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Selective gas sensing is of great importance for applications in health, safety, military, industry and environment. Many man-made and naturally occurring volatile organic compounds (VOCs) can harmfully affect human health or cause impairment to the environment. Gas analysis based on different principles has been developed to convert gaseous analytes into readable output signals. However, gas sensors such as metal-oxide semiconductors suffer from high operating temperatures that are impractical and therefore have limited its applications. The cost-effective quartz crystal microbalance (QCM) device represents an excellent platform if sensitive, selective and versatile sensing materials were available. Recent advances in affinity ionic liquids (AILs) have led them to incorporation with QCM to be highly sensitive for real-time detection of target gases at ambient temperature. The tailorable functional groups in AIL structures allow for chemoselective reaction with target analytes for single digit parts-per-billion detection on mass-sensitive QCM. This structural diversity makes AILs promising for the creation of a library of chemical sensor arrays that could be designed to efficiently detect gas mixtures simultaneously as a potential electronic in future. This review first provides brief introduction to some conventional gas sensing technologies and then delivers the latest results on our development of chemoselective AIL-on-QCM methods.

Selective gas sensing is of great importance for applications in health, safety, military, industry and environment. Many man-made and naturally occurring volatile organic compounds (VOCs) can harmfully affect human health or cause impairment to the environment. Gas analysis based on different principles has been developed to convert gaseous analytes into readable output signals. However, gas sensors such as metal-oxide semiconductors suffer from high operating temperatures that are impractical and therefore have limited its applications. The cost-effective quartz crystal microbalance (QCM) device represents an excellent platform if sensitive, selective and versatile sensing materials were available. Recent advances in affinity ionic liquids (AILs) have led them to incorporation with QCM to be highly sensitive for real-time detection of target gases at ambient temperature. The tailorable functional groups in AIL structures allow for chemoselective reaction with target analytes for single digit parts-per-billion detection on mass-sensitive QCM. This structural diversity makes AILs promising for the creation of a library of chemical sensor arrays that could be designed to efficiently detect gas mixtures simultaneously as a potential electronic in future. This review first provides brief introduction to some conventional gas sensing technologies and then delivers the latest results on our development of chemoselective AIL-on-QCM methods.

[EN] This paper explores the gas sensing properties of graphene nanolayers decorated with lead halide perovskite (CH3NH3PbBr3) nanocrystals to detect toxic gases such as ammonia (NH3) and nitrogen dioxide (NO2). A chemical-sensitive semiconductor film based on graphene has been achieved, being decorated with CH3NH3PbBr3 perovskite (MAPbBr3) nanocrystals (NCs) synthesized, and characterized by several techniques, such as field emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Reversible responses were obtained towards NO2 and NH3 at room temperature, demonstrating an enhanced sensitivity when the graphene is decorated by MAPbBr3 NCs. Furthermore, the effect of ambient moisture was extensively studied, showing that the use of perovskite NCs in gas sensors can become a promising alternative to other gas sensitive materials, due to the protective character of graphene, resulting from its high hydrophobicity. Besides, a gas sensing mechanism is proposed to understand the effects of MAPbBr3 sensing properties ; This work was funded in part by MINECO, MICINN and FEDER via grants no. RTI2018-101580-B-I00, by AGAUR under grant. 2017SGR 418 J.C.C gratefully acknowledges a doctoral fellowship from URV under the Marti i Franques fellowship program. E.L. is supported by the Catalan institution for Research and Advanced Studies via the 2012 and 2018 Editions of the ICREA Academia Award. P.A. acknowledges the financial support from the Spanish Government through 'Severo Ochoa"(SEV-2016-0683, MINECO) and PGC2018-099744-B-I00 (MCIU/AEI/FEDER, UE), and R.G.A. acknowledges FPI scholarship the Spanish Government-MINECO for a (TEC2015-74405-JIN), MAT2015-69669-P. ; Casanova-Cháfer, J.; García-Aboal, R.; Atienzar Corvillo, PE.; Llobet, E. (2019). Gas Sensing Properties of Perovskite Decorated Graphene at Room Temperature. Sensors. 19(20):1-14. https://doi.org/10.3390/s19204563 ; S ; 1 ; 14 ; 19 ; 20 ; 7 Million Premature Deaths Annually Linked to Air Pollution ...

AbstractIntelligent packaging has attracted research interest during the last decades. More specifically, food packaging is of great importance due to the utmost need to monitor and maintain food quality until consumption. Thus, there is a high demand for sensors capable of detecting gases such as CO2, emitted by packaged meat or chicken which serve as freshness indicators. In the present work, a sensor based on Cu2O nanocubes was fabricated and tested against CO2 at room temperature. Cu2O nanocubes were synthesized by solution‐based methods and deposited on commercial interdigitated electrodes. Specifically, the Cu2O‐based sensor successfully detected down to 5% CO2 (50,000 ppm) in the ambient atmosphere, at room temperature, with a response time of less than 90 s. This level of CO2 is in the range that indicates the unsuitability of packaged meat for consumption. Furthermore, the sensor was able to maintain its response to CO2 after being stored in the fridge for 20 days, showcasing its endurance under food maintenance conditions.

SCENT-ERC-2014-STG-639123 (2015-2020) UIDB/04378/2020 SFRH/BD/113112/2015 ; Fast, real-time detection of gases and volatile organic compounds (VOCs) is an emerging research field relevant to most aspects of modern society, from households to health facilities, industrial units, and military environments. Sensor features such as high sensitivity, selectivity, fast response, and low energy consumption are essential. Liquid crystal (LC)-based sensors fulfill these requirements due to their chemical diversity, inherent self-assembly potential, and reversible molecular order, resulting in tunable stimuli-responsive soft materials. Sensing platforms utilizing thermotropic uniaxial systems—nematic and smectic—that exploit not only interfacial phenomena, but also changes in the LC bulk, are demonstrated. Special focus is given to the different interaction mechanisms and tuned selectivity toward gas and VOC analytes. Furthermore, the different experimental methods used to transduce the presence of chemical analytes into macroscopic signals are discussed and detailed examples are provided. Future perspectives and trends in the field, in particular the opportunities for LC-based advanced materials in artificial olfaction, are also discussed. ; publishersversion ; published

Tungsten trioxide (WO3) is a wide-bandgap semiconductor. Its advantages include highchemical stability and low price. Furthermore, WO3 has chromogenic properties, that is, the abilityto switch between pale yellow and dark blue in response to various stimuli, including temperature,light irradiation, electric field, and exposure to hydrogen. Due to its high colouring efficiency andfast switching, it can be used in antidazzling mirrors and smart window applications, as well as in gassensing. In this paper, we present the influence of annealing on the properties of WO3 coatings that wereannealed at temperatures in the range from 200C to 400C. The sensing response was characterisedbased on the transmittance measurement during exposure to air and Ar/H2 mixture with hydrogenconcentrations from 25 ppm to 1000 ppm. Furthermore, the influence of annealing on the structureand morphology of the coatings was examined. Annealing at 400C led to a structure change fromamorphous to crystalline one. After the introduction of the Ar/H2 mixture, a decrease in transmittancewas observed for all of the analysed coatings. For films annealed at 200C and 300C, the transmittancevalue decreased during the entire colouring cycle, while for the coating annealed at 400C a plateau wasreached after 7 minutes of exposure. It was found that the best sensing characteristics were obtained forthe WO3 thin film annealed at 400C due to high sensor response to very low hydrogen concentrations(SR = 6.3 for 25 ppm H2) as well as short response and recovery times.Keywords: electronics, tungsten oxide, thin film, gas impulse magnetron sputtering, gas sensingproperties

Fast, real-time detection of gases and volatile organic compounds (VOCs) is an emerging research field relevant to most aspects of modern society, from households to health facilities, industrial units, and military environments. Sensor features such as high sensitivity, selectivity, fast response, and low energy consumption are essential. Liquid crystal (LC)-based sensors fulfill these requirements due to their chemical diversity, inherent self-assembly potential, and reversible molecular order, resulting in tunable stimuliresponsive soft materials. Sensing platforms utilizing thermotropic uniaxial systems—nematic and smectic—that exploit not only interfacial phenomena, but also changes in the LC bulk, are demonstrated. Special focus is given to the different interaction mechanisms and tuned selectivity toward gas and VOC analytes. Furthermore, the different experimental methods used to transduce the presence of chemical analytes into macroscopic signals are discussed and detailed examples are provided. Future perspectives and trends in the field, in particular the opportunities for LC-based advanced materials in artificial olfaction, are also discussed.

The subject of the current studies were mixtures of copper and titanium oxide thin films,with various elemental compositions, deposited by magnetron sputtering and annealed in the postprocess.The effect of elemental composition and annealing temperature on the morphology of thinfilms was determined using scanning electron microscope images. The crystal structure and chemicalcomposition of copper‒titanium oxide (CuTi)Ox mixtures were investigated by X-ray diffraction.Hydrogen gas sensing experiments were performed for hydrogen with concentrations ranging from 100to 1,000 ppm. The resistance of the prepared (CuTi)Ox mixtures increased during hydrogen exposure,demonstrating the applicability of these oxides in hydrogen sensing. In addition, better sensor responseswere obtained for the mixtures in comparison to single copper oxides or titanium oxides. Mixturesof copper oxides and titanium oxides may be promising materials for hydrogen sensor applications.Keywords: mixtures of copper and titanium oxides, hydrogen gas sensors, mixed copper and titaniumoxides, thin films, magnetron sputtering

Environmental pollutions and resources depletion motivates scientific research to innovate technologies for sustainable productive systems. To develop gas sensing substance with optimized performance a perovskite compound of HoxFe1-x FeO3 (where x= 0, 0.01, 0.03 and 0.05) were prepared by standard solid state reaction technique. The crystal structure was studied by XRD, which confirmed the formation of polycrystalline orthorhombic structure with space group Pbnm type perovskite. The preferred crystal growth of the main peak was (211). The structural parameters were also calculated and it was found that the lattice constants and particle size increased with the Ho doping ratio. The electrical properties were studied using the Hall effect, studied using the Hall effect, where the Hall coefficient, D.C conductivity (from 2.24E-06 (Ω-1.cm-1) at x=0) to 2.67E. -06 (Ω-1.cm-1) at x=0.05), mobility) 7.26 (cm2 / V.sec) at x=0 and decreased to 5.97 (cm2 / V .sec) at x=0.05 (and the concentration of charge carriers (2.14 E13 cm-3 at x=0 ) to 2.79E. 13 cm-3 at x=0.05 ) were calculated. The charge carrier concentration increased and charge mobility decreased with Ho addition. The Hall coefficient results revealed an n-type conduction mechanism. The dielectric constant ε r (in its real and imaginary parts) decreased with the increase in frequency of the applied electric field. tan δ and the AC conductivity were also calculated, and It was found that with the raise in the doping rate, the values of AC conductivity increase while tan δ decreases.

Molybdenum Trioxide (MoO3) films are grown on Si(100) substrates by reactive RF magnetron sputtering in plasma containing a mixture of Argon and Oxygen, using a pure Molybdenum target. In this paper, we report the deposition of (MoO3) films on Si(100) substrates under varying gas flow (O2 + Ar gas) (20 sccm to 30 sccm with the duration of deposition~ 1hr) by RF reactive magnetron sputtering at room temperature. To get crystalline MoO3 films annealing in O2 environment at 500 °C for 4 h is done. Phase formation and orientation of the film is characterized by Glancing incidence X-ray diffraction (GIXRD). The identification of the orthorhombic MoO3 phase is investigated by XRD and Raman spectroscopy. Raman lines at 819 cm-1 and 995 cm-1 are due to the (A1g, B1g) symmetric stretching (Mo-O–Mo) bond and asymmetric stretching band (Mo=O) respectively. Surface morphology and cross-sectional image of the deposited thin films were investigated by FE-SEM image. UV-Visible reflectance and cross-sectional FE-SEM image confirm the thickness of the MoO3 films with oxygen-rich and oxygen deficient phase formation occur. Reverse leakage current density of 20 sccm 1hr sample is low (1×10-6 mA/cm2) as compared to 30 sccm 1hr sample (1×10-3 mA/cm2). The higher leakage is due to crack formation during the ex-situ annealing of MoO3 films. This MoO3 films can be used in Gas sensing and switching devices.

By the chemical reduction of sol-gel synthesized TiO2, nanoscale black titanium dioxide in anatase modification, characterized by the presence of large quantity of oxygen vacancies and pronounced extrinsic absorption, was obtained. Semiconducting chemical gas sensors on the basis of the obtained highly defective titanium dioxide demonstrate high output value towards ethanol vapor. The output value significantly increases additionally under actinic radiation conditions.