Pyrazine-based iron metal organic frameworks (Fe-MOFs) with modulated O-Fe-N coordination for enhanced hydroxyl radical generation in Fenton-like process

Rational design of coordination environment of Fe-based metal-organic frameworks (Fe-MOFs) is still a challenge in achieving enhanced catalytic activity for Fenten-like advanced oxidation process. Here in, novel porous Fe-MOFs with modulated O-Fe-N coordination was developed by configurating amino terephthalic acid (H2ATA) and pyrazine-dicarboxylic acid (PzDC) (Fe-ATA/PzDC-7:3). PzDC ligands introduce pyridine-N sites to form O-Fe-N coordination with lower binding energy, which affect the local electronic environment of Fe-clusters in Fe-ATA, thus decreased its interfacial H2O2 activation barrier. O-Fe-N coordination also accelerate Fe(II)/Fe(III) cycling of Fe-clusters by triggering the reactive oxidant species mediated Fe(III) reduction. As such, Fe-ATA/PzDC-7:3/H2O2 system exhibited excellent degradation performance for typical antibiotic sulfamethoxazole (SMX), in which the steady-state concentration of hydroxyl radical (OH) was 1.6 times higher than that of unregulated Fe-ATA. Overall, this study highlights the role of O-Fe-N coordination and the electronic environment of Fe-clusters on regulating Fenton-like catalytic performance, and provides a platform for precise engineering of Fe-MOFs.

Achieving ultrafast and highly selective capture of radiotoxic tellurite ions on iron-based metal-organic frameworks through coordination bond-dominated conversion

Chemically durable and effective adsorbents for radiotoxic TeOx2- (TeIV and TeVI) anions remain in great demand for contamination remediation. Herein, a low-cost iron-based metal-organic framework (MIL-101(Fe)) was used as an adsorbent to capture TeOx2- anions from contaminated solution with ultrafast kinetics and record-high adsorption capacity of 645 mg g-1 for TeO32- and 337 mg g-1 for TeO42-, outperforming previously reported adsorbents. Extended X-ray absorption fine structure (EXAFS) and density functional theory (DFT) calculations confirmed that the capture of TeOx2- by MIL-101(Fe) was mediated by the unique C-O-Te and Fe-O-Te coordination bonds at corresponding optimal adsorption sites, which enabled the selective adsorption of TeOx2- from solution and further irreversible immobilization under the geological environment. Meanwhile, MIL-101(Fe) works steadily over a wide pH range of 4-10 and at high concentrations of competing ions, and it is stable under β-irradiation even at high dose of 200 kGy. Moreover, the MIL-101(Fe) membrane was fabricated to efficiently remove TeO32- ions from seawater for practical use, overcoming the secondary contamination and recovery problems in powder adsorption. Finally, the good sustainability of MIL-101(Fe) was evaluated from three perspectives of technology, environment, and society. Our strategy provides an alternative to traditional removal methods that should be attractive for Te contamination remediation.

ZnO-Doped Metal-Organic Frameworks Nanoparticles: Antibacterial Activity and Mechanisms

Metal-Organic Frameworks (MOFs) offer new ideas for the design of antibacterial materials because of their antibacterial properties, high porosity and specific surface area, low toxicity and good biocompatibility compared with other nanomaterials. Herein, a novel antimicrobial nanomaterial, MIL-101(Fe)@ZnO, has been synthesized by hydrothermal synthesis and characterized by FTIR, UV-vis, ICP-OES, XRD, SEM, EDS and BET to show that the zinc ions are doped into the crystal lattice of MIL-101(Fe) to form a Fe-Zn bimetallic structure. MIL-101(Fe)@ZnO was found to be effective against a wide range of antibacterial materials including Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, Acinetobacter junii and Staphylococcus epidermidis. It has a significant antibacterial effect, weak cytotoxicity, high safety performance and good biocompatibility. Meanwhile, MIL-101(Fe)@ZnO was able to achieve antibacterial effects by causing cells to produce ROS, disrupting the cell membrane structure, and causing protein leakage and lipid preoxidation mechanisms. In conclusion, MIL-101(Fe)@ZnO is an easy-to-prepare antimicrobial nanomaterial with broad-spectrum bactericidal activity and low toxicity.

Epoxidation of Fatty Acid Methyl Esters with Hydrogen Peroxide Catalyzed by Peroxopolyoxotungstate PW4 Encapsulated in the MIL-100(Cr) Framework

The MIL-100(Cr), PW12@MIL-100(Cr) and PW4@MIL-100(Cr) catalysts were prepared and characterized through XRD, FTIR, BET, SEM, EDS and Raman spectroscopy. A comparison of the catalytic properties of the synthesized materials in the epoxidation of FAMEs with hydrogen peroxide was made. The PW4@MIL-100(Cr) catalyst exhibited the highest catalytic activity and provided a high selectivity for the formation of epoxides. The effects of the reaction temperature, catalyst loading, reaction time and FAME:hydrogen peroxide molar ratio on the reaction performance were investigated, and the optimal process conditions were determined. An epoxide yield of 73% with a selectivity of 77% could be obtained using PW4@MIL-100(Cr) after 4 h at 40 °C. The catalytic stability test showed that PW4@MIL-100(Cr) could be easily separated and reused without any treatment for at least five consecutive cycles without a loss of activity or selectivity.

Mesoporous SBA-15 supported gold nanoparticles for solvent-free oxidation of cyclohexane: superior catalytic activity with higher cyclohexanone selectivity

Surface modification of mesoporous SBA-15 with (3-mercaptopropyl) trimethoxysilane greatly enhances its capability to adsorb the tetrachloroauric anion (AuCl₄^-). The calcination of the sample after the adsorption experiment led to the generation of homogeneously dispersed, spherical, single crystalline gold nanoparticles (Au⁰ NPs) of less than 5 nm size, embedded on SBA-15 as observed from the TEM images. The as-prepared SBA-15/Au⁰ nanohybrid material has offered excellent catalytic activity for the selective oxidation of cyclohexane using TBHP as the oxidant in the absence of any solvent. A maximum of 48.7% cyclohexane conversion was achieved and surprisingly, cyclohexanone (K) has much higher selectivity (>95%) than cyclohexanol (A). The hot-filtration study confirmed the leach-resistant characteristics as well as the true heterogeneous catalytic activity of the SBA-15/Au⁰ nanohybrid catalyst. The catalyst was recycled up to four times without significant loss in its catalytic activity.

Filling Polyoxoanions into MIL-101(Fe) for Adsorption of Organic Pollutants with Facile and Complete Visible Light Photocatalytic Decomposition

Transition metal-substituted polyoxometalates (POMs) were filled into a metal–organic framework (MOF) to construct a series of POM@MOF composites (PMo₁₂O₄₀@MIL-101, PMo₁₁VO₄₀@MIL-101, PMo₁₀V₂O₄₀@MIL-101). The composite materials possess ultra-high adsorption ability, especially for PMo₁₀V₂O₄₀@MIL-101, with an adsorption capacity of 912.5 mg·g⁻¹ for cationic antibiotic tetracycline in wastewater, much higher than that of isolated MIL-101(Fe) and the commonly used adsorption materials, such as activated carbon and graphene oxide. In particular, they can be used as efficient photocatalysts for the photodegradation of antibiotics under visible light irradiation. The complete photodegradation of the adsorbed species can induce the facile reusability of these composites for multiple cycles. This work opens an avenue to introduce POMs into an MOF matrix for the simultaneous adsorption and photodegradation of antibiotics.

Enhanced removal of P(V), Mo(VI) and W(VI) generated oxyanions using Fe-MOF as adsorbent from hydrometallurgical waste liquid: Exploring the influence of ionic polymerization

Environmentally hazardous P(V), Mo(VI) and W(VI) generated oxyanions exist widely in the waste liquid of nonferrous hydrometallurgy. In this work, Fe-MOF material was simply prepared via solvothermal synthesis and then used as an adsorbent to remove P(V), Mo(VI) and W(VI) oxyanions from hydrometallurgical waste liquid. Several important parameters, including solution pH, oxyanion concentration, contact time, adsorbent amount, temperature and coexistent heavy metal ions, were systematically investigated. The results demonstrate that adsorption process was almost pH-independent over a broad range of pH 3.0-10.0. The adsorption efficiency was strongly associated with the chemical species of oxyanions. The higher polymerisation degree of oxyanions was more favourable for removal efficiency. Additionally, the maximum removal efficiencies for P(V), Mo(VI) and W(VI) oxyanions under optimum conditions were approximately 100%. Furthermore, the adsorption kinetics and isotherms of oxyanions on the adsorbent separately belonged to the pseudo-second-order and Langmuir isotherm models. XPS analysis revealed that inner-sphere complexation played a dominant role in the adsorption removal process. Fe-MOFs with pH-independent properties, abundant binding sites and high stability are prospective adsorbents for treating waste liquids in the hydrometallurgical industry.

Recent developments in MIL-101 metal organic framework for heterogeneous catalysis

Metal organic frameworks (MOFs) are currently gaining considerable attention as heterogeneous catalysts. Since the functionality of the framework and the pore size of the MOFs can be adjusted over a wide range for various catalytic reactions, the usage of these materials as solid catalysts is attractive. One of the preferred catalytic mesoMOFs is MIL-101 (MIL: Material of Institute Lavoisier) family which has been mainly investigated. The large surface area, high pore volumes, and acceptable solvent/thermal stability (MIL-101(Cr) up to 300 °C) have led the MIL-101 family to be considered an ideal and widespread MOF for use as a great heterogeneous catalyst or solid support for a variety of reactions. The objective of this review is to present recent research on the use of the MIL-101 family for heterogeneous catalysis in gas and liquid phase reactions.

Multivariate metal-organic framework MTV-MIL-101 via post-synthetic cation exchange: is it truly achievable?

The post-synthetic exchange (PSE) method is a well-proven route to replace, modify, and add different functionalities to metal-organic frameworks (MOFs). Particularly, the solvent-assisted cation substitution (SACS) technique has been reported to prepare mixed-metal multivariate metal-organic frameworks (MTV-MOFs). However, such a technique does not apply to all types of MOFs. In 2013, Szilágyi et al. reported the achievement of the mixed-metal MTV-MIL-101 framework via PSE. Since then, a debate has been taking place about the validity of these findings. On the other hand, the attainment of the mixed-metal MIL-101 was reported to be obtainable through the direct synthesis, which is, to some, the only way to achieve it. Here, we settle this dispute by investigating Szilágyi's method not only as described, but also at extended conditions of time and different metal precursors: all attempts were vain. However, by reconsidering the refluxing solvent (dimethylformamide "DMF" instead of water) and the applied reaction conditions (110 °C-20 h), mixed-metal MIL-101(Cr/Fe) was achieved via a simple PSE method.

Selective reduction of nitrate into N2 by novel Z-scheme NH2-MIL-101(Fe)/BiVO4 heterojunction with enhanced photocatalytic activity

Nitrate and its metabolites as common pollutants in water had attracted widespread attentions. Converting nitrate to nontoxic and harmless nitrogen via photocatalysis was a promising approach. In this study, a novel Z-scheme NH₂-MIL-101(Fe)/BiVO₄ heterojunction was successfully prepared. As-prepared Z-scheme heterojunction along with built-in electric field facilitated the charge separation and enhanced the photocatalytic activity in nitrate reduction. The results showed that 0.10-MBiVO photocatalyst exhibited the highest nitrate removal rate of 94.8% (initial concentration 100 mgN/L) and final selectivity to N₂ of 93.4% in 50 min under ultraviolet irradiation. Moreover, formic acid was proved as better hole scavenger compared with methanol and oxalic acid. And the concentration of formic acid had significant influence on the process of nitrate photocatalytic reduction. 0.10-MBiVO photocatalyst exhibited excellent reusability in the recycling tests, indicating its great potential in practical application of nitrate photocatalytic removal. The mechanism of the enhancement as well as reaction pathways for nitrate photocatalytic reduction on NH₂-MIL-101(Fe)/BiVO₄ were comprehensively explored and described at the end.

Selenite capture by MIL-101 (Fe) through FeOSe bonds at free coordination Fe sites

Selective immobilization of SeO₃^2- is highly desired for the remediation of Se-contaminated water. Thus, the irreversible sorption of SeO₃^2- ions by adsorbents through unique coordination bonds with high affinity is needed. Herein, we demonstrated that Fe-based metal-organic framework (MOF) (Fe-MIL-101) with free coordination sites (FCSs) enabled selective and irreversible capture of SeO₃^2- ions from aqueous solution with fast kinetics and a high uptake capacity of 183.7 mg∙g^-1, owing to large MOF apertures and substantial numbers of FCSs as capture sites through forming Fe-O-Se bonds. Meanwhile, Fe-MIL-101 maintained excellent performance in a broad pH range (4-11) and high selectivity for SeO₃^2- ions in the presence of excessive competitive anions (e.g., CO₃^2-, PO₄^3-). Density functional theory (DFT) calculation, extended X-ray absorption fine structure (EXAFS), and Mössbauer fittings confirmed that the capture on Fe-MIL-101 was through the Fe-O-Se coordination bonds between FCSs and SeO₃^2-. Moreover, Fe-MIL-101 could effectively remove SeO₃^2- in simulated natural water and sewage by overcoming the influence of co-existing ions and organic matters. This study highlights new opportunities for the design of MOF-based materials for removing toxic and radioactive anions with irreversibility and high selectivity from natural and waste water.

In Situ Mapping and Local Negative Uptake Behavior of Adsorbates in Individual Pores of Metal-Organic Frameworks

Herein, we report the adsorbate behavior in individual local pores of MIL-101, which is a metal-organic framework (MOF) with two heterogeneous mesopores and different metal sites, by combining adsorbate isotherms and in situ crystallography profiles. The in situ mapping shows that the substrate-adsorbate interaction affects the initial adsorption and pore condensation steps. The monolayer adsorption gradient changes greatly depending on the framework metal-adsorbate attraction force. Also, broad inflection points are found in adsorption isotherms, and the initial shape depends on the different metals. Besides, the capillary condensation at a pore draws adsorbates from other local pores. This leads to the local negative uptake behavior in individual pore isotherms. At higher pressure, they move to a larger space, whereas in a relatively low-pressure range the attraction force between the MOF framework and guest molecule influences the amount of rearranged guest molecules. Furthermore, the origin of the characteristic adsorption behavior based on the metals constituting the MOFs and the relative strength of substrate-adsorbate and adsorbate-adsorbate interactions are elucidated through the combined study of electron densities in pores, electron paramagnetic resonance spectroscopy spectra, and density functional theory and Monte Carlo simulations to uncover the previously veiled information on adsorption behavior.

Magnetic porous carbons derived from iron-based metal-organic framework loaded with glucose for effective extraction of synthetic organic dyes in drinks

The conversion of metal-organic frameworks (MOFs) to porous carbon has attracted extensive attention for developing multifunctional adsorbent materials. Herein, we demonstrated a facile method to prepare magnetic porous carbon via calcinating MIL-101(Fe) precursor loaded with glucose at 700 °C in an N₂ atmosphere. The obtained magnetic porous carbon (MPCG) contained plenty of oxygen-containing functional groups and exhibited an enlarged specific surface area (177.7 m²/g) compared with its precursor (41.2 m²/g). In addition, MPCG can be easily separated from the matrix by a magnet. Benefitting from these advantages, the magnetic porous carbon exhibited high affinity toward four synthetic organic dyes (amaranth, ponceau 4R, sunset yellow, and lemon yellow) in an aqueous solution. Moreover, the adsorbent can be applied to quantitatively detect synthetic organic dyes in drinks coupled with chromatography. A new magnetic solid-phase extraction method for dye analysis yielded reasonable linearity (r □ 0.99), low limits of detection (0.047-0.076 μg/L), and good precision within the analyte concentration range of 0.25-50 μg/L.

Tailoring the electron density of cobalt oxide clusters to provide highly selective superoxide and peroxide species for aerobic cyclohexane oxidation

The catalytic aerobic cyclohexane oxidation to cyclohexanol and cyclohexanone (KA oil) is an industrially relevant reaction. This work is focused on the synthesis of tailor-made catalysts based on the well-known Co₄O₄ core in order to successfully deal with cyclohexane oxidation reaction. The catalytic activity and selectivity of the synthesized catalysts can be correlated with the electronic density of the cluster, modulated by changing the organic ligands. This is not trivial in cyclohexane oxidation. Furthermore, the reaction mechanism is discussed on the basis of kinetics and spin trapping experiments, confirming that the electronic density of the catalyst has a clear influence on the distribution of the reaction products. In addition, in situ Raman spectroscopy was used to characterize the oxygen species formed on the cobalt cluster during the oxidation reaction. Altogether, it can be concluded that the catalyst with the highest oxidation potential promotes the formation of peroxide and superoxide species, which is the best way to oxidize inactivated CH bonds in alkanes. Finally, based on the results of the mechanistic studies, the contribution of these cobalt oxide clusters in each single reaction step of the whole process has been proposed.

Experimental investigations into the irregular synthesis of iron(iii) terephthalate metal-organic frameworks MOF-235 and MIL-101

MOF-235(Fe) and MIL-101(Fe) are two well-studied metal-organic frameworks (MOFs) with dissimilar crystal structures and topologies. Previously reported syntheses of the former show that it has greatly varying surface areas, indicating a lack of phase purity of the products, i.e. the possible presence of both MOFs in the same sample. To find the reason for this, we have tested and modified the commonly used synthesis protocol of MOF-235(Fe), where a 3 : 5 molar ratio of iron(iii) ions and a terephthalic acid linker is heated in a 1 : 1 DMF : ethanol solvent at 80 °C for 24 h. Using XRD and BET surface area (SA_BET) measurements, we found that it is difficult to obtain a pure phase of MOF-235, as MIL-101 also appears to form during the solvothermal treatment. Comparison of the XRD peak height ratios of the synthesis products revealed a direct correlation between the MOF-235/MIL-101 content and surface area; more MOF-235 yields a lower surface area and vice versa. In general, using a larger (3 : 1) DMF : ethanol ratio than that reported in the literature and a stoichiometric (4 : 3) Fe(iii) : TPA ratio yields a nearly pure MOF-235 product (SA_BET = 295 m² g^-1, 67% yield). An optimized synthesis procedure was developed to obtain high-surface area MIL-101(Fe) (SA_BET > 2400 m² g^-1) in a large yield and at a previously unreported temperature (80 °C vs. previously used 110-150 °C). In situ X-ray scattering was utilized to investigate the crystallization of MOF-235 and MIL-101. At 80 °C, only MOF-235 formed and at 85 and 90 °C, only MIL-101 formed.

A Zr-Based Metal-Organic Framework with a DUT-52 Structure Containing a Trifluoroacetamido-Functionalized Linker for Aqueous Phase Fluorescence Sensing of the Cyanide Ion and Aerobic Oxidation of Cyclohexane

A zirconium (Zr) metal-organic framework having a DUT-52 (DUT stands for Dresden University of Technology) structure with face-centered cubic topology and bearing the rigid 1-(2,2,2-trifluoroacetamido) naphthalene-3,7-dicarboxylic acid (H₂NDC-NHCOCF₃) ligand was prepared, and its solid structure was characterized with the help of the X-ray powder diffraction (XRPD) technique. Other characterization methods like thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy were applied to verify the phase purity of the compound. In order to get the solvent-free compound (1'), 1 was stirred with methanol for overnight and subsequently heated at 100 °C overnight under vacuum. As-synthesized (1) and activated (1') compounds are thermally stable up to 300 °C. The Brunsuer Emmett-Teller (BET) surface area of 1' was found to be 1105 m² g^-1. Fluorescence titration experiments showed that 1' exhibits highly selective and sensitive fluorescence turn-on behavior toward cyanide (CN^-) anion. The interference experiments suggested that other anions did not interfere in the detection of CN^-. Moreover, a very short response time (2 min) was shown by probe 1' for CN^- detection. The detection limit was found to be 0.23 μM. 1' can also be effectively used for CN^- detection in real water samples. The mechanism for the selective detection of CN^- was investigated systematically. Furthermore, the aerobic oxidation of cyclohexane was performed with 1' under mild reaction conditions, observing higher activity than the analogous DUT-52 solid under identical conditions. These experiments clearly indicate the benefits of hydrophobic cavities of 1' in achieving higher conversion of cyclohexane and cyclohexanol/cyclohexanone selectivity. Catalyst stability was proved by two consecutive reuses and comparing the structural integrity of 1' before and after reuses by the XRPD study.

Microwave-Assisted Air Epoxidation of Mixed Biolefins over a Spherical Bimetal ZnCo-MOF Catalyst

Here, we report the synthesis of spherical bimetal ZnCo-MOF materials by a hydrothermal rotacrystallization method and their catalytic activity on the air epoxidation of mixed biolefins enhanced by microwaves. The structural and chemical properties of the ZnCo-MOF materials were fully characterized by XRD, IR, SEM, TG, XPS, and NH₃-TPD. The morphology of the material exhibited a three-dimensional spherical structure. From an NH₃-TPD test of the ZnCo-MOF catalyst, it could be concluded that the Zn_0.1Co₁-MOF-H-150 rpm material had the highest acidic content and the strongest acidity among the catalysts synthesized by different methods, which gave the best performance in the epoxidation of mixed biolefins. The air epoxidation reaction was carried out under atmospheric pressure and microwave conditions, in the absence of any initiator or coreducing agent. Moreover, the Zn_0.1Co₁-MOF catalyst could be recycled six times without reducing the catalytic activity significantly, which showed the stability of spherical catalyst material under microwaves.

Metal-Organic Frameworks in Oxidation Catalysis with Hydrogen Peroxide

In recent years, metal–organic frameworks (MOFs) have received increasing attention as selective oxidation catalysts and supports for their construction. In this short review paper, we survey recent findings concerning use of MOFs in heterogeneous liquid-phase selective oxidation catalysis with the green oxidant–aqueous hydrogen peroxide. MOFs having outstanding thermal and chemical stability, such as Cr(III)-based MIL-101, Ti(IV)-based MIL-125, Zr(IV)-based UiO-66(67), Zn(II)-based ZIF-8, and some others, will be in the main focus of this work. The effects of the metal nature and MOF structure on catalytic activity and oxidation selectivity are analyzed and the mechanisms of hydrogen peroxide activation are discussed. In some cases, we also make an attempt to analyze relationships between liquid-phase adsorption properties of MOFs and peculiarities of their catalytic performance. Attempts of using MOFs as supports for construction of single-site catalysts through their modification with heterometals will be also addressed in relation to the use of such catalysts for activation of H2O2. Special attention is given to the critical issues of catalyst stability and reusability. The scope and limitations of MOF catalysts in H2O2-based selective oxidation are discussed.

The Selective Oxidation of Cyclohexane via In-situ H2O2 Production Over Supported Pd-based Catalysts

The oxidation of cyclohexane via the in-situ production of H2O2 from molecular H2 and O2 offers an attractive route to the current industrial means of producing cyclohexanone and cyclohexanol (KA oil), key materials in the production of Nylon. The in-situ route has the potential to overcome the significant economic and environmental concerns associated with the use of commercial H2O2, while also allowing for the use of far lower reaction temperatures than those typical of the purely aerobic route to KA oil. Herein we demonstrate the efficacy of a series of bi-functional Pd-based catalysts, which offer appreciable concentrations of KA oil, under conditions where limited activity is observed using O2 alone. In particular the introduction of V into a supported Pd catalyst is seen to improve KA oil concentration by an order of magnitude, compared to the Pd-only analogue. In particular we ascribe this improvement in catalytic performance to the development of Pd domains of mixed oxidation state upon V incorporation as evidenced through X-ray photoelectron spectroscopy.

Graphic Abstract

Insights to perfluorooctanoic acid adsorption micro-mechanism over Fe-based metal organic frameworks: Combining computational calculation with response surface methodology

Adsorption performance, interfacial interaction mechanism and contribution of pores concerning PFOA adsorption to Fe-based metal-organic frameworks (MOFs) including Fe-BTC, MIL-100-Fe and MIL-101-Fe are investigated using experiments and computational calculation at molecular level even electronic level. Fe-BTC (418 mg/g) with more Lewis acid sites demonstrates higher adsorption capacity of PFOA in comparison with MIL-100-Fe (349 mg/g) and MIL-101-Fe (370 mg/g). Adsorption isotherms and kinetics indicate presence of monolayer adsorption and chemisorption in adsorption process. The pH dependence of PFOA adsorption to Fe-based MOFs is statistically revealed by experiments and analysis of variance of response surface methodology (RSM). XPS spectra of MOF-PFOA corroborate that decreasing binding energy of Fe2p and increasing binding energy of F1s, suggesting the presence of Lewis acid/base complexing (LAB) and hydrophobic interaction in adsorption process. Differential charge demonstrates that Fe center and benzene of organic ligands are respectively electron acceptor and donor in adsorption process. Electronic level mechanism finds that LAB complexing dominates adsorption process due to highest overlap of electron cloud. Smaller pores such as triangle and pentagonal pores of Fe-based MOFs contribute to the load of PFOA, while larger hexagonal one enable PFOA to enter into cages, as revealed by computational calculation.

Exploring the Tunability of Trimetallic MOF Nodes for Partial Oxidation of Methane to Methanol

Density functional theory is used to study the tunability of trigonal prismatic SBUs found in metal-organic frameworks (MOFs) such as MIL-100, MIL-101, and PCN-250/MIL-127 of chemical composition M³⁺₂M²⁺(μ₃-O)(RCOO)₆ for the partial oxidation of methane to methanol. We performed a combinatorial screening by varying the composition of the trimetallic node (M₁³⁺)₂(M₂²⁺) (where M₁ and M₂ = V, Cr, Mn, Fe, Co, and Ni) and calculated the reaction pathway on both M₁ and M₂ sites. The systematic replacement of metals in the trimetallic cluster allowed us to study the influence of spectator atoms on the catalytic activity of a specific metal site in the cluster toward the N₂O activation and C-H bond activation steps of the reaction. In the screening, we identified the top-performing node compositions with predicted barriers lower than those already reported for experimentally tested MOFs with trigonal prismatic SBUs. This work demonstrates the opportunity to tune the catalytic activity of MOFs for redox reactions by changing their metal node composition.

Transition Metal Oxodiperoxo Complex Modified Metal-Organic Frameworks as Catalysts for the Selective Oxidation of Cyclohexane

In this work, a series of modified metal-organic frameworks (MOFs) have been prepared by pre- and post-treatment with transition metal oxodiperoxo complexes (MoO(O₂)₂, WO(O₂)₂, and KVO(O₂)₂). The obtained materials are characterized by XRD, FTIR, SEM, TEM, inductively coupled plasma atomic emission spectrometry (ICP-AES), and X-ray photoelectron spectroscopy (XPS), as well as by N₂ adsorption/desorption measurement. The characterization results show that transition metal oxodiperoxo complexes are uniformly incorporated into the MOF materials without changing the basic structures. The performance of cyclohexane oxidation on metal oxodiperoxo complex modified MOFs are evaluated. UiO-67-KVO(O₂)₂ shows the best performance for cyclohexane oxidation, with 78% selectivity to KA oil (KA oil refers to a cyclohexanol and cyclohexanone mixture) at 9.4% conversion. The KA selectivity is found to depend on reaction time, while hot-filtration experiments indicates that the catalytic process is heterogeneous with no leaching of metal species.

Iron and chromium MOFs as sustainable catalysts for transfer hydrogenation of carbonyl compounds and biomass conversions

Fe and Cr based MOFs (MIL-88B) act as efficient and reusable catalysts for transfer hydrogenation of carbonyl compounds including bio-derived substrates.

Sustainability in Catalytic Cyclohexane Oxidation: The Contribution of Porous Support Materials

The development of green and sustainable protocols for synthetic routes is a growing area of research in chemistry worldwide. The development of sustainable processes and products through innovative catalytic materials and technologies, that allow a better use of resources, is undoubtedly a very important issue facing research chemists today. Environmentally and economically advanced catalytic processes for selective alkane oxidations reactions, as is the case of cyclohexane oxidation, are now focused on catalysts’ stability and their reuse, intending to overcome the drawbacks posed by current homogeneous systems. The aim of this short review is to highlight recent contributions in heterogeneous catalysis regarding porous support materials to be applied to cyclohexane oxidation reaction. Different classes of porous materials are covered, from carbon nanomaterials to zeolites, mesoporous silicas, and metal organic frameworks. The role performed by the materials to be used as supports towards an enhancement of the activity/selectivity of the catalytic materials and the ability of recycling and reuse in consecutive catalytic cycles is highlighted.

Density functional theory study of selective aerobic oxidation of cyclohexane: the roles of acetic acid and cobalt ion

A computational study of cyclohexane autoxidation and catalytic oxidation to a cyclohexyl hydroperoxide intermediate (CyOOH), cyclohexanol, and cyclohexanone has been conducted using a hybrid density functional theory method. The activation of cyclohexane and O₂ is the rate-determining step in the formation of CyOOH due to its relatively high energy barrier of 41.2 kcal/mol, and the subsequent reaction behavior of CyOOH controls whether the production of cyclohexanol or cyclohexanone is favored. Using CH₃COOH or (CH₃COO)₂Co as a catalyst reduces the energy barriers required to activate cyclohexane and O₂ by 4.1 or 7.9 kcal/mol, respectively. Employing CH₃COOH improves the CyOOH intramolecular dehydration process, which favors the formation of cyclohexanone. The energy barrier to the decomposition of CyOOH to CyO·, an important precursor of cyclohexanol, decreases from 35.5 kcal/mol for autoxidation to 25.9 kcal/mol for (CH₃COO)₂Co catalysis. (CH₃COO)₂Co promotes the autoxidation process via a radical chain mechanism. The computational results agree with experimental observations quite well, revealing the underlying role of CH₃COOH and Co ion in cyclohexane oxidation. Graphical abstract Through DFT analysis of cyclohexane autoxidation and catalytic oxidation, we reveal the mechanism of the effects of CH₃COOH and Co²⁺ on the reaction routes.

Highly efficient removal of Pb2+ by a sandwich structure of metal–organic framework/GO composite with enhanced stability

Sandwich-structured MIL-101(Fe)/GO was successfully synthesized by a one-step hydrothermal method, and exhibited a high adsorption capacity and fast adsorption kinetics.

Metal-organic frameworks-derived core-shell Fe3O4/Fe3N@graphite carbon nanocomposites as excellent non-precious metal electrocatalyst for oxygen reduction

Metal-organic frameworks (MOFs), as precursors for synthesizing new carbon materials, hold promise for applications in the oxygen reduction reaction (ORR) as efficient non-precious metal catalysts. Here, a facile template-assisted strategy was adopted to fabricate a core-shell structure derived from MIL-101(Fe) and polyaniline. MIL-101(Fe) nanoparticles obtained by microwave-assisted synthesis were combined with PAni in different ratios and carbonized at 900 °C under flowing N2. An optimized core-shell Fe3O4/Fe3N@graphite carbon structure was successfully prepared and exhibited attractive ORR activity, with a half-wave potential of 0.916 V vs. RHE and an electron transfer number of 4.0 at 0.4 V vs. RHE. Furthermore, the catalyst displayed excellent stability in an alkaline solution. The superior ORR performance of the catalyst is mainly attributed to its stable core-shell structure, large specific surface area and high content of electrocatalytically active N species.