Recent Advances of SnO2-Based Sensors for Detecting Fault Characteristic Gases Extracted From Power Transformer Oil

Tin oxide SnO2-based gas sensors have been widely used for detecting typical fault characteristic gases extracted from power transformer oil, namely, H2, CO, CO2, CH4, C2H2, C2H4, and C2H6, due to the remarkable advantages of high sensitivity, fast response, long-term stability, and so on. Herein, we present an overview of the recent significant improvement in fabrication and application of high performance SnO2-based sensors for detecting these fault characteristic gases. Promising materials for the sensitive and selective detection of each kind of fault characteristic gas have been identified. Meanwhile, the corresponding sensing mechanisms of SnO2-based gas sensors of these fault characteristic gases are comprehensively discussed. In the final section of this review, the major challenges and promising developments in this domain are also given

Chemiresistors Based on Li-Doped CuO–TiO2 Films

none14siChemiresistors based on thin films of the Li-doped CuO–TiO2 heterojunctions were synthesized by a 2-step method: (i) repeated ion beam sputtering of the building elements (on the Si substrates and multisensor platforms); and (ii) thermal annealing in flowing air. The structure and composition of the films were analyzed by several methods: Rutherford Backscattering (RBS), Neutron Depth Profiling (NDP), Secondary Ion Mass Spectrometry (SIMS), and Atomic Force Microscopy (AFM), and their sensitivity to gaseous analytes was evaluated using a specific lab-made device operating in a continuous gas flow mode. The obtained results showed that the Li doping significantly increased the sensitivity of the sensors to oxidizing gases, such as NO2, O3, and Cl2, but not to reducing H2. The sensing response of the CuO–TiO2–Li chemiresistors improved with increasing Li content. For the best sensors with about 15% Li atoms, the detection limits were as follows: NO2 → 0.5 ppm, O3 → 10 ppb, and Cl2 → 0.1 ppm. The Li-doped sensors showed excellent sensing performance at a lower operating temperature (200 °C); however, even though their response time was only a few minutes, their recovery was slow (up to a few hours) and incomplete.openTorrisi A.; Vacík J. ; Ceccio G. ; Cannavò A. ; Lavrentiev V.; Horák P.; Yatskiv R.; Vaniš J.; Grym J. ; Fišer L.; Hruška M. ; Fitl P. ; Otta J.; Vrňata M.Torrisi, A.; Vacík, J.; Ceccio, G.; Cannavò, A.; Lavrentiev, V.; Horák, P.; Yatskiv, R.; Vaniš, J.; Grym, J.; Fišer, L.; Hruška, M.; Fitl, P.; Otta, J.; Vrňata, M

Wo3 and ionic liquids: A synergic pair for pollutant gas sensing and desulfurization

This review deals with the notable results obtained by the synergy between ionic liquids (ILs) and WO3 in the field of pollutant gas sensing and sulfur removal pretreatment of fuels. Starting from the known characteristics of tungsten trioxide as catalytic material, many authors have proposed the use of ionic liquids in order to both direct WO3 production towards controllable nanostructures (nanorods, nanospheres, etc.) and to modify the metal oxide structure (incorporating ILs) in order to increase the gas adsorption ability and, thus, the catalytic efficiency. Moreover, ionic liquids are able to highly disperse WO3 in composites, thus enhancing the contact surface and the catalytic ability of WO3 in both hydrodesulfurization (HDS) and oxidative desulfurization (ODS) of liquid fuels. In particular, the use of ILs in composite synthesis can direct the hydrogenation process (HDS) towards sulfur compounds rather than towards olefins, thus preserving the octane number of the fuel while highly reducing the sulfur content and, thus, the possibility of air pollution with sulfur oxides. A similar performance enhancement was obtained in ODS, where the high dispersion of WO3 (due to the use of ILs during the synthesis) allows for noteworthy results at very low temperatures (50◦ C)

Aerosol-Assisted Chemical Vapour Deposition (AACVD) of Silver Nanoparticle Decorated Tungsten Oxide Nanoneedle for Use in Oxygen Gas Sensing

Semiconducting metal oxides (SMOX) gas sensors, such as tungsten oxide (WO3), have been developed in depth for use in toxic gas detection, such as nitrogen oxides (NOx). With the addition of catalytic nanoparticles, like Ag, Pt, Pd and etc., the sensing properties, the three ‘S’ (sensitivity, selectivity and stability), can be significantly improved. This thesis details a two-step synthesis method for the fabrication of Ag nanoparticle decorated WO3 nanoneedle by using different silver metal precursors, including silver nitrate (AgNO3), silver 2-aminoethanol (Ag-EA), silver 1-aminopropan-2-ol (Ag-AP) and silver 2-methyl-2-aminopropan-1-ol (Ag-AMP), in a vapour deposition process. A series of experiments were conducted to investigate the parameters that affect the growth of the materials microstructure including deposition temperature, deposition time, flow rate of N2 carrier gas and concentration of precursor solution. Physical property characterization techniques including UV/Vis, XRD, XPS, SEM and TEM, have been systematically applied for all WO3 and Ag-decorated WO3 samples and sensor materials. Oxygen sensors’ have been considered as the critical component of Engine Management System for several decades. Gas sensing performance was carried out toward different O2 concentration between 1 and 20% at various operating temperatures. The sensing response revealed that the decoration of Ag nanoparticle on WO3 sensors significantly improved sensing properties as compared to undecorated WO3 sensors. An optimal gas response with silver-decorated WO3 is enhanced 400% compared to an undecorated WO3 sensor at an optimum operating temperature at 350 °C towards 20% oxygen at a relative humidity level ~ 85% by using AgNO3 as a precursor. An enhancement was also observed for the Ag decorated WO3 sensors fabricated using organometallic silver precursors, with a dramatically increasing in baseline resistance for these Ag@WO3 sensors. Sensing mechanisms, are proposed to explain the enhancement in sensing response

Performance optimization of metal oxides for gas sensing: the case of WO3 and SnO2

Electrical gas sensors based on semiconducting metal oxides are now used in a wide range of applications and provided by many companies. They attracted the attention of many users and scientists due to the low cost, flexibility of production, ease of use, long-term stability and large number of detectable gases. The rising demand for gas sensors for a wide range of applications has highlighted not only the capabilities of these devices, but also their limits. Although common metal oxides, such as SnO2, TiO2, WO3 and ZnO, are catalytically active, different strategies are required to improve their selectivity and sensitivity. The quest for highly selective and high-performance gas sensors encouraged research into new sensing materials. Two approaches were used in this thesis to enhance the sensing capabilities of metal oxide-based thick films for detection of ethanol and hydrogen, i.e., two analytes of widespread interest for several applications. The first strategy aimed to control the size and shape of WO3 nanostructured powders used to produce thick films. WO3 nanoflakes have been synthetized through a simple and time effective solvothermal method. Two-dimensional (2D) WO3 was evaluated as most promising for the optimization of active surface area and film porosity for ethanol sensing. The second approach tuned the chemical composition and structure of SnO2 through substitution of Sn sites with Ti and Nb in different contents. Ti, Nb and Sn have similar ionic radii and bimetallic oxide solid solution of (Sn,Ti)xO2 and (Ti,Nb)xO2 have been claimed to enhance the sensing properties of single oxides, although some limitations remain. Nevertheless, the large number of compositional and structural combinations that these materials offer, makes it possible still unexplored possibilities. Indeed, what emerged from this work was that the incorporation of Nb in (Sn,Ti)xO2 offer a number of advantages, including increased film conductance and structural stability, as well as improved sensitivity to some gases, i.e. ethanol and hydrogen. Moreover, humidity (a common interferent) had a negligible influence on the baseline conductance of the (Sn,Ti,Nb)xO2 solid solution. While the reactions between the target gas and the surface of WO3 are well documented in the literature, those that occur over (Sn,Ti,Nb)xO2 are unknown due to the new chemical nature of the material. Therefore, operando Diffuse Reflectance Infrared Fourier Transform (DRIFT)-spectroscopy was employed to explore the interactions between ethanol, hydrogen and water vapour with the surface of the most promising (Sn,Ti,Nb)xO2 sensors while they were in operation.I sensori elettrici a base di ossidi metallici semiconduttori sono ad oggi ampiamente usati in numerose applicazioni e venduti da diverse compagnie. Hanno attratto l’attenzione di molti utilizzatori e scienziati grazie al loro basso costo, adattabilità di produzione, facilità di utilizzo, stabilità a lungo termine e largo numero di gas rilevabili. La crescente domanda per sensori di gas in applicazioni diversificate ha portato alla luce non solo le capacità di questi sensori, ma anche i loro limiti. Nonostante i comuni ossidi metallici, come SnO2, TiO2, WO3 e ZnO, siano cataliticamente attivi, diverse strategie devono essere adottate per migliorare la loro selettività e sensibilità. La richiesta di sensori di gas altamente performanti e selettivi ha incoraggiato la ricerca verso nuovi materiali sensibili. In questa tesi sono stati usati due approcci per ottimizzare film spessi a base di ossidi metallici per il rilevamento di etanolo ed idrogeno, ovvero due analiti di interesse diffuso per molte applicazioni. La prima strategia aveva l’obiettivo di controllare dimensione e forma di polveri nanostrutturate a base di WO3 usate per produrre film spessi. Nano lamine di WO3 sono state sintetizzate con un metodo solvotermale semplice e veloce. Il WO3 bidimensionale (2D) è stato considerato come il più promettente per ottimizzare la superficie attiva e la porosità del film verso il rilevamento di etanolo. Il secondo approccio ha modificato la struttura e composizione chimica dell’SnO2 tramite sostituzione di siti Sn con Ti e Nb, in diverse concentrazioni. Ti, Nb e Sn hanno raggi ionici simili e soluzioni solide di ossidi bimetallici come (Sn,Ti)xO2 and (Ti,Nb)xO2 hanno dimostrato di migliorare le proprietà di rilevamento dei singoli ossidi metallici, anche se rimangono alcune limitazioni. Ciononostante, l’ampio numero di combinazioni composizionali e strutturali che questi materiali offrono consentono ancora possibilità inesplorate. Ad esempio, dal lavoro di tesi è emerso che l’aggiunta di Nb in (Sn,Ti)xO2 offre diversi vantaggi, tra cui una maggiore conduttanza del film e stabilità strutturale, nonché una migliore sensibilità verso alcuni gas, come etanolo ed idrogeno. Inoltre, l’umidità (un comune interferente) ha un’influenza trascurabile sulla conduttanza della soluzione solida di (Sn,Ti,Nb)xO2. Mentre le reazioni tra i gas target e la superficie del WO3 sono documentate nella letterature, quelle che avvengono su (Sn,Ti,Nb)xO2 sono sconosciute a causa della nuova composizione chimica del materiale. Quindi, è stata impiegata la spettroscopia DRIFT (Diffuse Reflectance Infrared Fourier Transform) operando per investigare le interazioni tra etanolo, idrogeno e vapore acqueo con la superficie dei sensori (Sn,Ti,Nb)xO2 più promettenti mentre erano in funzione

The Morphologies of the Semiconductor Oxides and Their Gas-Sensing Properties

Semiconductor oxide chemoresistive gas sensors are widely used for detecting deleterious gases due to low cost, simple preparation, rapid response and high sensitivity. The performance of gas sensor is greatly affected by the morphology of the semiconductor oxide. There are many semiconductor oxide morphologies, including zero-dimensional, one-dimensional, two-dimensional and three-dimensional ones. The semiconductor oxides with different morphologies significantly enhance the gas-sensing performance. Among the various morphologies, hollow nanostructures and core-shell nanostructures are always the focus of research in the field of gas sensors due to their distinctive structural characteristics and superior performance. Herein the morphologies of semiconductor oxides and their gas-sensing properties are reviewed. This review also proposes a potential strategy for the enhancement of gas-sensing performance in the future