Morphology Of Metal-organic Frameworks Research Articles

Modulator Effect of Acetic Acid on the Morphology of Luminescent Mixed Lanthanide-Organic Frameworks

The control of the size and morphology of Metal-Organic Frameworks is a challenge that must be overcome to ensure the use of these materials in advanced applications. Mixed Lanthanide-Organic Frameworks (MLOFs) were synthesized via solvo(hydro)thermal method and then characterized by PXRD, IR, TG/DTA, SEM and PL spectroscopy. The effect of the modulator (acetic acid) on the morphological characteristics of the obtained powders was investigated. Trivalent terbium ions were successfully incorporated into La-framework conferring green luminescence to the prepared samples. It was observed that a gradual increase in acetic acid concentration led to the morphology change from micro-rods to flower-like small particle agglomerates. Moreover, a higher concentration of the acetic acid prevented the crystallization of secondary phases.

Atomically Dispersed (AD)Fe-N-C Oxygen Reduction Catalysts for Polymer Electrolyte Membrane Fuel Cells

Atomically dispersed (AD)Fe-N-C catalysts are the ultimate goal towards achieving Fe catalyst size reduction. Such catalysts are expected to have unique properties that can be exploited for the purpose of developing highly active and durable oxygen reduction reaction (ORR) catalysts. The biggest challenge during the fabrication of atomically dispersed catalysts is to prevent clustering of atoms on the support during synthesis. In this work we address this challenge by employing metal organic frameworks (MOFs) as the structural precursor for (AD)Fe-N-C catalysts. Specifically, we (i) synthesize Fe-containing MOFs (Fe-MOFs) followed by (ii) heat treatment of the Fe-MOFs to produce (AD)Fe-N-C catalysts. The heat treatment converts Fe-MOFs to N-doped carbons, with the Fe atoms contained in the MOF being uniformly distributed on the N-doped carbons without observable agglomeration. In the approach used, maintaining the initial morphology of MOFs after the heat treatment step is key to taking advantage of the MOF structural features. In a preliminary experiment, we synthesized an Fe-containing nano platelet-shaped MOF support and heat-treated it at 1000 °C in an oxygen-free atmosphere to obtain atomically dispersed Fe atoms anchored on N-doped carbon nano-plates, (AD)Fe-N-Cnano-plates. Figure 1a (high angle annular dark field scanning transmission electron microscopy (STEM) images)demonstrates that the initial plate-like shape of the MOF, which is typically 30-50 nm wide and up to hundreds of nm long, is successfully maintained during the heat treatment at 1000 °C. Microporosity within the nano-plates is generated during the heat treatment, assuring high accessibility to the Fe atoms within the catalyst. The nitrogen content in the nano-plates measured by X-ray photoelectron spectroscopy is ca. 5 at.%. X-ray diffraction (XRD) confirms the absence of crystalline particles in (AD)Fe-N-Cnano-plates,, e.g., Fe-rich particles in particular. As shown in Figure 1b, aberration-corrected (AC)-STEM clearly indicates that all of the Fe is atomically dispersed over the N-doped carbon nano-plates (individual white dots in the image). No Fe-rich clusters or particles are observed, corroborating successful synthesis of atomically dispersed Fe-N-Cnano-plates catalysts. Electrochemical and fuel cell performance data will be presented attesting to high ORR activity of the (AD)Fe-N-Cnano-plates catalysts. Figure 1

Metal Organic Frameworks-Templated Hollow Mn<sub>2</sub>NiO<sub>4 </sub>Flower for Enhanced Supercapacitor Electrodes

A facile strategy of uniform flower-shaped binary-metal-based metal-organic frameworks (MOFs) has been successfully synthesized via a simple hydrothermal method as the precursor of porous Mn2NiO4 nanostructures. After heat treatment at different temperatures, the as-prepared Mn2NiO4 inherits the morphologies of MOFs and can hold until 450°C. This porous Mn2NiO4, used as supercapacitor electrodes, exhibits a high specific capacitance (531.5 F g-1 at a current density of 1.0 A g-1), with a relatively high specific surface area (114.2 m2 g-1). The high capacitance is mainly attributed to the porous and hierarchical structure, which facilitates fast diffusion of active ions, improves structural stability and large contact area between Mn2NiO4 and the electrolyte. The developed synthetic strategy may provide design guidelines for constructing advanced ternary nanostructured supercapacitors electrode.

A facile preparation of novel positively charged MOF/chitosan nanofiltration membranes

A novel positively charged nanofiltration (NF) membrane was fabricated by incorporating metal-organic frameworks (MOFs) into chitosan polymeric matrix for enhanced removal of multivalent cations. The synthesized MOFs, NH2-MIL-101(Al) and NH2-MIL-101(Cr), could be homogeneously dispersed in the chitosan polymeric matrix. The morphologies of MOFs had a significant influence on the permeability of NF membranes. NF membrane filled with NH2-MIL-101(Al) with rod-like structure attained two times higher flux but similar rejection compared with that filled with NH2-MIL-101(Cr) with grainy structure. The effect of MOF loadings (NH2-MIL-101(Al)) on the membrane performance were evaluated by XRD, FTIR and SEM. These positively charged MOF/chitosan NF membranes were able to reject up to 93.0% of MgCl2, and the salt rejection followed the order of MgCl2>CaCl2>NaCl>Na2SO4.

Microwave activation as an alternative production of metal-organic frameworks

The review is devoted to analysis of the modern data concerning microwave-assisted synthesis of metal-organic frameworks (MOFs). The prospects for the microwave activation of the reaction mixture as an effective method of MOF formation with tuned crystallite size are considered. Other aspects of this approach including impact of various factors (reaction mixture composition, microwave synthesis parameters) on the texture properties and morphology of MOFs are discussed. Comparative studies concerning the influence of preparation methods in the microwave fields and other procedures of MOF fabrication on the physicochemical properties of the samples are considered. Advantages of microwave synthesis from green chemistry point are outlined.

Shape- and size-dependent catalysis activities of iron-terephthalic acid metal-organic frameworks

Precise control of the size and morphology of metal-organic frameworks (MOFs) presents an important direction for extending these inorganic-organic materials to many more advanced applications. However, because of the limit of the crystal-growth rule and mechanism, good-control of the size and morphology of MOFs remains challenging. In this contribution, an iron-terephthalic acid metal-organic framework with different shapes (octahedron, spindle and bipyramidal hexagonal) was easily and reproducibly synthesized via a solvothermal method. Sodium acetate and glycerol were used as modulators. Mechanism studies showed that the crystal nucleation rate and orientational growth both play important roles in determining the final shape of the MOFs. Further investigations showed that the as prepared MOFs exhibit shape-dependent catalytic activities, which means that MOFs can be designed to perform different catalytic functions. This investigation not only provides an effective guideline for the precise control of the size and morphology of metal-organic frameworks, but also extends MOFs to much more advanced applications in terms of catalyst chemistry.

Metal Organic Framework Micro/Nanopillars of Cu(BTC)·3H₂O and Zn(ADC)·DMSO.

In this work, we report the optical and thermal properties of Cu(BTC)·3H2O (BTC = 1,3,5-benzenetricarboxylic acid) and Zn(ADC)·DMSO (ADC = 9,10-anthracenedicarboxylic acid, DMSO = dimethyl sulfoxide) metal-organic frameworks (MOFs) micro/nanopillars. The morphologies of MOFs on surfaces are most in the form of micro/nanopillars that were vertically oriented on the surface. The size and morphology of the pillars depend on the evaporation time, concentration, solvent, substrate, and starting volume of solutions. The crystal structures of the nanopillars and micropillars are the same, confirmed by powder XRD. Zn(ADC)·DMSO pillars have a strong blue fluorescence. Most of ADC in the pillars are in the form of monomers, which is different from ADC in the solid powder.

32.Sulfonic acid functionalization of 2-aminoterephthalate metal−organic framework and silica nanoparticles by surface initiated radical polymerization: as proton-conducting solid electrolytes

A post-polymerization method for metal–organic frameworks (MOFs) and silica nanoparticles have been developed to produce super-acidic solid nanoparticle. Thus, silica and amino-functionalized metal−organic framework [NH2-MIL-101(Al)] were functionalized with 4.4′-Azobis(4-cyanovaleric acid) (ACVA) from hydroxyl and amine groups to yield initiator anchored silica and MOF nanoparticles. Then, sulfonated polymer/MOF and sulfonated polymer/silica hybrid nanoparticles were prepared by free radical polymerization of 2-acrylamido-2-methyl-1-propane sulfonic acid [(MOF-g-PAMPS) and (Si-g-PAMPS)], initiated onto the surfaces of initiator functionalized nanoparticles. Synthesis and modification of nanoparticles were characterized by fourier transform infrared (FTIR), thermogravimetric analysis (TGA). Also, the attachment of ACVA modifier agent on the surface of silica nanoparticles was studied using X-ray photoelectron spectroscopy (XPS). FTIR and TGA results indicated that AMPS monomer was successfully grafted onto the MOF and silica nanoparticles. The grafting efficiency of PAMPS polymer onto the silica and MOF nanoparticles were estimated from TGA thermograms to be 17 and 35 % for silica and MOF nanoparticles, respectively. Morphology of MOF and silica nanoparticles before and after modification processes were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively.

Functionalization of silicon nanowire surfaces with metal-organic frameworks

Metal-organic frameworks (MOFs) and silicon nanowires (SiNWs) have been extensively studied due to their unique properties; MOFs have high porosity and specific surface area with well-defined nanoporous structure, while SiNWs have valuable one-dimensional electronic properties. Integration of the two materials into one composite could synergistically combine the advantages of both materials and lead to new applications. We report the first example of a MOF synthesized on surface-modified SiNWs. The synthesis of polycrystalline MOF-199 (also known as HKUST-1) on SiNWs was performed at room temperature using a step-by-step (SBS) approach, and X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy elemental mapping were used to characterize the material. Matching of the SiNW surface functional groups with the MOF organic linker coordinating groups was found to be critical for the growth. Additionally, the MOF morphology can by tuned by changing the soaking time, synthesis temperature and precursor solution concentration. This SiNW/MOF hybrid structure opens new avenues for rational design of materials with novel functionalities.