Metal Oxide Semiconductor-based gas sensor for Acetone sensing

Abstract: This work reports a new technique for the selective determination of three organic vapors– ammonia, ethanol and acetone by employing two resistive sensors. These two resistive sensors are based on reduced graphene oxide (RGO) and RGO– rosebengal (RB) composites. The chemically synthesized RGO and RGO–RB based sensors were tested for four different concentrations of ammonia (400–2800 ppm) and two different concentrations (1000, 2000 ppm) of ethanol and acetone each, at room temperature. The RGO sensor was found to exhibit response of 10.3% to 25.3% to 400–2800 ppm of ammonia, 1.01% to 1.15% to 1000 and 2000 ppm of acetone respectively, and 1.05% to 1.56% to 1000 and 2000 ppm of ethanol respectively. The RGO–RB composite-based sensor exhibited an enhanced response ranging from ~17% to 36.6% for 400–2800 ppm of ammonia, 1.6% to 3.2% for 1000 and 2000 ppm of acetone and 1.1% to 1.7% for 1000 and 2000 ppm of ethanol at room temperature. An algorithm, based on the soft margin classifier was developed to accurately determine the concentrations of all the three organic vapors. The initial 100 s of the response values of both the sensors for all the targeted vapors were considered for this purpose. This resulted into classification of all the concentrations of the three organic vapors much before the full-scale response of the sensors. It is believed that this work will aid in development of portable devices comprising of array of sensors having the capability of determining the vapors and their concentrations accurately.

Abstract: In the present work, we analyzed the effect of doping (Bi, Hf, and Nb) on the performance of tungsten oxide (WO3) based supercapacitor. Through substitutional doping, the properties were altered to enhance its electrochemical charge storage performance. The doped samples were tested in different electrolytes (H+, Li+, Na+, Ca2+ and Al3+). The cyclic voltammetry, galvanostatic charge–discharge, and EIS studies were performed to identify the best suitable anode material for the fabrication of asymmetric supercapacitor. Nb:WO3 yielded the highest specific capacitance (Csp) of 782 Fg−1 in Ca electrolyte. An asymmetric device with Nb:WO3 as anode and MnO2 as a cathode using an aqueous Ca ion electrolyte exhibited a high potential window of 2 V and capacitance of 126 Fg−1. The factors responsible for performance of electrode material in different electrolytes were identified through experimental results, theoretical calculations, and relevant simulations. The effect of doping on WO3 crystal structure and electronic properties along with their binding nature/interaction with different electrolyte ions were first postulated through density functional theory (DFT) calculations.

Abstract: Since the sensing capability of semiconducting metal oxides was demonstrated in the 1960s, solid state gas sensors based on these materials have attracted considerable attention from both scientific and practical point of view. Because of the promising characteristics for detecting toxic gases and volatile organic compounds (VOCs) compared to conventional techniques, these devices are expected to play a key role in environmental monitoring, chemical process control, personal safety and so on in the near future. Therefore, in recent years, intensive studies have been conducted to improve their sensing performances, particularly to increase the sensitivity and detection limit of such devices. This can be accomplished by using metal oxide nanostructures with various shapes such as nanoparticles, nanowires, nanorods and nanotubes having sizes in the nanometer range. Owing to the high surface-to-volume ratios and consequently large number of surface sites exposed to target gas, nanostructured metal oxides enable a larger gas-sensing layer interaction and hence a higher sensitivity in comparison with conventional materials. This article extensively reviews recent developments in this field, focusing the attention on the detection of some common VOCs, including acetone (C3H6O), acetylene (C2H2), benzene (C6H6), cyclohexene (C6H10), ethanol (C2H5OH), formaldehyde (HCHO), n-butanol (C4H9OH), methanol (CH3OH) toluene (C7H8), and 2-propanol (C3H8O), by means of conductometric solid state sensors based on nanostructured semiconducting metal oxides.

Abstract: Acetone in the human breath is an important marker for noninvasive diagnosis of diabetes. Here, novel chemo-resistive detectors have been developed that allow rapid measurement of ultralow acetone concentrations (down to 20 ppb) with high signal-to-noise ratio in ideal (dry air) and realistic (up to 90% RH) conditions. The detector films consist of (highly sensitive) pure and Si-doped WO3 nanoparticles (10−13 nm in diameter) made in the gas phase and directly deposited onto interdigitated electrodes. Their sensing properties (selectivity, limit of detection, response, and recovery times) have been investigated as a function of operating temperature (325−500 °C), relative humidity (RH), and interfering analyte (ethanol or water vapor) concentration. It was found that Si-doping increases and stabilizes the acetone-selective e-WO3 phase while increasing its thermal stability and, thus, results in superior sensing performance with an optimum at about 10 mol % Si content. Furthermore, increasing the operation ...

Abstract: Nanostructured anatase TiO2 was produced by flame spray pyrolysis (FSP) and tested for sensing of volatile organic compounds and CO at 500 °C. The as-prepared powders were characterized by transmission/scanning electron microscopy, X-ray diffraction and nitrogen adsorption. Titania films about 30 μm thick on alumina substrates interdigitated with gold electrodes were prepared by drop-coating a heptanol suspension of these powders. The films showed a high signal of n-type sensor to isoprene, acetone and ethanol at concentrations ranging from 1 to 75 ppm in dry N2/O2 at 500 °C. The response (within seconds) and recovery (within minutes) times were very fast. Heat-treatment at 900 °C caused a nearly complete anatase to rutile transformation and a transition to p-type sensing behavior. That resulted in a poor sensor signal to all hydrocarbons tested and considerably longer recovery times than that of the anatase sensor. That rutile sensor could detect CO that the original, anatase sensor could not. For ethanol the sensor response changed back to n-type.

Abstract: Since the ancient discovery of the 'sweet odor' in human breath gas, pursuits of the breath analysis-based disease diagnostics have never stopped. Actually, the 'smell' of the breath, as one of three key disease diagnostic techniques, has been used in Eastern-Medicine for more than three thousand years. With advancement of measuring technologies in sensitivity and selectivity, more specific breath gas species have been identified and established as a biomarker of a particular disease. Acetone is one of the breath gases and its concentration in exhaled breath can now be determined with high accuracy using various techniques and methods. With the worldwide prevalence of diabetes that is typically diagnosed through blood testing, human desire to achieve non-blood based diabetic diagnostics and monitoring has never been quenched. Questions, such as is breath acetone a biomarker of diabetes and how is the breath acetone related to the blood glucose (BG) level (the golden criterion currently used in clinic for diabetes diagnostic, monitoring, and management), remain to be answered. A majority of current research efforts in breath acetone measurements and its technology developments focus on addressing the first question. The effort to tackle the second question has begun recently. The earliest breath acetone measurement in clearly defined diabetic patients was reported more than 60 years ago. For more than a half-century, as reviewed in this paper, there have been more than 41 independent studies of breath acetone using various techniques and methods, and more than 3211 human subjects, including 1581 healthy people, 242 Type 1 diabetic patients, 384 Type 2 diabetic patients, 174 unspecified diabetic patients, and 830 non-diabetic patients or healthy subjects who are under various physiological conditions, have been used in the studies. The results of the breath acetone measurements collected in this review support that many conditions might cause changes to breath acetone concentrations; however, the results from the six independent studies using clearly-defined Type 1 and Type 2 diabetic patients unanimously support that an elevated mean breath acetone concentration exists in Type 1 diabetes. Note that there is some overlap between the ranges of breath acetone concentration in individual T1D patients and healthy subjects; this reminds one to be careful when using an acetone breath test on T1D diagnostics. Comparatively, it is too early to draw a general conclusion on the relationship between a breath acetone level and a BG level from the very limited data in the literature.