Jiangyang Liu

Design of Au@ZnO yolk-shell nanospheres with enhanced gas sensing properties.

The Au@ZnO yolk-shell nanospheres with a distinctive core@void@shell configuration have been successfully synthesized by deposition of ZnO on Au@carbon nanospheres. Various techniques were employed for the characterization of the structure and morphology of as-obtained hybrid nanostructures. The results indicated that the Au@ZnO yolk-shell nanospheres have an average diameter of about 280 nm and the average thickness of the ZnO shell is ca. 40 nm. To demonstrate how such a unique structure might bring about more excellent gas sensing property, we carried out a comparison of the sensing performances of ZnO nanospheres with different inner structures. It was found that Au@ZnO yolk-shell nanospheres exhibited an obvious improvement in response to acetone compared with the pure ZnO nanospheres with hollow and solid inner structures. For instance, the response of the Au@ZnO nanospheres to 100 ppm acetone was about 37, which was about 2 (3) times higher than that of ZnO hollow (solid) nanostructures. The enhanced sensing properties were attributed to their unique microstructures (porous shell and internal voids) and the catalytic effect of the encapsulated Au nanoparticles.

Enhanced Gas Sensing Properties of SnO2 Hollow Spheres Decorated with CeO2 Nanoparticles Heterostructure Composite Materials.

CeO2 decorated SnO2 hollow spheres were successfully synthesized via a two-step hydrothermal strategy. The morphology and structures of as-obtained CeO2/SnO2 composites were analyzed by various kinds of techniques. The SnO2 hollow spheres with uniform size around 300 nm were self-assembled with SnO2 nanoparticles and were hollow with a diameter of about 100 nm. The CeO2 nanoparticles on the surface of SnO2 hollow spheres could be clearly observed. X-ray photoelectron spectroscopy results confirmed the existence of Ce(3+) and the increased amount of both chemisorbed oxygen and oxygen vacancy after the CeO2 decorated. Compared with pure SnO2 hollow spheres, such composites revealed excellent enhanced sensing properties to ethanol. When the ethanol concentration was 100 ppm, the sensitivity of the CeO2/SnO2 composites was 37, which was 2.65-times higher than that of the primary SnO2 hollow spheres. The sensing mechanism of the enhanced gas sensing properties was also discussed.

Hierarchical Assembly of α-Fe₂O₃ Nanosheets on SnO2₂Hollow Nanospheres with Enhanced Ethanol Sensing Properties.

We present the preparation of a hierarchical nanoheterostructure consisting of inner SnO2 hollow spheres (SHS) surrounded by an outer α-Fe2O3 nanosheet (FNS). Deposition of the FNS on the SHS outer surface was achieved by a facile microwave hydrothermal reaction to generate a double-shell SHS@FNS nanostructure. Such a composite with novel heterostructure acted as a sensing material for gas sensors. Significantly, the hierarchical composites exhibit excellent sensing performance toward ethanol, which is superior to the single component (SHS), mainly because of the synergistic effect and heterojunction.

Au@In2O3 core–shell composites: a metal–semiconductor heterostructure for gas sensing applications

Hybrid Au@In2O3 microstructures with a distinctive core–shell configuration have been successfully synthesized by employing Au@carbon spheres as sacrificial templates. The In2O3 shell can be easily decorated on the Au core by a facile aging process at room temperature (25 °C) combined with a subsequent calcination. Field emission electron microscopy and transmission electron microscopy images revealed that the Au@In2O3 core–shell structures had an average diameter of about 150 nm and the thickness of the porous In2O3 shell was ca. 50 nm. When tested as a potential sensing material for gas sensing, the resulting hybrid Au@In2O3 core–shell structures exhibited a higher response to formaldehyde compared with the pure In2O3 spheres. The enhanced sensing properties of Au@In2O3 core–shell structures were attributed to their intense electron depletion that arose from the catalytic activity of Au nanoparticles and the formation of metal–semiconductor junction.

A low temperature operating gas sensor with high response to NO2 based on ordered mesoporous Ni-doped In2O3

The ordered mesoporous Ni-doped In2O3 and undoped In2O3 nanostructures have been synthesized via a nanocasting method, which is an easy, repeatable and friendly route. The structure of the as-prepared product was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), nitrogen physisorption and scanning electron microscopy (SEM). The results of XRD and TEM revealed the ordered structure of undoped and Ni-doped In2O3. The wide-angle XRD of the samples revealed that Ni incorporation may lead to lattice deformation without destroying the original crystal structure. Gas sensors based on undoped and Ni-doped In2O3 were fabricated and their gas sensing properties were tested. The Ni-doped In2O3 based sensor showed excellent selectivity toward NO2 at the operating temperature of 58 °C and the detection limit was 10 ppb. The response of the sensor based on mesoporous Ni-doped In2O3 was nearly 4 times higher than that of the sensor based on mesoporous undoped In2O3.

Facile synthesis of hollow In2O3 microspheres and their gas sensing performances

Hollow In2O3 microspheres constructed by primary nanoparticles were successfully prepared by thermal treatment of the precursor, which was synthesized via a facile chemical solution route without any templates or surfactants. The images of field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) indicated that the sample was composed of a large number of hollow In2O3 microspheres with diameters of 1–2 μm. In addition, a gas sensor based on the In2O3 hollow microspheres was fabricated and its gas sensing performances were investigated. It was found that sensors based on the as-prepared sample had a low operating temperature (80 °C), and exhibited high response, low detection limit and excellent selectivity to NO2.

Gas sensing properties of flower-like ZnO prepared by a microwave-assisted technique

Flower-like ZnO hierarchical architectures consisting of different building blocks have been successfully synthesized by a simple microwave-assisted decomposition route. The scanning electron microscopy and transmission electron microscopy results indicated that the morphologies of ZnO hierarchical architectures could be tailored by changing the category of the additives. Gas sensors based on the resulting products were fabricated and their gas sensing properties were tested for a variety of target gases. The results indicated that the sensor based on ZnO with a needle-assembled structure exhibited excellent selectivity and a higher response to NO2 at 75 °C compared to those using the other two flower-like ZnO. The good performance observed here was likely to be the result of the high donor-related intrinsic defects.