Ming-Shui Yao

MOF Thin Film-Coated Metal Oxide Nanowire Array: Significantly Improved Chemiresistor Sensor Performance.

A strategy for combining metal oxides and metal-organic frameworks is proposed to design new materials for sensing volatile organic compounds, for the first time. The prepared ZnO@ZIF-CoZn core-sheath nanowire arrays show greatly enhanced performance not only on its selectivity but also on its response, recovery behavior, and working temperature.

A comprehensive review on synthesis methods for transition-metal oxide nanostructures

Nanostructured transition-metal oxides exhibit excellent properties, such as ferromagnetic, ferroelectric, photoluminescence and semiconductive behaviors, etc. The band gap and electronic structure of these oxides can be controlled by size and dimensions; they can also be used in a wide range of applications including microelectronics, energy storage, sensors, and biomedicine due to their tunable chemical and physical properties. Here, we give a comprehensive review of the controllable growth of some typical transition-metal oxide nanostructures (e.g., WOx, FeOx, ZnO, TiO2, VO2, etc.), which can be used to effectively understand the fabrication methods as well as the growth mechanism and inspire their potential applications.

A new synthetic route to hollow Co3O4 octahedra for supercapacitor applications

Co3O4 hollow octahedra were successfully synthesized via a facile one-step solvothermal route. Time-resolved electron microscopy and X-ray diffraction analyses revealed that the Co3O4 hollow octahedra were formed through the self-assembly of primary nanocrystals followed by subsequent Ostwald ripening. Subtle control over the reaction conditions led to different morphologies (hexagonal plates and nanocubes) and crystal structures (β-Co(OH)2–Co3O4 composite). The unique hollow nanostructure rendered our Co3O4 potentially useful for charge-storage applications. To prove its usefulness, the pseudocapacitive performance of the Co3O4 hollow octahedra as a supercapacitor electrode was evaluated and exhibited a charge storage capacity of 192 F g−1 with good long-term cyclability.

Semiconductive Nanotube Array Constructed from Giant [PbII18I54(I2)9] Wheel Clusters

Crystalline nanotube array would create great opportunity for novel electrical application. Herein we report the first example of a metal halide based crystalline nanotube array which is constructed from an unprecedented giant [Pb(II)18I54(I2)9] wheel cluster, as determined by synchrotron X-ray diffraction. The electrical properties of the single crystal were studied and the present compound shows typical semiconductivity and highly anisotropic conductivity.

Fabrication of ZnO nanorod-assembled multishelled hollow spheres and enhanced performance in gas sensor

In this work, ZnO multishelled hollow spheres with an average diameter of 5 μm were prepared by a facile solvothermal process in a ternary solvent system including water, ethanol and ethylene, and as-synthesized products were constructed by highly directional interactions of anisotropic single-crystalline ZnO nanorods. A two-step assembly process followed symmetric Ostwald ripening process is proposed to explain the formation mechanism of obtained products, which highlights the driving force of the solvents in promoting the nanorod aggregation and the solid evacuation of final products. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy were used to characterize the structure of synthesized products. The investigation of the gas-sensing properties indicated that control of the shape-defined building units and their assembled structure provides ZnO with high performance in gas sensing, and the double-wall hollow structures exhibit the highest sensitivity to formaldehyde gas than the nanorods and hollow spheres, which is contributed to their high donor-related and the low acceptor-related intrinsic defects in ZnO crystals.

Synthesis of uniform octahedral tungsten trioxide by RF induction thermal plasma and its application in gas sensing

Well-defined uniform octahedral WO3 are prepared via a simple one-step thermal plasma technique. The detailed structures of the synthesized materials are characterized by XRD, EDX, FESEM, SAED and HRTEM. Each octahedron is nearly perfect with a highly symmetric, regular shape containing 8 facets, 6 vertices, and 12 edges, which exhibit sharp edges and corners as well as smooth surfaces. Processing parameters dependent experiments are performed to control its shape and size distribution. The regular octahedral WO3 shows good sensing properties to benzene gas, which might mainly be due to its highly exposed {111} faces and the regular octahedral shape.

Layer-by-Layer Assembled Conductive Metal-Organic Framework Nanofilms for Room-Temperature Chemiresistive Sensing

The utility of electronically conductive metal-organic frameworks (EC-MOFs) in high-performance devices has been limited to date by a lack of high-quality thin film. The controllable thin-film fabrication of an EC-MOF, Cu3 (HHTP)2 , (HHTP=2,3,6,7,10,11-hexahydroxytriphenylene), by a spray layer-by-layer liquid-phase epitaxial method is reported. The Cu3 (HHTP)2 thin film can not only be precisely prepared with thickness increment of about 2 nm per growing cycle, but also shows a smooth surface, good crystallinity, and high orientation. The chemiresistor gas sensor based on this high-quality thin film is one of the best room-temperature sensors for NH3 among all reported sensors based on various materials.

Dopant-Controlled Morphology Evolution of WO3 Polyhedra Synthesized by RF Thermal Plasma and Their Sensing Properties

In this paper, a simple way is developed for the synthesis of Cr-doped WO3 polyhedra controlled by tailoring intrinsic thermodynamic properties in RF thermal plasma. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy are used to characterize the detail structures and surface/near-surface chemical compositions of the as-prepared products. Kinetic factors showed little effects on the equilibrium morphology of Cr-doped WO3 polyhedra, while equilibrium morphologies of WO3 polyhedra can be controlled by the thermodynamic factor (Cr doping). Set crystal growth habits of pure WO3 as an initial condition, coeffects of distortions introduced by Cr into the WO3 matrix, and a chromate layer on the crystal surface could reduce the growth rates along [001], [010], and [100] directions. The morphology evolution was turning out as the following order with increasing Cr dopants: octahedron-truncated octahedron-cuboid. 2.5 at. % Cr-doped WO3 polyhedra exhibit the highest sensing response due to coeffects of exposed crystal facets, activation energy, catalytic effects of Cr, and particle size on the surface reaction and electron transport units. By simply decorating Au on Cr-doped WO3 polyhedra, the sensing responses, detection limit, and response-recovery properties were significantly improved.

A new azodioxy-linked porphyrin-based semiconductive covalent organic framework with I2 doping-enhanced photoconductivity

A room-temperature solution phase reaction was developed to synthesize a covalent organic framework (COF) for the first time. The synthesized azodioxy-linked porphyrin-based COF (POR-COF) possesses a 2D chess board-like structure in the ab-plane and a 1D channel with an open-window size of around 1.9 nm along the c-axis in the modeled crystal structure. The electrical conductivity of POR-COF increases by more than 3 orders of magnitude through I2 doping. The photoconductivity of the I2-doped COF material was also studied firstly. POR-COF shows interesting doping-enhanced photo-current generation.

Synthesis of uniform α-Si3N4 nanospheres by RF induction thermal plasma and their application in high thermal conductive nanocomposites.

In this paper, single-crystalline α-Si3N4 nanospheres with uniform size of ∼50 nm are successfully synthesized by using a radio frequency (RF) thermal plasma system in a one-step and continuous way. All Si3N4 nanoparticles present nearly perfect spherical shape with a narrow size distribution, and the diameter is well-controlled by changing the feeding rate. Compact Si3N4/PR (PR = phenolic resin) composites with high thermal conductivity, excellent temperature stability, low dielectric loss tangent, and enhanced breakdown strength are obtained by incorporating the as-synthesized Si3N4 nanospheres. These enhanced properties are the results of good compatibility and strong interfacial adhesion between compact Si3N4 nanospheres and polymer matrix, as large amount of Si3N4 nanospheres can uniformly disperse in the polymer matrix and form thermal conductive networks for diffusion of heat flow.