Cr-based Metal-organic Framework Research Articles

Efficient atmospheric water harvesting enabled by hierarchically structured cellulose foam

The sorption-based atmospheric water harvesting technique is an appealing solution for addressing the challenge of freshwater shortages. In this study, a composite foam was fabricated by confining hygroscopic salt (CaCl2) into a Cr-based metal–organic framework (MIL-101), which was then integrated into a bacterial cellulose (BC) skeleton. The hierarchical structure, which contains micron- and nanoscale pores, enhances water storage, transport, and vapor evaporation throughout the whole water capture and release process. The pore confinement effect of MIL-101 and the interconnected BC network effectively restricted the leakage of the liquefied salt solution. Interestingly, the color of the CaCl2@MIL-101@BC foam changed from light green to dark green as the amount of absorbed water increased. This moisture-induced color darkening improves the light absorption ability during the water release stage under sunlight. At 30 % relative humidity, the foam can absorb up to 0.78 g g−1 of water per cycle (8 h) and desorb quickly under solar radiation. This makes foam a promising method for water production in arid areas.

Facilitated explosion of nitro compounds confined in metal–organic frameworks

TNT@MOF was prepared by confining 2,4,6-trinitrotoluene (TNT) into a Cr-based metal–organic framework (MOF). Compared with raw TNT, the initiation activity of TNT@MOF was enhanced due to the interplay between the nitro group of TNT and the CUS of MOFs.

Mesoporous metal-organic framework NH2-MIL-101(Cr) as an efficient photocatalyst for the epoxidation of styrene.

Oxidation of styrene is a key reaction in the synthesis of pharmaceuticals and fine chemicals, and therefore oxidizing styrene with selective, efficient, and recyclable heterogeneous catalysts is significant from an environmental and economic standpoint. In this study, we report the transition Cr-based metal-organic framework [NH2-MIL-101(Cr)] as a heterogeneous photocatalyst, which efficiently promotes styrene epoxidation using H2O2 as a green oxidant, achieving high conversion efficiency (98%) and excellent selectivity (82%) under ambient conditions. Radical detection and quenching experiments reveal that the superoxide radical anion (O2˙-) acts as an active oxygen species, selectively promoting the oxidation of styrene to its oxidized form. This work provides insight into the development of a sustainable and cost-effective method for producing styrene oxide.

Cr-based metal–organic frameworks (MOFs) with high adsorption selectivity and recyclability for Au (Ⅲ): Adsorption behavior and mechanism study

Preparation of efficient adsorbents is of great significance for the recovery of precious metals from secondary resources. Herein, –NH2 was successfully grafted on MIL-101(Cr) via hydrothermal reaction to improve the adsorption capacity of Au (Ⅲ) in aqueous solution. MIL-101(Cr)–NH2 had a huge specific surface area (1016.50 m2‧g−1), which can provide more adsorption sites for Au (III). At 298 K, the maximum adsorption capacity of Au (III) by MIL-101(Cr)–NH2 was 792.43 mg∙g−1 and was higher than that by MIL-101(Cr) (140.83 mg∙g−1). The adsorption data was well fitted by Langmuir and pseudo-second-order models, confirming that the adsorption process conformed to single molecule adsorption and chemical adsorption. Mechanism study indicated that the adsorption of Au (III) by MIL-101(Cr)–NH2 was initiated with electrostatic attraction and promoted by reduction and inner complexation between AuCl4- and protonated amino groups. During adsorption, Au (Ⅲ) was reduced to Au (0) and Au (I) by –NH2. Density functional theory (DFT) calculation demonstrated that MIL101(Cr)–NH2 possessed higher binding affinity and more adsorption sites for Au (III) than MIL-101(Cr). Moreover, MIL-101(Cr)–NH2 exhibited excellent selectivity towards Au (III) and good recyclability, which is promising in the recovery of precious metals.

Green Synthesis of MIL-88B(Cr) with the Co-Modulator of Nitric Acid and Acetic Acid

MIL-88B(Cr) is a prototypical flexible chromium-based metal-organic framework (MOF), which possesses extremely strong water/thermal stability and excellent “swelling/breathing” ability. However, in previous studies, there have been very few reports on MIL-88B(Cr) due to unclear synthesis details. Here, we found that the pure MIL-88B(Cr) can be facile synthesized through a hydrothermal method with the co-use of nitric acid and acetic acid (molar ratio = 1:15). The obtained MIL-88B(Cr) was sufficiently characterized by diverse techniques to assure its high-level quality. This work emphasizes a future valuable approach to expanding the production of flexible Cr-based MOF.

Boosting Methanol-Mediated CO2 Hydrogenation into Aromatics by Synergistically Tailoring Oxygen Vacancy and Acid Site Properties of Multifunctional Catalyst.

Even though the direct hydrogenation of CO2 into aromatics has been realized via a methanol-mediated pathway and multifunctional catalyst, few works have been focused on the simultaneously rational design of each component in multifunctional catalyst to improve the performance. Also, the structure-function relationship between aromatics synthesis performance and the different catalytic components (reducible metal oxide and acidic zeolite) has been rarely investigated. Herein, we increase the oxygen vacancy (Ov ) density in reducible Cr2 O3 by sequential carbonization and oxidation (SCO) treatments of Cr-based metal-organic frameworks. Thanks to the enriched Ov , Cr2 O3 -based catalyst affords high methanol selectivity of 98.1 % (without CO) at a CO2 conversion of 16.8 % under high reaction temperature (350 °C). Furthermore, after combining with the acidic zeolite H-ZSM-5, the multifunctional catalyst realizes the direct conversion of CO2 into aromatics with conversion and selectivity as high as 25.4 % and 80.1 % (without CO), respectively. The property of acid site in H-ZSM-5, especially the Al species that located at the intersection of straight and sinusoidal channels, plays a vital role in enhancing the aromatics selectivity, which can be precisely controlled by varying the hydrothermal synthesis conditions. Our work provides a synergistic strategy to boost the aromatics synthesis performance from CO2 hydrogenation.

The influence of Pd4Cr6@(NH2)M-MOF(Cr) catalyst on components of formic acid dehydrogenation gaseous products

ABSTRACT In the dehydrogenation of formic acid, catalyst has a great influence on the composition and formation rate of gaseous products. However, the hydrogen used in fuel cells has strict requirements on the content of carbon monoxide impurities. Therefore, it is very important to study the relationship between catalyst components and their synergistic effects and the composition of gaseous products. The role of Pd-Cr bimetallic nanoparticles supported on amino modified Cr-based metal-organic framework catalyst (Pd4Cr6@(NH2)M-MOF(Cr)) in the formic acid dehydrogenation was explored through comparative experiments and catalyst characterization. Results show that both Cr-based metal-organic framework (MOF(Cr)) and amino-modified Cr-based metal-organic framework ((NH2)M-MOF(Cr)) have no effect on promoting the generation of gaseous products. The presence of Cr and NH2 groups in Pd4Cr6@(NH2)M-MOF(Cr) greatly improves the formation rate of H2 and CO2 products, the gas production rate of Pd4Cr6@(NH2)M-MOF(Cr) is 2.89 times that of Pd4@(NH2)M-MOF(Cr), and the gas production rate of Pd4Cr6@(NH2)M-MOF(Cr) is 6.26 times of Pd4Cr6@MOF(Cr). However, the formation rate of H2 increases more in the presence of Cr. Synergy of Pd-Cr and Pd-NH2 in the Pd4Cr6@(NH2)M-MOF(Cr) catalyst promotes CO formation.

Dibenzothiophene Removal from Fuel Oil by Metal-Organic Frameworks: Performance and Kinetics.

Desulfurization of organic sulfur in the fuel oil is essential to cut down the emission of sulfur dioxide, which is a major precursor of the acid rain and PM2.5. Currently, hydrodesulfurization is regarded as a state-of-art technology for the desulfurization of fuel oil. However, due to the stringent legislation of the fuel oil, the deep desulfurization technology is urgent to be developed. Adsorptive desulfurization method is promising due to the high selectivity and easy operation. The development of efficient adsorbent is important to advance this technology into industrial application. In this work, the five types of metal-organic frameworks (MOFs), including Cu-BTC, UMCM-150, MIL-101(Cr), UIO-66, and Cu-ABTC were synthesized for the adsorption of dibenzothiophene (DBT), a typical organic sulfur compound in the fuel oil. The experimental results revealed that the adsorption capacity of the five MOFs followed the order of Cu-ABTC, UMCM-150, Cu-BTC, MIL-101(Cr), and UIO-66, which adsorption capacities were 46.2, 34.2, 28.3, 26.3, and 22.0 mgS/g, respectively. The three types of Cu-based MOFs such as Cu-ABTC, UMCM-150, and Cu-BTC outperformed the Cr-based MOFs, MIL-101, and Zr-based MOFs, UIO-66. Since the surface area and pore volumes of the Cu-based MOFs were not the greatest among the tested five MOFs, the physical properties of the MOFs were not the only limited factor for the DBT adsorption. The π-complexation between DBT and linkers/metal in the MOFs was also important. Kinetic analysis showed that the DBT adsorption onto the five tested MOFs follows the pseudo-second-order kinetics, confirming that the chemical π-complexation was also contributed to the DBT adsorption. Furthermore, the operation parameters such as oil-adsorbent ratio, initial sulfur concentration and adsorption temperature for the DBT adsorption onto Cu-ABTC were optimized to be 100:1 g/g, 1000 mgS/L and 30 °C, respectively. This work can provide some insights into the development of efficient adsorbent for the organic sulfur adsorption.

Front Cover: The Decisive Role of Spin States and Spin Coupling in Dictating Selective O2 Adsorption in Chromium(II) Metal–Organic Frameworks (Chem. Eur. J. 18/2022)

Using periodic DFT calculations, we have illustrated how selective binding of O2 over N2 and H2 occurs in Cr-based metal–organic frameworks (MOFs). In particular, the role of spin state and spin coupling in selective gas binding is highlighted. As selective O2 binding is required for oxygen concentrators, the proposed idea has high commercial value. More information can be found in the Research Article by S. Pal, G. Rajaraman et al. (DOI: 10.1002/chem.202104526).

Confined space synthesis of chromium–based metal–organic frameworks in activated carbon: Synergistic effect on the adsorption of contaminants of emerging concern from water

The steadfast presence of contaminants of emerging concern (CECs) in the environment calls for tailored remediation strategies. In this regard, Cr-based metal-organic frameworks (MOFs; MIL-100Cr and MIL-101Cr) were grown inside of activated carbon (AC) pores via confined synthesis for a superior adsorptive removal of those CECs from water. The composites CMOF-100Cr and CMOF-101Cr, as well as the apohost AC and pure MOFs, were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis by X-rays (EDAX), nitrogen adsorption–desorption, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy, and zeta potential measurements. XRD, SEM/EDAX, TGA, and pore size distribution data provided direct evidence of the successfully confined space syntheses of the hierarchical composites. Occupancy of the large voids of AC by the MOF was 100% and 43% for CMOF-100Cr and CMOF-101Cr, respectively. The adsorption capacity of the materials was evaluated in both single- and multi-component fashion at neutral pH and low CEC concentrations (μg L−1). The CECs were caffeine (CFN), carbamazepine (CBZ), clofibric acid (CA), naproxen (NPX), and metabolites 10,11-epoxycarbamazepine (Ep-CBZ), o-desmethylnaproxen (o-DMN), paraxanthine (PXN), and salicylic acid (SA). In general, the observed capacities for both single and multi-component adsorption of CECs increased as follows MIL-100Cr < < MIL-101Cr < CMOF-101Cr < AC < < CMOF-100Cr. Compared to the composite containing MIL-100Fe (i.e., CMOF-100Fe) previously developed by our group, the substitution of the metal node by Cr3+ produced significant enhancements in CEC uptake capacities. The affinity of CMOF-100Cr toward CECs increases as follow: SA < CA< o-DMN < NPX < PXN < CFN < Ep-CBZ < CBZ. Environmental significanceThe persistence of contaminants of emerging concern (CECs) in water mandates the development of tailored remediation strategies. To be suitable, these must consider efficacy and avoid undesired byproducts. An attempt to individually grow two chromium-based nanoporous metal-organic frameworks, each possessing particular linkers, within the pores of an activated carbon via confined space synthesis has proven to be effective in the adsorptive removal of a set of CECs that included metabolites. Furthermore, the adsorption was conducted in both single- and multi-component fashion to gain insight into the CECs competitive nature during uptake. The hierarchical composite adsorbents exhibited superior uptake capacity because of the synergistic combination of hydrophobicity and specific interactions between the metal node and the CECs, while multiple adsorption cycles were possible via thermal regeneration.

High cubicity of D2O ice inside spherical nanopores of MIL-101(Cr) framework: a neutron diffraction study.

Although cubic ice (ice Ic) is considered to be an important phase of water that impacts ice cloud formation in the Earth's upper atmosphere, its properties have not been studied to the same extent as those of hexagonal ice (ice Ih). This is because pristine ice Ic is not formed in simple laboratory conditions. Ice Ic formed in ambient conditions has a stacking disordered array of both hexagonal and cubic-structured hydrogen-bonded water molecules. It is therefore an active area of research to find ways of developing stacking disorder-free pure ice Ic. We demonstrate the evolution of almost pure ice Ic structure within the spherical nanopores of a hydrostable Cr-based metal-organic framework MIL-101(Cr) with an average pore size of 1 nm by low-temperature neutron diffraction study on D2O. It is observed that at temperatures below 230 K a fraction of liquid D2O transforms into ice and more than 94% of ice crystals evolved inside the pore are cubic in shape. This is a significantly high fraction of ice Ic formed under simple conditions inside the spherical pores of a Cr-based MOF. It is also observed that upon increasing the temperature, ice Ic remains stable until its melting point, without being transformed into ice Ih. This observation is in contrast to our previous observation of ice structure in the 2D cylindrical nanopores of MCM-41, where H2O ice after creeping out from the cylindrical channel was seen to be dominated by hexagonal shape. In the present study, the D2O molecules were confined into well-defined spherical nanopores, which hindered the growth of crystals above a certain size, thus minimizing the stacking disordered array. Nanoconfinement of water inside uniform spherical pores is therefore a promising method for the evolution of a significantly large fraction of cubic ice by minimizing the stacking disorder. This finding may open up the possibility of forming ice Ic with 100% cubicity under simple laboratory conditions, which will help in exploring the microphysics of ice cloud formation in the upper atmosphere.

Substituent-Induced Electron-Transfer Strategy for Selective Adsorption of N2 in MIL-101(Cr)-X Metal-Organic Frameworks.

N2 removal is of great significance in high-purity O2 production and natural gas purification. Here, we present a substituent-induced electron-transfer strategy for improving N2 capture performance by controlling the Lewis acidity of Cr(III) metal unsaturated sites in Cr-based metal-organic frameworks. With the enhancement of the electron-withdrawing ability of the modified group on terephthalic acid (-NO2 > -CH3), the N2 adsorption ability of MIL-101(Cr)-X was improved significantly. For MIL-101(Cr)-NO2, the adsorption enthalpy of N2 at zero coverage was 30.01 kJ/mol, which was much larger than that of MIL-101(Cr)-CH3 (14.31 kJ/mol). In situ infrared spectroscopy studies, Bader charges, and density functional theory calculations showed that the presence of -NO2 could enhance the Lewis acidity of Cr(III) metal unsaturated sites, which resulted in a strong interaction affinity for N2. The adsorption isotherms indicated that MIL-101(Cr)-NO2 had an excellent N2/O2 (79/21, v/v) selectivity of up to 10.8 and a good N2/CH4 separation performance (SN2/CH4 = 2.8, 298 K, 1 bar). Breakthrough curves showed that MIL-101(Cr)-NO2 had great potential for the efficient separation of N2/O2 and N2/CH4.

Hierarchical Porous MIL-101(Cr) Solid Acid-Catalyzed Production of Value-Added Acetals from Biomass-Derived Furfural.

Considering economic and environmental impacts, catalytic biomass conversion to valuable compounds has attracted more and more attention. Of particular interest is furfural, a versatile biorefinery platform molecule used as a feedstock for the production of fuels and fine chemicals. In this study, the Cr-based metal-organic frameworks (MOFs) MIL-101 were modified by chlorosulfonic acid, and MIL-101 was changed into a hierarchical MOF structure with smaller particles and lower particle crystallinity by CTAB, which significantly improved the acidic sites of the MOFs. The original and modified MIL-101(Cr) catalysts were characterized by XRD, N2 adsorption-desorption, SEM, TEM, and FT-IR. The effects of different catalysts, reaction temperature, catalyst amount, and alcohol type on the reaction were studied. Under the action of the MOFs catalyst, a new mild route for the condensation of furfural with various alkyl alcohols to the biofuel molecules (acetals) was proposed. The conversion route includes the conversion of furfural up to 91% yield of acetal could be obtained within 1 h solvent-free and in room-temperature reaction conditions. The sulfonic acid-functionalized MIL-101(Cr) is easy to recover and reuse, and can still maintain good catalytic activity after ten runs.

Synthesis of dihydropyrimidinones via multicomponent reaction route over acid functionalized Metal-Organic framework catalysts

Multi component reactions over heterogeneous solid acid catalysts are extremely important owing to easy separation, amenable recycling, and prospective scaling up of the process. Here, we are reporting the synthesis of biologically important dihydropyrimidinones over postsynthetic modified Cr-based metal–organic framework materials as heterogeneous catalysts containing the bifunctional Lewis and Brønsted acid sites. Cr-based metal–organic frameworks contained coordinatively unsaturated metal sites as inherent Lewis acid sites, whereas postsynthetic modifications introduced the Brønsted acid sites in the framework. A direct one pot synthesis route was employed to produce the pristine MOF in pure aqueous medium without using any additives. The bulk structure, morphology, surface and bonding properties of the synthesized materials were thoroughly characterized with powder XRD, FTIR, XPS, FE-SEM, TGA, and N2 sorption isotherms. A qualitative evolution of acid strength was carried out over the functionalized MOFs. Among the post synthetic functionalized materials, carboxylic acid functionalized framework exhibited a very high yield of dihydropyrimidinones under solvent less moderate reaction conditions. The catalyst also demonstrated a robust recyclability and wide substrate scope. Comparative study showed a very high catalytic activity of the postsynthetic modified MOFs in comparison to the reported literature. The reaction condition was optimized by varying parameters like solvent, temperature, reaction duration and catalyst loadings. The mechanistic studies indicated the involvement of both the Lewis and Brønsted sites acid sites of the catalysts in the multicomponent reaction.

Ru Catalyst Encapsulated into the Pores of MIL-101 MOF: Direct Visualization by TEM.

Ru catalyst nanoparticles were encapsulated into the pores of a Cr-based metal-organic framework (MOF)—MIL-101. The obtained material, as well as the non-loaded MIL-101, were investigated down to the atomic scale by annular dark-field scanning transmission electron microscopy using low dose conditions and fast image acquisition. The results directly show that the used wet chemistry loading approach is well-fitted for the accurate embedding of the individual catalyst nanoparticles into the cages of the MIL-101. The MIL-101 host material remains crystalline after the loading procedure, and the encapsulated Ru nanoparticles have a metallic nature. Annular dark field scanning transmission electron microscopy, combined with EDX mapping, is a perfect tool to directly characterize both the embedded nanoparticles and the loaded nanoscale MOFs. The resulting nanostructure of the material is promising because the Ru nanoparticles hosted in the MIL-101 pores are prevented from agglomeration—the stability and lifetime of the catalyst could be improved.

Influence of Pore Structure and Metal-Node Geometry on the Polymerization of Ethylene over Cr-Based Metal-Organic Frameworks.

Metal–organic frameworks (MOFs) have received increasing interest as solid single‐site catalysts, owing to their tunable pore architecture and metal node geometry. The ability to exploit these modulators makes them prominent candidates for producing polyethylene (PE) materials with narrow dispersity index (Ð) values. Here a study is presented in which the ethylene polymerization properties, with Et2AlCl as activator, of three renowned Cr‐based MOFs, MIL‐101(Cr)‐NDC (NDC=2,6‐dicarboxynapthalene), MIL‐53(Cr) and HKUST‐1(Cr), are systematically investigated. Ethylene polymerization reactions revealed varying catalytic activities, with MIL‐101(Cr)‐NDC and MIL‐53(Cr) being significantly more active than HKUST‐1(Cr). Analysis of the PE products revealed large Ð values, demonstrating that polymerization occurs over a multitude of active Cr centers rather than a singular type of Cr site. Spectroscopic experiments, in the form of powder X‐ray diffraction (pXRD), UV/Vis‐NIR diffuse reflectance spectroscopy (DRS) and CO probe molecule Fourier transform infrared (FTIR) spectroscopy corroborated these findings, indicating that indeed for each MOF unique active sites are generated, however without alteration of the original oxidation state. Furthermore, the pXRD experiments indicated that one major prerequisite for catalytic activity was the degree of MOF activation by the Et2AlCl co‐catalyst, with the more active materials portraying a larger degree of activation.

Rapid simultaneous adsorption and SERS detection of acid orange II using versatile gold nanoparticles decorated NH2-MIL-101(Cr)

Acid orange II (AO II), a typical azo pigment, is strictly controlled by legislation and prohibited in foodstuffs. Herein, we prepared gold nanoparticles decorated amino-functionalized Cr-based metal-organic frameworks [NH2-MIL-101(Cr)@Au] via an in-situ reduction method as a surface-enhanced Raman scattering (SERS) substrate for simultaneous adsorption and detection of AO II. Gold nanoparticles are uniformly dispersed on the surface of NH2-MIL-101(Cr) owing to its three-dimensional (3D) structure and the interaction between –NH2 and Au ions, providing more SERS-active “hot spots”. These NH2-MIL-101(Cr)@Au nanocomposites exhibited selective and high adsorption performance (419.85 mg g−1) for AO II, and could be used as superior SERS substrates for the detection of AO II with a low limit of detection (LOD) of 0.05 mg L−1 and wide detection range of 0.05–50 mg L−1 using portable Raman spectrometer. Furthermore, this SERS assay has been successfully used to determine AO II in orange juice and chili powder with good sensitivities.

Chromium-based metal-organic framework embedded with cobalt phthalocyanine for the sensitively impedimetric cytosensing of colorectal cancer (CT26) cells and cell imaging

In this study, we have prepared the series of nanohybrids of Cr-based metal-organic framework (Cr-MOF) and cobalt phthalocyanine (CoPc) nanoparticles (denoted as Cr-MOF@CoPc) and investigated them as novel platforms of electrochemical cytosensors for determining colorectal cancer (CT26) cells. The developed Cr-MOF@CoPc nanohybrids were composed of irregularly small nanoparticles, mixed metal valence states of Cr2+/Cr3+/Cr5+ and Co2+/Co3+, rich functional groups of C–O and COO and strong fluorescence performance, as well as high specific area and large pore volume. These intrinsic features of Cr-MOF@CoPc nanohybrids endowed them with strong immobilization ability toward aptamer strands via π- π* stacking, electrostatic interaction, and van der Waals force, excellent electrochemical property, strong fluorescence intensity, and good biocompatibility. Compared with cytosensors based on the sole metal MOFs (Cr-MOF and CoPc) and other reported bulk MOF-based sensors, the constructed Cr-MOF@CoPc-based cytosensor exhibited low detection limit toward CT26 cells, for which the sensing performance was modulated by changing the dosage of CoPc nanoparticles. Electrochemical impedance spectroscopy and differential pulse voltammetry results showed extremely low detection limits of 36 and 8 cells mL−1, respectively, within the concentration range of the CT26 cell suspension (50–1 × 107 cells mL−1), along with high selectivity, excellent stability, and acceptable reproducibility. Thus, the prepared cytosensor can be extensively applied for the analysis of other kinds of cancer cells when anchored their corresponding aptamer strands, providing great potential applications in the biosensor and biomedical fields.

Synthesis of Ni/NiO@MIL-101(Cr) Composite as Novel Anode for Lithium-Ion Battery Application.

The poor conductivity is one of the prime reasons restricted MOFs to be applied in the lithium-ion battery system. For the sake of ameliorate this issue, the Ni/NiO was well loaded on the surface of Cr-based metal organic frameworks (MIL-101) by solution impregnation and in situ reduction method to form Ni/NiO@MIL-101(Cr) composites. The as-synthesized Ni/NiO@MIL-101(Cr) was characterized by X-ray powder diffractions, X-ray photoelectron spectroscopy, field emission scanning electron microscope and transmission electron microscope techniques. When used as anode for LIBs, the Ni/NiO@MIL-101(Cr) composite exhibited high reversible capacity (891 mAh g-1 after 100 cycles at a current density of 200 mA g-1) and stable cycle performance, the coulombic efficiency can maintain in the whole cycle above 95.0%. The reasons for that Ni/NiO@MIL-101(Cr) behaved outstanding electrochemical properties were discussed also. The Ni/NiO@MIL-101(Cr) can be used as promising material for lithium-ion battery application.

Highly efficient and acid-resistant metal-organic frameworks of MIL-101(Cr)-NH2 for Pd(II) and Pt(IV) recovery from acidic solutions: Adsorption experiments, spectroscopic analyses, and theoretical computations

Cr-based metal-organic frameworks (MOFs) of MIL-101(Cr)-NH2 was post-synthesized from nitro-functionalized MIL-101(Cr) (MIL-101(Cr)-NO2) through a reduction process. Adsorption behaviors and interactions of MIL-101(Cr)-NH2 and MIL-101(Cr)-NO2 with platinum group metal (PGM) anions of Pd(II) (PdCl42−) and Pt(IV) (PtCl62−), were investigated through batch adsorption experiments, spectroscopic analyses, and theoretical computations. According to adsorption kinetics and isotherms, the uptakes of Pd(II) and Pt(IV) by in MIL-101(Cr)-NH2 were found to be much higher than their uptakes by MIL-101(Cr)-NO2. The abundant protonated amine groups (BDC-NH3+) in MIL-101(Cr)-NH2 were verified to be the main adsorptive binding sites by XPS and FTIR spectroscopy, and FE-SEM imageries. Additionally, BDC-NH3+ shows extremely high affinities (b value) and binding energies (Ebind) for PdCl42− and PtCl62− through electrostatic attraction, resulting in much higher adsorption capacities of MIL-101(Cr)-NH2 for these PGMs as compared to those of MIL-101(Cr)-NO2. Moreover, the MOFs’ Cr nodes without terminal −OH indicated positive electrostatic potentials, and certain values of Ebind for PGM anions. Thus, the few-amount cationic Cr sites could also make little contributions to the adsorption of PGM anions in MIL-101(Cr)-NH2 or MIL-101(Cr)-NO2. Furthermore, the perfect regeneration and reusability of MIL-101(Cr)-NH2 over five of adsorption-desorption cycles, suggesting its potential in practical applications.