A Ga‐MIL‐53‐type Framework based on 1,4‐Phenylenediacetate Showing Subtle Flexibility

The new MOF Ga‐MIL‐53‐PDA [Ga(OH)(O₂C‐C₈H₈‐CO₂)] · H₂O ( 1 ) was synthesized by a hydrothermal reaction of gallium nitrate, 1,4‐phenylenediacetic acid (H₂PDA) and sodium hydroxide at 100 °C for 24 h. The product is a structural analogue of the archetypical MIL‐53 framework. Its crystal structure was determined by Rietveld refinement of powder X‐ray diffraction (PXRD) data. Furthermore 1,4‐phenylenedipropionic acid (H₂PDP) was employed for further synthesis, which resulted in the dense layered coordination polymers [Ga₂(OH)₄(O₂C‐C₁₀H₁₂‐CO₂)] ( 2 ) and [Ga(OH)(O₂C‐C₁₀H₁₂‐CO₂)] ( 3 ), for which accurate structural models could be established. All compounds were fully characterized and tested regarding potential breathing behavior. Most remarkably, Ga‐MIL‐53‐PDA showed a subtle flexibility upon de/‐rehydration also confirming its porosity, but no drastic structural changes were observed.     

Effective removal of 2,4,6‐trinitrophenol over hexagonal metal–organic framework NH2‐MIL‐88B(Fe)

A nanostructured organic–inorganic framework, hexagonal NH₂‐MIL‐88B, has been prepared through a facile one‐pot reflux reaction and then it was characterized using various techniques. The as‐prepared sample with high specific surface area (414 m² g^?1) showed excellent adsorption for 2,4,6‐trinitrophenol (TNP) in the liquid phase. Detailed studies of the adsorption kinetics, adsorption mechanism, adsorption isotherm, activation energy and various thermodynamic parameters were conducted. The adsorption mechanism of NH₂‐MIL‐88B for TNP may be ascribed to hydrogen bond interaction, and the complexation between ─OH in TNP and unsaturated Fe(III) on the surface of NH₂‐MIL‐88B. The maximum adsorption capacity of NH₂‐MIL‐88B for TNP based on the Langmuir isotherm was 163.66 mg g^?1. The as‐prepared NH₂‐MIL‐88B adsorbent seems to be a promising material in practice for TNP removal from aqueous solution.     

One‐pot self‐assembly and photoreduction synthesis of silver nanoparticle‐decorated reduced graphene oxide/MIL‐125(Ti) photocatalyst with improved visible light photocatalytic activity

In recent years, tremendous research efforts have been made towards developing metal–organic framework (MOF)‐based composites for photocatalytic applications. In this work, bipyramid‐like MIL‐125(Ti) frustum enwrapped with reduced graphene oxide (rGO) and dispersed silver nanoparticles (Ag NPs) was fabricated using an efficient one‐pot self‐assembly and photoreduction strategy. The as‐obtained materials were characterized using field emission scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, nitrogen adsorption–desorption isotherms, and X‐ray photoelectron, ultraviolet–visible diffuse reflectance and photoluminescence spectroscopies. It is found that the as‐prepared Ag/rGO/MIL‐125(Ti) ternary hybrids have large surface area, microporous structure, enhanced visible light absorption and prolonged lifetime of charge carriers. Compared with pure MIL‐125(Ti) and its binary counterparts, the ternary composite exhibits more efficient photocatalytic performance for Rhodamine B (RhB) degradation from water under visible light irradiation. The photodegradation rate of RhB on Ag/rGO/MIL‐125(Ti) is 0.0644 min^?1, which is 1.62 times higher than that of the pure MIL‐125(Ti). The improved photocatalytic performance is ascribed to the indirect dye photosensitization, the Ag NP localized surface plasmon resonance, the Ti³⁺–Ti⁴⁺ intervalence electron transfer and the synergistic effect among MIL‐125(Ti), Ag NPs and rGO. Ag NPs serve as an efficient ‘electron reservoir’ and rGO as an electron transporter and collector. Therefore, this work provides a new pathway into the design of MOF‐based composites for application in environmental and energy fields. Copyright © 2016 John Wiley & Sons, Ltd.     

Syntheses,Characterizations and Adsorption Properties of MIL‐101/Graphene Oxide Composites

Composites of the Cr³⁺‐based metal‐organic framework (MIL‐101) and graphene oxide (GO) have been synthesized with different ratios of MIL‐101 and GO. The composites and the parent material MIL‐101 were characterized by X‐ray diffraction, scanning electron microscopy and nitrogen adsorption. The results indicated that the incorporation of large amounts of GO (10 and 20 wt%) almost did not prevent the formation of MIL‐101 units, but had an obvious impact on the size of MIL‐101 crystals. On the contrary, small amounts of GO added (2 and 5 wt%) prevented significantly the proper assembly of MIL‐101 units, thus resulting in a pronounced decrease in the porosities of composites.     

Elimination of 4‐chlorophenol in aqueous solution by the Novel Pd/MIL‐101(Cr)‐Hydrogen‐Accelerated catalytic fenton system

Excessive consumption of Fe (II) and massive generation of sludge containing Fe (III) from classic Fenton process remains a major obstacle for its poor recycling of Fe (III) to Fe (II). Therefore, the MHACF‐MIL‐101(Cr) system, by introducing H₂, Pd⁰ and MIL‐101(Cr) into Fenton reaction system, was developed at normal temperature and pressure. In this system, the reduction of Fe^III back to Fe^II by solid catalyst Pd/MIL‐101(Cr) for the storage and activation of H₂, was accelerated significantly by above 10‐fold and 5‐fold controlled with the H₂‐MIL‐101(Cr) system and H₂‐Pd⁰ system, respectively. However, the concentration of Fe (II) generated by the reduction of Fe (III) could not be detected with the only input of H₂ and without the addition of MOFs material. In addition, the apparent consumption of Fe (II) in MHACF‐MIL‐101(Cr) system was half of that in classical Fenton system, while more Fe (II) might be reused infinitely in fact. Accordingly, only trace amount of Fe (II) vs H₂O₂ concentration was needed and hydroxyl radicals through the detection of para‐hydroxybenzoic acid (p‐HBA) as the oxidative product of benzoic acid (BA) by·OH could be continuously generated for the effective degradation of 4‐chlorophenol(4‐CP). The effects of initial pH, concentration of 4‐CP, dosage of Fe²⁺, H₂O₂ and Pd/MIL‐101(Cr) catalyst, Pd content and H₂ flow were investigated, combined with systematic controlled experiments. Moreover, the robustness and morphology change of Pd/MIL‐101(Cr) were thoroughly analyzed. This study enables better understanding of the H₂‐mediated Fenton reaction enhanced by Pd/MIL‐101(Cr) and thus, will shed new light on how to accelerate Fe (III)/Fe (II) redox cycle and develop more efficient Fenton system.     

MIL‐53(Fe) Metal–Organic Frameworks (MOFs) as an Efficient and Reusable Catalyst for the One‐Pot Four‐Component Synthesis of Pyrano[2,3‐c]‐pyrazoles

A novel and simple approach for the efficient and rapid synthesis of pyrano[2,3‐c]‐pyrazoleshas been accomplished via the four‐component condensation reaction of malononitrile, hydrazine hydrate, ethyl acetoacetate, and substituted aldehydes using MIL‐53(Fe) metal–organic framework (MOF) as a catalyst in ethanol at room temperature. Recycling studies have shown that the MIL‐53(Fe) can be readily recovered and reused six times without significant loss of its activity. The present protocol offers the advantages including short reaction times, simple workup, high yields, elimination of toxic solvents, no chromatographic purification and recoverability of the catalyst. Also, the catalyst was fully characterized by SEM, EDX, FT‐IR, XRD, TGA and TEM analysis.     

Visible‐light photocatalytic activity of Ag@MIL‐125(Ti) microspheres

Ag nanoparticle (NP)‐decorated MIL‐125(Ti) microspheres (Ag@MIL‐125(Ti)) were firstly fabricated via a facile hydrothermal and following photo‐reduction method. The photocatalysts were characterized using X‐ray diffraction, scanning and transmission electron microscopies, X‐ray photoelectron spectroscopy and UV–visible diffuse reflectance spectroscopy. The characterization results indicated that Ag NPs were dispersed on the surface of MIL‐125(Ti) microspheres, and the Ag NPs had a uniform diameter of about 40 nm. The composites exhibited excellent visible‐light absorption, due to the modification with the Ag NPs. The photocatalytic activity for the visible‐light‐promoted degradation of Rhodamine B was improved through the optimization of the amount of Ag loaded as a co‐catalyst, this amount being determined as 3 wt%. Additionally, studies performed using radical scavengers indicated that O₂^? and e^? served as the main reactive species. The catalyst can be reused at least five times without significant loss of its catalytic activity. Furthermore, a photocatalytic mechanism for degradation of organics over Ag@MIL‐125(Ti) is also proposed. Copyright © 2015 John Wiley & Sons, Ltd.     

Study on the mechanism of catalytic synthesis of dimethyldichlorosilane by AlCl3/MIL‐53(Al)@γ‐Al2O3

Dimethyldichlorosilane, one of the most consumed organosilicon monomers in the industry, can be prepared in a highly efficient and environmentally friendly synthesis method of disproportionating methylchlorosilanes. However, the internal mechanism of the reaction remains unclear. In this paper, the mechanism catalyzed by AlCl₃/MIL‐53(Al) and AlCl₃/MIL‐53(Al)@γ‐Al₂O₃ catalysts was calculated at B3LYP/6‐311++G(3df, 2pd) level by using the density functional theory (DFT). The results showed that although the two catalysts had similar active structures, the catalytic effects were significantly different. The Lewis acid center on the surface of γ‐Al₂O₃ in the core‐shell catalyst is complementary to the classic Lewis acid AlCl₃ through the spatial superposition effect, which greatly improves the Lewis acid catalytic activity of AlCl₃/MIL‐53(Al)@γ‐Al₂O₃.     

Preparation of BiVO4/MIL‐125(Ti) composite with enhanced visible‐light photocatalytic activity for dye degradation

Because of their desired features, including very specific surface areas and designable framework architecture together with their possibility to be functionalized, Metal Framework (MOF) is a promising platform for supporting varied materials in respect of catalytic applications in water treatment. In this work, a novel visible‐light‐responsive photocatalyst that comprised BiVO₄ together with MIL‐125(Ti), was synthesized by a two‐step hydrothermal approach. The characterization of as‐obtained samples as performed by X‐ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, Fourier transform infrared spectroscope, X‐ray photoelectron spectroscopy and ultraviolet‐visible diffuse reflection spectra. Rhodamine B was selected being a target for the evaluation of the photocatalytic function of as‐developed photocatalyst. The photocatalytic reaction parameters, for example, the content of BiVO₄ as well as initial concentration of Rhodamine B was researched. The composite photocatalyst possessing Bi:Ti molar ratio of 3:2 brought to light the fact that the greatest photocatalytic activity had the ability to degrade 92% of Rhodamine B in 180 min. In addition to that, the BiVO₄/MIL‐125(Ti) composite could keep its photocatalytic activity during the recycling test. The phenomenon of disintegration of the photo‐generated charges in the BiVO₄/MIL‐125(Ti) composite was brought to discussion as well.     

Facile fabrication of g‐C3N4/MIL‐53(Al) composite with enhanced photocatalytic activities under visible‐light irradiation

A novel visible‐light‐driven g‐C₃N₄/MIL‐53(Al) composite photocatalyst was successfully prepared using a facile stirring method at room temperature. The g‐C₃N₄/MIL‐53(Al) composites were characterized and their effects on the photocatalytic activities for rhodamine B degradation were investigated. The g‐C₃N₄(20 wt%)/MIL‐53(Al) photocatalyst displayed optimal photocatalytic degradation efficiency, which was about five times higher than the photocatalytic activity of pure g‐C₃N₄. The improved photocatalytic performance of the g‐C₃N₄/MIL‐53(Al) photocatalyst was predominantly attributed to the efficient separation of electron–hole pairs and the low charge‐transfer resistance. g‐C₃N₄/MIL‐53(Al) also exhibited excellent stability and reusability. A proposed mechanism for the enhanced photocatalytic activity is also discussed based on the experimental results. Copyright © 2015 John Wiley & Sons, Ltd.     

Coordination Polymer Nanobamboos of {FexIn1−x}‐MIL‐88B: Induced Formation of a Virtual In‐MIL‐88B

A precise fabrication of nanobamboo structures made from hybrid coordination polymers of the type {Fe_xIn_1?x}‐MIL‐88B is demonstrated. The compositions of the hybrid coordination polymer nanobamboos of {Fe_xIn_1?x}‐MIL‐88B (x=0.06, 0.19, or 0.75) are regulated by altering the amount of metal ions used in the reactions. Interestingly, the formation of a virtual In‐MIL‐88B (precise structure, {Fe_0.06In_0.94}‐MIL‐88B), which cannot be created in a typical reaction, is induced by the assistance of a Fe‐MIL‐88B structure. The a and c cell parameters of {Fe_0.06In_0.94}‐MIL‐88B are calculated at 10.95 and 19.86 Å, respectively. These values of {Fe_0.06In_0.94}‐MIL‐88B are larger than those of pure Fe‐MIL‐88B owing to the large ionic size of In³⁺ within the framework.     

Nano palladium supported on high‐surface‐area metal–organic framework MIL‐101: an efficient catalyst for Sonogashira coupling of aryl and heteroaryl bromides with alkynes

Palladium nanoparticle‐incorporated metal–organic framework MIL‐101 (Pd/MIL‐101) was successfully synthesized and characterized using X‐ray diffraction, nitrogen physisorption, X‐ray photoelectron, UV–visible and infrared spectroscopies, and transmission electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL‐101 and high stability of nano‐size palladium particles. Pd/MIL‐101 nanocomposite was investigated for the Sonogashira cross‐coupling reaction of aryl and heteroaryl bromides with various alkynes under copper‐free conditions. The reusability of the catalyst was tested for up to four cycles without any significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Metal–organic framework MIL‐125(Ti) for efficient adsorptive removal of Rhodamine B from aqueous solution

A metal–organic framework material, MIL‐125(Ti), was solvothermally prepared and characterized using X‐ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and surface area measurements. MIL‐125(Ti) was then used as an adsorbent for Rhodamine B (RhB) removal in aqueous solution. The adsorption kinetics, adsorption mechanism, adsorption isotherm, activation energy and various thermodynamic parameters were studied in detail. The maximum adsorption capacity of MIL‐125(Ti) for RhB was 59.92 mg g^?1. MIL‐125(Ti) appears to be a promising material for RhB adsorption from aqueous solutions. Copyright © 2014 John Wiley & Sons, Ltd.     

Highly efficient oxidative cleavage of alkenes and cyanosilylation of aldehydes catalysed by magnetically recoverable MIL‐101

The catalytic activity of magnetically recoverable MIL‐101 was investigated in the oxidation of alkenes to carboxylic acids and cyanosilylation of aldehydes. MIL‐101 was treated with Fe₃O₄ and the prepared catalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, N₂ adsorption measurements, field emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and inductively coupled plasma analysis. The catalytic active sites in this heterogeneous catalyst are Cr³⁺ nodes of the MIL‐101 framework. This heterogeneous catalyst has the advantages of excellent yields, short reaction times and reusability several times without significant decrease in its initial activity and stability in both oxidation and cyanosilylation reactions. Its magnetic property allows its easy separation using an external magnetic field.     

Enhancing photocatalytic activity of titanium dioxide through incorporation of MIL‐53(Fe) toward degradation of organic dye

Photocatalytic activity of titanium(IV) oxide (TiO₂) can be enhanced through modification of its surface‐active sites. Here, iron(III) carboxylate [MIL‐53[Fe]]‐incorporated TiO₂ (as MIL‐53(Fe)/TiO₂) was prepared using a hydrothermal method. This material was then calcined at 500°C to obtain a MIL‐53(Fe)‐derived γ‐Fe₂O₃/TiO₂ photocatalyst. A photocatalytic study of MIL‐53(Fe)/TiO₂ and MIL‐53(Fe)‐derived γ‐Fe₂O₃/TiO₂ toward cationic methylene blue (MB) and anionic methyl orange (MO) showed that MIL‐53(Fe)/TiO₂ (0.25 wt%) and MIL‐53(Fe)‐derived γ‐Fe₂O₃/TiO₂ (0.75 wt%) resulted the best degree of dye degradation. The MIL‐53(Fe)‐derived γ‐Fe₂O₃/TiO₂ (0.75 wt%) composite for instance is capable of degrading almost 100% of 20‐ppm MB and MO, respectively, within 6 hr. Photocatalytic degradation of MB and MO was well fitted to the Langmuir‐Hinshelwood pseudo‐first order kinetics model, which indicates physisorption as the key partway that facilitates dye decomposition on the surface of a photocatalyst under UV‐A irradiation. This study provides new insights into the exploration of MILs/TiO₂ materials for the environmental remediation and pollution control.     

Ethylene diamine post‐synthesis modification on open metal site Cr‐MOF to access efficient bifunctional catalyst for the Hantzsch condensation reaction

Ethylene diamine functionalized MIL‐101(Cr) was established to be an efficient organocatalyst for single‐pot synthesis of polyhydroquinolines via four‐component condensation reaction between aldehydes, dimedone, β‐ketoecters and ammonium acetate in aqueous medium. Ethylene diamine of the parent open metal site MIL‐101(Cr) has been carried out through a post‐synthetic modification (PSM) technique. Efficient transformation, mild condition, easy product isolation and the potential high recycbility of the organocatalyst are the key feature of this protocol.     

In situ synthesis of metallophthalocyanines into pores of MIL‐101: A novel and green strategy for preparation of host–guest catalysts

A novel strategy is developed to encapsulate metallophthalocyanines (MPcs, M = Cu, Ni and Co) into MIL‐101 to give MPcs@MIL‐101 via in situ synthesis of MPcs from component fragments in 1‐butyl‐3‐methylimidazolium bromide as an ionic liquid. This strategy overcomes some drawbacks of existing methods for encapsulation of MPcs into metal–organic frameworks. The chemical and structural properties of MPcs@MIL‐101 were determined using scanning electron microscopy, powder X‐ray diffraction, and Fourier transformation infrared and flame atomic absorption spectroscopies. The results showed that CuPc@MIL‐101, which was used as a ‘ship‐in‐a‐bottle’ catalyst, demonstrates excellent catalytic performance in the oxidative amidation of aldehydes with amine salts. It is confirmed that CuPc@MIL‐101 can be reused up to five times without significant loss of its activity.     

Metal–organic framework of amine‐MIL‐53(Al) as active and reusable liquid‐phase reaction inductor for multicomponent condensation of Ugi‐type reactions

Metal–organic framework of NH₂‐MIL‐53(Al), with coordinative unsaturated aluminium sites, has been shown to be active in the Groebke–Blackburn–Bienaymé multicomponent coupling reaction based on Ugi‐type amine and aldehyde condensation over isocyanide and then a cyclization process. Interestingly this reaction occurred under solvent‐free conditions with high yield, in which the NH₂‐MIL‐53(Al) could be recovered and reused for five reaction cycles, giving a total turnover number of 455.     

Fe3O4/MIL‐101(Fe) nanocomposite as an efficient and recyclable catalyst for Strecker reaction

A highly porous metal‐organic framework, MIL‐101(Fe), was prepared by a solvothermal method in the presence of amino‐modified Fe₃O₄@SiO₂ nanoparticles, in order to achieve Fe₃O₄/MIL‐101(Fe) nanocomposite, which was characterized by XRD, FT‐IR, SEM, TEM, BET, and VSM. This hybrid magnetic nanocomposite was employed as heterogeneous catalyst for α‐amino nitriles synthesis through three‐component condensation reaction of aldehydes (ketones), amines, and trimethylsilyl cyanide in EtOH, at room temperature. The recoverability and reusability was admitted for the heterogeneous magnetic catalyst; no significant reduction of catalytic activity was observed even after five consecutive reaction cycles.     

A New Solution—phase Parallel Synthesis of 2—Alkyamino—3—aryl—5—phenylmethylene—3,5—dihydro—4H—imidazol—4—ones

Thirteen new 2-alkylaminoimidazolones(4) wre rapidly synthesized by a new solution-phase parallel synthetic method,which includes aza-Wittig reaction of iminophosphorane(1) with aromatic isocyanate to give carbodi-imide(2) and subsequent reaction of 2 with various aliphatic primary amine in a parallel fashion.The products were confirmed by ^1H NMR,MS,IR and X-ray crystallographic analysis.The unusual selectivity of the cyclization was probably due to the deometry of the guanidine intermediate.