A review on WO3 based gas sensors: Morphology control and enhanced sensing properties

The development of gas sensor that is capable of detecting ppb-level detection of acetone and possesses high response toward low-concentration acetone remains a great challenge. Herein, we present the construction of the W18O49/Ti3C2Tx composites based on the in situ grown of the 1D W18O49 nanorods (NRs) on the surfaces of the 2D Ti3C2Tx Mxene sheets via a facile solvothermal process. The W18O49/Ti3C2Tx composites exhibit high response to low concentration acetone (11.6 to 20 ppm acetone), ideal selectivity, long-term stability, very low limit of detection of 170 ppb acetone, and fast response and recover rates (5.6/6 s to 170 ppb acetone). Compared to the W18O49 NRs and Ti3C2Tx sheets, the W18O49/Ti3C2Tx composites show significant improvement on the acetone-sensing performance, which can be ascribed to the homogeneous distribution of the W18O49 NRs on the Ti3C2Tx surface, the removal of the fluorine-containing groups from the Ti3C2Tx after the solvothermal process, and the synergistic interfacial interactions between the W18O49 NRs and the Ti3C2Tx sheets. The synthesis of the 1D/2D W18O49/Ti3C2Tx Mxene composites provides a new avenue to develop other promising hybrids for acetone sensing.

W18O49/Ti3C2Tx Mxene nanocomposites for highly sensitive acetone gas sensor with low detection limit

Here we report a hierarchical flower-like SnO/SnO2 gas sensing material for detecting formaldehyde vapor at a low temperature. It was rationally designed and successfully synthesized via a one-step hydrothermal route. The crystal phase, defects, element composition and morphology of the obtained samples were characterized in detail by XRD, FESEM, TEM, Raman, PL, and XPS. The characterized results reveal that hierarchical SnO/SnO2 nano-flowers are assembled from ultrathin nanosheets with about 9–11 nm in thickness. Gas sensing performance shows that the sensor based on SnO/SnO2 nano-flowers has crucial advantages for formaldehyde detection, such as low operating temperature (120 °C), excellent selectivity, short response time (7 s), high response value (80.9) and low detection limitation (8.15 ppb). The excellent gas responses of the sensor can be attributed to its unique hierarchical microstructure (for decrease of Rg and increase of Ra) and p-n junction between SnO and SnO2 (for increase of Ra). Finally, the sensing mechanism of the prepared was proposed in detail.

A low temperature formaldehyde gas sensor based on hierarchical SnO/SnO2 nano-flowers assembled from ultrathin nanosheets: Synthesis, sensing performance and mechanism

Room-temperature gas sensors based on ZnO nanorod/Au hybrids: Visible-light-modulated dual selectivity to NO2 and NH3

In this work, three-dimensional (3D) hierarchical In2O3@SnO2 core-shell nanofiber (In2O3@SnO2) was designed and successfully prepared via a facile electrospinning and further hydrothermal methods. Vertically aligned SnO2 nanosheets uniformly grown on the outside surface of In2O3 nanofibers were clearly observed by field emission scanning electron microscopy. Besides, hierarchical core-shell nanostructure of In2O3@SnO2 was characterized by elemental maps using scanning transmission electron microscopy. The formaldehyde (HCHO) sensing performances of pure In2O3 nanofibers, SnO2 nanosheets, and In2O3@SnO2 core-shell nanocomposite were compared, and the In2O3@SnO2 nanocomposite possessed highest response value, fast response/recovery speed, best selectivity, and lowest HCHO detection limit. Specifically, the response value (Ra/Rg) of the In2O3@SnO2 nanocomposite reached 180.1 toward 100 ppm of HCHO gas, which was near 9 and 6 times higher than that of the pure In2O3 nanofibers (Ra/Rg = 19.7) and pure SnO2 nanosheets (Ra/Rg = 33.2), respectively. In addition, the gas sensor showed instantaneous response/recovery time (3/3.6 s) toward 100 ppm of HCHO at the optimal operation temperature of 120 °C. More importantly, the detection limit toward HCHO gas was as low as 10 ppb (Ra/Rg = 1.9), which could be used for trace HCHO gas detection. The excellent sensing properties of the In2O3@SnO2 were attributed to the synergistic effect of large specific surface areas of SnO2 nanosheet arrays, abundant adsorbed oxygen species on the surface, unique electron transformation between core-shell heterogeneous materials, and long electronic transmission channel of SnO2 transition layer. This work provides an efficient route for the preparation of novel hierarchical sensitive materials.

Hierarchical In2O3@SnO2 Core-Shell Nanofiber for High Efficiency Formaldehyde Detection.

In this study, SnO2 nanosheets (NSs) was firstly prepared by the hydro-solvothermal treatment, and then decorated with Pd, Au and PdAu bimetallic nanoparticles (NPs) by an in situ reduction with ascorbic acid (AA). Their morphology, chemistry, and crystal structure were characterized at the nanoscale. It was found that SnO2 NSs were flower-like with thickness of 7–12 nm, and PdAu NPs with the size of 3–10 nm were dispersed uniformly on the surface of SnO2 NSs. Their gas sensing properties were carefully studied. The results demonstrated that the PdAu/SnO2 sensor can not only effectively detect acetone at 250 °C with response of 6.6 to 2 ppm acetone, but also detect formaldehyde at 110 °C with response of 4.1–2 ppm formaldehyde, and the corresponding detection limit is as low as 45 ppb and 30 ppb, respectively. Moreover, the PdAu/SnO2 sensor exhibited excellent reusability, and reliability to the low concentration of acetone and good anti-interference to humidity and other biomarkers in human breath. Compared with that decorated with their parent metal (Pd or Au), the enhanced response of SnO2 NSs decorated with PdAu bimetallic NPs may be ascribed to the chemical sensitization of Au, the electronic sensitization of Pd and the synergistic effect of PdAu bimetallic NPs. The PdAu/SnO2 sensor has a great potential application in detecting formaldehyde and diabetes diagnosis.

Bimetal PdAu decorated SnO2 nanosheets based gas sensor with temperature-dependent dual selectivity for detecting formaldehyde and acetone

Bimetallic nanoparticles (NPs) usually exhibit some novel properties due to the synergistic effects of the two distinct metals, which is expected to play an important role in the field of gas sensing. PdPt bimetal NPs with Pd-rich shell and Pt-rich core were successfully synthesized and used to modify SnO2 nanosheets. The 1P-PdPt/SnO2-A sensor obtained by self-assemblies of PdPt NPs exhibited temperature-dependent dual selectivity to CO at 100 °C and CH4 at 320 °C. Furthermore, the sensor possessed good long term stability and antihumidity interference. The activation energy of adsorption for CO and CH4 were estimated by the temperature-dependent response process modeled using Langmuir adsorption kinetics, which proved that the lower activation energy of adsorption corresponded to better sensing performance. The gas-sensing mechanism based on the diffusion depth of the tested gas in the sensing layer was discussed. The dramatically improved sensing performance could be ascribed to the high catalytic activity of PdPt bimetal, the electron sensitization of PdO, and Schottky barrier-type junctions at the interface between SnO2 and PdPt NPs. Our present results demonstrate that bimetal NPs with special structure and components can significantly improve the gas-sensing performance of metal oxide semiconductor and the obtained sensor has great potential in monitoring coal mine gas.

PdPt Bimetal-Functionalized SnO2 Nanosheets: Controllable Synthesis and its Dual Selectivity for Detection of Carbon Monoxide and Methane.

Hexagonal WO3 (h-WO3) nanosheets (NSs), nanoparticles (NPs) and nanorods (NRs) were synthesized by a facile, low-cost and environmentally friendly hydrothermal and sol-hydrothermal methods. The structure and morphology of the products were characterized by several techniques, such as XRD, FESEM, TEM, and HRTEM. These results showed that the as-prepared WO3 were hexagonal nanosheets and the diameter was about 400 nm. Gas sensing tests of side-heating sensors indicated that the h-WO3 NSs had the superior selectivity and sensitivity for BTEX vapors (benzene, toluene, ethylbenzene, and p-xylol), which was 9 times more than h-WO3 NPs and NRs. At the optimal working temperature of 320 °C, the values of response based on the h-WO3 NSs sensor to 50 ppm BTEX vapors were 12.33, 27.73, 43.17, 36.27, respectively. The gas sensing mechanism of h-WO3 NSs was discussed in terms of DFT calculation, together with the XRD patterns. The results revealed that the adsorption energy of (100) facet to chemically adsorbed O2 molecules was more than that of (200) facet, which demonstrated strongly dependence on its exposed crystal facets to enhance gas sensing performance.

Highly sensitive BTEX sensors based on hexagonal WO3 nanosheets

By using WCl6 as a precursor and absolute ethanol as a solvent, ultrafine W18O49 nanowires (UFNWs) were synthesized by a one-pot solution-phase method and used as gas sensing materials. Their cryst...

Ultrafine Tungsten Oxide Nanowires: Synthesis and Highly Selective Acetone Sensing and Mechanism Analysis.

A series of zeolitic imidazolate frameworks (ZIFs) were synthesized by a facile and environmental friendly biomimetic method. The textural properties of the ZIFs were characterized by PXRD, FESEM, TEM and FT-IR spectra. These results showed ZIF 90 having typical rhombic dodecahedron crystals with a diameter of 800–1200 nm. Furthermore, the presence of rich aldehyde groups is confirmed through chemical analysis. Gas-sensing tests of quartz crystal microbalance (QCM) transducers based on ZIFs were investigated. The results showed that ZIF-90 based sensors exhibited excellent sensing performance towards low concentration of acetone vapor, such as high sensitivity (the frequency shift was 95 Hz @ 1 ppm), fast response (the response/recovery time was 12 s/17 s, respectively) and good selectivity. On the basis of temperature-varying experimental method, a moderate adsorption enthalpy (the value of ΔHθ was −57.93 kJ/mol) was obtained, indicating the existence of weak and reversible chemisorption between ZIF-90 and acetone molecules. The value of adsorption enthalpy (ΔH = −60.10 kJ/mol) obtained from Density functional theory is in close agreement with the experimental results.

Gaojie Li

Papers

Bimetal PdAu decorated SnO2 nanosheets based gas sensor with temperature-dependent dual selectivity for detecting formaldehyde and acetone

PdPt Bimetal-Functionalized SnO2 Nanosheets: Controllable Synthesis and its Dual Selectivity for Detection of Carbon Monoxide and Methane.

Highly sensitive BTEX sensors based on hexagonal WO3 nanosheets

Ultrafine Tungsten Oxide Nanowires: Synthesis and Highly Selective Acetone Sensing and Mechanism Analysis.

Biomimetic synthesis of zeolitic imidazolate frameworks and their application in high performance acetone gas sensors