Fangmeng Liu

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.

Synthesis, characterization and gas sensing properties of porous flower-like indium oxide nanostructures

In this work, flower-like In2O3 nanostructures were prepared with a solvothermal method in the presence of K3C6H5O7·H2O. The as-synthesized samples were characterized by using X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The results indicate that the synthesized flower-like In2O3 nanostructures were constructed by porous nanosheets. The gas sensing properties of the as-obtained products were investigated. It was found that the sensor based on such flower-like In2O3 nanostructures exhibited high response and good selectivity to NO2.

The enhanced CO gas sensing performance of Pd/SnO2 hollow sphere sensors under hydrothermal conditions

Pd-doped SnO2 hollow spheres were synthesized via a facile one-step hydrothermal route. Utilized as the materials in sensors, the 3.0 wt% Pd-doped SnO2 demonstrated more excellent gas-sensing properties towards CO than 1.5 wt% and 4.5 wt% Pd-doped SnO2. Compared with the SnO2 hollow spheres gas sensor, the optimum operating temperature of the Pd-doped SnO2 hollow spheres gas sensor dropped to 200 °C from 250 °C; the response value to 100 ppm CO was raised to 14.7 from 2.5 accordingly. Furthermore, the response and recovery times of the 3.0 wt% Pd-doped SnO2 sensor are 5 s and 92 s, respectively, to 100 ppm CO at 200 °C. It is believed that its enhanced gas-sensing performances are derived from the synergistic interactions between the dispersed Pd and the characteristic configuration of the SnO2 hollow sphere. In addition, theoretical calculations have also been performed with periodic slab models by using density functional theory, which explain well our experimental phenomenon.

Hydrothermal synthesis of hierarchical CoO/SnO2 nanostructures for ethanol gas sensor

In this work, ethanol gas sensor with high performance was fabricated successfully with hierarchical CoO/SnO2 heterojunction by two-steps hydrothermal method. The response value of CoO/SnO2 sensor is up to 145 at 250 °C when exposed to 100 ppm ethanol gas, which is much higher than that (13.5) of SnO2 sensor. These good sensing performances mainly attribute to the formation of the CoO/SnO2 heterojunction, which makes great variation of resistance in air and ethanol gas. Thus, the combination of n-type SnO2 and p-type CoO provides an effective strategy to design new ethanol gas sensors. The unique nanostructure also played an important role in detecting ethanol, due to its contribution in facilitating the transport rate of the ethanol gas molecules. Also, we provide a general two-step strategy for designing the heterojunction based on the SnO2 nanostructure.

Highly sensitive mixed-potential type ethanol sensors based on stabilized zirconia and ZnNb2O6 sensing electrode

A mixed-potential type stabilized zirconia (YSZ)-based gas sensor using columbite type composite oxide sensing electrode was developed and fabricated, aiming at sensitive detection of ethanol. Among the different oxide sensing electrodes (SEs) developed, the sensor attached with ZnNb2O6-SE was found to achieve the largest sensitivity to ethanol at 625 °C. Furthermore, the result of the effect of sintering temperature on sensing characteristic showed that the sensor utilizing ZnNb2O6-SE sintered at 1000 °C displayed the highest response of −175 mV to 100 ppm ethanol and a low detection limit of 0.5 ppm at 625 °C. ΔV of the present sensor exhibited a segmentally linear relationship to the logarithm of ethanol concentration in the ranges of 0.5–5 ppm and 5–200 ppm, for which the sensitivities were −29 and −112 mV decade−1, respectively. Moreover, the fabricated device also displayed fast response and recovery times, good repeatability, small fluctuation during 30 days continuous high temperature of 625 °C measured periods, and acceptable selectivity to some other interfering gases. Additionally, the sensing mechanism involving mixed potential was further demonstrated by polarization curves.

Self-Assembly Template Driven 3D Inverse Opal Microspheres Functionalized with Catalyst Nanoparticles Enabling a Highly Efficient Chemical Sensing Platform

The design of semiconductor metal oxides (SMOs) with well-ordered porous structure has attracted tremendous attention owing to their larger specific surface area. Herein, three-dimensional inverse opal In2O3 microspheres (3D-IO In2O3 MSs) were fabricated through one-step ultrasonic spray pyrolysis (USP) which employed self-assembly sulfonated polystyrene (S-PS) spheres as a sacrificial template. The spherical pores observed in the 3D-IO In2O3 MSs had diameters of about 4 and 80 nm. Subsequently, the catalytic palladium oxide nanoparticles (PdO NPs) were loaded on 3D-IO In2O3 MSs via a simple impregnation method, and their gas sensing properties were investigated. In a comparison with pristine 3D-IO In2O3 MSs, the 3D-IO PdO@In2O3 MSs exhibited a 3.9 times higher response (Rair/Rgas = 50.9) to 100 ppm acetone at 250 °C and a good acetone selectivity. The detection limit for acetone could extend down to ppb level. Furthermore, the 3D-IO PdO@In2O3 MSs-based sensor also possess good long-term stability. The extraordinary sensing performance can be attributed to the novel 3D periodic porous structure, highly three-dimensional interconnection, larger specific surface area, size-tunable (meso- and macroscale) bimodal pores, and PdO NP catalysts.

Ultrasensitive gas sensor based on hollow tungsten trioxide-nickel oxide (WO3-NiO) nanoflowers for fast and selective xylene detection

In this work, 5-20 at% gas-accessible WO3-NiO hollow nanoflowers were synthesized through a one-step hydrothermal route and used to fabricate metal oxide semiconductor (MOS) based gas sensor. The gas-accessible WO3-NiO hollow nanostructures showed much larger BET surface areas (168.0-203.8 m2 g-1) than that of the pure NiO (45.9 m2 g-1). In the comprehensive gas sensing test, the gas device based on 10 at% WO3-NiO hollow microspheres exhibited the best xylene sensing performance, showing ultrahigh xylene sensitivity (354.7-50 ppm) with short response-recovery times within 1 min. (51 and 57 s respectively) and ultralow detection limit (1.5-50 ppb xylene). Additionally, the 10 at% WO3-NiO based sensor also showed superior xylene selectivity against other interfering gases in a wide temperature range (250-350 °C). Especially at the optimal 300 °C, the 50-ppm xylene sensitivity was 8.1 and 10.3 times higher than that of 50-ppm representative acetone (Sxylene/Sacetone = 8.1) and ethanol (Sxylene/Sethanol = 10.3) gases, respectively. The mechanisms for the excellent xylene sensing performance were also discussed.

Preparation of silver-loaded titanium dioxide hedgehog-like architecture composed of hundreds of nanorods and its fast response to xylene

Hedgehog-like titanium dioxide (TiO2) architectures composed of hundreds of one-dimensional (1D) nanorods and silver (Ag) loaded TiO2 with different amounts (0.2 at%, 0.5 at% and 1 at%) were successfully prepared by facile hydrothermal process and simple isometric impregnation route. The high electron mobility of 1D nanorods on the surface of TiO2 and the high porosity of Ag loaded hedgehog-like TiO2 architectures enable the sensor with fast responsive and recovered properties. TiO2 loaded with 0.5 at% Ag exhibited the highest response to xylene with low response/recovery time at the operating temperature of 375 °C. In addition, the sensitivity and selectivity of the TiO2 sensor were enhanced markedly with Ag loading.

Facile synthesis of nitrogen and sulfur co-doped carbon dots for multiple sensing capacities: alkaline fluorescence enhancement effect, temperature sensing, and selective detection of Fe3+ ions

In this work, we prepared nitrogen and sulfur co-doped carbon dots (C-dots) via a one-pot facile hydrothermal method using methionine and ethylenediamine as the precursors. TEM, HRTEM, FTIR and XPS were used to characterize the morphology and surface molecular structures of the N,S co-doped C-dots. The obtained C-dots showed good aqueous solubility and attractive fluorescence properties. The C-dots responded rapidly towards Fe3+ ions, and could be used as a fluorescent probe for Fe3+ ion detection. In addition, the C-dots also exhibited temperature- and pH-sensitive properties, possessing good temperature recoverability and significantly enhanced fluorescence under alkaline conditions. These excellent characteristics promise extensive potential applications for such C-dots in physiological and environmental monitoring.

The facile synthesis of MoO3 microsheets and their excellent gas-sensing performance toward triethylamine: high selectivity, excellent stability and superior repeatability

In this work, MoO3 microsheets were successfully prepared by thermally oxidizing the MoO2 nanospheres synthesized by a hydrothermal method. The crystal structures and morphologies of precursor MoO2 and the final product were characterized by XRD, FESEM, and TEM. Gas sensors based on MoO3 were fabricated and their gas sensing properties were tested. These results revealed that they exhibited excellent sensing performance towards triethylamine (TEA) with high selectivity, good repeatability, relatively high response and short response time (<3 s). In particular, the fabricated sensor displayed excellent long-term stability and superior selectivity, making it a promising triethylamine gas sensor. The possible reasons related to these characteristics of MoO3 microsheets are further discussed.