Xishuang Liang

Nanosheet-assembled ZnFe2O4 hollow microspheres for high-sensitive acetone sensor.

Semiconductor oxides with hierarchically hollow architecture can provide significant advantages as sensing materials for gas sensors by facilitating the diffusion of target gases. Herein, we develop a facile template-free solvothermal strategy combined with the subsequent thermal treatment process toward the successful synthesis of novel ZnFe2O4 hollow flower-like microspheres. The images of electron microscopy unambiguously indicated that the ZnFe2O4 nanosheets with thickness of around 20 nm assembled hierarchically to form the unique flower-like architecture. As a proof-of-concept demonstration of the function, the as-prepared product was utilized as sensing material for gas sensor. Significantly, in virtue of the porous shell structure, hollow interior, and large surface area, ZnFe2O4 hierarchical microspheres exhibited high response, excellent cyclability, and long-term stability to acetone at the operating temperature of 215 °C.

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.

Double-Shell Architectures of ZnFe2O4 Nanosheets on ZnO Hollow Spheres for High-Performance Gas Sensors

In this study, double-shell composites consisting of inner ZnO hollow microspheres (ZHS) surrounded by outer ZnFe2O4 nanosheets were successfully synthesized. The growth of the ultrathin ZnFe2O4 nanosheets (∼10 nm) on the ZHS outer surface was carried out at room temperature via solution reactions in order to generate a double-shell configuration that could provide a large surface area. As a proof-of-concept demonstration of the design, a comparative sensing investigation between the sensors based on the as-obtained ZnO/ZnFe2O4 composites and its two individual components (ZnO hollow spheres and ZnFe2O4 nanosheets) was performed. As expected, the response of the ZnFe2O4-decorated ZnO composites to 100 ppm acetone was about 3 times higher than that of initial ZnO microspheres. Moreover, a dramatic reduction of response/recover time has been achieved at different operating temperature. Such favorable sensing performances endow these ZnO/ZnFe2O4 heterostructures with a potential application in gas sensing.

Highly Enhanced Sensing Properties for ZnO Nanoparticle-Decorated Round-Edged α-Fe2O3 Hexahedrons

ZnO/α-Fe2O3 composites built from plenty of ZnO nanoparticles decorated on the surfaces of uniform round-edged α-Fe2O3 hexahedrons were successfully prepared via a facile solvothermal method. Various techniques were employed to obtain the crystalline and morphological characterization of the as-prepared samples. In addition, a comparative sensing performance investigation between the two kinds of sensing materials clearly demonstrated that the sensing properties of ZnO/α-Fe2O3 composites were substantially enhanced compared with those of the single α-Fe2O3 component, which manifest the superiority of the ZnO decoration as we expected. For instance, the response of ZnO/α-Fe2O3 composites to 100 ppm acetone is ∼30, which is ∼3.15-fold higher than that of primary α-Fe2O3 hexahedrons. The synergetic effect is believed to be the source of the improvement of gas-sensing properties.

Gas sensing with hollow α-Fe2O3 urchin-like spheres prepared via template-free hydrothermal synthesis

Hollow α-Fe2O3 urchin-like spheres were prepared by annealing the FeOOH precursor, which was synthesized via a template-free hydrothermal method. Interestingly, the size and hollowness of spheres could be tailored by adjusting the concentration of ferric sulphate. The sensing properties of the as-prepared samples were investigated.

Acetone gas sensor based on NiO/ZnO hollow spheres: Fast response and recovery, and low (ppb) detection limit

NiO/ZnO composites were synthesized by decorating numerous NiO nanoparticles on the surfaces of well dispersed ZnO hollow spheres using a facile solvothermal method. Various kinds of characterization methods were utilized to investigate the structures and morphologies of the hybrid materials. The results revealed that the NiO nanoparticles with a size of ∼10nm were successfully distributed on the surfaces of ZnO hollow spheres in a discrete manner. As expected, the NiO/ZnO composites demonstrated dramatic improvements in sensing performances compared with pure ZnO hollow spheres. For example, the response of NiO/ZnO composites to 100ppm acetone was ∼29.8, which was nearly 4.6 times higher than that of primary ZnO at 275°C, and the response/recovery time were 1/20s, respectively. Meanwhile, the detection limit could extend down to ppb level. The likely reason for the improved gas sensing properties was also proposed.

Facile synthesis and gas-sensing properties of monodisperse α-Fe2O3 discoid crystals

Monodisperse α-Fe2O3 discoid crystals have been prepared through a hexamethylenetetramine (HMT)-assisted hydrothermal process combined with subsequent acid-dissolution. First, uniform α-Fe2O3 round-edged hexahedrons with a size of about 1.2 μm were synthesized. Subsequently, by a controlled acid etching process, the as-obtained α-Fe2O3 uniform hexahedrons could be facilely transformed into monodisperse α-Fe2O3 discoid crystals, without influencing the original crystal phase. Both field emission scanning electron microscope results and transmission electron microscope results revealed that the “discuses” were made of piled up nanoparticles. The selected area electron diffraction pattern from the whole discoid crystal displayed that all the nanoparticles were highly oriented, which resulted in the single-crystal “discus” features. To demonstrate the usage of such α-Fe2O3 discoid crystals, the obtained sample was applied to fabricate a gas sensor which was then tested for sensitivity to three kinds of gases (ethanol, methanol and acetone). The results of the test showed that the sensor had a high level of response and good recovery characteristics towards ethanol at the operating temperature of 238 °C.

Growth of SnO2 nanowire arrays by ultrasonic spray pyrolysis and their gas sensing performance

The direct synthesis of tin dioxide (SnO2) nanowire arrays on a glass substrate by using an ultrasonic spray pyrolysis method combined with sintering is demonstrated. The products obtained are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM) and high-resolution TEM. The results show that the SnO2 nanowire arrays consist of single crystalline nanowires, each with a diameter of 50–70 nm and a length of 5–7 μm. There are two different nanowire growth directions because of the oxygen defect growth. The mechanism of the formation and growth of SnO2 nanowire arrays was investigated. A platform gas sensor based on these arrays was fabricated. The sensor exhibits better sensitivity to and selectivity for NO2 than do SnO2 nanoparticles. The gas sensing mechanism is also discussed.

Flower-like In2O3 modified by reduced graphene oxide sheets serving as a highly sensitive gas sensor for trace NO2 detection

In this work, we described gas sensors based on the materials composed of hierarchical flower-likeIn2O3 and reduced graphene oxide (rGO), which were fabricated by a facile one-step hydrothermal method. The rGO-In2O3 composites exhibited enhanced sensing performance towards NO2 through comparison with the pure In2O3 sample. The operating temperature can be tuned by the percentage of rGO in the composites. The sensor based on 5wt% rGO-In2O3 could work at room temperature with a high response value to 1ppm NO2. 3wt% rGO-In2O3 composite was adopted for the ultra-sensitivity gas sensor owing to its extremely low limit of detection of 10ppb with rapid response time to NO2. The sensor also exhibited excellent selectivity and stability. The ultra-sensitivity of rGO-In2O3 should be related to synergistic effect of the hierarchical structure of In2O3 and the presence of rGO in the composites, which provided enhanced surface area and local p-n heterojunctions in rGO/In2O3 composites.

Fabrication of Well-Ordered Three-Phase Boundary with Nanostructure Pore Array for Mixed Potential-Type Zirconia-Based NO2 Sensor

A well-ordered porous three-phase boundary (TPB) was prepared with a polystyrene sphere as template and examined to improve the sensitivity of yttria-stabilized zirconia (YSZ)-based mixed-potential-type NO2 sensor due to the increase of the electrochemical reaction active sites. The shape of pore array on the YSZ substrate surface can be controlled through changing the concentration of the precursor solution (Zr(4+)/Y(3+) = 23 mol/L/4 mol/L) and treatment conditions. An ordered hemispherical array was obtained when CZr(4+) = 0.2 mol/L. The processed YSZ substrates were used to fabricate the sensors, and different sensitivities caused by different morphologies were tested. The sensor with well-ordered porous TPB exhibited the highest sensitivity to NO2 with a response value of 105 mV to 100 ppm of NO2, which is approximately twice as much as the smooth one. In addition, the sensor also showed good stability and speedy response kinetics. All these enhanced sensing properties might be due to the structure and morphology of the enlarged TPB.