Room temperature ferromagnetism (RTFM) was observed in unirradiated rutile TiO2 single crystals prepared by the floating zone method due to oxygen vacancy (VO) defects. D-D neutrons mainly collide elastically with TiO2, producing VO, titanium vacancies (VTi) and other point defects; the density and kind of defect is related to the neutron irradiation fluence. D-D neutron irradiation is used to regulate the concentration and type of defect, avoiding impurity elements. As the irradiation fluence increases, the saturation magnetization (Ms) first increases, then decreases and then increases. To verify the origin of RTFM, the CASTEP module was used to calculate the magnetic and structural properties of point defects in TiO2. VO induces a 2.39 μB magnetic moment, Ti3+ and F+ induce 1.28 μB and 1.70 μB magnetic moments, respectively, while VTi induces a magnetic moment of ∼4 μB. Combining experimental and theoretical results, increases in VO concentration lead to Ms increases; more VO combine with electrons to form F+, inducing a smaller magnetic moment. VO and VTi play a key role and Ms changes accordingly with larger fluence. VO, F+ and VTi are the most likely origins of RTFM.
Abstract The discovery of metal–organic frameworks (MOFs) mimicking inorganic minerals with intricate topologies requires elaborate linker design guidelines. Herein, the concept of linker desymmetrization into the design of tetratopic linker based Zr‐MOFs is applied. A series of bent tetratopic linkers with various substituents are utilized to construct Zr‐MOFs with distinct cluster connectivities and topologies. For example, the assembly between a bent linker L‐SO 2 with C 2v symmetry and an 8‐connected Zr 6 cluster leads to the formation of an scu topology, while another flu topology can be obtained by the combination of a novel 8‐connected Zr 6 cluster and a bent linker L‐O with C 1 symmetry. Further utilization of restricted bent linker [(L‐(CH 3 ) 6 )] gives rise to a fascinating (4, 6)‐c cor net, originated from the corundum lattice, with an unprecedented 6‐c Zr 6 cluster. In addition, the removal of toxic selenite ions in aqueous solution is performed by PCN‐903‐(CH 3 ) 6 which exhibits rapid and efficient detoxification. This work uncovers new structural opportunities for Zr‐MOFs via linker desymmetrization and provides novel design strategies for the discovery of sophisticated topologies for practical applications.
A novel Eu(III)-based cationic metal–organic framework (Eu-CMOF), formulated as [Eu(bcbp)(tdc)(H2O)3]·Cl·5H2O (H2bcbpCl2 = 1,1′-bis(4-carboxyphenyl)-(4,4′-bipyridinium) dichloride, H2tdc = 2,5-thiophenedicarboxylic acid), has been solvothermally synthesized. Eu-CMOF displays a four-fold interpenetrating three-dimensional cationic diamondoid network, in which the positive charges of the framework are derived from the bipyridinium moiety of the bcbp ligand. Notably, Eu-CMOF exhibits a good sensing ability to nitrofurantoin and nitrofurazone in aqueous solution with high selectivity and a low limit of detection. And the quenching coefficient and mechanism have also been further investigated. Meanwhile, Eu-CMOF also possesses high uptake kinetics and adsorption capacity for MnO4–, which is mainly attributed to the cationic framework, as well as the decentralized distribution of the positive charge.
This investigation on metal-organic framework (MOF) HUKUST-1 films focuses on comparing the undoped pristine state and with the case of doping by TCNQ infiltration of the MOF pore structure. We have determined the temperature dependent charge transport andp-type conductivity for HKUST-1 films. Furthermore, the electrical conductivity and the current-voltage characteristics have been characterized in detail. Because the most common forms of MOFs, bulk MOF powders, do not lend themselves easily to electrical characterization investigations, here in this study the electrical measurements were performed on dense, compact surface-anchored metal-organic framework (SURMOF) films. These monolithic, well-defined, and (001) preferentially oriented MOF thin films are grown using quasi-liquid phase epitaxy (LPE) on specially functionalized silicon or borosilicate glass substrates. In addition to the pristine SURMOF films also the effect of loading these porous thin films with TCNQ has been investigated. Positive charge carrier conduction and a strong anisotropy in electrical conduction was observed for highly oriented SURMOF films and corroborated with Seebeck coefficient measurements. Van der Pauw four-point Hall sample measurements provide important insight into the electrical behavior of such porous and hybrid organic-inorganic crystalline materials, which renders them attractive for potential use in microelectronic and optoelectronic devices and thermoelectric applications.
A general method for Ir-catalyzed asymmetric hydrogenation of tetrasubstituted α-acylpyrazole-β-alkyl cycloalkenes has been developed, furnishing 1,2- cis substituted carbo- or heterocycles with high yields and excellent enantioselectivities.
Surface Anchored Metal-organic-framework (SURMOF) films are designed quasi-crystalline compounds that consists of metal ions connected by organic ligands, forming highly ordered porous structures. The SURMOF films initially were considered to have limited applications in electronic devices because of their insulating character. Recently, several approaches were found to tune the electrical conductivity of MOFs [1]. One of the effective methods found is to infiltrate guest molecules inside the porous framework to transport ions, and hence to modulate the electrical properties of the host framework. MOF Cu 3 (BTC) 2 (BTC: benzene tricarboxylate) is a typical MOF film known as HKUST-1 (Hong Kong University of Science and Technology 1). Its electrical conductivity could increase up to 7 orders of magnitude by introducing tetracyano-quinodimethane (TCNQ) guest molecules. Recently MOFs films received more attention in the fields of switching nanodevices [2], sensors, and thermoelectrics. reported MOF films loaded with TCNQ@Cu 3 (BTC) 2 exhibiting high Seebeck coefficients and low thermal conductivity [3]. However, the low electrical conductivity reduces the figure of merit ZT of MOFs. In this work we present alternating MOF/PbTe and MOF/PbSe nanolaminate structure synthesized by alternately depositing SURMOF films and lead chalcogenide films. The SURMOFs were fabricated by liquid phase epitaxy (LPE) technique. Ethanoic solution of copper acetate hydrate (1mM) and organic linker solution (1, 3, 5-benzenetricarboxylic acid) (0.2mM) were used as precursors for HKUST-1 MOFs. TCNQ was loaded to modulate electrical conductivity of MOFs. PbTe and PbSe were synthesized on the top of MOFs by thermal ALD technology. Lead bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C 11 H 19 O 2 ) 2 ), (trimethylsilyl) telluride ((Me 3 Si) 2 Te) and (trimethylsilyl) selenide ((Me 3 Si) 2 Se) were employed as the chemical ALD precursors for lead, telluride and selenide, respectively. 20 sccm N 2 was used as a carrier gas to transport the chemical precursors into the ALD reaction chamber. The ALD growth temperature was 150 ˚ C. The solid lead precursor was volatilized at a temperature of 170 ˚ C, the liquid Te precursor required heating to 40 ˚ C, and the liquid Se precursor was kept at room temperature. The chamber base pressure was kept at 30 mTorr. Composite nanolaminate structure of MOF/PbTe and MOF/PbSe with film thickness of 10 nm/ 10 nm, 20 nm/ 20 nm, and 60 nm/ 60 nm were fabricated and investigated. Several physical characterization techniques have been employed to determine the surface characters of the sample. The samples were characterizated by X-ray diffraction (XRD) for film crystal structure, and by field emission scanning electron microscopy (FE-SEM) for film morphology and structure. For thermoelectrical properties of the sample, Seebeck coefficient both in vertical and horizontal directions were measured. Electrical conductivity and thermal conductivity of the films were investigated as well to envaluate ZT value of the samples. Figure 1 shows the IV characteristics of MOF films loaded with TCNQ. The linear IV curve indicates Ohmic conduction in TCNQ loaded MOFs. Figure 2 displays the Seebeck coefficient of TCNQ loaded MOF films over a temperature range of 290 K ~330 K. The maximum Seebeck coefficient of the film occurs at 290 K and the positive Seebeck coefficient reveals positive charge carriers in the MOF film. References: 1. Talin, A.A., et al., Tunable electrical conductivity in metal-organic framework thin-film devices. Science, 2014. 343 (6166): p. 66-69. 2. Wang, Z., et al., Resistive Switching Nanodevices Based on Metal–Organic Frameworks. ChemNanoMat, 2016. 2 (1): p. 67-73. 3. Erickson, K.J., et al., Thin Film Thermoelectric Metal–Organic Framework with High Seebeck Coefficient and Low Thermal Conductivity. Advanced Materials, 2015. 27 (22): p. 3453-3459. Figure 1
A new biobased allyl ether monomer with acetal groups is synthesized from renewable vanillin for building flexible transparent thiol–ene networks with good degradability under mild acidic conditions.
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