, and was used to adsorb microcystin-LR (MC-LR) from aqueous solution.

A non-enzymatic voltammetric xanthine sensor based on the use of platinum nanoparticles loaded with a metal-organic framework of type MIL-101(Cr). Application to simultaneous detection of dopamine, uric acid, xanthine and hypoxanthine.

A Cr-based metal-organic framework MIL-101(Cr) was used to load platinum nanoparticles (PtNPs) that were placed on a glassy carbon electrode (GCE). The modified GCE was used as a non-enzymatic xanthine sensor. Compared to bare GCE, it requires a strongly decreased working potential and an increased signal current for xanthine oxidation. This is due to the crystalline ordered structure and large specific surface of the MIL-101(Cr), and to the high conductivity of the Pt NPs. Differential pulse voltammetry (DPV) shows the sensor to have a wide linear range (0.5 - 162μM), a low detection limit (0.42μM), and high selectivity. It was applied to the simultaneous determination of dopamine, uric acid, xanthine and hypoxanthine at working potentials of 0.13, 0.28, 0.68 and 1.05V, respectively (vs. Ag/AgCl) and to quantify xanthine in spiked serum samples. Graphical abstract This is the first report of non-enzymatic xanthine electrochemical sensor based on metal-organic framework loaded with nanoparticles.

Improved CO2 capture and separation performances of a Cr-based metal–organic framework induced by post-synthesis modification of amine groups

A composite adsorbent based on a metal–organic framework MIL-101 (Cr3F(H2O)2O(BDC)3; BDC: terephthalic acid) loaded with N,N′-dimethylethylenediamine (dmeda) was synthesized by post-synthesis modification method, and the crystal structure and thermal stability of MIL-101 were maintained. The composite is shown to enhance capacity and selectivity for post-combustion carbon dioxide capture, even if its BET specific surface area decreases by 52% compared to MIL-101. At 273 K and 298 K under 1 bar, dmeda-MIL-101 exhibited 8.7% and 18.7% increase in CO2 capacity respectively (from 2.30 mmol/g of MIL-101 to 2.50 mmol/g at 273 K, and from 1.35 mmol/g of MIL-101 to 1.59 mmol/g at 298 K). At 273 K and 298 K under a 0.15 bar CO2/0.75 bar N2 mixture, the CO2/N2 selectivities of MIL-101 and dmeda-MIL-101 were calculated by Ideal Adsorbed Solution Theory (IAST), according to single-component gas sorption experiment data. The improved capacity and selectivity are consequences of the higher isosteric heat of CO2 adsorption (33.9 kJ/mol at zero coverage), which is due to the interaction between amines and CO2.

Fabrication of amine-functionalized metal-organic frameworks with embedded palladium nanoparticles for highly sensitive electrochemical detection of telomerase activity

As a critical biomarker for early cancer diagnostics, telomerase activity has attracted extensive attention concerning its monitoring and detection. Herein, a simple and sensitive electrochemical biosensor is constructed for the detection of telomerase activity based on the electrocatalysis of Pd nanoparticles anchored on amine functionalized Cr-based metal-organic frameworks (Pd/MIL101-NH2) as a redox mediator. Upon telomerase triggered extension, the telomerase activity is related to the amount of the adsorbed electrocatalyst, leading to the different electrochemical signals for readout. Integrating with the efficient electrocatalysis of Pd/MIL101-NH2 towards oxidation of acetaminophen, this biosensor shows wide dynamic correlation of telomerase activity from 5 × 102 to 1.62 × 107 HeLa cells mL−1 and the limit of detection was calculated to be 11.25 HeLa cells mL−1, providing a powerful platform for detecting telomerase activity.

Coupling Ru nanoparticles and sulfonic acid moieties on single MIL-101 microcrystals for upgrading methyl levulinate into γ-valerolactone

Heterogeneous catalytic conversion of biomass-derived methyl levulinate (ML) to γ-valerolactone (GVL) is highly attractive as a sustainable route to mitigating the dependence on nonrenewable fossil resources. However, this route is limited by its low selectivity toward GVL and severe reaction conditions. Here, we present a synergistic catalytic process that offers exclusive GVL selectivity with complete ML conversion under mild conditions (80 °C, 0.5 MPa of H2 pressure). This is achieved over a dual-functionalized catalyst of Ru nanoparticles (Ru-NPs) and Brønsted acid SO3H groups in a Cr-based metal-organic framework (MIL-101). The Ru-NPs served as metal sites for the hydrogenation of ML to methyl-3-hydroxyvalerate (MHV) and the acidic SO3H moieties promoted the cyclization of MHV to generate GVL via lactonization. In contrast, GVL production was significantly suppressed over the physically mixed congener (2.0 wt% Ru/MIL-101 + MIL-101-SO3H). This result demonstrates an unrivalled advantage of the dual integration of metal/acid sites in a single MOF crystal, and the relative amount of sulfonic acid groups in the catalyst can exert significant influence on the overall catalytic performances. The activation energies for the hydrogenation and lactonization steps with the developed catalyst were 29.5 and 42.1 kJ/mol, respectively, which are much lower than those observed with the traditional 5.0 wt% Ru/AC catalyst.

Sensitive electrochemical detection of picloram utilising a multi-walled carbon nanotube/Cr-based metal-organic framework composite-modified glassy carbon electrode

ABSTRACTThis study describes the utilisation of a glassy carbon electrode modified with a composite of multi-walled carbon nanotube and Cr-based metal-organic framework (MIL-101, Cr-BDC, BDC = 1,4-benzenedicarboxylate) for the sensitive, simple and fast voltammetric determination of picloram in environmental samples. Under optimum conditions, additions of picloram using square wave voltammetry showed linear ranges of picloram concentrations from 24.15 to 3018 µg∙L‒1 (0.1–12.5 μM) and from 3018 to 9658 µg∙L‒1 (12.5–40 μM) with a detection limit of 14.49 µg∙L‒1 (0.06 µM). The method was successfully applied to the determination of picloram in tap and river water samples spiked with picloram without any purification step by the standard addition method. The good recovery values obtained ranging from 97.5% to 105.0% revealed the reliability and accuracy of the method.

Comparisons of glyphosate adsorption properties of different functional Cr-based metal-organic frameworks.

A Cr-based metal-organic framework, namely, MIL-101(Cr), was modified with amino (NH2 -) and urea (UR2 -) groups, and the materials were evaluated as adsorbents for glyphosate, and a comparison with commercial activated carbon was also discussed. The effects of the adsorption factors, such as adsorbent concentration, adsorption time, pH and ionic strength were mainly investigated. The results showed that a pseudo-second-order rate equation described the adsorption kinetics mechanisms well, while the Langmuir model and the Freundlich model fitted different adsorption isotherms, respectively. Among the adsorbents we studied, NH2 -MIL-101(Cr) showed the maximum adsorbing capacity, which is 64.25mg/g when pH=3.0, while UR2 -MIL-101(Cr) did not reach the best adsorption performance due to the steric hindrance. The work opens up a new way for the modification of metal-organic frameworks for adsorption process.

Reversing the Dye Adsorption and Separation Performance of Metal–Organic Frameworks via Introduction of −SO3H Groups

In this work, two hydrostable Cr-based metal–organic frameworks (MOFs), MIL-101(Cr) and MIL-101(Cr)-SO3H, were successfully synthesized and applied in the adsorption and separation of ionic dye fluorescein sodium (FS) and cationic dye safranine T (ST). Interestingly, MIL-101(Cr) can efficiently adsorb FS dye but hardly adsorbs ST dye, and MIL-101(Cr)-SO3H exhibits the thoroughly opposite phenomenon. More importantly, the reversed adsorption with high selectivity on the two MOFs can also be attained in the mixed solutions of the dyes. Finally, a mechanism analysis indicates that this significant reversal in performance for the dyes is mainly attributed to the opposite surface charges of the two MOFs caused by −SO3H groups.

Hierarchical Cr2O3@OPC composites with octahedral shape for rechargeable nonaqueous lithium-oxygen batteries

The development of catalyst materials is the most significant issue that hinders the practical applications of Li-O2 batteries. Herein we show the design and synthesis of the hierarchical chromic oxide-octahedral porous carbon (Cr2O3@OPC) composites catalyst with octahedral shape that derived from Cr-based metal-organic frameworks (MIL-101(Cr)) precursor. When applied as cathode catalysts in rechargeable Li-O2 batteries, the electrode with Cr2O3@OPC composites catalyst exhibits a low charge and discharge over-potential, high discharge capacity and excellent cycling stability. What's more, the electrode with Cr2O3@OPC composite shows a discharge capacity up to ∼4800 mAh g(catalyst + carbon)−1 at a current density of 0.1 mA cm−2, and exhibits a very stable discharge voltage plateau of 2.7 V and a charge voltage plateau of ∼3.9 V. With the addition of Cr2O3@OPC composite, the Li-O2 batteries can obtain good cycle performance over 50 cycles at a fixed capacity of 800 mAh g(catalyst + carbon)−1. These results indicating that the Cr2O3@OPC composite derived from MIL-101(Cr) would be a promising catalyst for Li-O2 batteries.

Synthesis of a hybrid MIL-101(Cr)/ZTC composite for hydrogen storage applications

Metal–organic frameworks (MOFs) hybrid composites have recently attracted considerable attention in hydrogen storage applications. In this study a hybrid composite of zeolite templated carbon (ZTC) and Cr-based MOF (MIL-101) was synthesised by adding the templated carbon in situ during the synthesis of MIL-101(Cr). The obtained sample was fully characterized and hydrogen adsorption measurements performed at 77 K up to 1 bar. The results showed that the surface areas and the hydrogen uptake capacities of individual MIL-101 (2552 m2 g−1, 1.91 wt%) and zeolite templated carbon (2577 m2 g−1, 2.39 wt%) could be enhanced when a hybrid MIL-101(Cr)/ZTC composite (2957 m2 g−1, 2.55 wt%) was synthesized. The procedure presents a simple way for enhancement of hydrogen uptake capacity of the individual Cr-MOF and templated carbon samples.

Adsorptive Removal of Pb(II) Ions from Aqueous Samples with Amino-Functionalization of Metal–Organic Frameworks MIL-101(Cr)

Metal organic frameworks (MOFs) have been regarded as robust adsorbents for the adsorptive removal of organic pollutants because of their unique characteristics. However, the application of MOFs in the removal of metals from water is still rare. In this paper, amino-functionalization of Cr-based MOFs MIL-101 are modified through coordination bonding of unsaturated Cr metal centers with the -NH2 group in ethylenediamine (ED), and we demonstrate their excellent performance for the removal of Pb(II) ions from water. The Fourier transform infrared verifies that the ethylenediamine was grafted successfully on MIL-101. Furthermore, the results of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that the structure of ED-MIL-101 with an appropriate amount of ED almost does not collapse and retains the original performance of MIL-101. The adsorption capacity of ED-MIL-101, which is more than five times that of MIL-101, is 81.09 mg.g(-1) for Pb(II) ions from aqueous samples. The selectivity coefficients of ED-MIL-101 for Pb(II)/Cu(II), Pb(II)/Zn(II), Pb(II)/Co(II), and Pb(II)/Ni(II) are 6.92, 24.02, 15.69, and 14.53, respectively. The adsorption kinetics of Pb(II) ions shows that the process fits well with a pseudo-second-order model, and the adsorption equilibrium time is only about 30 min. Moreover, the practical application of ED-MIL-101 achieves almost 97.22% removal efficiency for Pb(II) ions. These results indicate that ED-MIL-101 has great potential in selectively removing Pb(II) ions from water environment.

Graphene supported chromium carbide material synthesized from Cr-based MOF/graphene oxide composites

A composite (Cr–G) made from chromium carbide (Cr3C2) and chemically converted graphene (G) was synthesized by calcining a Cr-based metal-organic framework (MIL-101) embedded with graphene oxide (GO). The MIL-101 embedded with graphene oxide (MGO) was synthesized by the self-assembly process of Cr(NO3)3·9H2O and terephthalic acid in the presence of exfoliated GO in hydrothermal way. The incorporation of large amounts of GO did not prevent the formation of MIL-101 units. After calcination, the MGO decomposes to form a conductive composite consisting of sheet-like Cr3C2 and G sheets with CrN and Cr2O3 impurities confirmed by X-ray diffraction. The Cr–G modified glassy electrode (Cr–G/GCE) showed excellent response to the electro-oxidation of dopamine. Significantly, not like most other electro-catalysts, Cr–G/GCE maintained the linear growth meaning a single diffusion controlled process even at high scan rate of 300mVs−1. There was a low detection limit and broad linear range for Cr–G complex detection of dopamine.

Hydrocarbon oxidation over Fe- and Cr-containing metal-organic frameworks MIL-100 and MIL-101–a comparative study

Catalytic properties of Fe- and Cr-based metal-organic frameworks (MOFs) MIL-100 and MIL-101 have been assessed in two liquid-phase reactions: solvent-free allylic oxidation of alkenes (cyclohexene, α- and β-pinenes) with molecular oxygen and oxidation of anthracene (AN) with tert-butyl hydroperoxide (TBHP). In the oxidation of alkenes, the product selectivity strongly depends on the nature of metal (Fe or Cr) but, for the same metal, only slightly differs for the MIL-100 and MIL-101 structures. The Fe-containing MOFs afford the formation of unsaturated alcohols while Cr-based MOFs give mainly unsaturated ketones. Both Cr-MIL-100 and Cr-MIL-101 favor decomposition of cyclohexenyl hydroperoxide to produce 2-cyclohexen-1-one with 67–69% selectivity. Stability toward destruction reduced in the order Cr-MIL-101, Cr-MIL-100>Fe-MIL-100>Fe-MIL-101. In the oxidation of anthracene over both Cr-MOFs and Fe-MIL-101, the selectivity toward 9,10-anthraquinone (AQ) attained 100% at 92–100% AN conversion. The turnover frequency (TOF) decreased in the order Cr-MIL-101>Fe-MIL-101>Cr-MIL-100>Fe-MIL-100. Cr-MIL-101 revealed superior catalytic performance in terms of AN conversion, AQ selectivity and TOF. Nearly quantitative yield of AQ was obtained after 1.5h at 100°C in chlorobenzene as solvent. No leaching of active metal occurred under optimal reaction conditions and the MOFs could be recycled several times without deterioration of the catalytic properties.

Hybrid Improper Ferroelectricity in a Multiferroic and Magnetoelectric Metal‐Organic Framework

On the basis of first-principles calculations, we design a novel Cr-based metal-organic framework to be both multiferroic and magnetoelectric. The compound shows a “double-hybrid” nature: it is a hybrid organic-inorganic compound and it shows hybrid improper ferroelectricity. Here, the coupling of non-polar distortions, such as Jahn-Teller pseudo-rotations and tilting, pave the way to a polar behavior, with the coupling being realized through hydrogen bonds.

Au nanoparticles supported on Cr-based metal-organic framework as bimetallic catalyst for selective oxidation of cyclohexane to cyclohexanone and cyclohexanol

Abstract Two bimetallic catalysts Au/MIL-53(Cr) and Au/MIL-101(Cr) were prepared by urea deposition–precipitation. The catalytic performances of these catalysts were investigated via selective oxidation of cyclohexane to cyclohexanone and cyclohexanol by molecular oxygen in the absence of solvent and initiator. It is believed that framework Cr ions are effective catalytic sites, which accounts for that Au/MIL-53(Cr) and Au/MIL-101(Cr) exhibit superior catalytic performance. The confinement effect of MIL-101(Cr) cages to Au nanoparticles results in