Metal–Organic Frameworks Derived from Zero‐Valent Metal Substrates: Mechanisms of Formation and Modulation of Properties

The replicative construction of metal–organic frameworks (MOFs) templated with solvent‐insoluble solid substrates is of marked importance, as it allows for the assembly of 2D and 3D macro‐ and mesoscopic architectures with properties that are challenging to attain by the conventional solution‐based synthesis approach. This work reports an in situ and direct construction of MOFs from zero‐valent metal substrates via a green hydrothermal oxidation–MOF construction chemistry without the use of any additional metal source, chemical reagents, or acidification of solvent, and elucidates the zero‐valent metal derived formation mechanisms of MOFs and their structure modulation to 1D nanofibers (NFs), 2D film, and 3D core–shell microstructures. Through modulation of the competing surface oxidation‐dissolution and MOF crystallization kinetics, Al@MIL‐53 core–shell microstructures and MIL‐53 (Al) NFs are obtained that exhibit unique morphologies and marked properties superior to the conventional MIL‐53 (Al) powders. The generality of zero‐valent metal‐templated synthesis of MOFs is demonstrated with formation of MIL‐53 (Al), HKUST‐1, and ZIF‐7 polycrystalline films on Al, Cu, and Zn metal meshes, elucidating the significance of the approach utilizing solid metal substrate that can be easily processed into various shapes, architectures, and compositions.     

ZnO/ZnS核/壳纳米结构的形态及其演变模式

用两步生长的方法在醋酸锌和六亚甲基四胺水溶液中生长ZnO纳米棒阵列,然后以ZnO纳米棒阵列为模板,在Na2S水溶液中硫化0.5～6 h形成ZnO/ZnS纳米结构.用XRD,SEM和TEM表征了ZnO/ZnS核/壳纳米结构的晶体结构、表面形貌.研究了ZnO/ZnS核/壳纳米结构的形态及其转变的模式.在硫化过程中,ZnO首先形成ZnO/ZnS核/壳纳米棒,随着硫化程度的增强,核/壳结构顶部出现空洞,空洞扩展形成管状结构,进一步硫化,管状结构坍塌.硫化形成的ZnO/ZnS结构的形态不仅依赖于初始纳米棒的直径大小和硫化时间的长短,还依赖于纳米棒的分布密度.     

Monodisperse Hollow Supraparticles via Selective Oxidation

A novel and general strategy to fabricate monodisperse hollow supraparticles (SPs) via selective chemical oxidation is developed. Core‐shell SPs made of semiconductor nanocrystals (NCs) are first obtained by an in situ assembly method. Subsequently, the cores can be selectively removed by preferential oxidation with dilute H₂O₂, resulting in formation of monodisperse hollow SPs. The structural parameters of the products, such as size, shell thickness, and composition, are tailored easily. The hollow structures achieved from CdSe/CdS core‐shell SPs possess high fluorescence quantum yields and a large Stokes shift, the latter is remarkably different from that of conventional organic dyes and quantum dots. In addition to simple hollow structures, rattle‐type nanostructures composed of semiconductor SPs or noble metal‐semiconductor hybrids are also prepared, exemplifying the versatility of the proposed strategy.     

Synthesis of Au–CdS Core–Shell Hetero‐Nanorods with Efficient Exciton–Plasmon Interactions

The synthesis of large lattice mismatch metal‐semiconductor core–shell hetero‐nanostructures remains challenging, and thus the corresponding optical properties are seldom discussed. Here, we report the gold‐nanorod‐seeded growth of Au–CdS core–shell hetero‐nanorods by employing Ag₂S as an interim layer that favors CdS shell formation through a cation‐exchange process, and the subsequent CdS growth, which can form complete core–shell structures with controllable shell thickness. Exciton–plasmon interactions observed in the Au–CdS nanorods induce shell thickness‐tailored and red‐shifted longitudinal surface plasmon resonance and quenched CdS luminescence under ultraviolet light excitation. Furthermore, the Au–CdS nanorods demonstrate an enhanced and plasmon‐governed two‐photon luminescence under near‐infrared pulsed laser excitation. The approach has potential for the preparation of other metal‐semiconductor hetero‐nanomaterials with complete core–shell structures, and these Au–CdS nanorods may open up intriguing new possibilities at the interface of optics and electronics.     

“Ship‐in‐a‐Bottle” Growth of Noble Metal Nanostructures

Noble metal nanostructures are grown inside hollow mesoporous silica microspheres using “ship‐in‐a‐bottle” growth. Small Au seeds are first introduced into the interior of the hollow microspheres. Au nanorods with synthetically tunable longitudinal plasmon wavelengths and Au nanospheres are obtained through seed‐mediated growth within the microspheres. The encapsulated Au nanocrystals are further coated with Pd or Pt shells. The microsphere‐encapsulated bimetallic core/shell nanostructures can function as catalysts. They exhibit high catalytic performance and their stability is superior to that of the corresponding unencapsulated core/shell nanostructures in the catalytic oxidation of o‐phenylenediamine with hydrogen peroxide. Therefore, these hollow microsphere‐encapsulated metal nanostructures are promising as recoverable and efficient catalysts for various liquid‐phase catalytic reactions.     

Vertically Aligned Hybrid Core/Shell Semiconductor Nanowires for Photonics Applications

A family of 1D organic/inorganic core/shell materials formed by an inner organic nanowire (ONW) conformally covered with an inorganic wide band gap semiconductor (ZnO or TiO₂) layer is presented. The developed procedure is a two‐steps vacuum methodology involving the formation of supported single crystal small‐molecule nanowires by physical vapor deposition and plasma enhance chemical vapor deposition (PECVD) of the inorganic shell. Critical characteristics of the last technique are the possibilities of low temperature and remote configuration deposition. Additionally, an initial step has to be included in order to create nucleation centers for the growth of the ONWs. The procedure and its general character in terms of the variability in organic core and inorganic shells composition and the applicability of the technique to different substrates are presented. The formation of the inorganic shell with no damage of the organic core single‐crystalline structure is demonstrated by high resolution transmission electron microscopy. The vertical alignment of the hybrid nanostructure is achieved thanks to the interaction of the 1D organic nanostructured surfaces and the glow discharge during the deposition of the inorganic shell by PECVD. The optical properties of these core/shell NWs are studied by fluorescence spectroscopy and microscopy, and their application as nanoscale waveguides in the 550–750 nm range addressed.     

Self‐Organization and/or Nanocrystallinity of Co Nanocrystals Effects on the Oxidation Process Using High‐Energy Electron Beam

The enhanced stability of Co nanocrystals (NCs) when they are highly ordered at both nanometer and micrometer scales is reported. For the first time, it is shown that both the crystalline structure of Co nanoparticles (NPs) and their 2D hexagonal organization have a significant impact on the oxidation process rate enabling to produce various types of nanostructures including core‐shell NPs. The Co core can be either polycrystalline or hexagonal close‐packed (hcp) single‐crystalline, whereas the oxide shell is composed either of CoO or of the spinel structrure Co₃O₄. The present results are evidenced through a careful high‐resolution transmission electron microscopy (HRTEM) study and are highly reproducible.     

A Three‐Dimensional Gold‐Decorated Nanoporous Copper Core–Shell Composite for Electrocatalysis and Nonenzymatic Biosensing

Bimetallic core–shell nanostructures have attracted increasing attention due to their low material costs along with enhanced chemico‐physical properties in comparison with their monometallic counterparts. Here, a novel gold‐decorated nanoporous copper (Au@NPC) core–shell composite fabricated by a facile in situ hydrometallurgy approach is reported. Thin gold shells with a controllable thickness are homogeneously deposited onto the internal surfaces of 3D nanoporous copper via a spontaneous displacement reaction while nanoporous copper is utilized as a reduction agent as well as 3D template and substrate. The resulting inexpensive core–shell nanostructure exhibits significant electrocatalytic activity for the oxidation of methanol and high non‐enzymatic sensitivity in detecting glucose.     

The Development of Yolk–Shell‐Structured Pd&ZnO@Carbon Submicroreactors with High Selectivity and Stability

Design of multicomponent yolk–shell structures is crucial for the fabrication of micro/nanoreactors for a variety of applications. This work reports the rational design and synthesis of yolk–shell‐structured submicroreactors with loaded metal nanoparticles into ZnO–microporous carbon core–shell structures. The solvothermal treatment and carbonization process of uniform zeolitic imidazolate framework‐8 (ZIF‐8)@resin polymer core–shell structures leads to the generation of yolk–shell‐structured ZnO@carbon. The synthesis conditions are optimized to track the evolution of ZIF‐8 in a confined space of resin polymer as a submicroreactor itself. It is found that nanoribbon evolution occurs via the formation of the intermediate needle‐like particles. The Pd&ZnO@carbon submicroreactor is shown to be a highly selective catalyst (selectivity >99%) for hydrogenation of phenylacetylene to phenylethylene. The excellent performance of Pd&ZnO@carbon particles is evidenced by higher conversion and selectivity than that of Pd/ZnO and Pd/C with similar Pd loading. Furthermore, Pd&ZnO@carbon submicroreactors show superior catalytic stability, and no deactivation after 25 h of reaction. The proposed strategy is promising for the design of multifunctional micro/nanoreactors or nanocontainers for construction of artificial cells.     

多种ZnO纳米结构和ZnO/ZnS核壳结构的制备

以Zn(NO3)2.6H2O和CO(NH2)2为原料,采用均匀沉淀法,制备出了棒状、花状、球状纳米氧化锌(ZnO)。将ZnO微球体分散在Na2S溶液中,通过离子替代法,成功制备了ZnO/ZnS核壳结构。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)等测试手段对ZnO纳米结构和ZnO/ZnS核壳结构的晶体结构和表面形貌进行了表征,初步探讨了纳米ZnO和ZnO/ZnS核壳结构的生长机理。根据测试结果得知,ZnO纳米棒呈现六方纤锌矿结构,随着Zn2+浓度逐渐增加,ZnO纳米结构形貌由单分散的棒状聚集成花状,最后演变成球形。ZnO/ZnS复合结构为内核ZnO,外面包覆一层ZnS的核壳结构。所有的纳米ZnO均具有相似的发光特点,ZnO/ZnS核壳结构的发光性能有了很大的改善。     

Control of the Oxygen and Cobalt Atoms Diffusion through Co Nanoparticles Differing by Their Crystalline Structure and Size

The size‐dependent Kirkendall effect is studied by using Co nanoparticles. The sizes of Co nanoparticles differing by their crystal structures called nanocrystallinity, namely amorphous, polycrystalline fcc, single crystalline hcp, and single crystalline ε phase, are modulated from 4 to 10 nm. The nanoparticles self‐assembled in 2D superlattices and differing by their nanocrystallinities are subjected to oxygen at 200 °C for 10 min. With single‐domain nanocrystals differing by their crystalline structure (ε and hcp phases), marked changes in the final structures are observed: upon increasing the nanocrystal size, the ε phase favors formation of a hollow structure whereas a transition from single‐domain hollow to multidomain core/shell structures takes place with the hcp phase. With polycrystalline fcc Co nanocrystals, a transition from a hollow to a yolk/shell structure is observed, whereas with amorphous cobalt, solid CoO nanoparticles are produced at the smaller size and are converted to the core/shell structure at the larger one. These differences in size effect are attributed to the change in the control of the inward flow of oxygen atoms and the outward flow of Co atoms with the crystalline structure of cobalt nanoparticles. Such a diffusion process described here on the Kirkendall effect can be studied for other metal nanocrystals.     

Zn/Co金属有机框架的制备及其对正丁醇的气敏特性

采用水热法合成了Co3O4、ZnO和Zn/Co金属有机框架(Zn/Co-MOF)纳米结构。利用扫描电子显微镜(SEM)和X射线衍射仪(XRD)对其形貌和晶体结构进行了表征,分析结果表明制备的Zn/Co-MOF为边长约300 nm的立方体结构。制备了基于Co3O4、ZnO和Zn/Co-MOF纳米结构的气体传感器,并对正丁醇进行了气敏性能研究。实验结果表明:三种气体传感器对正丁醇均有明显的响应,其中Zn/Co-MOF气体传感器的气敏性能最优。Zn/Co-MOF气体传感器最佳工作温度为200℃,其对体积分数为1×10^-4正丁醇气体的灵敏度为59.18,响应/恢复时间分别约为39 s和40 s。同时,Zn/Co-MOF传感器还具有良好的选择性、重复性和长期稳定性。     

Controlled Growth and Properties of One‐Dimensional ZnO Nanostructures with Ce as Activator/Dopant

A large amount of one‐dimensional (1D) Ce‐doped ZnO nanostructures with different morphologies has been successfully synthesized by annealing a polymeric precursor at various temperatures. The evolution of the morphologies and microstructures was investigated by field‐emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), and high‐resolution TEM (HRTEM). The results show that the morphologies vary drastically with increasing synthesis temperature and the photoluminescence (PL) of the products depends on both the synthesis and measurement temperatures. The CeO layer forms first and becomes a catalytic center for the ZnO growth. At a synthesis temperature lower than the boiling point of Zn, Zn and O atoms can stack epitaxially along the CeO catalytic layer and form a bicrystal nanobelt‐like structure with a trapezoid‐like end and a concave growth fault center. At a synthesis temperature higher than the boiling point of Zn, however, nanowires with an incommensurately modulated superstructure are obtained due to the high reaction rate and the formation of a periodic separation of the CeO layer. As for the room‐temperature PL of ZnO, the incorporation of donor Ce leads to the disappearance of the green band and the appearance of a purplish‐blue emission peak, whose position shifts towards the red and whose intensity decreases with increasing synthesis temperature. Analysis of this temperature‐dependent luminescence indicates that the purplish‐blue emission of nanobelts prepared at 850 °C originates from a donor‐bound exciton emission, and, contrary to the nanowires, it undergoes a change from an emission of the electron–hole plasma (EHP) to an emission of the donor‐bound exciton with decreasing measurement temperature.     

From Layered Basic Zinc Acetate Nanobelts to Hierarchical Zinc Oxide Nanostructures and Porous Zinc Oxide Nanobelts

Novel hierarchical ZnO nanostructures, porous ZnO nanobelts, and nanoparticle chains are prepared from a precursor of synthetic bilayered basic zinc acetate (BLBZA) nanobelts. BLBZA nanobelts are obtained by a simple synthetic route under mild conditions. X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, and thermal analysis are used to characterize the BLBZA nanobelts and ZnO nanostructures. The obtained BLBZA precursor consists of a lamellar structure with two interlayer distances of 1.33 and 2.03 nm, exhibits a beltlike morphology, and has widths of 200 to 600 nm, thicknesses of 10 to 50 nm, and lengths of up to 50 μm. Refluxing an aqueous dispersion of BLBZA nanobelts at 120 °C for 12 h leads to the formation of well‐defined hierarchical ZnO nanostructures. The time‐dependent shape‐evolution process suggests that spindlelike ZnO particles form first, and then the ringlike nanosheets grow heterogeneously on the backbone of these spindles. In addition, calcination in air can remove ligand molecules and intercalated water molecules from BLBZA nanobelts, resulting in the formation of porous ZnO nanobelts and nanoparticle chains. The BLBZA nanobelts serve as templates during the transformation to form ZnO beltlike nanoparticle chains without morphological deformation. Photoluminescence results show that both the as‐synthesized hierarchical ZnO nanostructures and porous ZnO nanobelts show a narrow and sharp UV emission at 390 nm and a broad blue–green emission at above 466 nm when excited by UV light.     

具有核/壳结构的纳米复合高频软磁材料

具有核/壳结构的复合纳米材料兼有外壳层和内核材料的性能,由于其结构和组成能够在nm尺度上进行设计和剪裁,因而具有许多独特的光、电、磁、催化等物理与化学性质。简要介绍了实验室在过渡金属纳米复合高频软磁材料研究方面的最新进展,内容包括:绝缘壳层(如SiO2、Al2O3、C-SiO2等)复合材料,能显著改善过渡金属纳米颗粒的热温度性,有效防止氧化和团聚,具有饱和磁化强度高、高频软磁性能优异的特点;半导体壳层(如ZnO)复合材料,研究了材料的光致发光性能,观测到在ZnO材料中较少出现的700nm发光峰;螺旋碳纳米管与Fe组成的复合材料,实验结果表明该复合材料具有良好的高频吸波性能,有望成为新一代轻质高频吸波材料。     

Pseudobinary Solid‐Solution: An Alternative Way for the Bandgap Engineering of Semiconductor Nanowires in the Case of GaP–ZnSe

Bandgap engineering of semiconductor nanostructures is of significant importance either for the optical property tailoring or for the integration of functional optoelectronic devices. Here, an efficient way to control the bandgap and emission wavelength is reported for a binary compound semiconductor through alloying with another binary compound. Taking GaP‐ZnSe system as an example, the bandgap of quaternary GaP‐ZnSe solid‐solution nano­wires can be selectively tailored in the range of 1.95–2.2 eV by controlling the solubility of ZnSe dopants in GaP host. High‐resolution transmission electron microscopy measurement and chemical analyses using an X‐ray energy dispersive spectrometer (EDS) demonstrate the solid‐solution feature of GaP‐ZnSe semiconductor alloy, while X‐ray photoelectron spectroscopy (XPS) characterization verifies the formation of some new chemical bonds corresponding to Zn‐P and Ga‐S bonds in GaP‐ZnSe nanowires. The strategy to tailor the optoelectronic property of semiconductor nanostructures through the solid‐solution of two different binary compounds represents a general routine to the property modification of all pseudobinary systems and will open more opportunity for their applications in electronics, optics and optoelectronics.     

Formation of Gold and Silver Nanoparticle Arrays and Thin Shells on Mesostructured Silica Nanofibers

Mesostructured silica nanofibers synthesized in high yields with cetyltrimethylammonium bromide as the structure‐directing agent in HBr solutions are used as templates for the assembly of Au and Ag nanoparticles and the formation of thin Au shells along the fiber axis. Presynthesized spherical Au and Ag nanoparticles are adsorbed in varying amounts onto the silica nanofibers through bifunctional linking molecules. Nonspherical Au nanoparticles with sharp tips are synthesized on the nanofibers through a seed‐mediated growth approach. The number density of nonspherical Au nanoparticles is controlled by varying the amount of seeded nanofibers relative to the amount of supplied Au precursor. This seed‐mediated growth is further used to form continuous Au shells around the silica nanofibers. Both the Au‐ and Ag‐nanoparticle/silica‐nanofiber hybrid nanostructures and silica/Au core/shell fibers exhibit extinction spectra that are distinct from the spectra of Au and Ag nanoparticles in solution, indicating the presence of new surface plasmon resonance modes in the silica/Au core/shell fibers and surface plasmon coupling between closely spaced metal nanoparticles assembled on silica nanofibers. Spherical Au‐ and Ag‐nanoparticle/silica‐nanofiber hybrid nanostructures are further used as substrates for surface‐enhanced Raman spectroscopy, and the enhancement factors of the Raman signals obtained on the Ag‐nanoparticle/silica‐nanofiber hybrid nanostructures are 2 × 10⁵ for 4‐mercaptobenzoic acid and 4‐mercaptophenol and 7 × 10⁷ for rhodamine B isothiocyanate. These hybrid nanostructures are therefore potentially useful for ultrasensitive chemical and biological sensing by using molecular vibrational signatures.     

基于多孔氧化铝模板的一维ZnO纳米线的制备

多孔氧化铝由于具有纳米级的孔径、尺寸可调等独特的优点,成为合成纳米材料的一种常用模板.以多孔氧化铝为模板,制备出了纳米量级的纤维、纳米棒、金属管、半导体等新型材料.制备出了优良的多孔氧化铝有序孔洞阵列;以其为模板,采用直流电化学沉积的方法,在其规则排列的孔中沉积得到锌的纳米线;然后将其在高温下氧化,得到氧化锌的纳米线.利用X射线衍射谱、扫描电子显微镜等手段研究了它们的微结构性质,X射线衍射谱表明,用电化学沉积方法得到的锌和氧化锌纳米线均为多晶结构.     

Properties of phosphorus-doped (Zn,Mg)O thin films and device structures

The properties of phosphorus-doped (Zn,Mg)O polycrystalline and epitaxial thin films are described. The as-deposited (Zn,Mg)O:P films are n type with high electron carrier density. High resistivity is induced in the films with moderate temperature annealing, which is consistent with suppression of the donor state and activation of the deep acceptor. The resistivity of the as-deposited and annealed film is an order of magnitude higher than similar samples with no Mg, consistent with a shift in the conduction band edge relative to the defect-related donor state. The capacitance-voltage characteristics of annealed metal/insulator/P-doped (Zn,Mg)O structures in which the (Zn,Mg)O is polycrystalline exhibit p-type polarity. In addition, multiple polycrystalline devices comprising n-type ZnO/P-doped (Zn,Mg)O thin-film junctions display asymmetric I–V characteristics that are consistent with the formation of a p-n junction at the interface, although the ideality factor is anomalously high.     

Modus Operandi of Simultaneous Covering Synthesis from Precursor Heterogeneity for Shelled Nanorods for Multipotent Cancer Theranostics

The synthesis of nanostructures using homogeneous precursors in the solution phase is widely used to achieve uniformity and well‐defined morphological control. However, drawbacks such as the lack of diversity due to the limited reaction rate modulation exist. One‐step, core–shell nanorod formation using simultaneous covering synthesis using solid and ionic heterogeneous precursors is proposed in this study. A Te‐Bi₂Te₃/TeO₂ core–shell structure is successfully synthesized by precisely controlling various influencing factors, including concentration, temperature, and pH, and its physicochemical and photochemical properties are thoroughly investigated. The proposed nanostructure overcomes the oxidation susceptibility of Te and can be applied to multipotent cancer theranostics in vitro and in vivo in combination with computed tomography imaging.