Electronic and vibrational properties of a MOF-5 metal-organic framework: ZnO quantum dot behaviour

UV-Vis DRS and photoluminescence (PL) spectroscopy, combined with excitation selective Raman spectroscopy, allow us to understand the main optical and vibrational properties of a metal-organic MOF-5 framework. A O(2-)Zn(2+)[rightward arrow] O(-)Zn(+) ligand to metal charge transfer transition (LMCT) at 350 nm, testifies that the Zn(4)O(13) cluster behaves as a ZnO quantum dot (QD). The organic part acts as a photon antenna able to efficiently transfer the energy to the inorganic ZnO-like QD part, where an intense emission at 525 nm occurs.     

Room temperature synthesis of metal-organic frameworks: MOF-5, MOF-74, MOF-177, MOF-199, and IRMOF-0

Room temperature synthesis of metal-organic frameworks (MOFs) has been developed for four well-known MOFs: MOF-5, MOF-74, MOF-177, and MOF-199. A new isoreticular metal framework (IRMOF), IRMOF-0, having the same cubic topology as MOF-5, has been synthesized from acetylenedicarboxylic acid using this method to accommodate the thermal sensitivity of the linker. Despite acetylenedicarboxylate being the shortest straight linker that can be made into an IRMOF, IRMOF-0 forms as a doubly interpenetrating structure, owing to the rod-like nature of the linker.     

Adsorption properties of the MOF-5 metal-organic framework in relation to water and benzene

Adsorption properties of synthesized metal-organic frameworks based on 1,4-dicarboxylate ligands and zinc ions were studied. It was shown that the adsorption properties of these metal-organic frameworks in relation to water and benzene are much higher than those for the known adsorbents: KT-1 and KT-2 coals, USY and ZSM-5 zeolites, and pentasil.     

Ab initio parametrized MM3 force field for the metal-organic framework MOF-5

A new valence force field has been developed and validated for a particular class of coordination polymers known as nanoporous metal-organic frameworks (MOFs), introduced recently by the group of Yaghi. The experimental, structural, and spectroscopic data in combination with density functional theory calculations on several model systems were used to parametrize the bonded terms of the force field, which explicitly treats the metal-oxygen interactions as partially covalent as well as distinguishes different types of oxygens in the framework. Both the experimental crystal structure of MOF-5 and vibrational infrared spectrum are reproduced reasonably well. The proposed force field is believed to be useful in atomistic simulations of adsorption/diffusion of guest molecules inside the flexible pores of this important class of MOF materials.     

Capture of nerve agents and mustard gas analogues by hydrophobic robust MOF-5 type metal-organic frameworks

In this communication, a series of observations and data analyses coherently confirms the suitability of the novel metal-organic framework (MOF) [Zn(4)(μ(4)-O)(μ(4)-4-carboxy-3,5-dimethyl-4-carboxy-pyrazolato)(3)] (1) in the capture of harmful volatile organic compounds (VOCs). It is worthy of attention that 1, whose crystal structure resembles that of MOF-5, exhibits remarkable thermal, mechanical, and chemical stability, as required if practical applications are sought. In addition, it selectively captures harmful VOCs (including models of Sarin and mustard gas, which are chemical warfare agents), even in competition with ambient moisture (i.e., under conditions mimicking operative ones). The results can be rationalized on the basis of Henry constant and adsorption heat values for the different essayed adsorbates as well as H(2)O/VOC partition coefficients as obtained from variable-temperature reverse gas chromatography experiments. To further strengthen the importance of 1, its performance in the capture of harmful VOCs has been compared with those of well-known materials, namely, a MOF with coordinatively unsaturated metal sites, [Cu(3)(btc)(2)] and the molecular sieve active carbon Carboxen. The results of this comparison show that coordinatively unsaturated metal sites (preferential guest-binding sites) are ineffective for the capture of VOCs in the presence of ambient moisture. Consequently, we propose that the driving force of the VOC-MOF recognition process is mainly dictated by pore size and surface hydrophobicity.     

Theoretical investigations on the chemical bonding, electronic structure, and optical properties of the metal-organic framework MOF-5

The chemical bonding, electronic structure, and optical properties of metal-organic framework-5 (MOF-5) were systematically investigated using ab initio density functional calculations. The unit cell volume and atomic positions were optimized with the Perdew-Burke-Ernzerhof (PBE) functional leading to a good agreement between the experimental and the theoretical equilibrium structural parameters. The calculated bulk modulus indicates that MOF-5 is a soft material. The estimated band gap from a density of state (DOS) calculation for MOF-5 is about 3.4 eV, indicating a nonmetallic character. As MOFs are considered as potential materials for photocatalysts, active components in hybrid solar cells, and electroluminescence cells, the optical properties of this material were investigated. The detailed analysis of chemical bonding in MOF-5 reveals the nature of the Zn-O, O-C, H-C, and C-C bonds, that is, Zn-O having mainly ionic interaction whereas O-C, H-C, and C-C exhibit mainly covalent interactions. The findings in this paper may contribute to a comprehensive understanding about this kind of material and shed insight into the synthesis and application of novel and stable MOFs.     

In vitro and intracellular sensing by using the photoluminescence of quantum dots

Quantum dots (QDs) have attracted increasing attention due to their unique physical and chemical properties. This article introduces recent advances in using QDs’ photoluminescence (PL) for in vitro and intracellular sensing analytes, in particular ions, and biomolecules from the last 3 years. Different sensing strategies are demonstrated and compared for increasing the detecting/sensing selectivity. The perspectives for in vitro and intracellular sensing based on QDs’ PL are also discussed.     

New method for catalyst preparation based on metal-organic framework MOF-5 for the partial hydrogenation of phenylacetylene

Small (less than 2 nm) Pd nanoparticles immobilized in the matrix of the microporous phenylenecarboxylate metal-organic framework MOF-5 were prepared for the first time by the fluid method. The catalytic properties of samples Pd@MOF-5 were studied in the selective hydrogenation of phenylacetylene to styrene (methanol, 20 °C, P _H2 = 1 atm). The catalytic experimental data and results of physicochemical studies indicate that palladium nanoparticles are mostly localized in pores of the composite material 1%Pd@MOF-5 obtained by the fluid synthesis. The specific positions of active sites in the intracrystalline volume results in the suppression of the undesirable conversion of styrene to ethylbenzene.     

A synergy establishment by metal-organic framework and carbon quantum dots to enhance electrochemical water oxidation

Available online Integrating transition metal centered MOFs with conductive materials is a feasible route to enhance electron transfer efficiency of materials. Herein, a composite porous structure CQDs₁₀@Ni FeMOF-A was fabricated via introducing carbon quantum dots（CQDs） into porous Ni Fe-MOF. The CQDs would make partial loss of lattice in MOF during its growth, leading to the composite building block with the coexistance of crystalline region and amorphous region. The calcining treat...     

A synergy establishment by metal-organic framework and carbon quantum dots to enhance electrochemical water oxidation

Available online Integrating transition metal centered MOFs with conductive materials is a feasible route to enhance electron transfer efficiency of materials. Herein, a composite porous structure CQDs₁₀@Ni FeMOF-A was fabricated via introducing carbon quantum dots（CQDs） into porous Ni Fe-MOF. The CQDs would make partial loss of lattice in MOF during its growth, leading to the composite building block with the coexistance of crystalline region and amorphous region. The calcining treat...     

ZnO twin-cones: synthesis, photoluminescence, and catalytic decomposition of ammonium perchlorate

ZnO twin-cones, a new member to the ZnO family, were prepared directly by a solvothermal method using a mixed solution of zinc nitrate and ethanol. The reaction and growth mechanisms of ZnO twin-cones were investigated by X-ray diffraction, UV-visible spectra, infrared and ion trap mass spectra, and transmission electron microscopy. All as-prepared ZnO cones consisted of tiny single crystals with lengths of several micrometers. With prolonging of the reaction time from 1.5 h to 7 days, the twin-cone shape did not change at all, while the lattice parameters increased slightly and the emission peak of photoluminescence shifted from the green region to the near orange region. ZnO twin-cones are also explored as an additive to promote the thermal decomposition of ammonium perchlorate. The variations of photoluminescence spectra and catalytic roles in ammonium perchlorate decomposition were discussed in terms of the defect structure of ZnO twin-cones.     

金属有机骨架材料MOF-5吸附苯并噻吩性能

苯并噻吩类硫化物的脱除是燃油实现深度脱硫的关键。实验研究了典型的金属有机骨架材料MOF-5吸附苯并噻吩性能。结果表明,MOF-5对模型油中苯并噻吩的吸附动力学过程满足拟二级动力学模型。Langmuir、Freundlich和Dubinin-Radushkevich (D-R) 三种等温吸附模型均可较好地描述MOF-5对苯并噻吩的等温吸附行为 (Freundlich>D-R>Langmuir)。热力学参数表明,MOF-5对苯并噻吩的吸附是自发的吸热吸附过程。     

Porous phosphate heterostructures containing CdS quantum dots: assembly, characterization and photoluminescence

The synthesis and characterization of cadmium sulphide (CdS) quantum dots, conjugated in a porous phosphate heterostructure functionalized with aminopropyl groups is described. The resulting material has fluorescence properties with maximum emission intensity at 575 nm. The fluorescent materials are not soluble in water and exhibit high stability in aqueous solution in the pH ranges from 2 to 9. Energy dispersive X-ray spectroscopy confirmed the qualitative elemental composition of the synthesized materials and X-ray photoelectron spectra showed a surface S/Cd atomic ratio of 1.09. SEM images show that the materials are amorphous, possessing porous with sizes of several tens nanometres, homogeneous and exhibit a layered morphology. The adsorption–desorption analysis by N₂ at 77 K showed the accessibility of the CdS quantum dots onto the pores of the structure. The CdS quantum dots were stabilized by mercaptopropionic acid and bounded to the host materials by amine groups.     

Dual-functional photocatalysis boosted by electrostatic assembly of porphyrinic metal-organic framework heterojunction composites with CdS quantum dots

Photocatalytic dual-functional reaction under visible light irradiation represents a sustainable development strategy. In detail, H₂ production coupled with benzylamine oxidation can remarkably lower the cost by replacing sacrificial agents. In this work, Cd S quantum dots(Cd S QDs) were successfully loaded onto the surface of a porphyrinic metal-organic framework(Pd-PCN-222) by the electrostatic selfassembly at room temperature. The consequent Pd-PCN-222/CdS heterojunction composites...     

MAA-modified and luminescence properties of ZnO quantum dots

The precursor of ZnO has been prepared by refluxing in ethanol at 70°C for 4 h using ZnAc₂·H₂O as the initial agent. Then ZnO has been prepared from the reaction of LiOH·H₂O and the precursor. The ZnO is modified by mercaptoacetic acid (MAA) and detected by SEM and XRD. These ZnO particles have single phase, like-sphere and size of 4.6 nm. The modified effectivity of MAA for the quantum dots (QDs) has been investigated with UV-visible and fluorescence analysis, and the mechanism and property of ZnO light emitting have been discussed under given conditions. The reasons why the fluorescent emission peak of surface defects disappear and the exciton emission peak increase are that MAA effectively covers the surface defects of ZnO and stably coats ZnO particles. At the same time, the effect of the added amount of the MAA, temperature and electrolyte on light-emitting properties of modified product has also been studied. The result shows that the modified ZnO QDs have good fluorescence property, stability and suitable capability of resisting electrolyte. These results are important for biological analysis.     

Enhancing the photoluminescence intensity of conjugated polycationic polymers by using quantum dots as antiaggregation reagents

The aggregation in conjugated polyelectrolytes (CPs) can be effectively reduced by the formation of CP/nanoparticle assemblies. The photophysical properties of various nanoassemblies were studied by means of UV-visible and fluorescence spectroscopy in solution and as thin films. The dissociation of the polymer chains is caused by favorable electrostatic interactions between the cationic substituents of the CPs and the anionic charges present on the surface of the nanoparticles. Such an efficient displacement of pi-stacking by competitive positive interactions constitutes the first example of positive aggregation modulation.     

The fabrication strategies and enhanced performances of metal-organic frameworks and carbon dots composites: State of the art review

Metal-organic frameworks (MOFs) with large specific surface area, considerable pore volume, controllable structure, and high concentration of active metal sites have been applied widely in researches like catalysis and sensing. However, potential applications of MOFs in both photocatalysis and luminescence sensors are facing major challenges arising from their severe charge recombination, low utilization of solar energy, low quantum yield, limited charge transfer between the metal ions/clusters and the ligand. Recent studies revealed that rational introduction of carbon dots (CDs) with excellent optical properties, unique quantum confinement and high conductivity can greatly enhance the functions of MOFs. In this paper, typical synthesis methods of these CD-MOF composites as well as their potential applications in photocatalysis and sensing are reviewed with emphasis. Representative examples of these CD-MOF composites are discussed, and key features and advantages of CD-MOF composites that will facilitate future applications are highlighted.