•Electrospinning is a well-known technique for the synthesis of WO3 1D fibers with unique morphological properties.•WO3 nanofibers can exhibit a high gas sensor response and good selectivity toward ...oxidizing gases.•Gas sensors for the detection of toxic gases as NO2 are widely studied using n-type semiconductors.•Selective detection is one of the most important gas sensing properties.
WO3 is a widely studied gas sensor material that commonly exhibits excellent sensitivity and selectivity toward NO2 detection. In this study, the influence of the heating rate on the thickness and grain size of WO3 nanofibers synthesized by electrospinning was evaluated. The materials were analyzed using XRD, Raman, and UV-Vis spectroscopies, as well as FEG-SEM, TG-DTA, and the BET method. Results showed that continuous nanofibers with particle size dependent on the heating rate were obtained at 500 °C. The gas sensing performance of WO3 nanofibers calcined at 10 °C/min (NF500–10) was investigated due to its higher surface area. NF500–10 device presented a high sensor signal for low and high NO2 concentrations at temperatures ranging from 150 °C to 300 °C. The sensor signals for 25 ppm of NO2 at 150 °C are substantially higher than those of several previous reports. Moreover, high selectivity against potential interferents (H2 and CO) was observed at all operating temperatures. A sensing mechanism based on the interaction between NO2 molecules and the surface of the WO3 nanofibers was proposed to explain the high sensor response. In conclusion, WO3 nanofibers were found to be an attractive sensing material to detect both low and high NO2 concentrations with excellent selectivity.
The development of gas sensors with innovative designs and advanced functional materials has attracted considerable scientific interest given their potential for addressing important technological ...challenges. This work presents new insight towards the development of high‐performance p‐type semiconductor gas sensors. Gas sensor test devices, based on copper (II) oxide (CuO) with innovative and unique designs (urchin‐like, fiber‐like, and nanorods), are prepared by a microwave‐assisted synthesis method. The crystalline composition, surface area, porosity, and morphological characteristics are studied by X‐ray powder diffraction, nitrogen adsorption isotherms, field‐emission scanning electron microscopy and high‐resolution transmission electron microscopy. Gas sensor measurements, performed simultaneously on multiple samples, show that morphology can have a substantial influence on gas sensor performance. An assembly of urchin‐like structures is found to be most effective for hydrogen detection in the range of parts‐per‐million at 200 °C with 300‐fold larger response than the previously best reported values for semiconducting CuO hydrogen gas sensors. These results show that morphology plays an important role in the gas sensing performance of CuO and can be effectively applied in the further development of gas sensors based on p‐type semiconductors.
High‐performance gas sensors based on CuO hierarchical morphologies with in situ gas sensor comparison are reported. Urchin‐like morphologies with high hydrogen sensitivity and selectivity that show chemical and thermal stability and low temperature operation are analyzed. The role of morphological influences in p‐type gas sensor materials is discussed.
In this study, individual nanofabricated SnO micro-disks, previously shown to exhibit exceptional sensitivity to NO
, are investigated to further our understanding of gas sensing mechanisms. The SnO ...disks presenting different areas and thickness were isolated and electrically connected to metallic electrodes aided by a Dual Beam Microscope (SEM/FIB). While single micro-disk devices were found to exhibit short response and recovery times and low power consumption, large interconnected arrays of micro-disks exhibit much higher sensitivity and selectivity. The source of these differences is discussed based on the gas/solid interaction and transport mechanisms, which showed that thickness plays a major role during the gas sensing of single-devices. The calculated Debye length of the SnO disk in presence of NO₂ is reported for the first time.
The gas sensor response of tin monoxide micro-disks, functionalized with noble metal nanoparticles (Pd and Ag), to NO2, H2 and CO were studied by monitoring changes in their resistance upon exposure ...to the various gases. The tin monoxide, with unusually low Sn oxidation state, was synthetized by carbothermal reduction. Surface modification by Pd and Ag catalysts was achieved by coating the micro-disks by metallic nanoparticle dispersions, prepared by the polyol reduction process, followed by thermal treatment. SEM and TEM analysis showed nanoparticles to be well-dispersed over the SnO surfaces. The decorated SnO micro-disks exhibited high sensor response to reducing gases such as H2 and CO. On the other hand, the catalytic particles tended to reduce the sensor response to oxidizing gases such as NO2. The catalytic activity of Pd nanoparticles was tied to chemical sensitization while that of Ag nanoparticles to electronic sensitization. Impedance spectroscopy enabled deconvolution of different contributions to the sensor response with only the Ag-decorated specimens exhibiting two RC time constants. Thus, in contrast to undecorated and Pd-decorated specimens, nearly 80% of Ag modified SnO’s response to H2 was controlled by changes in the interface between particles and disks. Sensor response to H2 was optimal at higher temperatures (300°C), NO2 at 200°C while that for Pd-decorated materials; maximum sensor response to CO was observed at lower temperatures (under 150°C), where CO absorption by metal nanoparticles is favored.
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•Tin monoxide nanobelts were decorated with Pt and Pd nanoparticles for gas sensor application.•Pristine devices are both sensitive and selective for nitrogen dioxide between 100 and ...250 °C.•Both Pd- and Pt-decorated devices present excellent selectivity to H2 at 300 and 350 °C.•Pt-decorated sensor present good selectivity for high concentrations of CO (>200 ppm) at low temperatures (100 and 150 °C).•Electronic sensitization mechanism is elucidated based on the band diagram of materials.
This work reports on the gas sensor response of undecorated 1D stannous oxide nanobelts and those decorated with Pt and Pd nanoparticles. The sensor device responses to H2, CO and NO2 were measured in dry air baseline atmosphere as functions of the analyte concentration (1–1000 ppm) and temperature (100-350 °C). Noble metal decorated SnO devices exhibited enhanced chemical sensitization, resulting in increased sensitivity upon exposure to reducing gases at different working temperatures. Differences in enhancement levels are attributed to strong electronic sensitization effects that are dependent on the respective Pt and Pd work functions and the unique SnO band structure, characterized by a small band gap. Gas sensing results also showed superior selectivity to H2 for metal-decorated nanobelts. Based on the findings in this work, we propose an array based on SnO structures capable of detecting and distinguishing reducing and oxidizing gases.
The determination of particle size distribution is an important parameter for controlling industrial processes, particularly in the field of pharmaceuticals. It is also an important parameter for ...characterizing nanoparticles. The best technique for determining particle size distribution is scanning electron microscopy. The process of counting particles is typically performed manually, which requires both more time and a higher standard deviation than automatic methods. This study shows the results of a particle counting procedure that relies on a fully automated method that was found to improve the reproducibility of the measurement. The effect on the diameter of near-spherical polymer nanospheres between 20 and 100 nm (mean of 60 nm) when samples were coated by a conducting layer (such as gold or carbon) was also evaluated. The images were collected using a field emission scanning electron microscope and then processed using the ImageJ program. Results showed that the method proposed in this work produces mean diameter values in accordance with NIST-traceable near-spherical polymer nanospheres for the sample without coating. The study also revealed two main effects of the conductive coating: changes to topography and an increase in mean particle diameter.
The structure of electrical double layers at electrified interfaces is of utmost importance for electrochemical energy storage as well as printable, flexible, and bioelectronic devices, such as ...ion-gated transistors (IGTs). Here we report a study based on atomic force microscopy force–distance profiling on electrical double layers forming at the interface between the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and sol–gel films of mesoporous tungsten oxide. We successfully followed, under in operando conditions, the evolution of the arrangement of the ions at the interface with the tungsten oxide films used as channel materials in IGTs. Our work sheds light on the mechanism of operation of IGTs, thus offering the possibility of optimizing their performance.
NO2 is one of the main greenhouse gases, which is mainly generated by the combustion of fossil fuels. In addition to its contribution to global warming, this gas is also directly dangerous to humans. ...The present work reports the structural and gas sensing properties of the CaCu3Ti4O12 compound prepared by the sol-gel technique. Rietveld refinement confirmed the formation of the pseudo-cubic CaCu3Ti4O12 compound, with less than 4 wt% of the secondary phases. The microstructural and elemental composition analysis were carried out using scanning electron microscopy and X-ray energy dispersive spectroscopy, respectively, while the elemental oxidation states of the samples were determined by X-ray photoelectron spectroscopy. The gas sensing response of the samples was performed for different concentrations of NO2, H2, CO, C2H2 and C2H4 at temperatures between 100 and 300 °C. The materials exhibited selectivity for NO2, showing a greater sensor signal at 250 °C, which was correlated with the highest concentration of nitrite and nitrate species on the CCTO surface using DRIFT spectroscopy.
Contemporary chemical sensing research is rapidly growing, leading to the development of new technologies for applications in almost all areas, including environmental monitoring, disease diagnostics ...and food quality control, among others ...
Intense research has been done in the field of clean and renewable sources and energy storage. Supercapacitors are a promising technology for portable and wearable electronic systems. The combination ...of metal oxides with graphene is attractive to form nanocomposite materials to achieve energy storage devices with enhanced properties. Here, we study the fabrication of nanofilms as supercapacitor electrodes using two nanostructures of zinc oxide, tetrapod ZnO(t) and star ZnO(s), complexed with reduced graphene oxide (rGO) and arranged with poly(allylamine hydrochloride) (PAH), by using the layer-by-layer (LbL) technique on a flexible indium–tin–oxide (ITO) electrode. The morphology of both ZnO-based films was investigated by scanning electron microscopy, which revealed the incorporation of ZnO with rGO and led the formation of nanostructured films with high surface area in two distinct morphologies. Cyclic voltammetry and galvanostatic charge–discharge measurements exhibit profile curves of a supercapacitor-based double-layer energy storage mechanism with high cycling stability over 10,000 cycles. The highest capacitance was achieved for a 20-bilayer LbL film at a 1 mV/s and 1 A/g with values of ca. 5 mF/cm
2
and 140 F/g for ZnO(t)-based film and of ca. 19 mF/cm
2
and 90 F/g for ZnO(s)-based film. Also, films with ZnO(t) presented energy and power densities of ca. 9.5 Wh/kg and 207 W/kg, respectively, while the same parameters exhibited values of ca. 6.0 Wh/kg and 130 W/kg for films with ZnO(s). Our findings indicate that nanofilms-based ZnO-rGO exhibit electrocapacitive properties that permits to be further investigated for energy storage nanostructured systems.
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