Jiaqiang Xu

Self-assemblies of Pd nanoparticles on the surfaces of single crystal ZnO nanowires for chemical sensors with enhanced performances

Single-crystalline ZnO nanowires were synthesized, and further modified with Pd nanoparticles through self-assemblies. The self-assembly strategy shows advantages of tailoring the surface modification of ZnO nanowires with monodispersed Pd nanoparticles and further tuning of the functionalities of nano-architectures. It was found that poly(vinylpyrrolidone) (PVP) plays a key role in loading Pd nanoparticles onto the surfaces of ZnO nanowires. Having been turned into chemical sensors, the nano-architectures constructed from ZnO nanowires and Pd nanoparticles exhibit a highly enhanced response to H2S gas, compared to the devices from pure ZnO nanowires.

Decoration of ZnO nanowires with Pt nanoparticles and their improved gas sensing and photocatalytic performance

Pt nanoparticles were introduced on the surface of ZnO nanowires using a chemically driven self-assembly method. Through this controllable method, Pt-nanoparticle-functionalized ZnO nanowires (Pt NPs-ZnO NWs) with uniform particle dispersion, tunable Pt particle sizes, and narrow particle size distribution were obtained. Changes in the morphology of the decorative preparation were observed as the amount of linker reagent and the concentration of Pt nanoparticle solution were altered. The as-prepared Pt NPs-ZnO NWs with optimal morphology showed excellent gas sensing and photocatalytic performance. Tuning of the functionalities of photocatalytic and gas sensors can be obtained by tailoring the morphology of Pt NP-ZnO NW composite materials.

Amine-functionalized SBA-15 with uniform morphology and well-defined mesostructure for highly sensitive chemosensors to detect formaldehyde vapor.

Amine-functionalized SBA-15 with uniform morphology and well-defined mesostructure was prepared using a postgrafting route. The morphology, mesostructure, and functionality of the materials were characterized by scanning electron microscopy, transmission electron microscopy, small-angle X-ray scattering, nitrogen adsorption-desorption, Fourier transform infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy techniques. The results show that hexagonal lamelliform SBA-15 with a uniform particle size and short vertical channels plays two significant roles in uniformly dispersing amine-functionalizing groups and effectively adjusting the loadings of the functional groups within the mesopore channels. To confirm the potential application of the hybrids in gas sensors, using amine-functionalized SBA-15 as a sensing material and a quartz crystal microbalance as a transducer, a parts per billion level formaldehyde sensor with high sensitivity (response time about 11 s, recovery time about 15 s) and good chemoselectivity was achieved. This material holds great potential in the area of rapid, sensitive, and highly convenient formaldehyde detection.

Enhanced gas sensing by assembling Pd nanoparticles onto the surface of SnO2 nanowires

SnO(2) nanowires with an average 0.6 microm in length and about 25 nm in diameter were prepared by a hydrothermal method. The sensors were fabricated using SnO(2) nanowires assembled with Pd nanocrystals. The sensing properties of the sensors such as selectivity, response-recovery time and stability were tested at 290 degrees C. After assembling Pd nanocrystals onto the surface of SnO(2) nanowires, the gas sensing properties of the sensors toward H(2)S were improved. The sensors based on Pd nanoparticle@SnO(2) nanowires exhibit high stability owing to stable single crystal structure. The mechanism of promoting sensing properties with Pd nanoparticles is discussed.

Porous corundum-type In2O3 nanoflowers: controllable synthesis, enhanced ethanol-sensing properties and response mechanism

Porous rhombohedral In2O3 (corundum-type In2O3, rh-In2O3) with a morphology of uniform nanoflowers was fabricated by using a mild, facile solvent-thermal method. The formation mechanism and transformation of phase were studied. The results revealed that the precursors were transformed from In(OH)3 to InOOH with an increase in reaction time. The phase transformation was attributed to the stability of the InOOH phase at small crystal volume, less water molecules and small pH value, which in turn led to the formation of metastable rh-In2O3. The optimal working temperature of the sensor based on porous rh-In2O3 nanoflowers was proved to be 280 °C, corresponding to chemisorbed oxygen analysis based on a temperature changeable XPS, further demonstrating the surface resistance controlled gas sensing mechanism of In2O3. The sensor exhibited an enhanced response and rapid response/recovery toward ethanol vapour, which was ascribed to hierarchical porous structures and more active defects.

Evolution of ZnO microstructures from hexagonal disk to prismoid, prism and pyramid and their crystal facet-dependent gas sensing properties

Herein, the evolution of ZnO structures from hexagonal disk to prismoid, prism and pyramid was found via a facile two-step low temperature hydrothermal reaction, and the evolution was achieved by only adjusting the pH value of the reactive solution without the assistance of a template or a surfactant. The characterization results showed that the precursor (hexagonal Zn5(OH)8Cl2·2H2O disk) played a key role in the morphology evolution of ZnO during the early stage of the growth process and that the disks tended to stack together layer by layer in both directions (up and down) to form prismoid, prism and pyramid structures with the increase in pH value from 7 to 10. After calcination, the corresponding hexagonal ZnO microstructures were obtained. This structure evolution resulted in the weakening dominance of the (0001) plane in the total exposed crystal facets. Furthermore, despite the similar specific surface areas of the four hexagonal ZnO microstructures, the gas sensing properties of the sensors based on these microstructures deteriorated sequentially. At a working temperature of 330 °C, the ZnO disk with the most exposed (0001) plane showed the highest gas response toward ethanol, which was nearly 2, 3, and 6 times higher than those of the prismoid, prism and pyramid structures, respectively. This superior gas sensing performance strongly depends on the predominantly exposed polar facets (0001), which can provide more active sites for oxygen adsorption and subsequent reaction with the detected gas than other apolar facets. It demonstrates that the (0001) crystal facet plays a significant role in the gas sensing behavior of ZnO. This research will bring some inspiration to researchers for the fabrication of a high performance ZnO gas sensor as well as other metal oxides.

Fluoroalcohol and fluorinated-phenol derivatives functionalized mesoporous SBA-15 hybrids: high-performance gas sensing toward nerve agent

Two new mesoporous SBA-15/organic hybrids featuring fluoroalcohol and fluorinated-phenol derivatives were successfully synthesized via a co-condensation route. Hexafluorobisphenol and hexafluoroisopropanol were chosen to graft onto mesostructured silica, respectively. The as-synthesized hybrids preserve their mesoscopic structures with relative large surface areas and pore volume, as confirmed by SAXS, TEM and N2 adsorption–desorption porosimetry. Moreover, FT-IR and solid-state MAS NMR spectroscopy proved covalent anchoring of the organic functional groups onto the SBA-15. In order to confirm the potential application of the hybrids in gas sensing, investigations on the sensing properties toward the nerve agent simulant dimethyl methylphosphonate (DMMP) were carried out by QCM transducer. The QCM sensors based on hybrid materials exhibit excellent sensitivity toward trace DMMP vapour down to 26 ppb. In comparison with pristine SBA-15, the hybrids also show remarkably enhanced selectivity to DMMP due to suitable H-bonding interactions. Therefore, the well-defined mesoscopic porosity of the organic–inorganic hybrids together with the grafted fluoroalcohol and fluorinated-phenol derivatives lead to excellent sensing properties to DMMP vapour, and show great potential in the area of nerve agent detection.

Synthesis and chlorine sensing properties of nanocrystalline hierarchical porous SnO2 by a phenol formaldehyde resin-assisted process

Nanocrystalline tin dioxide (SnO2) materials with very interesting architectures (well-defined pores, hierarchical pores) were synthesized by a suitable heat treatment of SnO2/phenol formaldehyde resin (PFR) nanocomposite. The composite was obtained through a facile hydrothermal approach by using tin(IV) tetrachloride pentahydrate (SnCl4·5H2O) as a raw material, hexamethylenetetramine (HMT) as a pore-forming agent and monomer (HCHO) source for polymerization with phenol. Compared with the fine porous SnO2 sensor, the hierarchical porous SnO2 sensor showed a higher response. Owing to the hierarchical porous structure, the as-prepared materials exhibit satisfactory selectivity to chlorine along with high-sensitivity (249.3 at 10 ppm), fast response (7 s), very short recovery time (15 s), long-term stability as well as low power. The excellent sensing performance was discussed concerning the architectures of the materials.

Monodispersed mesoporous SBA-15 with novel morphologies: controllable synthesis and morphology dependence of humidity sensing

Monodispersed mesoporous SBA-15 materials with hexagonal lamelliform, hexagonal prism and snow-like morphologies were controllably synthesized by a facile hydrothermal method. The novel morphology SBA-15 materials were then coated on the quartz crystal micro-balances to construct highly stable and sensitive humidity sensors (response range of humidity: 1–100% RH).

CdSnO3 micro-cubes with porous architecture: synthesis and gas-sensing properties

CdSnO3 micro-cubes with porous architecture were obtained exclusively via a simple co-precipitation method at 80 °C for 6 hours, with which a good response to ethanol vapor in ppb was observed.