Tong Zhang

Three-Dimensional Hierarchical Flowerlike α-Fe2O3 Nanostructures: Synthesis and Ethanol-Sensing Properties

The α-Fe(2)O(3) hierarchical nanostructures have been successfully synthesized via a simple solvothermal method. The as-prepared samples are loose and porous with flowerlike structure, and the subunits are irregularly shaped nanosheets. The morphology of the α-Fe(2)O(3) structures was observed to be tunable as a function of reaction time. To demonstrate the potential applications, we have fabricated a gas sensor from the as-synthesized hierarchical α-Fe(2)O(3) and investigated it for ethanol detection. Results show that the hierarchical α-Fe(2)O(3) sensor exhibits significantly improved sensor performances in comparison with the compact α-Fe(2)O(3) structures. The enhancement of sensing properties is attributed to the unique porous and well-aligned nanostructure.

Branch-like Hierarchical Heterostructure (α-Fe2O3/TiO2): A Novel Sensing Material for Trimethylamine Gas Sensor

A novel hierarchical heterostructure of α-Fe2O3 nanorods/TiO2 nanofibers with branch-like nanostructures was fabricated using a simple two-step process called the electrospinning technique and hydrothermal process. A high density of α-Fe2O3 nanorods (about 200 nm in diameter) was uniformly deposited on a TiO2 nanofibers backbone. The phase purity, morphology, and structure of hierarchical heterostructures are investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) analysis. The highly branched α-Fe2O3/TiO2 heterostructures provided an extremely porous matrix and high specific surface area required for high-performance gas sensors. Different nanostructured α-Fe2O3/TiO2 heterostructures are also investigated by controlling the volume ratio of the reactants. The α-Fe2O3/TiO2 heterostructures with a proper mixture ratio of the reactants sensor exhibit obviously enhanced sensing characteristics, including higher sensing response, lower operating temperature, faster response speed, and better selectivity in comparison with other ones. Moreover, the α-Fe2O3/TiO2 heterostructures sensor also exhibits excellent sensing performances compared with α-Fe2O3 nanorods and TiO2 nanofibers sensors. Thus, the combination of TiO2 nanofibers backbone and α-Fe2O3 nanorods uniformly decorated endows a fascinating sensing performance as a novel sensing material with high response and rapid responding and recovering speed.

Ethanol Gas Detection Using a Yolk-Shell (Core-Shell) α-Fe2O3 Nanospheres as Sensing Material

Three-dimensional (3D) nanostructures of α-Fe2O3 materials, including both hollow sphere-shaped and yolk-shell (core-shell)-shaped, have been successfully synthesized via an environmentally friendly hydrothermal approach. By expertly adjusting the reaction time, the solid, hollow, and yolk-shell shaped α-Fe2O3 can be selectively synthesized. Yolk-shell α-Fe2O3 nanospheres display outer diameters of 350 nm, and the interstitial hollow spaces layer is intimately sandwiched between the inner and outer shell of α-Fe2O3 nanostructures. The possible growth mechanism of the yolk-shell nanostructure is proposed. The results showed that the well-defined bilayer interface effectively enhanced the sensing performance of the α-Fe2O3 nanostructures (i.e., yolk-shell α-Fe2O3@α-Fe2O3), owing predominantly to the unique nanostructure, thus facilitated the transport rate and augmented the adsorption quantity of the target gas molecule under gas detection.

Cross-linked p-type Co3O4 octahedral nanoparticles in 1D n-type TiO2 nanofibers for high-performance sensing devices

Quasi-1D nanofibers with heterostructure were prepared via a simple two-step process called the electrospinning technique and hydrothermal process. The nanostructures exhibit the unique feature of TiO2 nanofibers (250 nm) kept inside and well-structured Co3O4 octahedral nanoparticles loading outside. The cross-linked Co3O4/TiO2 nanostructures exhibit intriguing morphologies, architectures and chemical compositions. As a potential sensing material in chemosensor applications, the quasi-1D heterostructure nanofibers exhibit a relatively high catalysis response to CO, and good CO-sensing performance even exposure to a humid environment.

Humidity-Sensing Properties of Urchinlike CuO Nanostructures Modified by Reduced Graphene Oxide

Urchinlike CuO modified by reduced graphene oxide (rGO) was synthesized by a one-pot microwave-assisted hydrothermal method. The as-prepared composites were characterized using various characterization methods. A humidity sensor based on the CuO/rGO composites was fabricated and tested. The results revealed that the sensor based on the composites showed much higher impedance than pure CuO. Compared with the sensors based on pristine rGO and CuO, the sensor fabricated with the composites exhibited relatively good humidity-sensing performance in terms of response time and response value. The humidity-sensing mechanism was also briefly introduced. The enlargement of the impedance and improvement of the humidity-sensing properties are briefly explained by the Schottky junction theory.

Zinc oxide core–shell hollow microspheres with multi-shelled architecture for gas sensor applications

A new type of spherically multilayered core–shell structure was prepared via a simple hard template strategy in the case of ZnO. The structure and morphology characteristics of the resultant product were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The ZnO microspheres with hollow interior and porous shells are multilayered structures with diameters ranging from 0.4 to 3.5 μm. Further investigation of the formation mechanism reveals that the preheating program is vital to the formation of the multishelled structures. To demonstrate the usage of such a multilayered nanomaterial, a chemical gas sensor has been fabricated and investigated for toluene detection. The sensor exhibits excellent sensing performances in terms of high response, low detection limit, rapid response-recovery, and superior selectivity.

Templating synthesis of ZnO hollow nanospheres loaded with Au nanoparticles and their enhanced gas sensing properties

Au-loaded ZnO hollow nanospheres have been successfully synthesized by using carbon nanospheres as sacrificial templates. This simple strategy could be expected to be extended for the fabrication of similar metal–oxide loaded hollow nanospheres using different precursors. The structural and morphological characteristics of the resultant product were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The hollow nanospheres are porous, with the diameters ranging from 220 to 280 nm. To demonstrate the usage of such Au-loaded ZnO nanomaterial, a chemical gas sensor has been fabricated and investigated for NH3 detection. The Au-loaded ZnO sensor exhibits excellent sensing performances compared with hollow ZnO and compact ZnO sensors. The dynamic transients of the Au-loaded ZnO sensors demonstrated both their fast response (0.8–1.5 s) and recovery (3–4 s) towards NH3 gases. The combination of ZnO hollow structure and catalytic activity of Au loaded gives a very attractive sensing behavior for applications as real-time monitoring gas sensors with fast responding and recovering speed.

Synthesis and gas-sensing characteristics of WO3 nanofibers via electrospinning

WO(3) nanofibers were synthesized using an electrospinning method and characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The obtained WO(3) nanofibers were used as sensitive materials for the detection of NH(3). Indirect-heating sensors based on WO(3) nanofibers were prepared. When the WO(3) nanofiber-based sensors were exposed to 100 ppm NH(3) at 500°C, the response is 5.5, and the response and recovery times are 1 and 5s, respectively. These results indicate that the gas sensors based on WO(3) nanofibers express high and fast response and recovery characteristics to NH(3), and the WO(3) nanofibers are promising sensitive materials for NH(3) detecting.

Surface state studies of TiO2 nanoparticles and photocatalytic degradation of methyl orange in aqueous TiO2 dispersions

Abstract Nanocrystalline TiO2 is prepared using a stearic acid gel method. Their surface state is analyzed by means of X-ray photoelectron spectroscopy (XPS). The photocatalytic degradation of methyl orange in TiO2 suspension is investigated. The relationships between surface state and photocatalytic activity are discussed.

Synthesis, optical and gas sensitive properties of large-scale aggregative flowerlike ZnO nanostructures via simple route hydrothermal process

Large-scale aggregative flowerlike ZnO nanostructures, consisting of many bunches of nanorods at different orientations with a diameter of about 60 nm and a length of 1 µm, have been synthesized through a simple hydrothermal process at a lower temperature. The x-ray power diffraction pattern indicates that the novel flowerlike ZnO nanostructures are hexagonal, and the selected area electron diffraction reveals that the ZnO nanorods are single crystal in nature and preferentially grow along [0 0 1]. Raman spectrum, room-temperature photoluminescence and UV–vis absorption spectra are also discussed. Furthermore, the influence of the reaction time on the morphology of the ZnO nanostructures is investigated, and a possible growth model is proposed. Finally, the gas sensor based on the ZnO nanostructures exhibits high sensitivity for ethanol as well as quick response and recovery time due to the high surface-to-volume ratio.