Pd-grafted open metal site copper-benzene-1,4-dicarboxylate metal organic frameworks (Cu-BDC MOF’s) as promising interfacial catalysts for sustainable Suzuki coupling

Encapsulation of metal oxide nanoparticles inside metal-organic frameworks via surfactant-assisted nanoconfined space

Encapsulation of metal oxide nanoparticles (MO NPs) inside metal-organic frameworks (MOFs) has been realized successfully via surfactant-assisted nano-confined space strategy, which is a universal method for various MO NPs@MOFs. The size of MO NPs was limited by the confined nano-space and could be adjusted to a certain extent. The synthesis mechanism of MO NPs@MOFs was revealed via detailed structural characterizations and a series of control experiments. Surfactants introduced during MOFs (CuBDC, BDC = 1,4-benzenedicarboxylic acid) formation process plays a very important role in producing uniform voids of nano-confined space. Cu ions in MOF frameworks were directly used as precursors to fabricate CuO NPs in these confined void spaces. The synthesized CuO@CuBDC composites showed excellent catalytic activity in C-S cross-coupling reactions and dye pollutant photo-degradation reactions.

Boosting Aerobic Oxidation of Alcohols via Synergistic Effect between TEMPO and a Composite Fe3O4/Cu-BDC/GO Nanocatalyst

Fabrication of a nanocomposite catalyst via a novel and efficient strategy remains a challenge; Fe₃O₄ nanoparticles anchored on graphene oxide (GO) sheet-supported metal-organic frameworks (MOFs). In this study, the physicochemical properties of the ensuing Fe₃O₄/Cu-BDC/GO are investigated using Fourier transform infrared spectrum, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray detector, and atomic absorption spectroscopy. The salient features of the nanocomposite such as Cu-MOF, synergistic effect with GO sheets, and magnetic separation characteristics make it an excellent ternary heterostructure for aerobic oxidation of alcohols. The proposed nanocatalyst and co-catalyst 2,2,6,6-tetramethylpiperidine-N-oxyl substantially enhance the catalytic performance for the aerobic oxidation under very mild and sustainable reaction conditions. The heterogeneity of Fe₃O₄/Cu-BDC/GO composite catalyst is affirmed with the added advantage that the initial activity is well maintained even after seven cycles.

Iron-copper bimetallic metal-organic frameworks for efficient Fenton-like degradation of sulfamethoxazole under mild conditions

Iron and copper bimetallic MOF material (Fe_xCu_1-x(BDC)) as a novel Fenton-like catalyst was prepared by a simple solvothermal method, and its performances were evaluated in the catalytic degradation of sulfamethoxazole (SMX) in the presence of hydrogen peroxide. The results indicated that the Fe_xCu_1-x(BDC)/H₂O₂ system was highly effective for SMX degradation over a wide pH range (4.0-8.6). At initial solution pH of 5.6, the bimetallic Fe_0.75Cu_0.25(BDC) catalyst exhibited a 100% SMX (20 mg L^-1) removal within 120 min, which was superior to the SMX removal efficiency over monometallic Fe(BDC) and Cu(BDC) catalysts. Combined with the physical-chemical characterization, the synergistic effect between Fe and Cu species were responsible for the efficient catalytic activity. Moreover, the Fe_0.75Cu_0.25(BDC) catalyst showed good reusability for SMX degradation. The possible reaction mechanism in Fe_xCu_1-x(BDC)/H₂O₂ system was also tentatively proposed. This work has not only suggested the potential of bimetallic Fe_xCu_1-x(BDC) catalysts in Fenton-like treatment of antibiotics, but also provided useful information to develop MOF-based catalysts for efficient environmental remediation.

Cu-metal organic frameworks (Cu-MOF) as an environment-friendly and economical catalyst for one pot synthesis of tacrine derivatives

The present work describes the catalytic activity of Cu-MOF for the one-pot synthesis of tacrine derivatives via a four-component reaction of 2-hydroxynaphthalene-1,4-dione, aldehydes, malononitrile and cycloketones in the presence of AlCl3. The structure of the synthesized compound is confirmed by 1H NMR, 13C NMR, IR, and MASS. The catalyst prepared under pressure is characterized by powder X-ray diffraction and SEM. The noteworthy advantages of this procedure include its broad substrate scope, high yields up to 93%, atom economy, using readily available starting materials and a powerful recyclable nano catalyst. Additionally, there is no need to use column chromatography for purifying products so, it has the potential for large-scale applications in pharmaceutical industries. Another advantage of this method is the ability to recycle the catalyst up to 3 times and reuse it.

Coordinatively unsaturated metal sites (open metal sites) in metal–organic frameworks: design and applications

The defined synthesis of OMS in MOFs is the basis for targeted functionalization through grafting, the coordination of weakly binding species and increased (supramolecular) interactions with guest molecules.

Engineering Metal-Organic Framework Catalysts for C-C and C-X Coupling Reactions: Advances in Reticular Approaches from 2014-2018

Metal-organic frameworks (MOFs) are a class of crystalline porous materials that have been actively used for several industrial and synthetic applications. MOFs are spatially and geometrically extrapolated coordination polymers with intriguing properties such as tunable porosity and dimensionality. In terms of their catalytic efficiency, MOFs combine the easy recoverability of heterogeneous catalysts with the increased selectivity of biological catalysts. It is therefore not surprising that a lot of work on optimizing MOF catalysts for organic transformations has been carried out over the past decade. In this review, recent developments in MOF catalysis are summarized, with special attention being paid to C-C, C-N, and C-O coupling reactions. The influence of pore size, pore environment, and load on catalytic activity is described. Post-synthetic stabilization techniques and host-guest interactions in caged MOF scaffolds are detailed. Mechanistic aspects pertaining to the use of MOFs in asymmetric heterogeneous catalysis are highlighted and categorized.

Preparation of polydopamine-modified zeolitic imidazolate framework-8 functionalized electrospun fibers for efficient removal of tetracycline

This work shows a simple and environmental friendly methodology to obtain a kind of polydopamine coating assisted preparation of zeolitic imidazolate framework-8 (ZIF-8) functionalized composite electrospun fiber (ZIF-8/PDA/PAN fibers) adsorbent. Characterization of the composite electrospun fiber was carried out and the tetracycline (TC) adsorption properties from water were also studied in detail. At the same time, principle adsorption mechanisms were thoroughly studied. The results show that the pseudo-second-order model can simulate sorption kinetics well, while sorption isotherms are able to significantly conform to the Freundlich model, and the adsorption capacity of the fibers can reach 478.18 mg/g at 298 K. In addition, the Weber-Morris model indicates that the processes of adsorption of ZIF-8/PDA/PAN fibers for TC involve surface adsorption as well as intraparticle diffusion, and the limit rate step is not only the intraparticle diffusion but also the binding of the sorbate to the sorbent. Moreover, the adsorption efficiency toward TC by ZIF-8/PDA/PAN fibers still reached over 85% of its initial adsorption capacity after five adsorption/desorption cycles, which signified that the adsorbents is stable and recyclable. This work indicates that the obtained ZIF-8/PDA/PAN fibers have practical application prospects in the field of antibiotic adsorption.

Monometallic and bimetallic Cu–Ag MOF/MCM-41 composites: structural characterization and catalytic activity

Monometallic and bimetallic MOF/MCM-41 composites (Cu, Ag and Cu–Ag) were synthesized via a solvothermal method. The synthesized composites were characterized by XRD, FTIR, SEM, EDX and BET surface area measurements. The acidity was determined through two techniques; potentiometric titration with n-butyl amine for determining the strength and the total number of acid sites and FTIR spectra of chemisorbed pyridine on the surface of MOFs for determining the type of acid sites (Brønsted and/or Lewis). All the prepared MOFs showed Lewis-acid sites and the higher acidity was observed for the bimetallic Cu–Ag MOF/MCM-41 composite. The catalytic activity was examined on the synthesis of 1-amidoalkyl-2-naphthol via the reaction of benzaldehyde, 2-naphthol and benzamide. The best yield (92.86%) was obtained in the least time (10 min) with a molar ratio 1.2 : 1.2 : 1.7 of benzaldehyde : β-naphthol : benzamide and 0.1 g bimetallic Cu–Ag MOF/MCM-41 composite under solvent-free conditions at 130 °C. Reuse of the catalysts showed that they could be used at least four times without any reduction in the catalytic activity.

Monometallic and bimetallic MOF/MCM-41 composites (Cu, Ag and Cu–Ag) were synthesized via a solvothermal method.

PdII Immobilized on Ferromagnetic Multi-Walled Carbon Nanotubes Functionalized by Aminated 2-Chloroethylphosphonic Acid with S-Methylisothiourea (FMMWCNTs@CPA@SMTU@PdII NPs) Applied as a Highly Efficient and Recyclable Nanostructured Catalyst for Suzuki–Miyaura and Mizoroki–Heck Cross-Coupling Reactions in Solvent-Free Conditions

The new ferromagnetic nanostructured FMMWCNTs@CPA@SMTU@PdII NPs (IV) as an eco-friendly heterogeneous nanocatalyst with a particle size of ~20–30nm reported earlier by our group has been found to be very effective for Suzuki–Miyaura and Mizoroki–Heck cross-coupling reactions at ambient temperature. The procedure has been applied for a wide range of aryl halides, arylboronic acids, and alkenes. The magnetic separation by an external magnetic field, mild reaction conditions, and catalyst reusability up to four times without significant decrease in catalytic activity (reduced catalytic activity from 11 to 18% in the fifth, sixth, and seventh cycles) made the present method sustainable and economically viable for C–C cross-coupling reactions.

Highly Effective Removal of Metal Cyanide Complexes and Recovery of Palladium Using Quaternary-Ammonium-Functionalized MOFs

In this study, quaternary-ammonium-functionalized metal–organic frameworks (MOFs) Et-N-Cu(BDC-NH₂)(DMF), were prepared, characterized, and applied for the highly effective removal of metal cyanide complexes, including Pd(CN)₄²⁻, Co(CN)₆³⁻, and Fe(CN)₆³⁻. Batch studies were carried out, and the maximum adsorption capacities of Pd(II), Co(III), and Fe(III) reached 172.9, 101.0, and 102.6, respectively. Adsorption was rapid, and equilibrium was established within 30 min. Et-N-Cu(BDC-NH₂)(DMF) exhibited high thermal and chemical stability. Furthermore, absorbed Pd(CN)₄²⁻ was selectively recovered by two-step elution. First, Co(CN)₆³⁻ and Fe(CN)₆³⁻ were eluted with a 1.5 mol L⁻¹ KCl solution. Elution rates of Co(CN)₆³⁻ and Fe(CN)₆³⁻ were greater than 98.0%, whereas the elution percentage of Pd(CN)₄²⁻ was less than 2.0%. Second, >97.0% Pd(CN)₄²⁻ on the loaded MOFs was eluted using a 2.0 mol L⁻¹ KI solution. The recovery rate of Pd(CN)₄²⁻ was greater than 91.0% after five testing cycles. Adsorption isotherms, kinetics models, and adsorption thermodynamics of Pd(CN)₄²⁻ on Et-N-Cu(BDC-NH₂) (DMF) were also systematically investigated. The Et-N-Cu(BDC-NH₂) (DMF) absorbent exhibited a rapid, excellent ability for the adsorption of metal cyanide complexes.