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Metal oxide nanocomposite sensors based on γ-Fe 2 O 3 and WO 3 were investigated in acetone vapor of various concentrations (1–100 ppm) at operating temperatures between 250 and 350 °C. The composites were prepared by simple solid state mixing and porous thick-film gas sensors were fabricated on alumina substrates. The γ-Fe 2 O 3 :WO 3 (50:50) nanocomposite showed a marked enhancement in sensing response down to 1 ppm acetone vapor detection at 300 °C. The response was ~2-fold better compared to pure WO 3 or pure γ-Fe 2 O 3 with a very fast response (1 s) and very short recovery time (3 s). No appreciable sensitivity was observed towards alcohol vapor (an interfacing agent for diabetics) and in moisture (present in breath). The enhanced performance was due to n–n heterojunction effect. [ABSTRACT FROM AUTHOR]

• A ternary nanocomposite containing 3 wt% rGO decorated ZnO-SnO 2 was prepared using a facile sol-gel procedure. • Pristine ZnO-SnO 2 nanocomposite sensor exhibited ~ 60% response towards 10 ppm acetone at operating temperature of 300°C. • ~3wt% rGO addition enhanced the response upto ~ 91% for 10 ppm acetone as well as operating temperature reduced to 150°C. • rGO decorated sensor was capable to detect very low concentration (~1 ppm) of VOCs with fast response and recovery time. • The sensor shows reproducible performance over time with negligible sensing response in other reducing gases. [Display omitted] A ternary p-n-n heterojunction has been prepared by introducing reduced graphene oxide (rGO) in ZnO-SnO 2 nanocomposite and its ppm level volatile organic compounds (VOCs) sensing properties have been exploited. Using a simple, facile sol-gel process, initially, ZnO-SnO 2 nanocomposites containing different concentrations of ZnO and SnO 2 were prepared and subsequently this was followed by rGO incorporation. The as-synthesized powders were well characterized through XRD, FTIR, Raman spectroscopy, FESEM, TEM, and XPS analyses. The sensing study revealed that, the ternary nanocomposite sensor delineated ~91% n-type sensing response towards ~10 ppm acetone gas at an optimum working temperature of 150 °C. Even it could sense ~1 ppm acetone with appreciable sensing response of ~71%. Additionally, the sensor displayed fast response (~10 s) and recovery time (~100 s) suitable for detection of multiple pulses in short time duration. It also exhibited a considerable ~65% sensing response towards ~10 ppm ethanol at 150 °C. These superior sensing performances of rGO decorated ZnO-SnO 2 nanocomposite illustrated with band structure modification. Our results indicated that, the fabricated rGO decorated ZnO-SnO 2 sensor, with remarkable high sensing response, minimum interference from other toxic, inflammable gases and profound long term stability, could be considered as a prolific candidate for real time detection of low concentration VOCs in versatile commercial applications. [ABSTRACT FROM AUTHOR]

In the present work, reduced graphene oxide (rGO) decorated NiO-SnO 2 nanocomposites were synthesized by using a facile sol-gel process and their structural (XRD, FTIR, Raman), morphological (BET, FESEM, TEM), and optical (UV-Vis, PL) characterizations were carried out. The as-synthesized NiO-SnO 2 nanocomposite exhibited an enhancement of surface area after the incorporation of rGO and this substantial increment was expected to be beneficial for gas sensing at room temperature. Therefore, Taguchi-type sensors were fabricated and deployed for the detection of VOCs. The optimized sensor containing ∼ 3 wt% rGO in NiO-SnO 2 nanocomposite demonstrated an excellent sensing response (R g /R a ∼ 7.8) towards ∼ 10 ppm acetone at room temperature (30 ± 5 °C) with response and recovery time of ∼ 10 s and ∼ 30 s respectively. It also exhibited good reproducibility and stability over ∼ 3 months. Additionally, this sensor selectively detected trace concentration (< 1 ppm) of acetone in exhaled human breath (ethanol present in a healthy person's exhaled breath is insignificant), which is a non-invasive biomarker of diabetes. The sensing performance was analyzed from an electronic transportation point-of-view and consequent band structure modulation. The electrical property of the sensing material was illustrated using impedance spectroscopy to support the sensing mechanism. [Display omitted] • rGO decorated NiO-SnO 2 nanocomposites were prepared using sol-gel process. • Optimized Taguchi type sensor showed ∼ 7.8 response in ∼10 ppm acetone at ∼ 30 °C. • Sensor showed reproducible sensing performance and cross sensitivity was negligible. • Optimized sensor used to detect acetone (biomarker of diabetes) in exhaled breath. • The electrical properties of sensors were elucidated by impedance spectroscopy. [ABSTRACT FROM AUTHOR]

Chemiresistive MOS-based acetone sensing device is a futuristic pathway for non-invasive diagnosis of diabetes. Although their potential deployment is restricted till now due to lack of selective, low temperature operated ppm-level sensors. In this work, we demonstrated synthesis of iron doped reduced graphene oxide (rGO) decorated WO 3 nanocomposites in a facile, environment friendly wet chemical sol-gel process. The as-synthesized nanocomposites were comprehensively characterized by using different characterization techniques. A maximum ~78% sensing response was obtained for the optimized composition of ~10 wt% Fe doped 3 wt% rGO decorated WO 3 based thin film (thickness ~700 nm) sensor towards ~10 ppm acetone gas. This sensing performance was observed at comparatively low working temperature of ~130 °C with fast response (~20 s) and recovery (~75 s) time. The efficacy of the fabricated sensors was established by their capabilities to sense a very low concentration of ~1 ppm acetone under similar working environment. Further illustration of versatility of the sensors revealed that, the sensors could be able to manifest a repeatable and reproducible sensing performance with prolong stability and superior selectivity for acetone over other interfering gases. The acetone sensing mechanism was illustrated with the help of electron depletion model and impedance spectroscopy study. Impedance spectroscopy quantifies different electrical properties and enlightens the smooth electronic transition mechanism between analyte and sensing material. [Display omitted] • Novel Fe doped reduced graphene oxide (rGO) decorated WO 3 nanocomposite was prepared using a facile sol-gel procedure. • Fabricated Taguchi type thin film sensor exhibited ~ 78 % sensing response towards ~10 ppm acetone at 130°C. • The sensor was also capable to detect very low concentration (~1 ppm) of acetone with fast response and recovery time. • The sensor revealed reproducible performance over time with minimum interference from other interfering gases. • Impedance spectroscopy was used to analyze the sensing mechanism with comprehensive illustration of electrical properties. [ABSTRACT FROM AUTHOR]

• Room temperature ppm level acetone sensing by Pt/Sb 2 O 3 impregnated Fe 2 O 3 thin film. • ~6 µm films were drop casted on planar alumina substrates with platinum electrodes. • Enhanced sensing response ~2.4 with ~95 s recovery time observed for 1 ppm acetone. • Even at 0.25 ppm acetone vapour, the response observed ~1.4. • Real time breath acetone measurement was also carried out. • The sensor revealed reproducible performance over a period of about two months. In the present report, an enhanced sub-ppm level acetone sensing performance of a novel Pt and Sb 2 O 3 impregnated nanocrystalline Fe 2 O 3 thin film operating at room temperature has been explored. Starting from organic precursor sols, thin films of thickness ~ 6 µm were drop-casted on planar alumina substrates pre-attached with the platinum electrodes and cured at ~ 350°C. The characterizations of the materials have been carried out using X-ray Diffraction, FTIR, Raman Spectroscopy, micro structural study through FESEM and TEM as well as XPS analyses. The sensing characteristics including sensing response, lowest detection limit, recovery time etc. of these chemiresistive thin films were studied on exposing them to various concentrations (0.25 to 1 ppm) of acetone at room temperature. The sensing response of ~2.4 with ~ 95 s recovery time was observed on exposure to 1 ppm acetone for 10 s. Even at 0.25 ppm acetone, the response observed ~ 1.4. Selectivity study on different alcohols and other interfering gases of breath has also been tested. Additionally, a real time breath acetone measurement was carried out and acetone sensing mechanism has been elucidated. [ABSTRACT FROM AUTHOR]