Metal-organic frameworks from zinc sulfite clusters, chains, and sheets: 4-connected, (3,4)-connected 3-D frameworks and 2-D arrays of catenane-like interlocking rings

Even though open-framework solids have been made in a variety of compositions such as silicates, phosphates, germanates, borates, and phosphites, few are known that are based on trigonal-pyramidal sulfite anions. We report here the first synthetic and structural studies of metal-organic framework materials in the zinc sulfite composition. It is demonstrated here that Zn2+ and SO32- can form various neutral inorganic subunits that can be 0-D clusters, 1-D chains, or 2-D sheets. These inorganic subunits of different dimensionality can subsequently be connected into extended frameworks of higher dimensionality through bifunctional ligands. In (ZnSO3)2en, infinite corrugated ZnSO3 layers are pillared by ethylenediamine (en) molecules into a 3-D network that can be classified as a (3,4)-connected net based on tetrahedral Zn nodes and trigonal-pyramidal S nodes. In (ZnSO3)pip, infinite ZnSO3 chains are cross-linked with piperazine molecules into a 3-D framework that can be classified as 4-connected net based on tetrahedral Zn nodes only. In (ZnSO3)2(TMDPy)2, (ZnSO3)2 dimers are doubly bridged by trimethylenedipyridine molecules into an infinite chain with a string of circles. Each circle along the chain is interlocked with another circle from a chain in the perpendicular direction, creating a 2-D pattern with an infinite-square array of catenane-like units.     

A critical assessment of the specific role of microwave irradiation in the synthesis of ZnO micro- and nanostructured materials

A rapid, microwave-assisted hydrothermal method has been developed to access ultrafine ZnO hexagonal microrods of about 3-4 μm in length and 200-300 nm in width by using a 1:5 zinc nitrate/urea precursor system. The size and morphology of these ZnO materials can be influenced by subtle changes in precursor concentration, solvent system, and reaction temperature. Optimized conditions involve the use of a 1:3 water/ethylene glycol solvent system and 10 min microwave heating at 150 °C in a dedicated single-mode microwave reactor with internal temperature control. Carefully executed control experiments ensuring identical heating and cooling profiles, stirring rates, and reactor geometries have demonstrated that for these preparations of ZnO microrods no differences between conventional and microwave dielectric heating are observed. The resulting ZnO microrods exhibited the same crystal phase, primary crystallite size, shape, and size distribution regardless of the heating mode. Similar results were obtained for the ultrafast preparation of ZnO nanoparticles with diameters of approximately 20 nm, synthesized by means of a nonaqueous sol-gel process at 200 °C from a Zn(acac)(2) (acac=acetylacetonate) precursor in benzyl alcohol. The specific role of microwave irradiation in enhancing these nanomaterial syntheses can thus be attributed to a purely thermal effect as a result of higher reaction temperatures, more rapid heating, and a better control of process parameters.     

A Critical Assessment of the Specific Role of Microwave Irradiation in the Synthesis of ZnO Micro‐ and Nanostructured Materials

A rapid, microwave‐assisted hydrothermal method has been developed to access ultrafine ZnO hexagonal microrods of about 3–4 μm in length and 200–300 nm in width by using a 1:5 zinc nitrate/urea precursor system. The size and morphology of these ZnO materials can be influenced by subtle changes in precursor concentration, solvent system, and reaction temperature. Optimized conditions involve the use of a 1:3 water/ethylene glycol solvent system and 10 min microwave heating at 150 °C in a dedicated single‐mode microwave reactor with internal temperature control. Carefully executed control experiments ensuring identical heating and cooling profiles, stirring rates, and reactor geometries have demonstrated that for these preparations of ZnO microrods no differences between conventional and microwave dielectric heating are observed. The resulting ZnO microrods exhibited the same crystal phase, primary crystallite size, shape, and size distribution regardless of the heating mode. Similar results were obtained for the ultrafast preparation of ZnO nanoparticles with diameters of approximately 20 nm, synthesized by means of a nonaqueous sol–gel process at 200 °C from a Zn(acac)₂ (acac=acetylacetonate) precursor in benzyl alcohol. The specific role of microwave irradiation in enhancing these nanomaterial syntheses can thus be attributed to a purely thermal effect as a result of higher reaction temperatures, more rapid heating, and a better control of process parameters.     

Aqueous pathways for the formation of zinc oxide nanoparticles

We examine the effect of reactant concentrations, temperatures and feeding methods on the morphology of ZnO formed when reacting solutions of ZnSO(4) and NaOH. The catalytic effect of hydroxide in excess relative to the stoichiometric ratio is considered. It is shown that, having fixed other reaction conditions, the end-products, particle structures and size strongly depend on the mole ratio of the precursors. The presence of zinc salt hydroxide species was confirmed at sub-stoichiometric ratios in slightly acidic conditions. At the stoichiometric ratio both zinc hydroxide and zinc oxide are formed, while only zinc oxide forms in an excess of hydroxide. The method of feeding the reactants into the reaction vessel also has a strong influence on the end-product properties, as does the reaction temperature. By control of these parameters the specific surface area could be varied from 10 to 33 m(2) g(-1), the particle shape could be varied from equiaxed, through to star-like and needle-like, and the particle size may be varied from 50 to over 300 nm.     

助剂前体ZnSO_4浓度对苯选择加氢制环己烯Ru-Zn催化剂性能的影响

共沉淀法制备了Ru-Zn催化剂,在ZrO_2作分散剂下考察了助剂前体ZnSO_4浓度对苯选择加氢制环己烯Ru-Zn催化剂性能的影响.并用X-射线衍射(XRD)、X-射线荧光光谱(XRF)、N_2-物理吸附、透射电镜(TEM)和X-射线光电子能谱(XPS)等手段对催化剂进行了表征.结果表明,当ZnSO_4前体浓度低于0.10 mol/L时,Ru-Zn催化剂中Zn以ZnO形式存在,在加氢过程中ZnO可以与反应修饰剂ZnSO_4反应生成(Zn( OH)_2)_3(ZnSO_4)(H_2O)_3盐.继续增加ZnSO_4前体浓度,催化剂中Zn以ZnO和NaZn_4(SO_4)(Cl)(OH)_6·6H_2O盐存在,在加氢过程中ZnO和NaZn_4(SO_4)(Cl)(OH)_6·6H_2O盐可以与反应修饰剂ZnSO_4反应生成(Zn( OH)_2)_3(ZnSO_4)(H_2O)_5.(Zn( OH)_2)_3(ZnSO_4)(H_2O)_x(x=3或5)盐的Zn~(2+)可以转移金属Ru的部分电子.因此,随ZnSO_4前体浓度的增加,(Zn( OH)_2)_3(ZnSO_4)(H_2O)_x的量逐渐增加,金属Ru失电子越多,催化剂活性越低,环己烯选择性越高.0.08 mol/L ZnSO_4前体制备Ru-Zn催化剂给出了59.1%的环己烯收率,而且该催化剂具有良好的重复使用性能和稳定性.     

Proton-promoted dissolution of α-FeOOH nanorods and microrods: Size dependence, anion effects (carbonate and phosphate), aggregation and surface adsorption

Iron-containing oxide nanoparticles are of great interest from a number of technological perspectives and they are also present in the natural environment. Although recent evidence suggests that particle size plays an important role in the dissolution of metal oxides, a detailed fundamental understanding of the influence of particle size is just beginning to emerge. In the current study, we investigate whether nanoscale size-effects are observed for the dissolution of iron oxyhydroxide under different conditions. The dissolution of two particle sizes of goethite, α-FeOOH in the nanoscale and microscale size regimes (herein referred to as nanorods and microrods), in aqueous suspensions at pH 2 is investigated. It is shown here that in the presence of nitrate, nanorods shows greater dissolution on both a per mass and per surface area basis relative to microrods, in agreement with earlier studies. In the presence of carbonate and phosphate, however, dissolution of α-FeOOH nanorods at pH 2 is significantly inhibited, despite the fact that these anions result in a three- to fivefold enhancement of the dissolution of microrods relative to the nitrate anion. Light scattering techniques and electron microscopy show that nanorod suspensions are less stable compared to microrod suspensions resulting in nanorod aggregation under conditions where microrods stay more dispersed. Furthermore, spectroscopic studies using ATR-FTIR spectroscopy show distinct differences in phosphate and carbonate adsorption on nanorods compared to microrods. These results demonstrate that aggregation and the details of surface adsorption are important in the dissolution behavior of nanoscale materials.     

Vapor-transportation preparation and reversible lithium intercalation/deintercalation of alpha-MoO3 microrods

We report on the preparation and electrochemical application of rechargeable lithium-ion batteries of alpha-MoO3 microrods. A simple and efficient vapor-transportation approach was developed to yield large-scale alpha-MoO3 microrods. The as-prepared products were present in long, uniform, rodlike structures with a diameter of approximately 2 approximately 6 microm, and the proportion of the rod morphology was about 95% according to the analysis of scanning electron microscopy (SEM). The electrochemical lithium intercalation/deintercalation characteristic of the as-prepared microrods was investigated by cyclic voltammetry and a galvanostatic charge-discharge method. The results showed that the alpha-MoO3 microrods exhibited high capacity (225 mAh g(-1)) and excellent cycling reversibility, and are thus promising cathode candidates in advanced rechargeable lithium-ion batteries. The correlation between the specific structural features of the microrods and their superior electrode performance is discussed in detail, revealing that the unique rodlike structure plays an important role in optimizing the electrochemical performance of the electrode.     

Synthesis, characterization, and electrochemical properties of Ag2V4O11 and AgVO3 1-D nano/microstructures

We report on the synthesis, characterization, and electrochemical properties of Ag(2)V(4)O(11) nanowires, alpha-AgVO(3) microrods, and beta-AgVO(3) nanowires that were synthesized through a simple and facile low-temperature hydrothermal approach without any template or catalyst. It was found that by simply controlling the hydrothermal reaction parameters such as pH and dwell time, the transformation of alpha-AgVO(3) microrods to beta-AgVO(3) nanowires were readily achieved through a "ripening-splitting model" mechanism. Electrochemical measurements revealed that the as-prepared Ag(2)V(4)O(11) nanowires, alpha-AgVO(3) microrods, and beta-AgVO(3) nanowires exhibited high discharge capacities and excellent high-rate dischargeability. In particular, the beta-AgVO(3) nanowires have much higher capacity above 3 V than that of alpha-AgVO(3) microrods, Ag(2)V(4)O(11) nanowires, and commercial Ag(2)V(4)O(11) bulk. The mechanisms for electrochemical lithium intercalation of the AgVO(3) nanostructures were also discussed. It is anticipated that the novel Ag(2)V(4)O(11) and AgVO(3) one-dimensional nano/microstructures are promising cathode candidates in the application of primary lithium ion batteries for implantable cardioverter defibrillators (ICDs).     

Lanthanide Metal–Organic Framework Microrods: Colored Optical Waveguides and Chiral Polarized Emission

Lanthanide metal–organic frameworks (Ln-MOFs) have received much attention owing to their structural tunability and widely photofunctional applications. However, successful examples of Ln-MOFs with well-defined photonic performances at micro-/nanometer size are still quite limited. Herein, self-assemblies of 1,3,5-benzenetricarboxylic acid (BTC) and lanthanide ions afford isostructural crystalline Ln-MOFs. Tb-BTC, Eu@Tb-BTC, and Eu-BTC have 1D microrod morphologies, high photoluminescence (PL) quantum yields, and different emission colors (green, orange, and red). Spatially PL resolved spectra confirm that Ln-MOF microrods exhibit an optical waveguide effect with low waveguide loss coefficient (0.012≈0.033 dB μm⁻¹) during propagation. Furthermore, these microrods feature both linear and chiral polarized photoemission with high anisotropy.     

ZnO-CdSe nanoparticle clusters as directional photoemitters with tunable wavelength

Reaction of 3-aminopropylsilyl-modified ZnO microrods with trioctylphosphineoxide-coated CdSe/CdS core/shell nanocrystals in THF produces rod-shaped nanoparticle clusters that show directional photoemission that can be tuned with the size of the CdSe nanocrystals. The observed waveguiding effect of these microstructures is due to total internal reflection of light at the cluster-air interface.     

Supramolecular microrods can be prepared by mixing aqueous Ru(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>Cl<Subscript>3</Subscript> and K<Subscript>3</Subscript>Fe(CN)<Subscript>6</Subscript> solutions at room temperature

This paper describes the ionic self-assembly method to fabricate supramolecular one-dimensional microrods in solution. Such microrods were formed in a one-step process through the mixing aqueous Ru(NH₃)₆Cl₃ and K₃Fe(CN)₃ solutions at room temperature. Chemical composition of the resulting structures, which are composed of from Fe(CN)₆⁴⁻ and Ru(NH₃)₆³⁺, was determined by energy-dispersed spectroscopy. The data show that the formation of microrods depends on the molar ratio and concentration of the reactants.     

二乙醇胺作添加剂Ru-Zn催化剂上苯选择加氢制环己烯

采用共沉淀法制备了Ru-Zn催化剂,考察了二乙醇胺的添加对Ru-Zn催化剂上苯选择加氢制环己烯性能的影响,并采用N2物理吸附、透射电镜、X射线衍射、X射线荧光、傅里叶变换红外和程序升温还原等手段对催化剂进行了表征.结果表明,二乙醇胺可以与浆液中ZnSO4反应生成(Zn(OH)2)3(ZnSO4)(H2O)3和硫酸二乙醇胺盐.随着二乙醇胺用量的增加,化学吸附在催化剂表面的(Zn(OH)2)3(ZnSO4)(H2O)3增多,它与硫酸二乙醇胺盐的协同作用提高了Ru-Zn(4.9%)催化剂上苯选择加氢生成环己烯的选择性.当二乙醇胺用量为0.3g时,(Zn(OH)2)3(ZnSO4)(H2O)3在Ru-Zn(4.9%)催化剂加氢后样品的表面高度分散,反应性能最佳,循环使用第3次时苯转化率为84.3%,环己烯选择性和收率分别达75.5%和63.6%;使用至第4次时,反应25min时苯转化率和环己烯选择性仍可达75%以上,环己烯收率为58%以上.     

Lanthanide Metal–Organic Framework Microrods: Colored Optical Waveguides and Chiral Polarized Emission

Lanthanide metal–organic frameworks (Ln‐MOFs) have received much attention owing to their structural tunability and widely photofunctional applications. However, successful examples of Ln‐MOFs with well‐defined photonic performances at micro‐/nanometer size are still quite limited. Herein, self‐assemblies of 1,3,5‐benzenetricarboxylic acid (BTC) and lanthanide ions afford isostructural crystalline Ln‐MOFs. Tb‐BTC, Eu@Tb‐BTC, and Eu‐BTC have 1D microrod morphologies, high photoluminescence (PL) quantum yields, and different emission colors (green, orange, and red). Spatially PL resolved spectra confirm that Ln‐MOF microrods exhibit an optical waveguide effect with low waveguide loss coefficient (0.012≈0.033 dB μm⁻¹) during propagation. Furthermore, these microrods feature both linear and chiral polarized photoemission with high anisotropy.     

三元杂质砷锑钴对锌电沉积阴极过程的影响

采用电化学研究方法探讨了在锌电积过程中砷、锑、钴杂质对阴极极化过程的单一和共同影响,得出了单一杂质和三元杂质对锌电积过程影响的动力学方程及参数,并对其极化机理进行了研究.结果表明,含一元杂质的ZnSO4/H2SO4溶液的动力学参数与理论值基本一致,而含三元的ZnSO4/H2SO4溶液的传递系数α要比理论值小,说明杂质的存在及其含量的大小、品种的多少对锌电积影响程度不同.     

助剂Fe和反应修饰剂修饰的Ru催化剂上苯选择加氢制环己烯

共沉淀法制备了Ru-Fe(x)催化剂,并利用X射线衍射(XRD)、X射线荧光光谱(XRF)、N2物理吸附和透射电镜等手段对催化剂进行了表征.结果表明,Ru-Fe(x)催化剂中助剂Fe以Fe3O4形式存在.单独Fe3O4并不能提高Ru催化剂的环己烯选择性.但在加氢过程中Fe3O4可与反应修饰剂ZnSO4反应生成(Zn(OH)2)3(ZnSO4)(H2O)x(x=1 or 3).化学吸附的(Zn(OH)2)3(ZnSO4)(H2O)x(x=1 or 3)在提高Ru催化剂环己烯选择性中起着关键作用.此外,Ru-Fe(x)催化剂的性能还与浆液中的Zn2+浓度和pH值有关.在0.61 mol/L ZnSO4溶液中Ru-Fe(0.47)催化剂不但给出了56.7%的环己烯收率,而且具有良好的稳定性和重复使用性能.化学吸附在Ru表面的Fe2+同样能提高Ru催化剂的环己烯选择性.在0.29 mol/L和0.61 mol/L FeSO4溶液中Ru-Fe(0.47)催化剂上化学吸附Fe2+量近似,性能近似.因为Fe2+和Zn2+性质的差异,在0.29 mol/L和0.61 mol/L FeSO4溶液中Ru-Fe(0.47)催化剂的环己烯选择性分别低于在同浓度的ZnSO4溶液中的.     

Polymer-directed synthesis and magnetic property of nanoparticles-assembled BiFeO3 microrods

Nanoparticles-assembled BiFeO₃ microrods were successfully prepared via a polymer-directed solvothermal route. The phase and morphology of the products were characterized by powder X-ray diffraction (XRD), energy dispersive spectrometry (EDS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), FT-IR spectroscopy and scanning electron microscopy (SEM). Experiments indicated that the linking effect originated from the interactions between polymer molecules could direct the self-assembly of building blocks into one-dimensional nanoparticles-assembled BiFeO₃ microrods. Some factors influencing the morphologies of the products were systematically investigated and a possible mechanism of the formation of the microrods was suggested. Moreover, the magnetic properties of the products were studied.     

Enhanced Bioelectrocatalysis Using Single‐Walled Carbon Nanotubes (SWCNTs)/Polyaniline Hybrid Systems in Thin‐Film and Microrod Structures Associated with Electrodes

The charge transport properties in composites consisting of pyrene sulfonic acid‐functionalized single‐walled carbon nanotubes embedded in polyaniline, PAn/SWCNTs, and polystyrene sulfonate‐doped PAn, PAn/PSS, are compared in thin‐film and microrods configurations. The PAn/SWCNTs and PAn/PSS microrods were prepared by the electropolymerization of the respective components in porous alumina membranes coated with a conductive gold support, followed by the dissolution of the membrane template. The charge transport upon the oxidation of the PAn/SWCNTs planar film or microrods structures is ca. 3.5–4.0‐fold faster than upon the oxidation of the PAn/PSS planar film or microrods structures, respectively. The faster charge transport in the PAn/SWCNTs films and microrods is used to enhance the mediated bioelectrocatalyzed oxidation of glucose in the presence of glucose oxidase (GOx). The bioelectrocatalyzed oxidation of glucose in the presence of the PAn/SWCNTs in the planar film and microrods structures is ca. 2‐fold and up to 6‐fold (depending on the potential) enhanced as compared to the respective PAn/PSS configurations.     

ZnO纳米片/微棒复合体的制备、结构及光学性能

以十六烷基三甲基溴化铵(CTAB)为表面活性剂,以氯化锌和氢氧化钠为原料,在低温水热条件下制备出具有纳米片状接枝结构的ZnO微棒。通过扫描电镜(SEM)、X射线衍射(XRD)、透射电镜(TEM)、光致发光(PL)和拉曼光谱(Raman)对产物的形貌、晶体结构和光学性能进行了表征。结果表明,表面活性剂CTAB对产物最终形貌的形成具有重要作用;微棒表面所接枝的薄片为多晶结构;产物光致发光峰是较少见的弱蓝光发射与强红光发射;同时对这种ZnO微棒的生长机理进行了探讨。     

Amine-controlled assembly of metal-sulfite architecture from 1D chains to 3D framework

Whereas open-framework materials have been made in a variety of chemical compositions, few are known in which 3-connected SO3(2)- anions serve as basic building units. Here, we report four new metal-sulfite polymeric structures, (ZnSO3)Py (1, py = pyridine), (ZnSO3)2(2,2'-bipy)H2O (2, 2,2'-bipy = 2,2'-bipyridine), (ZnSO3)2(TMDPy) (3, TMDPy = 4,4'-trimethylenedipyridine), and (MnSO3)2en (4, en = ethylenediamine) that have been synthesized hydrothermally and structurally characterized. In these compounds, low-dimensional 1D and 2D inorganic subunits are assembled into higher 2D or 3D covalent frameworks by organic ligands. In addition to the structure-directing effect of organic ligands, the flexible coordination chemistry of Zn2+ and SO3(2)- also contributes to the observed structural diversity. In compounds 1-3, Zn2+ sites alternate with trigonal pyramidal SO3(2)- anions to form three types of [ZnSO3]n chains, whereas in compound 4, a 2D-corrugated [MnSO3]n layer is present. Compound 1 features a rail-like chain with pendant pyridine rings. The pi-pi interaction between 2,2'-bipy ligands is found between adjacent chains in compound 2, resulting in 2D sheets that are further stacked through interlayer hydrogen bonds. Compound 3 exhibits a very interesting inorganic [(ZnSO3)2]n chain constructed from two chairlike subunits, and such chains are bridged by TMDPy ligands into a 2D sheet. In compound 4, side-by-side helical chains permeate through 2D-corrugated [MnSO3]n layers, which are pillared by neutral ethylenediamine molecules into a 3D framework that can be topologically represented as a (3,6)-connected net. The results presented here illustrate the rich structural chemistry of metal-sulfites and the potential of sulfite anions as a unique structural building block for the construction of novel open-framework materials, in particular, those containing polymeric inorganic subunits that may have interesting physical properties such as low-dimensional magnetism or electronic properties.     

The Molecular Pathway to ZIF‐7 Microrods Revealed by In Situ Time‐Resolved Small‐ and Wide‐Angle X‐Ray Scattering,Quick‐Scanning Extended X‐Ray Absorption Spectroscopy,and DFT Calculations

We present an in situ small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) and quick‐scanning extended X‐ray absorption fine‐structure (QEXAFS) spectroscopy study on the crystallization of the metal–organic framework ZIF‐7. In combination with DFT calculations, the self‐assembly and growth of ZIF‐7 microrods together with the chemical function of the crystal growth modulator (diethylamine) are revealed at all relevant length scales, from the atomic to the full crystal size.