WO3-based Sensors Research Articles

Observation on Switching Properties of WO3-Based H2 Sensor Regulated by Temperature and Gas Concentration.

Transition metal oxide semiconductors have great potential for use in H2 sensors, but in recent years, the strange phenomena about gas-sensitive performance associated with their special properties have been more widely discussed in research. In some cases, the resistance of transition metal oxide gas sensors will emerge with some changes contrary to their intrinsic semiconductor characteristics, especially in gas sensor research of WO3. Based on the hydrothermal synthesis of WO3, our work focuses on the abnormal change of tungsten oxide resistance to different gases at low temperature (80-200 °C) and high temperature (above 200 °C). Through in situ FT-IR and in situ XPS, combined with density functional theory calculations, a new reasonable explanation of WO3 is proposed for the abnormal resistance change caused by temperature and the strange response due to gas concentration. The occurrence of these findings can be attributed to the synergistic effect resulting from the presence of two contributing factors. One of them is attributed to the alteration in the surface valence state of WO3 induced by gas, resulting in the reduction of W6+. The other one is due to the reaction between gas and adsorbed oxygen on the surface of WO3. This work presents a novel and rational concept for addressing the reaction mechanism between gas and transition metal oxide semiconductors, thereby paving the way for the development of highly efficient gas sensors based on transition metal oxide semiconductors.

In Situ Synthesis of Hierarchical Co(CO3)0.5(OH)·0.11H2O@ZIF-67/WO3 With High Humidity Immunity and Response to H2S Sensing.

H2S gas sensors with facile preparation, low detection limits, and high selectivity are crucial for environmental and human health monitoring. However, it is difficult to maintain a high response of H2S gas sensors under high humidity in practical applications. To face this dilemma, a layer-by-layer growth method is applied to in situ prepare a nanostructured Co(CO3)0.5(OH)·0.11H2O/WO3 coated by a hydrophobic hierarchical ZIF-67 as the H2S sensor. This novel composite exhibits excellent humidity immunity without sacrificing the excellent sensitivity and selectivity of H2S. At a low operating temperature of 90°C, a remarkable response value of 1052.3 to 100ppm H2S has been achieved, which is 779 and 9.36 times higher than that of pure WO3 and Co(CO3)0.5(OH)·0.11H2O/WO3, respectively. More importantly, an 82.2% relative response value remains at a high humidity of 75%RH. The sensing mechanisms are investigated using gas chromatography-mass spectrometry (GC-MS), which revealed that the reaction products are H2O and SO2. The high humidity immunity and fast response of the Co(CO3)0.5(OH)·0.11H2O@ZIF-67/WO3 demonstrate the layer-by-layer in situ synthesis method holds the potential application for the development of high-performance WO3-based H2S sensors.

Lab-on-Device Synthesis of Hierarchical Macro/Mesoporous WO3 Semiconducting Films for High-Performance H2S Sensing.

The performance consistency of the gas sensor is strongly dependent on the interface binding between the sensitive materials and the electrodes. Traditional powder coating methods can inevitably lead to differences in terms of substrate-film interface interaction and device performance, affecting the stability and lifetime. Thus, efficient growth of sensitive materials on device substrates is crucial and essential to enhance the sensing performance, especially for stability. Herein, hierarchically ordered macro/mesoporous WO3 films are in situ synthesized on the electrode via a facile soft/hard dual-template strategy. Orderly arrayed uniform polystyrene (PS) microspheres with tailored size (ca. 1.2µm) are used as a hard template, and surfactant Pluronic F127 as a soft template can co-assemble with tungsten precursor into ordered mesostructure in the interstitials of PS colloidal crystal induced by solvent evaporation. Benefiting from its rich porosity and high stability, the macro/mesoporous WO3-based sensor shows high sensitivity (Rair/Rgas = 307), fast response/recovery speed (5/9 s), and excellent selectivity (SH2S/Smax > 7) toward 50ppm H2S gas (a biomarker for halitosis). Significantly, the sensors exhibit an extended service life with a negligible change in sensing performance within 60 days. This lab-on-device synthesis provides a platform method for constructing stable nanodevices with good consistency and high stability, which are highly desired for developing high-performance sensors.

Low traces of acetone detection with WO3-based chemical sensors

This work presents the ability of WO3-based sensors to detect low traces of acetone, specifically within the range of 0.25–5 ppm, specific to the in-field atmosphere. The WO3 powder was synthesised through the hydrothermal method. Morpho-structural investigations showed a monoclinic structure and a good crystallization of the WO3 powder, containing well-grown and faceted grains along low-index crystallographic planes. The paste obtained by mixing the powder with propanediol was screen-printed as a thick layer onto commercial alumina substrates, obtaining the chemical sensors. A dynamic computer-controlled Gas Mixing System was utilized to ensure controlled airflow with variable relative humidity and acetone concentrations. The sensor response was explained based on physico-chemical equations, taking into consideration pre-adsorbed species of oxygen and water, both of which are relevant constituents of atmospheric conditions. The results highlight the applicative potential of WO3, having a good signal-to-noise ratio in relative humidity conditions up to 90% and a pronounced sensitive selectivity to acetone.

The Influence of 2-Methoxyethanol as Capping Agent on WO3-Based Carbon Monoxide Gas Sensor Characteristics

Carbon monoxide (CO) gas detection using a modified WO3-based sensor is being developed. The solvent for solvothermal use, a combination of 2-Propanol and 2-Methoxyethanol, was employed as a capping agent before graphene was used as a component of nanocomposites. Following the creation of the powder, it is combined with ethyl glycol and applied to an alumina substrate using the Doctor Blade process.By X-ray diffraction research, it was discovered that the solvent combinations of 2-Propanol and 2-Methoxyethanol formed monoclinic WO3 in the amounts of 40-0 and 30-10, respectively, while the solvent combinations of 20-20 are thought to have produced W18O49 and 10-30, WO2.9, respectively. According to the SEM examination, the WO3 generated was first present as nanowires and nanorods before being calcined at 500 degrees Celsius, and it then appeared as nanoparticles. The sensor may work at a low temperature of 150°C, and the best sensitivity is found when the sensor is used at a temperature of 250°C, according to the CO gas test findings.

Synergistic Integration of Machine Learning with Microstructure/Composition-Designed SnO2 and WO3 Breath Sensors.

A high-performance semiconductor metal oxide gas sensing strategy is proposed for efficient sensor-based disease prediction by integrating a machine learning methodology with complementary sensor arrays composed of SnO2- and WO3-based sensors. The six sensors, including SnO2- and WO3-based sensors and neural network algorithms, were used to measure gas mixtures. The six constituent sensors were subjected to acetone and hydrogen environments to monitor the effect of diet and/or irritable bowel syndrome (IBS) under the interference of ethanol. The SnO2- and WO3-based sensors suffer from poor discrimination ability if sensors (a single sensor or multiple sensors) within the same group (SnO2- or WO3-based) are separately applied, even when deep learning is applied to enhance the sensing operation. However, hybrid integration is proven to be effective in discerning acetone from hydrogen even in a two-sensor configuration through the synergistic contribution of supervised learning, i.e., neural network approaches involving deep neural networks (DNNs) and convolutional neural networks (CNNs). DNN-based numeric data and CNN-based image data can be exploited for discriminating acetone and hydrogen, with the aim of predicting the status of an exercise-driven diet and IBS. The ramifications of the proposed hybrid sensor combinations and machine learning for the high-performance breath sensor domain are discussed.

Creating oxygen vacancies on porous tungsten oxide nanospheres via one-step muffle calcination for ultra-fast detection of ppb-level hydrogen sulfide sensors

Exploring the relationship between tungsten oxides with a controlled amount of oxygen vacancies and their gas-sensing properties with respect to hydrogen sulfide is interesting for developing excellent comprehensive gas-sensing performance materials with fast and accurate response. In this work, the WO3 nanoparticles with oxygen defective structure were synthesized by a straightforward one-step muffle calcining method. The WO3 nanoparticles prepared at the calcination temperature of 600 ℃ (Ov-WO3-600) display the high response value (2777) and ultra-fast response time (2 s) to 5 ppm hydrogen sulfide (H2S) at 100 ℃. Moreover, it also exhibits low practical detection limit (100 ppb), long-term stability, as well as remarkable admirable selectivity. The gas sensing mechanism can be explained by the fact that oxygen vacancies, as donor energy levels provide more electrons, increase the carrier mobility and narrow the band gap. This makes it easier for oxygen to capture electrons to form more adsorbed oxygen, which improves the gas sensing performance of WO3-based sensors. Hence, our study can offer guidance for the construction of fast and accurate sensing materials based on WO3.

New Approach for the Detection of Sub-ppm Limonene: An Investigation through Chemoresistive Metal-Oxide Semiconductors.

R-(+)-limonene, one of the major constituents of citrus oils, is a monoterpene that is widely used as a fragrance additive in cosmetics, foods, and industrial solvents. Nowadays, its detection mainly relies on bulky and expensive analytical methods and only a few research works proved its revelation through affordable and portable sensors, such as electrochemical and quartz crystal microbalance sensors. In response to the demand for effective miniaturized sensing devices to be integrated into Internet of Things systems, this study represents a pioneering investigation of chemoresistive gas sensor capabilities addressed to R-(+)-limonene detection. An array of seven metal-oxide sensors was exploited to perform a complete electrical characterization of the target analyte. The experimental evidence allowed us to identify the WO3-based sensor as the most promising candidate for R-(+)-limonene detection. The material was highly sensitive already at sub-ppm concentrations (response of 2.5 at 100 ppb), consistent with applicative parameters, and it resulted in selective vs. different gases at a lower operating temperature (200 °C) than the other sensors tested. Furthermore, it exhibited a humidity-independent behavior under real-life conditions (relative humidity > 20%). Finally, the WO3 sensor also demonstrated a remarkable cross-selectivity, thus enabling its exploitation in cutting-edge applications.

Au-decorated WO3-based sensor for chemiresistive detection of NO2 at 80 °C

Nitrogen dioxide (NO2), a hazardous gas of acidic nature, is constantly released into the atmosphere by human activities. Based on the noble metal sensitization, the NO2 sensing performance of Au decorated WO3 sensors (Rg/Ra = 4.3@ 1 ppb, 746.0@ 5 ppm) was found to be superior to that of pristine WO3 (Rg/Ra = 1.2@ 1 ppb). In addition, the dynamic processes that occur in Au–WO3-3 during NO2 sensing reactions were analyzed using ex-situ X-ray photoelectron spectroscopy. Density functional theory containing adsorption energy, is further used to analyse mechanism accurate electron transfer sensing process. Furthermore, the effects of the oxygen partial pressure and relative humidity on the sensing performance of the sensors were studied. The enhanced sensing mechanisms of Au–WO3 sensors can be attributed to the electronic and chemical sensitization effects of Au, increased number of active sites, decrease in the activation energy of the sensing reactions and three-dimensional hierarchical structure, which boosts the adsorption of gas molecules and charge transfer efficiency.

Ultrahigh-response sensor based on hierarchical Pd-WO3 nanoflowers for rapid hydrogen detection

In this research, four tungsten trioxide materials were synthesized in precursor solutions with different pH values by hydrothermal method. Then, Pd nanoparticles were loaded on the hierarchical WO3 nanoflowers, which exhibited the best hydrogen sensitivity among the four as-synthesized materials. The hydrogen sensing test results demonstrated that the 0.50 at% Pd-WO3 sensor showed a fairly high response of 8658.98, a fast response/recovery time of 1/3 s and excellent selectivity to 500 ppm H2 at a working temperature of 150 °C, which properties were superior to previous WO3-based hydrogen sensors. The wonderful H2 sensing property was shown due to the increase of oxygen vacancies, adjustment of basic sensor resistance and spill-over effect of Pd. This work will provide a feasible strategy for designing H2 sensors with a fairly high response and fast response/recovery speed.

Humidity Sensing Mechanism and Respiration Monitoring of WO3 Nanoplates with a Monoclinic Crystal Phase

Functioning of hydrothermally synthesized WO3 nanoplates was investigated for humidity sensing and respiration monitoring under different breathing conditions. The monoclinic phase was identified by the X-ray diffraction (XRD) technique. The average crystallite size was calculated by Williamson-Hall (W–H) plot (27 nm) and modified Scherrer equation (24 nm). The optical band gap was calculated as 2.7 eV using UV–visible spectroscopy. The field emission electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM) micrographs of readied WO3 have confirmed the formation of microstructured nanoplates having an average diameter of 216 nm. Fluorine-doped tin oxide (FTO) substrate was used for the deposition of film and also used as an electrode. The investigation of humidity was carried out at different relative humidity (RH)−11%, 33%, 44%, 54%, 74%, and 95%. The fabricated humidity sensor has shown excellent reversibility, stability and very small humidity hysteresis (<2%) at room temperature. The maximum response was observed as 41.95% at 95% RH with response and recovery time as 2 s and 134 s respectively. During the 30 d of observation, only a 0.4% decrease in response was observed. The fabricated WO3-based humidity sensor was investigated for human respiration having respiration rates of 2.51 min−1, 3.09 min−1 and 3.74 min−1.

Room temperature operable solid-state sensors for selective methanol vapour detection from orthorhombic WO3 nanoplates

Facile hydrothermal synthesis of tungsten oxide (WO3) has been successfully done without using any surfactant. The average crystallites size and band gap were calculated as 24 nm and 2.60 eV, respectively. During the selectivity analysis, WO3-based sensor possessed the highest response towards methanol among various volatile organic compounds (VOCs) (methanol, ethanol, isopropanol, acetone and toluene) at room temperature. The response of the sensor towards methanol was calculated to be 1.35, 1.85, 3.00, 4.85 and 12.77 at 20 ppm, 50 ppm, 100 ppm, 300 ppm and 500 ppm respectively. The response and recovery time was calculated as 8.70 s and 3.22 s respectively at 500 ppm. The sensor’s response was also investigated under various relative humidity (RH) environments of 33 %, 44 %, 54 %, 75 %, 97 %. It was found that the response gets decreased with increased RH. After 20 days of observation, very low decrease (from 12.77 to 10.99) was observed in response.

MXene decorated tungsten trioxide nanocomposite-based sensor capable of detecting NO2 gas down to ppb-level at room temperature

In this study, we reported the fabrication of WO3/Ti3C2TX nanocomposite-based sensing platform for the sub-ppb detection of NO2 gas at room temperature. The WO3/Ti3C2TX nanocomposite comprising WO3 nanoparticles and two-dimensional Ti3C2TX (MXene) was prepared using a one-step hydrothermal method. The morphological and structural characterizations of the WO3/Ti3C2TX nanocomposite were performed using field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and nitrogen adsorption–desorption techniques. Further, the gas sensing properties of the WO3/Ti3C2TX nanocomposite-based sensors were investigated by estimating their sensing response and selectivity toward different target gases at room temperature. The WO3/Ti3C2TX nanocomposite-based sensor exhibited high response toward 15–500 ppb of NO2. In particular, the fabricated sensor showed a high response of 78, which was approximately eight times higher than the pristine WO3-based sensor (9.8) with short response time (182 s) and recovery time (75 s) toward 200-ppb NO2 at room temperature. The improved sensing characteristics were attributed to the synergistic behavior of WO3 nanoparticles and the layered morphology of 2D Ti3C2TX that provides large number of gas adsorption sites and highly conducting pathway for efficient charge transportation.

Sea urchins-like WO3 as a material for resistive acetone gas sensors

Tungsten oxide (WO3) with different morphologies (nanorods, spheres, sea urchins and flowers) were synthesized by a hydrothermal method. Among them, the WO3 based gas sensor with sea urchin morphology (WO3-3) exhibits excellent sensitivity, selective and ultrafast response to acetone in the concentration range of 2–5000 ppm at 200 ℃. The response of WO3-3 sensor to 100 ppm acetone can reach 29.7 and the response time is ultrafast (3 s), which makes the sensors a promising candidate for practical applications. As temperature is one of the important factors that affect the sensor performance, we also investigated the effects of temperature on the as-prepared WO3 structures using Raman spectroscopy. Changes in the spectra measured for the different WO3 structures were seen over a temperature range from 60 to 200 ℃. Raman spectra were also measured for the WO3-3-based sensor exposed to air and acetone at room temperature and the optimum working temperature. The temperature studies using Raman spectroscopy expanded our understanding of the interactions between the gas and gas sensing materials in the WO3-based sensors. The excellent sensing properties of the WO3-3-based sensors is attributed to the special, urchin-shaped structure as well as the oxygen activity and oxygen vacancy regulation in these materials.

WO3 Nanoparticles and Nanoflakes Based Sensors for Selective Detection of Alcohols

Ethanol is an important chemical raw material widely used in chemical industry, medicine, cosmetics, paints, and biofuels [1]. It is volatile and flammable and a human exposure to its vapours could result in headache, drowsiness, irritation of eyes and difficulty in breathing. It derives that the precise quantitative detection of ethanol vapours is of interest for many applications. Different studies were focused on semiconducting metal oxides as sensing materials for the selective ethanol detection. It is well known that, despite their high stability over time and the low cost of production, these semiconductors suffer of low selectivity, which affects their effective use for real applications.Among the wide palette of the metal oxides, tungsten oxide (WO3) is an important intrinsic n-type wide gap semiconductor, which has attracted considerable attention to detect various hazardous gases. However, it is still challenging to significantly enhance the sensibility and selectivity of WO3 based gas sensors by tuning its crystal structures, morphology and adding dopants [2]. WO3 can be a promising candidate for alcohols detection for the presence of acidic sites that can promote the alcohol decomposition through dehydration [3].In this work, the synthesis of WO3 nanoflakes (WO3-NF) was achieved via solvothermal route [4]. The peculiar morphology was characterized by SEM microscopy. XRD analysis reveals that the investigated sample is biphasic, composed by triclinic (s.g. P-1) and hexagonal (s.g. form with P63/mcm) WO3 with a phase fraction of about 97 and 3 wt.%, respectively.Sensing performance of the WO3-NF were studied and compared to those of WO3 nanoparticles synthetized by precipitation method. Tested sensors were realized by screen-printing of the functional material on alumina substrates with interdigitated electrodes. After a systematic investigation on the optimal working temperature, WO3 based sensors were tested at 250°C and 300°C for WO3-NF and WO3-NP, respectively. Gas measurements were performed testing the WO3-based sensors towards various gaseous molecules: H2S (10 ppm), H2 (50 ppm), CO (35 ppm), NO2 (1 ppm), NH3 (2 ppm) and different concentrations of methanol, ethanol and butanol (5-10, 25, 50 ppm). The sensing analysis indicates that the WO3-NF is sensitive towards alcohols, remarkably to ethanol, with negligible responses to other analytes.Fig. 1a, where the dynamic response to different concentration of ethanol for WO3-based sensors is shown, clearly highlights the enhanced sensing performance of the WO3-NF based sensor when compared to that of the WO3-NP. The influence of humidity on WO3-based sensors exposed to ethanol was also investigated (Fig. 1b). Even at low ethanol concentration (5 ppm), the influence of water vapour is limited, and after a partial drop up to 30 RH%, the WO3-based sensors performance seems to reach a stabilization, and no variations are observed up to 60 RH%. Noteworthy, the WO3-NF response to ethanol is always more than two times higher when compared to that of WO3-NP. The sensing response towards 50 ppm of methanol, ethanol and butanol are shown in Fig. 1c. While WO3-NP sensibility increases with the length of the alcohol chain, this trend is not observed for WO3-NF, which has higher response for ethanol. This peculiar behaviour will be the object of further investigation.

Bimetal Au-Pd decorated hierarchical WO3 nanowire bundles for gas sensing application

This study has developed a simple but effective synthesis method to deposit bimetal Au-Pd nanoparticles onto WO3 hierarchical bundle nanowires through an in-situ redox reaction in a reducing aqueous medium. Hydrothermal method was used for the synthesis of WO3 hierarchical bundles ultrathin nanowire subunits, and the mechanisms controlling the segregation behavior and growth based on Na2SO4, citric acid, and ethylene glycol are discussed. It was found that the Pd-WO3 and/or Au-Pd-WO3 nanocomposites decorated with Au 2.4 wt% and Pd 0.48 wt% showed exemplary sensitivity (S) for 50 ppm n-butanol as S = 91 at 200 °C, approximately 14 and 1.4 times better than pristine WO3 (S = 5.7) and Pd-WO3 (S = 59), respectively. Moreover, the Pd-WO3 sensing results demonstrated that the Pd decoration could significantly reduce the operating temperature, similarly to the Au-Pd-WO3 sensor, which is particularly effective for n-butanol gas among common volatile organic compounds (VOCs). The analysis demonstrates that the bimetal Au-Pd decoration have resulted a synergistic effect in boosting the sensitivity of the WO3-based sensor toward n-butanol gas. The underlying sensing mechanism of such an Au-Pd-WO3 hybrid nanostructure is further discussed, based on chemical and electronic sensitizations in promoting the spillover of oxygen species and rectifying Schottky barriers at the interface of noble metal(s) and semiconductor oxide (e.g., WO3). This work may be beneficial for designing a unique Au-Pd-WO3 sensor with great potential to develop oxide-based sensors for detecting other hazardous gases at low temperature.

Generic Approach to Boost the Sensitivity of Metal Oxide Sensors by Decoupling the Surface Charge Exchange and Resistance Reading Process

As one of bottlenecking parameters for practical applications of metal oxide semiconductor based gas sensors, sensitivity enhancement has attracted significant attention in the past few decades. In this work, alternative to conventional strategies of designing sensitive surfaces via morphology/defect/heterojunction control (then operating at an optimized isothermal temperature with a maximal response), a facile enhancement approach by decoupling surface charge exchange and resistance reading process (possessing different temperature-dependent behaviors) through pulsed temperature modulation (PTM) is reported. Substantially magnifying electrical responses of a generic metal oxide (e.g.WO3) MEMS sensor toward diverse analyte molecules is demonstrated. Under the optimal PTM conditions, the response toward 10 ppm NO2 can be boosted from (isothermal) 99.7 to 842.7, the response toward 100 ppm acetone is increased from (isothermal) 2.7 to 425, respectively, which are comparable to or even better than most of the state-of-the-art WO3 based sensors. In comparison to conventional (isothermal) operation, PTM allows to sequentially manipulate the physi/chemisorption of analyte molecules, generation of surface reactive oxygen species (ROS) and sensor resistance reading, and thus provides additional opportunity in boosting electrical response of oxide sensors for advanced health and/or environment monitoring in future.

Enhanced performances of WO3-based hydrogen sensors with an amorphous SiO2 layer working at low temperatures

Hydrogen sensors, working at low temperatures while highly sensitive to low hydrogen concentrations, are essential, due to the low autoignition temperature, flammability and high explosibility of hydrogen. In this work, we report hydrogen sensors based on Pt-decorated WO3, which are coated with SiO2 membranes to decrease the working temperature and improve the selectivity and sensitivity. SiO2 is deposited in-situ by chemical vapor deposition (CVD). The SiO2 membrane enables the Pt-decorated WO3 sensor a low working temperature of 150 °C, and an ultra-high sensitivity, i.e. a response of 100,000 towards 150 ppm H2. In contrast, the sensor without the SiO2 membrane shows a response of only 400 towards 150 ppm. The outstanding properties can be attributed to the low diffusion rate of oxygen in the SiO2 membrane, which results in little oxygen absorption on the WO3 surfaces. In addition, the SiO2 membrane also contributes high selectivity to hydrogen. This work lays down the foundation for engineering ultra-sensitive and highly selective gas sensors. Beyond the particular WO3 material, this work could also be a benefit to boost performances of hydrogen sensors based on other materials.

Enhanced Photo-Assisted Acetone Gas Sensor and Efficient Photocatalytic Degradation Using Fe-Doped Hexagonal and Monoclinic WO3 Phase-Junction.

The development of WO3-based gas sensors for analysis of acetone in exhaled breath is significant for noninvasive diagnosis of diabetes. A series of Fe-doped hexagonal and monoclinic WO3 phase−junction (Fe−h/m−WO3) sensors were synthesized by the hydrothermal calcination method, and the influences of operating temperature and light irradiation on the response were studied. Under light emitting diode (LED) illumination, Fe−h/m−WO3 exhibited higher responses to acetone than those of the undoped WO3-based sensors at an operating temperature of 260 °C with 90% relative humidity, and good linearity between response and acetone concentration (0.5 to 2.5 ppm) was achieved under the 90% relative humidity condition. Meanwhile, the optimal Fe−h/m−WO3 sensor exhibited high selectivity and stability for a duration of three months. The excellent sensing performance of Fe−h/m−WO3 was attributed to the formation of phase−junction and Fe doping, and these were beneficial for the separation of photon−generated carriers and oxygen adsorption on the WO3 surface, promoting the generation of superoxide radicals, which was demonstrated by electron paramagnetic resonance and photocurrent tests. Additionally, the Fe−doped WO3 phase−junction sample also showed good photocatalytic performance for rhodamine B degradation. This study may provide some insights into rational design of new types of gas sensors and offer an alternative for noninvasive diagnosis of diabetes.

Insight into highly selective dimethyl trisulfide detection based on WO3 nanorod bundles with exposed (002) facets

Metal oxide semiconductors (MOS)-based gas sensor for food-borne pathogens detecting via special biological metabolites, require high selectivity due to the possible sensing interference, which is an issue still to be resolved [1–4]. In this work, WO3 nanorod bundles were synthesized via a hydrothermal method, and its rapid response, high sensitivity and selectivity are demonstrated for detecting dimethyl trisulfide (DMTS), the biomarker of Listeria monocytogenes. The WO3-based sensor with high selectivity exhibited rapid response (10 s) and high response (94) behavior towards 10 ppm DMTS. The in situ Raman spectrum measurement results suggest that the excellent sensing behavior can be ascribed to the strong interaction between S atoms in DMTS and W sites on the (002) surface of WO3. Moreover, Density Functional Theory (DFT) calculation results also prove that the DMTS molecule exhibits the largest adsorption energy of 3.39 eV by S at W sites. The cleavage of SSS bonds through a catalytic behavior on W sites, which greatly enhances the reaction of the O− with DMTS, is suggested to be the mechanism of the WO3 sensor for detecting DMTS, which is in contrast to the sensing mechanism based on the traditional oxygen depletion theory.