Advanced Electroanalysis for Electrosynthesis

Electrosynthesis is a popular, environmentally friendly substitute for conventional organic methods. It involves using charge transfer to stimulate chemical reactions through the application of a potential or current between two electrodes. In addition to electrode materials and the type of reactor employed, the strategies for controlling potential and current have an impact on the yields, product distribution, and reaction mechanism. In this Review, recent advances related to electroanalysis applied in electrosynthesis were discussed. The first part of this study acts as a guide that emphasizes the foundations of electrosynthesis. These essentials include instrumentation, electrode selection, cell design, and electrosynthesis methodologies. Then, advances in electroanalytical techniques applied in organic, enzymatic, and microbial electrosynthesis are illustrated with specific cases studied in recent literature. To conclude, a discussion of future possibilities that intend to advance the academic and industrial areas is presented.

A Theoretical Perspective to Decipher the Origin of High Hydrogen Storage Capacity in Mn(II) Metal-Organic Framework

Herein, we report a detailed periodic DFT investigation of Mn(II)-based [(Mn₄ Cl)₃ (BTT)₈ ]^3- (BTT^3- =1,3,5-benzenetristetrazolate) metal-organic framework (MOF) to explore various hydrogen binding pockets, nature of MOF…H₂ interactions, magnetic coupling and, H₂ uptake capacity. Earlier experiments found an uptake capacity of 6.9 wt % of H_2, with the heat of adsorption estimated to be ∼10 kJ/mol, which is one among the highest for any MOFs reported. Our calculations unveil different binding sites with computed binding energy varying from -6 to -15 kJ/mol. The binding of H₂ at the Mn²⁺ site is found to be the strongest (site I), with H₂ found to bind Mn²⁺ ion in a η² fashion with a distance of 2.27 Å and binding energy of -15.4 kJ/mol. The bonding analysis performed using NBO and AIM reveal a strong donation of σ (H₂ ) to the d_z ² orbital of the Mn²⁺ ion responsible for such large binding energy. The other binding pockets, such as -Cl (site II) and BTT ligands (site III and IV) were found to be weaker, with the binding energy decreasing in the order I>II>III>IV. The average binding energy computed for these four sites put together is 9.6 kJ/mol, which is in excellent agreement with the experimental value of ∼10 kJ/mol. We have expanded our calculations to compute binding energy for multiple sites simultaneously, and in this model, the binding energy per site was found to decrease as we increased the number of H₂ molecules suggesting electronic and steric factors controlling the overall uptake capacity. The calculated adsorption isotherm using the GCMC method reproduces the experimental observations. Further, the magnetic coupling computed for the unbound MOF reveals moderate ferromagnetic and strong antiferromagnetic coupling within the tetrameric {Mn₄ } unit leading to a three-up-one-down spin configuration as the ground state. These were then coupled ferromagnetically to other tetrameric units in the MOF network. The magnetic coupling was found to alter only marginally upon gas binding, suggesting that both exchange interaction and the spin-states are unlikely to play a role in the H₂ uptake. This is contrary to the O₂ uptake studied lately, where strong dependence on exchange-coupling/spin state was witnessed, suggesting exchange-coupling/magnetic field dependent binding as a viable route for gas separation.

Catalytic Oxidation of Benzoins by Hydrogen Peroxide on Nanosized HKUST-1: Influence of Substituents on the Reaction Rates and DFT Modeling of the Reaction Path

In this research, the oxidation of a series of benzoins, R-C(=O)-CH(OH)-R, where R = phenyl, 4-methoxyphenyl, 4-bromophenyl, and 2-naphthyl, by hydrogen peroxide in the presence of nanostructured HKUST-1 (suspension in acetonitrile/water mixture) was studied. The respective benzoic acids were the only products of the reactions. The initial average reaction rates were experimentally determined at different concentrations of benzoin, H₂O₂ and an effective concentration of HKUST-1. The sorption of the isotherms of benzoin, dimethoxybenzoin and benzoic acid on HKUST-1, as well as their sorption kinetic curves, were measured. The increase in H₂O₂ concentration expectedly led to an acceleration of the reaction. The dependencies of the benzoin oxidation rates on the concentrations of both benzoin and HKUST-1 passed through the maxima. This finding could be explained by a counterplay between the increasing reaction rate and increasing benzoin sorption on the catalyst with the increase in the concentration. The electronic effect of the substituent in benzoin had a significant influence on the reaction rate, while no relation between the size of the substrate molecule and the rate of its oxidation was found. It was confirmed by DFT modeling that the reaction could pass through the Baeyer-Villiger mechanism, involving an attack by the HOO^- anion on the C atom of the activated C=O group.

Enzyme Immobilization on Metal Organic Frameworks: the Effect of Buffer on the Stability of the Support

Metal organic frameworks (MOFs) have been used to encapsulate an array of enzymes in a rapid and facile manner; however, the stability of MOFs as supports for enzymes has not been examined in detail. This study examines the stability of MOFs with different compositions (Fe-BTC, Co-TMA, Ni-TMA, Cu-TMA, and ZIF-zni) in buffered solutions commonly used in enzyme immobilization and biocatalysis. Stability was assessed via quantification of the release of metals by inductively coupled plasma optical emission spectroscopy. The buffers used had varied effects on different MOF supports, with incubation of all MOFs in buffers resulting in the release of metal ions to varying extents. Fe-BTC was completely dissolved in citrate, a buffer that has a profound destabilizing effect on all MOFs analyzed, precluding its use with MOFs. MOFs were more stable in acetate, potassium phosphate, and Tris HCl buffers. The results obtained provide a guide for the selection of an appropriate buffer with a particular MOF as a support for the immobilization of an enzyme. In addition, these results identify the requirement to develop methods of improving the stability of MOFs in aqueous solutions. The use of polymer coatings was evaluated with polyacrylic acid (PAA) providing an improved level of stability. Lipase was immobilized in Fe-BTC with PAA coating, resulting in a stable biocatalyst with retention of activity in comparison to the free enzyme.

Metal-Organic Frameworks for NOx Adsorption and Their Applications in Separation, Sensing, Catalysis, and Biology

Nitrogen oxide (NO_x ) is a family of poisonous and highly reactive gases formed when fuel is burned at high temperatures during anthropogenic behavior. It is a strong oxidizing agent that significantly contributes to the ozone and smog in the atmosphere. Thus, NO_x removal is important for the ecological environment upon which the civilization depends. In recent decades, metal-organic frameworks (MOFs) have been regarded as ideal candidates to address these issues because they form a reticular structure between proper inorganic and organic constituents with ultrahigh porosity and high internal surface area. These characteristics render them chemically adaptable for NO_x adsorption, separation, sensing, and catalysis. In additional, MOFs enable potential nitric oxide (NO) delivery for the signaling of molecular NO in the human body. Herein, the different advantages of MOFs for coping with current environmental burdens and improving the habitable environment of humans on the basis of NO_x adsorption are reviewed.

A Review on Metal-Organic Frameworks as Congenial Heterogeneous Catalysts for Potential Organic Transformations

Metal-organic frameworks (MOFs) have emerged as versatile candidates of interest in heterogeneous catalysis. Recent research and developments with MOFs positively endorse their role as catalysts in generating invaluable organic compounds. To harness the full potential of MOFs in value-added organic transformation, a comprehensive look at how these materials are likely to involve in the catalytic processes is essential. Mainstays of MOFs such as metal nodes, linkers, encapsulation materials, and enveloped structures tend to produce capable catalytic active sites that offer solutions to reduce human efforts in developing new organic reactions. The main advantages of choosing MOFs as reusable catalysts are the flexible and robust skeleton, regular porosity, high pore volume, and accessible synthesis accompanied with cost-effectiveness. As hosts for active metals, sole MOFs, modified MOFs, and MOFs have made remarkable advances as solid catalysts. The extensive exploration of the MOFs possibly led to their fast adoption in fabricating new biological molecules such as pyridines, quinolines, quinazolinones, imines, and their derivatives. This review covers the varied MOFs and their catalytic properties in facilitating the selective formation of the product organic moieties and interprets MOF’s property responsible for their elegant performance.

Vapor Deposition-Prepared MIL-100(Cr)- and MIL-101(Cr)-Supported Iron Catalysts for Effectively Removing Organic Pollutants from Water

Metal organic framework (MOF)-supported Fe catalysts belong to an important class of catalysts used for the advanced oxidation of organic pollutants in water. The successful preparation of the Fe/MIL-100(Cr) and Fe/MIL-101(Cr) catalysts in this work reinforced that a recently established carrier-gas free vapor deposition method can be a general one for preparing Fe/MOF catalysts. The Fe loading was in the range of 7.8-27.2 wt % on Fe/MIL-101(Cr) at a deposition temperature of 110-150 °C, and it was only 4.35 wt % on Fe/MIL-100(Cr) at 110 °C in comparison. The results obtained from the characterization using the N2-isotherm and EDX mapping showed that the Fe components resided uniformly within the pore of the MOF supports. Both of Fe/MIL-100(Cr) and Fe/MIL-101(Cr) were rather effective for the catalytic removal of aniline from water with Fenton oxidation. Fe/MIL-100(Cr) can effectively remove the total organic carbon (TOC) of the aniline solutions, while Fe/MIL-101(Cr) had a lower TOC removal efficiency. Both of the Fe/MIL-100(Cr) and Fe/MIL-101(Cr) catalysts showed good stability in the crystalline form compared to the previously prepared Fe/UiO-66 catalyst, implicating that they can be potentially more useful than Fe/UiO-66 for treating organic pollutants in water.

High loading of Mn(ii)-metalated porphyrin in a MOF for photocatalytic CO2 reduction in gas-solid conditions

A high loading of Mn(ii)-metalated porphyrin was achievable in a 2D porphyrin-based Mn-MOF induced by an ionic liquid. The excellent stability, sufficient redox potential, atomically dispersed porphyrin Mn(ii) sites, desired CO₂ affinity, high visible light-harvesting and efficient charge separation, endow this MOF with the overall photocatalytic conversion of CO₂ to CH₄ in gas-solid conditions.

Polyoxometalate-based metal–organic frameworks for heterogeneous catalysis

POM-based MOFs simultaneously possessing the virtues of POMs and MOFs exhibit excellent heterogeneous catalytic properties.

Trinuclear Mn2+/Zn2+ based microporous coordination polymers as efficient catalysts for ipso-hydroxylation of boronic acids

Two microporous coordination polymers based on hourglass trinuclear building units, [Mn₃(bpdc)₃(bpy)]·2DMF and [Zn₃(bpdc)₃(bpy)]·2DMF·4H₂O (bpdc = 4,4'-biphenyl dicarboxylic acid, bpy = 4,4'-bipyridine), have been synthesized under solvothermal conditions employing DMF as the solvent. Each structure consists of two crystallographically distinct M²⁺ (M1 and M2) centers that are connected via carboxylate bridges from six bpdc ligands, generating a trinuclear metal cluster, [M₃(bpdc)₃(bpy)]. Cluster representation of the structure resulted in an interpenetrated net of rare hex topological type. Catalytic activities of the CPs have been assessed for the oxidative hydroxylation of phenylboronic acids (PBAs) using aqueous hydrogen peroxide (H₂O₂). Various substituted aryl/hetero-arylboronic acids RB(OH)₂ [R = phenyl, 2,4-difluorophenyl, 4-aminophenyl, 2-thiophene etc.] underwent ipso-hydroxylation smoothly at room temperature to generate the corresponding phenols in excellent yields. The main advantages of this protocol are the aqueous medium reaction, heterogeneous catalytic system, and short reaction time with excellent yield.

UiO-66-supported Fe catalyst: a vapour deposition preparation method and its superior catalytic performance for removal of organic pollutants in water

A vapour deposition (VD) method was established for preparation of the UiO-66-supported Fe (Fe/UiO-66) catalyst, which provided the first case of the metal-organic framework (MOF)-supported Fe catalyst prepared by using the vapour-based method. The Fe loading was around 7.0-8.5 wt% under the present preparation conditions. The crystal structure of UiO-66 was not obviously influenced by the Fe loading, while the surface area significantly decreased, implicating most of the Fe components resided in the pores on UiO-66. The results for the methyl orange (MO) removal tests showed that MO in aqueous solution can be removed by UiO-66 by adsorption, and in contrast, it can be oxidized by H2O2 with the catalysis of Fe/UiO-66. Further catalytic tests showed that Fe/UiO-66 was rather effective to catalyse the oxidation of benzene derivatives like aniline in water in terms of chemical oxygen demand (COD) removal efficiency. The catalytic test results for Fe/UiO-66 were compared to those of Fe/Al2O3 with the same Fe loading and to the catalysts reported in the literature. This paper provides a general strategy for VD preparation of MOF-supported Fe catalyst on the one hand, and new catalysts for removing organic pollutants from water, on the other hand.

Metal Organic Framework with Coordinatively Unsaturated Sites as Efficient Fenton-like Catalyst for Enhanced Degradation of Sulfamethazine

A novel Fenton-like catalyst, metal organic framework MIL-100(Fe) with Fe^II/Fe^III mixed-valence coordinatively unsaturated iron center (CUS-MIL-100(Fe)), was synthesized, characterized, and used for the degradation of sulfamethazine (SMT). The catalytic performance of CUS-MIL-100(Fe) was investigated on the basis of various parameters, including initial pH, H₂O₂ concentration, catalyst dosage, and initial SMT concentration. The results showed that CUS-MIL-100(Fe) could effectively degrade SMT, with almost 100% removal efficiency within 180 min (52.4% mineralization efficiency), under the reaction conditions of pH 4.0, 20 mg L^-1 SMT, 6 mM H₂O₂, and 0.5 g L^-1 catalyst. Moreover, CUS-MIL-100(Fe) displayed a higher catalytic activity than that of MIL-100(Fe) for SMT degradation. Combined with the physical-chemical characterization, the enhanced catalytic activity can be ascribed to the incorporation of Fe^II and Fe^III CUSs (coordinatively unsaturated metal sites), the large specific surface area, as well as the formation of mesopores. Furthermore, CUS-MIL-100(Fe) exhibited a good stability and reusability. The possible catalytic mechanism of CUS-MIL-100(Fe) was tentatively proposed.

Homochiral metal–organic frameworks as heterogeneous catalysts

Homochiral metal–organic frameworks (HMOFs) are attractive materials for asymmetric catalysis because they possess high surface area and uniform active sites.

An efficient and sustainable catalytic reduction of carbon–carbon multiple bonds, aldehydes, and ketones using a Cu nanoparticle decorated metal organic framework

Economical, reusable, eco-friendly sustainable process is reported that involve low amount of hydrazine hydrate.

Coordination supramolecules with oxazoline-containing ligands

This highlight focuses on the recent development of oxazoline-based discrete coordination complexes and coordination polymers.

Enhanced performance for Eu(iii) ion remediation using magnetic multiwalled carbon nanotubes functionalized with carboxymethyl cellulose nanoparticles synthesized by plasma technology

Synthesis of sodium carboxymethyl cellulose/iron oxides/MWCNTs composites by a plasma technique and their application to the decontamination of europium ions from aqueous solutions under controlled laboratory conditions.

Incorporation of Molecular Catalysts in Metal-Organic Frameworks for Highly Efficient Heterogeneous Catalysis

Porous metal-organic frameworks (MOFs) are built from periodically alternate organic moieties and metal ions/clusters. The unique features of the open framework structures, the high surface areas, the permanent porosity, and the appropriate hydrophilic and hydrophobic pore nature mean that MOF materials are a class of ideal host matrices for immobilization of molecular catalysts. The emerging porous materials can not only retain but are also able to enhance the catalytic functions of the single individuals. MOF catalysts have the following super characters: i) uniformly dispersed catalytic sites on the pore surfaces to improve the utility, ii) appropriate hydrophilic and hydrophobic pore nature to facilitate the recognition and transportation of reactant and product molecules, iii) a collaborative microenvironment to realize synergistic catalysis, and iv) simple separation and recovery for long-term usage. Accompanying the development of the synthetic strategies and the technologies for the characterization of MOF materials, MOF catalysis has undergone an upsurge, which has transcended the stage of opportunism. Here, the rational design and synthesis of MOF catalysts are discussed, along with the key factors of active sites, microenvironments, and transmission channels that lead to the distinct catalytic properties of MOF catalysts.

Unravelling chromism in metal–organic frameworks

Chromophoric MOFs are reviewed, focussing on those which change colour on application of external stimuli such as heat, pressure, light or chemical environment.

Fe3O4@HKUST-1 and Pd/Fe3O4@HKUST-1 as magnetically recyclable catalysts prepared via conversion from a Cu-based ceramic

A Fe₃O₄/Cu- ceramic system converted into a magnetic HKUST-1 composite was used as a recyclable catalyst for one-pot cascade and hydrogenation reactions.

Design and synthesis of coordination polymers with chelated units and their application in nanomaterials science

The advances and problems associated with the preparation, properties and structure of coordination polymers with chelated units are presented and assessed.

Fe-based metal organic framework/graphene oxide composite as an efficient catalyst for Fenton-like degradation of methyl orange

A MIL-100(Fe)/graphene oxide (GO) composite was prepared by a one-step hydrothermal method and utilized as a heterogeneous Fenton-like catalyst for methyl orange (MO) degradation.

Synthesis of Fe/M (M = Mn, Co, Ni) bimetallic metal organic frameworks and their catalytic activity for phenol degradation under mild conditions

Results show that the incorporation of Mn can significantly promote the catalytic process, Co exhibits no obviously favorable behavior, and Ni presents an apparently inhibitory impact.

Tuning the iron redox state inside a microporous porphyrinic metal organic framework

Tuning the iron redox state inside a microporous porphyrinic metal organic framework.

NiO-PTA supported on ZIF-8 as a highly effective catalyst for hydrocracking of Jatropha oil

Nickel oxide (NiO) and phosphotungstic acid (PTA) supported on a ZIF-8 (NiO-PTA/ZIF-8) catalyst was first synthesized and it showed high activity and good selectivity for the hydrocracking of Jatropha oil. The catalyst was characterized by SEM, SEM-EDS, TEM, N₂ adsorption, FT-IR, XRD and XPS. Compared with the NiO-PTA/Al₂O₃ catalyst, the selectivity of C15-C18 hydrocarbon increased over 36%, and catalytic efficiency increased 10 times over the NiO-PTA/ZIF-8 catalyst. The prepared NiO-PTA/ZIF-8 catalyst was stable for a reaction time of 104 h and the kinetic behavior was also analyzed. This catalyst was found to bypass the presulfurization process, showing promise as an alternative to sulfided catalysts for green diesel production.

A strategically designed porous magnetic N-doped Fe/Fe3C@C matrix and its highly efficient uranium(vi) remediation

Magnetic N-doped Fe/Fe₃C@C derived from metal–organic frameworks and highly efficient U(vi)-contaminated wastewater remediation.

Two-step warming solvothermal syntheses, luminescence and slow magnetic relaxation of isostructural dense LnMOFs based on nanoscale 3-connected linkers

Two isostructural 3D dense LnMOFs exhibiting either photoluminescence or slow magnetic relaxation are assembled under two-step warming solvothermal conditions.

Ionothermal synthesis, magnetic transformation and hydration–dehydration properties of Co(ii)-based coordination polymers

A series of low-coordinated coordination polymers obtained under an ionic liquid medium exhibit interesting hydration–dehydration behaviour and magnetic transformations.

AIE-active tetraphenylethene functionalized metal–organic framework for selective detection of nitroaromatic explosives and organic photocatalysis

A luminescent MOF containing an AIE-active TPE moiety works as a selective sensor for detecting nitroaromatic explosives, as well as an efficient heterogeneous photocatalyst for CDC reactions mediated by visible light.

Crystal structure of an unknown solvate of {2,2'-[ethane-1,2-diylbis(nitrilo-methanylyl-idene)]diphenolato-κ(4) O,N,N',O'}(N-ferrocenylisonicotinamide-κN (1))cobalt(II): a Co(II)-salen complex that forms hydrogen-bonded dimers

The title compound, [CoFe(C5H5)(C16H14N2O2)(C11H9N2O)], was prepared as an air-stable red-brown solid by mixing equimolar amounts of {2,2'-[ethane-1,2-diylbis(nitrilo-methanylyl-idene)]diphenolato}cobalt(II) and N-ferrocenylisonicotinamide in dry di-chloro-methane under nitro-gen and was characterized by ESI-MS, IR, and single-crystal X-ray diffraction. The structure at 100 K has triclinic (P-1) symmetry and indicates that the complex crystallizes as a mixture of λ and δ conformers. It exhibits the expected square pyramidal geometry about Co, and forms hydrogen-bonded dimers through amide N-H groups and phenolate O atoms on an adjacent mol-ecule. The involvement of only half of the salen ring structure in hydrogen-bonding inter-actions results in slight folding of the salen ring away from the pyridine coordination site in the δ conformer with an inter-salicyl-idene fold angle of 9.9 (7)°. In contrast, the λ conformer is nearly planar. The dimers pack into an open structure containing channels filled with highly disordered solvent mol-ecules. These solvent molecules' contributions to the intensity data were removed with the SQUEEZE procedure [Spek (2015). Acta Cryst. C71, 9-18] available in PLATON.

Designed synthesis of a series of zwitterion–polyoxometalate hybrid materials for selective scavenging and photolysis of dyes

An effective strategy to immobilize both zwitterion and POM moieties into porous hybrid materials was developed. These materials demonstrate remarkable efficiency for selective scavenging and photolysis of cationic dyes from polluted water.

Positioning of the HKUST-1 metal–organic framework (Cu3(BTC)2) through conversion from insoluble Cu-based precursors

A Cu-based metal–organic framework (HKUST-1) was synthesized from insoluble precursors and positioned using sol–gel based coatings.

Preparation and catalytic properties of Pd nanoparticles supported on micro-crystal DUT-67 MOFs

The obtained Pd/DUT-67 composites exhibited high catalytic performance in Suzuki coupling and nitrobenzene hydrogenation reactions.

A porous metal–organic framework containing multiple active Cu2+sites for highly efficient cross dehydrogenative coupling reaction

A 3D porous metal–organic framework, containing multiple coordination unsaturated Cu^IIsites, is highly active in the catalytic cross dehydrogenative coupling reaction.