Fe₃O₄@MOF core-shell magnetic microspheres as excellent catalysts for the Claisen-Schmidt condensation reaction

CoFe2O4@MIL-100(Fe) hybrid magnetic nanoparticles exhibit fast and selective adsorption of arsenic with high adsorption capacity

In this study, we report the synthesis and application of mesoporous CoFe₂O₄@MIL-100(Fe) hybrid magnetic nanoparticles (MNPs) for the simultaneous removal of inorganic arsenic (iAs). The hybrid adsorbent had a core-shell and mesoporous structure with an average diameter of 260 nm. The nanoscale size and mesoporous character impart a fast adsorption rate and high adsorption capacity for iAs. In total, 0.1 mg L⁻¹ As(V) and As(III) could be adsorbed within 2 min, and the maximum adsorption capacities were 114.8 mg g⁻¹ for As(V) and 143.6 mg g⁻¹ for As(III), higher than most previously reported adsorbents. The anti-interference capacity for iAs adsorption was improved by the electrostatic repulsion and size exclusion effects of the MIL-100(Fe) shell, which also decreased the zero-charge point of the hybrid absorbent for a broad pH adsorption range. The adsorption mechanisms of iAs on the MNPs are proposed. An Fe-O-As structure was formed on CoFe₂O₄@MIL-100(Fe) through hydroxyl substitution with the deprotonated iAs species. Monolayer adsorption of As(V) was observed, while hydrogen bonding led to the multi-layer adsorption of neutral As(III) for its high adsorption capacity. The high efficiency and the excellent pH- and interference-tolerance capacities of CoFe₂O₄@MIL-100(Fe) allowed effective iAs removal from natural water samples, as validated with batch magnetic separation mode and a portable filtration strategy.

A magnetic metal–organic framework as a highly active heterogeneous catalyst for one-pot synthesis of 2-substituted alkyl and aryl(indolyl)kojic acid derivatives

A novel magnetic metal–organic framework, NiFe₂O₄@MOF-5, was prepared and demonstrated to be a highly efficient catalyst for the one-pot three-component reaction of aldehyde, indole, and kojic acid.

Incorporation of CuO NPs into modified UiO-66-NH2 metal–organic frameworks (MOFs) with melamine for catalytic C–O coupling in the Ullmann condensation

The UiO-66-NH₂ is initially modified with melamine via a post-synthetic approach. CuO NPs are then anchored via the available functional groups on the surface of the modified MOF.

Cu2O-directed in situ growth of Au nanoparticles inside HKUST-1 nanocages

Controllable integration of metal nanoparticles (MNPs) and metal-organic frameworks (MOFs) is attracting considerable attention as the obtained composite materials always show synergistic effects in applications of catalysis, delivery, as well as sensing. Herein, a Cu₂O-directed in situ growth strategy was developed to integrate Au nanoparticles and HKUST-1. In this strategy, Cu₂O@HKUST-1 core-shell heterostructures, HKUST-1 nanocages, Cu₂O@Au@HKUST-1 sandwich core-shell heterostructures and Au@HKUST-1 balls-in-cage heterostructures were successfully synthesized. Cu₂O@HKUST-1 core-shell heterostructures were synthesized by soaking Cu₂O nanocrystals in benzene-1,3,5-tricarboxylic acid solution. The well-defined Cu₂O@HKUST-1 core-shell heterostructures were demonstrated to be dominated by the ratio of Cu²⁺ cations to btc^3- ligands in solution during the period of HKUST-1 formation. Cu₂O@Au@HKUST-1 sandwich core-shell or Au@HKUST-1 balls-in-cage heterostructures were obtained by impregnating HAuCl₄ into Cu₂O@HKUST-1 core-shell heterostructures. Due to the porosity of HKUST-1 and reducibility of Cu₂O, HAuCl₄ could pass through the HKUST-1 shell and be reduced by the Cu₂O core in situ forming Au nanoparticles. Finally, CO oxidation reaction at high temperatures was carried out to assess the catalytic functionality of the obtained composite heterostructures. This strategy can circumvent some drawbacks of the existing approaches for integrating MNPs and MOFs, such as nonselective deposition of MNPs at the outer surface of the MOF matrices, extreme treatment conditions and additional surface modifications.

Preparation of Cu@Cu₂O Nanocatalysts by Reduction of HKUST-1 for Oxidation Reaction of Catechol

HKUST-1, a copper-based metal organic framework (MOF), has been investigated as a catalyst in various reactions. However, the HKUST-1 shows low catalytic activity in the oxidation of catechol. Therefore, we synthesized Fe₃O₄@HKUST-1 by layer-by layer assembly strategy and Cu@Cu₂O by reduction of HKUST-1 for enhancement of catalytic activity. Cu@Cu₂O nanoparticles exhibited highly effective catalytic activity in oxidation of 3,5-di-tert-butylcatechol. Through this method, MOF can maintain the original core-shell structure and be used in various other reactions with enhanced catalytic activity.

Surface modification of hollow magnetic Fe3O4@NH2-MIL-101(Fe) derived from metal-organic frameworks for enhanced selective removal of phosphates from aqueous solution

Hollow magnetic Fe3O4@NH2-MIL-101(Fe) derived from metal-organic frameworks are fabricated through a general facile strategy. The synthetic parameters are regulated to control the shape of the as-prepared samples. The concentration of phosphates decreased sharply from the initial 0.60 to 0.045 mg.L(-1) with the exposure time in 50 minutes. The correlation between the most significant parameters such as contact time, adsorbent dose, pH, as well as adsorption capacities was optimized, and the effects of these parameters on the removal efficiency of phosphates were investigated. Surface functionalization of magnetic hollow materials is a well-designed way to bridge the gap between high adsorption activity, excellent separation and recovery of phosphates from the water treatment system. Therefore, it exhibits a remarkable selective removal of phosphates from aqueous solution.

Ca(OH)2-Catalyzed Condensation of Aldehydes with Methyl ketones in Dilute Aqueous Ethanol: A Comprehensive Access to α,β-Unsaturated Ketones

Cheap, abundant but seldom-employed Ca(OH)2 was found to be an excellent low-loading (5-10 mol%) catalyst for Claisen-Schmidt condensation of aldehydes with methyl ketones under mild conditions. It was interesting that dilute aqueous ethanol (20 v/v%) was unexpectedly discovered to be the optimal solvent. The reaction was scalable at least to 100 mmol and calcium could be precipitated by CO2 and removed by filtration. Evaporation of solvent directly afforded the product in the excellent 96% yield with high purity, as confirmed by its (1)H NMR spectrum.

Hierarchical hollow Fe2O3@MIL-101(Fe)/C derived from metal-organic frameworks for superior sodium storage

A facile generic template-free strategy is employed to prepare hierarchical hollow hybrid Fe₂O₃@MIL-101(Fe)/C materials derived from metal-organic frameworks as anode materials for Na-ion batteries. The intrinsic hollow nanostructure can shorten the lengths for both electronic and ionic transport, enlarge the surface areas of electrodes, and improve accommodation of the volume change during Na⁺ insertion/extraction cycling. Therefore, The stable reversible capacity of Fe₂O₃@MIL-101(Fe)/C electrode is 710 mAhg⁻¹, and can be retained at 662 mAhg⁻¹ after 200 cycles with the retention of 93.2%. Especially, its overall rate performance data confirm again the importance of the hierarchical hollow structures and multi-elements characteristics toward high capacities in both low and high current rates. This general strategy may shed light on a new avenue for fast synthesis of hierarchic hollow functional materials for energy storage, catalyst, sensor and other new applications.

MOF-Derived ZnO/Ni3ZnC0.7/C Hybrids Yolk-Shell Microspheres with Excellent Electrochemical Performances for Lithium Ion Batteries

In this study, ZnO/Ni3ZnC0.7/C spheres were synthesized successfully via a simple method based on metal-organic frameworks (MOFs). The experimental results show that the reaction time has a great influence on the structure of the material. ZnO/Ni3ZnC0.7/C spheres with controlled solid and yolk-shell structures have been obtained by altering the reaction time. When applied as anode materials, both the solid and the yolk-shell ZnO/Ni3ZnC0.7/C composites present excellent electrochemical performance. In addition, it is worth mentioning that the yolk-shell structure composite's property is superior to that of the solid one's in terms of lithium storage. The stable reversible capacity of yolk-shell ZnO/Ni3ZnC0.7/C can be retained at 1002 mA h g(-1) at 500 mA g(-1) after completion of 750 cycles, and it also exhibits superior rate performance. In contrast, the solid ZnO/Ni3ZnC0.7/C under the same conditions of testing shows a reversible capacity of 824 mA h g(-1).

Synthesis of magnetic metal-organic framework (MOF) for efficient removal of organic dyes from water

A novel, simple and efficient strategy for fabricating a magnetic metal-organic framework (MOF) as sorbent to remove organic compounds from simulated water samples is presented and tested for removal of methylene blue (MB) as an example. The novel adsorbents combine advantages of MOFs and magnetic nanoparticles and possess large capacity, low cost, rapid removal and easy separation of the solid phase, which makes it an excellent sorbent for treatment of wastewaters. The resulting magnetic MOFs composites (also known as MFCs) have large surface areas (79.52 m² g⁻¹), excellent magnetic response (14.89 emu g⁻¹), and large mesopore volume (0.09 cm³ g⁻¹), as well as good chemical inertness and mechanical stability. Adsorption was not drastically affected by pH, suggesting π–π stacking interaction and/or hydrophobic interactions between MB and MFCs. Kinetic parameters followed pseudo-second-order kinetics and adsorption was described by the Freundlich isotherm. Adsorption capacity was 84 mg MB g⁻¹ at an initial MB concentration of 30 mg L⁻¹, which increased to 245 mg g⁻¹ when the initial MB concentration was 300 mg L⁻¹. This capacity was much greater than most other adsorbents reported in the literature. In addition, MFC adsorbents possess excellent reusability, being effective after at least five consecutive cycles.

In situ fabrication of a perfect Pd/ZnO@ZIF-8 core-shell microsphere as an efficient catalyst by a ZnO support-induced ZIF-8 growth strategy

Controllable encapsulation of nanoparticles with metal organic frameworks (MOFs) has been an efficient way to impart the unique chemical and physical properties of the nanoparticles to metal organic frameworks and create new types of multifunctional MOF core-shell materials with enhanced properties. Here, a novel ZnO support-induced encapsulation strategy is reported to efficiently fabricate a Pd/ZnO@ZIF-8 core-shell catalyst, with Pd/ZnO as the core and ZIF-8 as the shell. The novel synthesis procedure involves first loading Pd nanoparticles onto the surface of the ZnO microsphere to form a Pd/ZnO core and then coating the core with a layer of defect-free ZIF-8 shell via ZnO-induced in situ ZIF-8 growth to obtain the Pd/ZnO@ZIF-8 core-shell catalyst. It was crucial that the ZIF-8 was in situ formed from the ZnO core in an ethanol solution only containing 2-methylimidazole under mild conditions. This strategy allowed for the growth of ZIF-8 right on the surface of Pd/ZnO via the reaction between ZnO and the 2-methylimidazole ligands, and thus avoided the random deposition of ZIF-8 crystals on the Pd/ZnO core as in the case of the conventional ZIF-8 synthesis solution. Furthermore, use of ethanol as the solvent also favored achievement of the well-defined Pd/ZnO@ZIF-8 structure, since the ethanol solution of 2-methylimidazole was able to keep the balance between ZnO dissolution and ZIF-8 formation. The as-prepared Pd/ZnO@ZIF-8 core-shell microsphere as an efficient catalyst displayed excellent performance in terms of size-selectivity, stability and anti-poisoning in the liquid hydrogenations of alkenes.

Selective recognition of 6-mercaptopurine based on luminescent metal-organic frameworks Fe-MIL-88NH₂

A novel and rapid spectrofluorometry method for the recognition of 6-mercaptopurine (6-MP) has been developed based on luminescent metal-organic frameworks Fe-MIL-88NH2 as fluorescent probe. The strong fluorescence of Fe-MIL-88NH2 at 430 nm could be quenched by 6-MP directly, and the Fe-MIL-88NH2 shows high selectivity for 6-MP compared to other thiol-containing amino acids such as homocysteine (Hcy), cysteine (Cys), glutathione (GSH), etc. Under optimal conditions, the relative fluorescence intensity was linearly proportional to the concentration of 6-MP in the range of 5-600 μM with the detection limit at 1.17 μM (S/N=3). Furthermore, the present approach has been successfully applied to the determination of 6-MP in human serum samples. The possible fluorescence quenching mechanism has also been investigated, where it is revealed that the quenching was attributed to competition of absorption of the light source energy as well as electron transfer between Fe-MIL-88NH2 and 6-MP.

Spherical core-shell magnetic particles constructed by main-chain palladium N-heterocyclic carbenes

The encapsulation of the functional species on magnetic core is a facile approach for the synthesis of core-shell magnetic materials, and surface encapsulating matrices play crucial roles in regulating their properties and applications. In this study, two core-shell palladium N-heterocyclic carbene (NHC) particles (Fe3O4@PNP1 and Fe3O4@PNP2) were prepared by a one-pot reaction of semi-rigid tripodal imidazolium salts and palladium acetate in the presence of magnetite nanoparticles. The magnetite nanoparticles are encapsulated inside the main-chain palladium, which act as cores. The conjugated effects of triphenyltriazine and triphenylbenzene in the imidazolium salts have important influence on their physical properties and catalytic performances. Fe3O4@PNP2 shows better recyclability than Fe3O4@PNP1. Unexpectedly, Pd(ii) is well maintained after six consecutive catalytic runs in Fe3O4@PNP2, and Pd(0) and Pd(ii) coexist in Fe3O4@PNP1 under the same conditions; moreover, the morphologies of these spherical core-shell particles show no significant variation after six consecutive catalytic runs.

Facile synthesis of Fe3O4nanoparticles on metal organic framework MIL-101(Cr): characterization and catalytic activity

Fe₃O₄nanoparticles can be effectively incorporated into the matrix of MIL-101(Cr) to fabricate a Fe₃O₄@MIL-101 magnetic nanocomposite which behaves as a magnetic nanocatalyst for the solvent free oxidation of benzyl alcohol.

Imparting magnetic functionality to iron-based MIL-101 via facile Fe3O4 nanoparticle encapsulation: an efficient and recoverable catalyst for aerobic oxidation

The development of sustainable, easily synthesizable and highly efficient catalysts is a fundamental goal of catalysis science.

Fe3O4@ZIF-8: magnetically recoverable catalysts by loading Fe3O4 nanoparticles inside a zinc imidazolate framework

Synthesis and characterization of Fe₃O₄ nanoparticles encapsulated in ZIF-8 crystals along with their catalytic properties and reusability are presented.