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[Display omitted] • Pd/SnO 2 nanoparticles were synthesized using Pluronic F-127 to control the size of Pd. • Numerous nanojunctions in Pd/SnO 2 nanoparticles contribute toa sensitive and fast response to H 2. • The real-time H 2 detection in water splitting system was demonstrated. H 2 energy has gained massive attraction as a promising candidate for future energy sources. However, the explosive properties of H 2 arouse significant safety concerns, emphasizing the need for the development of real-time H 2 detection systems. This study presents the fabrication of an ultrasensitive and selective H 2 gas sensor using Pd/SnO 2 nanoparticles (NPs) synthesized through the utilization of Pluronic F-127. Pluronic F-127 improves the dispersion and regulates the particle size of Pd NPs. Pd/SnO 2 NPs, which are comprised of numerous nanojunctions, exhibit H 2 response of 27,190 and a response time of 3 s when exposed to 50 ppm of H 2 at 100 °C. The practical applicability of Pd/SnO 2 NPs was demonstrated by detecting H 2 generated from water-splitting cells, exhibiting promising features for H 2 energy industries. Overall, the synthetic method of this study proposes advanced strategies for development of sensing materials with maximized gas sensing performance. [ABSTRACT FROM AUTHOR]

In this research, electrospun polyacrylonitrile (PAN) nanofibrous layers are investigated as substrate for palladium‐based resistive type hydrogen sensors. The fabricated sensors showed sensitivity to hydrogen with a concentration as low as 12 ppm at room temperature. Up to 50 ppm hydrogen concentration, hydrogen induced lattice expansion (HILE) constituted the mechanism, whereas, with concentrations of 125 ppm and higher, palladium hydride formation (PdHx) mechanism ruled. For equal palladium thickness, the response of the sensors increased with increasing nanofiber diameter. With constant diameter of nanofibers, response and response time increased with thicker palladium layer. The sensor with 104 nm nanofibers and 4 nm palladium layer showed the best behavior. The sensor with nanofibrous substrate showed a higher response and lower response time in comparison to glass, PAN film, and PAN fibrous (fiber diameter: 16 μm, non‐nanofiber) substrate. [ABSTRACT FROM AUTHOR]

Gas sensors based on p-type semiconducting metal oxides have recently received significant attention due to their superior gas selectivity compared to those based on n-type metal oxides. Nevertheless, p-type metal oxides-based gas sensors have limitations such as low sensitivity and slow response. Herein, we present highly sensitive and fast responding ethanol (C 2 H 5 OH) gas sensors that are composed of p-type SrTi 1−x Fe x O 3 (STF) with various Fe compositions deposited on vertically aligned SiO 2 nanorods (NRs) with a larger surface-to-volume ratio than STF thin films. As the Fe content increases, the charge transfer energy between adsorbed oxygen species and transition cations decreases, and the amount of oxygen vacancy increases, This results in the acceleration of charge transfer and the generation of active sites. The fabricated STF on SiO 2 NRs exhibited gas responses ranging from 74 to 528 for 50 ppm ethanol gas depending on the Fe content with fast response and recovery time, overcoming the low sensitivity and slow response of previously reported p-type gas sensors. The observed unprecedented synergistic effects of STF on SiO 2 NRs for highly selective ethanol sensing establish a new perspective on quaternary p-type perovskites for selective gas sensing in which n-type metal oxides have been used. • Fast responding to VOCs was achieved by Fe substitution in STO deposited on SiO 2 NRs. • Increased Fe contents in STF has an effect on enhanced ethanol sensing properties. • Enhancement in sensing properties was explained through DFT and XPS analysis. • This work presents new perspectives on p-type perovskite in gas sensing applications. [ABSTRACT FROM AUTHOR]

Rare-earth oxycarbonates have been proposed as promising chemoresistive materials for CO2 sensors. In this contribution we present the results of a broad investigation focused on selecting the best candidates in the rare-earth compounds and, in the case of the best performing material, preliminary results dealing with the understanding of sensing by the operando methods.

Commercial carbon fibers have been coated by a brush-like layer of ZnO nanowires using a seeded chemical bath deposition. Both single carbon fibers or large tows can be functionalized in such a way. Exploiting the electrical conductivity of carbon fibers and the functional properties of ZnO nanostructures, we demonstrated that the intersection at the crossing of two functionalized carbon fibers can act not only as a piezoelectric strain sensor, but also as a chemoresistive gas sensor. The small volume of added nanostructures prevents delamination issues. The “crossing” configuration, which is typical of carbon fiber fabrics used for composites, paves the way to transform a typical texture with simple mechanical and structural properties into a “smart” material with noninvasive integrated arrays of micron-scale sensors. [ABSTRACT FROM AUTHOR]

A bias circuit is required for chemoresistive gas sensors to appropriately adjust their operating temperature and facilitate the readout of their output response. If the sensor is properly biased, its overall performance regarding sensitivity, selectivity, and power consumption can be greatly enhanced. We have introduced the concept of self-regulated biasing as an alternative to the conventional fixed biasing methods. In self-regulated bias circuits, the gas sensor is an active component in its own bias circuit, so the operating point is dynamically adjusted during a measurement. This will provide the sensor with different modes of operation. Here, we have proposed two self-regulated bias circuits the operation of which is analytically and experimentally studied. Results show that the first circuit puts the sensor in a low-power idle mode when no target gas is presented, and hence the power consumption is considerably reduced and the sensor lifetime may be prolonged. The second circuit puts the sensor in a power-down mode upon sensing a gas. This state is held until the circuit is reset. So the second bias circuit acts as a gas latch besides other important features like increased safety in explosive environments. Obviously, other self-regulated bias circuits can be designed for additional desired modes of operations. [ABSTRACT FROM PUBLISHER]

The properties of multi-wall carbon nanotubes decorated with iridium oxide nanoparticles (IrOx-MWCNTs) are studied to detect harmful gases such as nitrogen dioxide and ammonia. IrOx nanoparticles were synthetized using a two-step method, based on a hydrolysis and acid condensation growth mechanism. The metal oxide nanoparticles obtained were employed for decorating the sidewalls of carbon nanotubes. Iridium-oxide nanoparticle decorated carbon nanotube material showed higher and more stable responses towards NH3 and NO2 than bare carbon nanotubes under different experimental conditions, establishing the optimal operating temperatures and estimating the limits of detection and quantification. Furthermore, the nanomaterials employed were studied using different morphological and compositional characterization techniques and a gas sensing mechanism is proposed.

Abstract: The response of a chemoresistive gas sensor (CRGS) to the presence of a contaminant in the surrounding air can be substantially drifted by the fluctuations in the ambient humidity and temperature. This renders the appropriate compensation measures essential for the quantitative contamination level assessments. Here, the combined effect of the ambient humidity and temperature variations on the CRGS responses to different concentrations of a contaminant is experimentally investigated, and a systematic technique for the elimination of these drift-like terms is presented. The CRGS is considered as a nonlinear reverse multi-input-single-output system. The ambient humidity and temperature along with the as-measured steady-state value of the sensor''s resistance are the inputs to the system, while the contaminant concentration is defined as the output. The system was analyzed based on the experimental data collected; the results facilitated the design and training of an artificial neural network which could determine the prevailing contamination level based on the sensor''s resistance recorded at different ambient conditions. The effectiveness of the presented drift compensation technique was demonstrated by the verification tests carried out. [Copyright &y& Elsevier]

Abstract: The response patterns of a temperature-modulated chemoresistive gas sensor were transformed to multi-exponential functions which facilitated the extraction of their discriminative features for gas diagnosis. The patterns were generated for air contaminated with different concentrations of various volatile organic compounds by applying a staircase heating voltage waveform to the microheater of a tin oxide-based sensor that modulated its operating temperature in the 50–400°C range. Padé-Z transform was utilized for the transformation, and a novel heuristic procedure facilitated the extraction of the components of the feature vectors from the transformed data. These vectors were classified by the available techniques. The method differentiated the patterns generated for methanol, ethanol, 1-propanol, 1-butanol, and acetone contaminations in the wide concentration range examined. The method was also used to separately estimate the amount of the discriminative information in various steady state and transient response features; the results are anticipated to help design more elaborate temperature-modulated sensors for gas diagnosis. [Copyright &y& Elsevier]

• The nanostructured Nb 2 O 5 film was obtained by programmed precipitation • The chemoresistive gas-sensitive properties of the obtained Nb 2 O 5 film are comprehensively studied • Nb 2 O 5 film has been shown to be highly sensitive to O 2 and H 2 S at low operating temperatures • Gas detection processes studied in detail at a humid environment [Display omitted] Nb 2 O 5 powder obtained by programmable precipitation was used to form a thick gas-sensing film as part of a chemoresistive gas sensor, by screen-printing. The coating of orthorhombic Nb 2 O 5 consisted of nanoparticles with a size of 41.0 ± 2.5 nm. XPS revealed Nb5+, Nb4+ and Nb2+ as well as oxygen vacancies in the crystal structure of niobium oxide. As a result of studying the chemoresistive gas-sensing properties of Nb 2 O 5 , it has been shown that among the analysed gases (H 2 , CO, NH 3 , H 2 S and О 2), the greatest sensitivity was observed for oxygen and hydrogen sulphide. Nanocrystalline niobium oxide showed a high and reproducible response to 0.02–20% О 2 (S 1 = 1.1–19.0) at a very low detection temperature of 200 °C for oxygen sensors. At an operating detection temperature of 250 °C, a high and reproducible response to low concentrations of hydrogen sulphide of 4–100 ppm (S 2 = 1.2–6.6) was detected for Nb 2 O 5. The influence of humidity on the received signals when detecting oxygen and hydrogen sulphide was studied in detail: there was a decrease in the resistance and the response value at 95% humidity in the medium of both gases. However, unlike the process of detecting H 2 S (when the response of S 2 was almost lost), when determining oxygen, the response of S 1 was reduced by a factor of two only, which suggests the possibility of determining the content of O 2 in high humidity conditions. [ABSTRACT FROM AUTHOR]

Acetone is known as the breath biomarker of diabetes. In this paper we have reported on a highly sensitive, stable cobalt chromite (CoCr 2 O 4) thick film-based trace acetone sensor with quick response and recovery times promising for the detection of diabetes from exhaled breath. CoCr 2 O 4 nanoparticles were prepared by a cost-effective and easy sol-gel method. The as prepared nanoparticles were well characterized by sophisticated characterization techniques, such as, XRD, FESEM. TEM, HRTEM, XPS, and BET. Further these nanoparticles were exploited to fabricate a Taguchi type chemoresistive sensor using a customized drop coater. The developed sensor was characterized by I–V measurement. The developed sensor exhibited high p-type response towards 1 ppm of acetone vapor (~3.81 folds), and appreciable resolution between 1 ppm, 2 ppm (response = ~4.82 folds), and 5 ppm (response = ~6.64 folds) acetone vapor at 300 °C. Further, the sensor exhibited fast response and recovery times of ~1.65 s and ~62 s, respectively. Also, the response of the sensor to 1 ppm acetone vapor is appreciably higher than that of 0.2 ppm ethanol, 0.25 ppm ammonia vapor, and saturated moisture. Finally, the sensor is stable for at least 6 months and exhibits repeatable measurements. Image 1 • Facile sol-gel synthesis of cobalt chromite (CoCr 2 O 4) nanoparticles. • High p-type response to 1 ppm acetone vapor (~3.81 folds). • Appreciable resolution between 1 ppm, 2 ppm, and 5 ppm acetone vapor. • Minimal cross-sensitivities to 0.25 ppm ammonia, 0.2 ppm ethanol, and saturated moisture. • Fast response (~1.65s) and recovery (~62s) times and prolonged stability (≥6 months). [ABSTRACT FROM AUTHOR]

A tin oxide (SnO2) and reduced graphene oxide (rGO) hybrid composite gas sensor for high-performance carbon dioxide (CO2) gas detection at room temperature was studied. Since it can be used independently from a heater, it emerges as a promising candidate for reducing the complexity of device circuitry, packaging size, and fabrication cost; furthermore, it favors integration into portable devices with a low energy density battery. In this study, SnO2-rGO was prepared via an in-situ chemical reduction route. Dedicated material characterization techniques including field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX) spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) were conducted. The gas sensor based on the synthesized hybrid composite was successfully tested over a wide range of carbon dioxide concentrations where it exhibited excellent response magnitudes, good linearity, and low detection limit. The synergistic effect can explain the obtained hybrid gas sensor's prominent sensing properties between SnO2 and rGO that provide excellent charge transport capability and an abundance of sensing sites. [ABSTRACT FROM AUTHOR]

• Ln 2 O 2 CO 3 (Ln = La, Nd, Sm) and Ln 2 O 3 (Ln = Sm, Gd, Dy, Er, Yb) are sensitive to CO 2. • Hexagonal La 2 O 2 CO 3 exhibits the best performance for CO 2 sensors among them. • Enough sensitivity, stability, humidity effect, and selectivity for practical use. • Operando XRD and DRIFTS for basic understanding of the CO 2 sensing. Rare-earth oxycarbonates Ln 2 O 2 CO 3 (Ln = rare-earth element) have been identified as materials for chemoresistive CO 2 gas sensors. Among them, previous studies identified monoclinic La 2 O 2 CO 3 as the best performing one. However, not all rare-earth elements have been investigated and, moreover, La 2 O 2 CO 3 monoclinic phase is metastable and this can influence the long term performance. In this work, we have synthesized rare-earth oxycarbonates Ln 2 O 2 CO 3 (Ln = La, Nd, and Sm) including monoclinic and hexagonal La 2 O 2 CO 3 , rare-earth oxides Ln 2 O 3 (Ln = Nd, Sm, Gd, Dy, Er, and Yb) and LnO 2 (Ln = Ce) by calcination of oxalate hydrate or the acetate hydrate precursors in air. All the materials, except for CeO 2 and Nd 2 O 3 , were sensitive to CO 2. All CO 2 sensitive materials, except for monoclinic La 2 O 2 CO 3 and Nd 2 O 2 CO 3 , were stable and their performance is sufficient for practical use. Hexagonal La 2 O 2 CO 3 shows the best overall performance. The results of operando investigations indicate that the origin of CO 2 sensing is the competitive adsorption between carbonates and hydroxyl groups. [ABSTRACT FROM AUTHOR]

• The surface reactivity and chemoresistive properties of nanostructured SiC can be thermo-activated under proper condition. • SiC nanopowder resulted to be an extremely selective functional material for the detection of SO 2 , both in dry and wet air. • The surface reactivity of SiC nanoparticles vs. SO 2 is promoted by the SiC-SiOC core-shell formation, at high temperatures. Silicon carbide is a well-known material with high thermal, mechanical and chemical stability. These properties have allowed, over time, its wide use as an inert material to be employed as a substrate or support in different applications. In this work, we demonstrate that, under proper conditions, it is possible to activate the chemical reactivity of nanostructured SiC, which can be employed for chemoresistive purposes. With this aim, a commercial powder of SiC has been characterized from a morphological, structural and thermal point of view. Then, screen–printed thick films were obtained from SiC powder and thus tested as a functional material for chemoresistive gas sensors, in thermo-activation mode. The samples were exposed to 13 gases with important chemical differences. Analyses showed that SiC is an extremely selective functional material for the detection of sulphur dioxide (SO 2) in concentrations within the ppm range. This interesting result was found at high working temperatures (600−800 °C), useful for harsh environments, and the measurements proved to be completely free from humidity negative interference. Thermo-gravimetric and X-ray photoelectron spectroscopy characterizations highlighted that the high selectivity of the SiC layer is promoted by the thermal formation of a SiC/SiOC core-shell, tunable by controlling temperature and humidity parameters. An interpretation of the gas sensing mechanism occurring between SO 2 molecules and SiC/SiOC core-shell has been proposed. The unexpected chemical activity, identified for nanostructured SiC, can be exploited for the specific detection of SO 2 , since this gaseous compound plays an important role in air pollution, industrial processes and winemaking. [ABSTRACT FROM AUTHOR]

Our previous studies demonstrated that rare-earth oxycarbonates Ln 2 O 2 CO 3 (Ln = La, Nd, and Sm) and rare-earth oxides Ln 2 O 3 (Ln = Nd, Sm, Gd, Dy, Er, and Yb) are sensitive to CO 2 and that hexagonal La 2 O 2 CO 3 is the best among them in terms of sensitivity, stability, and selectivity. In this study, we have conducted a comprehensive operando characterization on a hexagonal La 2 O 2 CO 3 based sensor for the basic understanding of the sensing mechanism. This was done by performing under actual operating conditions simultaneous DC resistance and work function changes measurements, AC impedance spectroscopy measurements, and simultaneous DC resistance and DRIFT spectroscopy measurements. The results demonstrate that the double Schottky barriers at grain-grain boundaries are dominant contribution to sensor resistance; there is a competitive adsorption between carbonate species and hydroxyl groups, which depends on both CO 2 concentration and humidity and leads to the change in height of the Schottky barriers. Finally, we propose a reaction model stating that there are three types of adsorbates, -CO 3 2- , -OH - , and -O 2- , and the relative concentration of which is controlled by a reaction with ambient humidity and CO 2 . This model is able to consistently explain all our experimental findings.

The properties of multi-wall carbon nanotubes decorated with iridium oxide nanoparticles (IrOx-MWCNTs) are studied to detect harmful gases such as nitrogen dioxide and ammonia. IrOx nanoparticles were synthetized using a two-step method, based on a hydrolysis and acid condensation growth mechanism. The metal oxide nanoparticles obtained were employed for decorating the sidewalls of carbon nanotubes. Iridium-oxide nanoparticle decorated carbon nanotube material showed higher and more stable responses towards NH3 and NO2 than bare carbon nanotubes under different experimental conditions, establishing the optimal operating temperatures and estimating the limits of detection and quantification. Furthermore, the nanomaterials employed were studied using different morphological and compositional characterization techniques and a gas sensing mechanism is proposed. [ABSTRACT FROM AUTHOR]

The properties of multi-wall carbon nanotubes decorated with iridium oxide nanoparticles (IrO x -MWCNTs) are studied to detect harmful gases such as nitrogen dioxide and ammonia. IrO x nanoparticles were synthetized using a two-step method, based on a hydrolysis and acid condensation growth mechanism. The metal oxide nanoparticles obtained were employed for decorating the sidewalls of carbon nanotubes. Iridium-oxide nanoparticle decorated carbon nanotube material showed higher and more stable responses towards NH₃ and NO₂ than bare carbon nanotubes under different experimental conditions, establishing the optimal operating temperatures and estimating the limits of detection and quantification. Furthermore, the nanomaterials employed were studied using different morphological and compositional characterization techniques and a gas sensing mechanism is proposed.