Mingqing Yang

Fine tuning of the morphology of copper oxide nanostructures and their application in ambient degradation of methylene blue.

In this work, flower-like, boat-like, plate-like and ellipsoid-like copper oxide (CuO) nanostructures were fabricated by simple modulation of reaction conditions. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, nitrogen adsorption-desorption measurements and UV-visible diffuse reflectance spectra were employed to characterize the obtained CuO nanostructures. Reactants, hydrothermal temperature and time were found to largely affect the morphology and structure of CuO nanostructures. Flower-like and boat-like CuO nanostructures were successively fabricated by increasing hydrothermal time. Plate-like and ellipsoid-like CuO nanostructures were produced by modulating the use of polyethylene glycol (PEG) and NH(3)·H(2)O. The formation mechanisms were proposed based on the experimental results, which show that both PEG and NH(3)·H(2)O play an important role in the formation of the morphology and structure of CuO. The catalytic activity of the as-prepared CuO nanostructures was demonstrated by catalytic oxidation of methylene blue (MB) in presence of hydrogen peroxide (H(2)O(2)). The as-prepared CuO nanostructures all show good catalytic activity.

CuO Nanostructures As Quartz Crystal Microbalance Sensing Layers for Detection of Trace Hydrogen Cyanide Gas

In this work, quartz crystal microbalance (QCM) sensors for detection of trace hydrogen cyanide (HCN) gas were developed based on nanostructural (flower-like, boat-like, ellipsoid-like, plate-like) CuO. Responses of all the sensors to HCN were found to be in an opposite direction as compared with other common volatile substances, offering excellent selectivity for HCN detection. The sensitivity of these sensors is dependent on the morphology of CuO nanostructures, among which the plate-like CuO has the highest sensitivity (2.26 Hz/μg). Comparison of the specific surface areas of CuO nanostructures shows that CuO of higher surface area (9.3 m(2)/g) is more sensitive than that of lower surface area (1.5 m(2)/g), indicating that the specific surface area of these CuO nanostructures plays an important role in the sensitivity of related sensors. On the basis of experimental results, a sensing mechanism was proposed in which a surface redox reaction occurs between CuO and Cu(2)O on the CuO nanostructures reversibly upon contact with HCN and air, respectively. The CuO-functionalized QCM sensors are considered to be a promising candidate for trace HCN gas detection in practical applications.

Glycine-assisted hydrothermal synthesis of peculiar porous α-Fe2O3 nanospheres with excellent gas-sensing properties

In this work, peculiar porous alpha-Fe(2)O(3) nanospheres were fabricated by a glycine-assisted hydrothermal method. They have large mesopores (ca. 10nm) in the core and small mesopores (<4 nm) in the shell. To our best knowledge, there have been so far no reports on the synthesis of such peculiar porous alpha-Fe(2)O(3) nanospheres. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy were employed to characterize the obtained Fe(2)O(3) nanospheres. Effects of preparation conditions, such as reactants, reaction temperature and reaction duration, were investigated on the morphology and structure of Fe(2)O(3) nanospheres. It was shown that the morphology and structure could be readily controlled by the time and temperature of hydrothermal treatment. The formation mechanism was proposed based on experimental results, which shows that glycine molecules play an important role in the formation of the morphology and porous structure of alpha-Fe(2)O(3). The alpha-Fe(2)O(3) porous nanospheres were used as gas sensing layer, and exhibited excellent gas-sensing properties to ethanol in terms of response and selectivity. The sensors showed good reproducibility and stability as well as short response (9 s) and recovery time (43 s) even at an ethanol concentration as low as 50 ppm. The gas-sensing properties of porous alpha-Fe(2)O(3) nanospheres are also significantly better than those of previously reported Fe(2)O(3) nanoparticles (ca. 30 nm). The sensitivity of the former is over four times higher than that of the latter at varied ethanol concentrations. The gas-sensing mechanism was discussed in details. Both fast response and steady signal make these peculiar nanostructures a promising candidate for ethanol detection.

Porous magnetic manganese oxide nanostructures: Synthesis and their application in water treatment

Magnetic manganese oxide nanostructures are fabricated at room temperature by mixing a KMnO(4) solution and oleic acid capped Fe(3)O(4) particles. Oleic acid molecules capped Fe(3)O(4) particles are oxidized by potassium permanganate (KMnO(4)) in an aqueous solution to produce porous magnetic manganese oxide nanostructures. The synthesis technique can be extended to other MnO(x) structures with composition of different nanocrystals, such as quantum dots, noble metal crystals which may have important applications as catalysts, adsorbents, electrodes and advanced materials in many scientific disciplines. Transmission electron microscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, and nitrogen adsorption-desorption measurements are employed to characterize the structures. As an adsorbent in water treatment, the nanostructures possess a large adsorption capability and high organic pollutant removal rates due to the large surface area and pore volume. The nanostructures are recyclable as their adsorption capability can be recovered by combustion. Furthermore, the strong magnetism exhibited by the structures provides an easy and efficient separation means in wastewater treatment under an external magnetic field.

Single crystal WO3 nanoflakes as quartz crystal microbalance sensing layer for ultrafast detection of trace sarin simulant

Tungsten oxide (WO(3)) nanoflakes were synthesized, and characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Thermogravimetry and X-ray photoelectron spectroscopy demonstrate the existence of strongly bound surface water molecules on the surface of tungsten oxide nanoflakes. WO(3) nanoflake functionalized quartz crystal microbalance sensors were fabricated, and firstly used for detection of trace sarin simulant, dimethyl methylphosphonate (DMMP). The sensors have better reproducibility and stability as well as much shorter response (30s) and recovery time (73s) than those functionalized by conventional hydrogen-bond acidic branched copolymers. The strongly bound surface water molecules on the surface of WO(3) nanoflakes are believed to play a key role in achieving such excellent DMMP sensing characteristics.

Tailoring the structure of metal oxide nanostructures towards enhanced sensing properties for environmental applications.

The present article reviews recent works in our laboratory about the sensing properties to toxic gases using nanostructured WO(3), TiO(2), FTiO(2), and CuO functionalized quartz crystal microbalance (QCM) sensors. WO(3) and TiO(2) functionalized QCM sensors have much shorter response time than those functionalized by conventional hydrogen-bond acidic branched copolymers for detection of dimethyl methylphosphonate (DMMP). FTiO(2) functionalized QCM sensors can improve the gas sensing characteristics by shortening the response time but at the price of partial irreversibility. The sensing mechanism was examined by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Varied CuO nanostructures were synthesized by simple modulation of reaction conditions. All the as-prepared CuO was applied on QCM resonators and explored for HCN sensing. Surprisingly, responses of all the sensors to HCN were found to be in an opposite direction as compared with other common volatile substances, offering excellent selectivity for HCN detection. The sensitivity was very high, and the response and recovery were very fast. Comparison of the specific surface areas of CuO nanostructures showed that CuO of higher surface area is more sensitive than that of lower surface area, indicating that the specific surface area of these CuO nanostructures plays an important role in the sensitivity of related sensors. Based on experimental results, a sensing mechanism was proposed in which a surface redox reaction occurs between CuO and Cu(2)O on the CuO nanostructures reversibly upon contact with HCN and air, respectively. The CuO functionalized QCM sensors are considered to be a promising candidate for trace HCN gas detection in practical applications.

Hydrothermal synthesis of nanostructured flower-like Ni(OH)2 particles and their excellent sensing performance towards low concentration HCN gas

Hierarchically structured Ni(OH)2 particles with a well-defined flower-like morphology were synthesized via a hydrothermal route. The molar ratio of SDBS/Ni, hydrothermal temperature and reaction time were found to have a profound influence on the size and morphology of the resulting products. These hierarchically structured flower-like Ni(OH)2 were employed on quartz crystal microbalance resonators for HCN sensing. The flower-like Ni(OH)2 modified QCM resonators exhibited excellent sensing performance. The sensitivity of flower-like Ni(OH)2 modified QCM resonators has reached 5.14 Hz (μg ppm)−1, nearly 40-fold as high as previous reports. The high sensitivity is attributed to its high specific surface area (61 m2 g−1), special morphology and especially to its surface structure. A sensing mechanism that involves surface vacancy sites and their adsorption and activation of oxygen molecules was proposed on the basis of experimental results. Effects of relative humidity show high tolerance of the sensors to relative humidity. The prefect linear relationship between response signal (ΔF) and HCN concentration, and a fast and sensitive response to low concentration HCN coupled with high selectivity show a promising future for these Ni(OH)2 modified QCM resonators in the detection of trace gaseous HCN.

A copper–manganese composite oxide as QCM sensing layers for detection of formaldehyde gas

A copper–manganese composite oxide was synthesized by controlling the molar ratio of Cu to Mn and calcination temperature. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption–desorption measurements were employed to characterize the obtained products. The as-prepared copper–manganese composite oxide functionalized QCM resonators were fabricated and explored for HCHO sensing. The copper–manganese composite oxide functionalized QCM resonators had a significant response to HCHO, and the sensitivity of the resonators reached 6.35 Hz (μg ppm)−1. Neither the response nor the sensing profile observed significant changes after 60 days. The linear equation between the response of the QCM resonator and HCHO concentration endows the copper–manganese composite oxide functionalized QCM resonators with a capability of HCHO quantitative analysis. The adsorption–desorption process via hydrogen bonding between the oxygen of the copper–manganese composite oxide and HCHO molecules may be a plausible sensing mechanism for HCHO sensing.