Propanol Vapors Research Articles

UV activated single aligned TiO2 nanofiber embedded silver nanoparticles as room temperature ammonia gas sensor

In this work, by using an electro-spinning process and a secondary electrostatic field on rectangular electrodes, a single-aligned nanofiber of silver nanoparticle (SNP)-TiO2 fabricated for NH3 gas sensing with UV irradiation at room temperature. XRD, FE-SEM and UV spectroscopy adopted for characterization of the single nanofiber. The response of SNP-TiO2 single nanofiber sensor evaluated for 70 ppb to 12 ppm ammonia gas at room temperature up to the optimum temperature of 150 °C. The response of this sensor for 5 ppm ammonia gas is 46.1 at the optimum temperature of 150 °C. However, the response is also evaluated at room temperature under 365 nm UV illumination. The response improved up to 4 times from 11 at dark condition to 45.1 under UV illumination for the ammonia gas concentration of 5 ppm. In addition, UV light exposure led to a considerable reduction in both the response and recovery times. Moreover, the results for detecting other gases such as methanol, ethanol, propanol and water vapor compare to ammonia shows that for SNP-TiO2 sensor the best response is for ammonia gas, whereas its sensitivity to humidity is considerably low (about 9%). This shows the sensor can be used in related applications like breath analysis.

Enhanced propanol gas sensing performance of p-type NiO gas sensor induced by exceptionally large surface area and crystallinity

Real-time detection of n-propanol vapour is important in human health protection. Thus, we report on the influence of large surface area and crystallinity of p-type NiO nanostructures on propanol sensing characteristics. Structural properties of p-type NiO were investigated by using an X-ray diffractometer and the morphology was analysed by scanning electron microscopy. A Brunauer-Emmett-Teller confirmed the surface area and porosity of the NiO nanostructures. The elemental composition and existences of potential defects were investigated by X-ray photoelectron spectroscopy and photoluminescence, respectively. A systematic comparison study was performed on the annealed nanostructures prepared by hexamethylenetetramine and urea precursors by subjecting all the sensors to volatile organic compounds like ethanol, propanol, toluene, and other reducing and oxidizing gases like methane and nitrogen dioxide using different controlled gas concentrations and operating temperatures. The NiO based sensor derived from the urea precursor and calcined at 400 °C, exhibited a significantly improved sensing response (Ra/Rg ratio of 1.59), higher sensitivity (0.02 ppm−1), ultra-low theoretical detection limit (20 ppb) and excellent selectivity towards 60 ppm propanol vapour Additionally, the fundamental sensing mechanism was elucidated. The high sensitivity and selectivity of NiO based sensors for the detection of propanol is promising.

Acetone Vapor-Sensing Properties of Chitosan-Polyethylene Glycol Using Surface Plasmon Resonance Technique.

To non-invasively monitor and screen for diabetes in patients, there is need to detect low concentration of acetone vapor in the range from 1.8 ppm to 5 ppm, which is the concentration range of acetone vapor in diabetic patients. This work presents an investigation for the utilization of chitosan-polyethylene glycol (PEG)-based surface plasmon resonance (SPR) sensor in the detection of trace concentration acetone vapor in the range of breath acetone in diabetic subjects. The structure, morphology, and elemental composition of the chitosan-PEG sensing layer were characterized using FTIR, UV-VIS, FESEM, EDX, AFM, and XPS methods. Response testing was conducted using low concentration of acetone vapor in the range of 0.5 ppm to 5 ppm using SPR technique. All the measurements were conducted at room temperature and 50 mL/min gas flow rate. The sensor showed good sensitivity, linearity, repeatability, reversibility, stability, and high affinity toward acetone vapor. The sensor also showed better selectivity to acetone compared to methanol, ethanol, and propanol vapors. More importantly, the lowest detection limit (LOD) of about 0.96 ppb confirmed the applicability of the sensor for the non-invasive monitoring and screening of diabetes.

Designing SnO2 Nanostructure-Based Sensors with Tailored Selectivity toward Propanol and Ethanol Vapors.

The application of metal oxide-based sensors for the detection of volatile organic compounds is restricted because of their high operating temperatures and poor gas sensing selectivity. Driven by this fact, we report the low operating temperature and high performance of C3H7OH and C2H5OH sensors. The sensors comprising SnO2 hollow spheres, nanoparticles, nanorods, and fishbones with tunable morphologies were synthesized with a simple hydrothermal one-pot method. The SnO2 hollow spheres demonstrated the highest sensing response (resistance ratio of 20) toward C3H7OH at low operating temperatures (75 °C) compared to other tested interference vapors and gases, such as C3H5O, C2H5OH, CO, NH3, CH4, and NO2. This improved response can be associated with the higher surface area and intrinsic point defects. At a higher operating temperature of 150 °C, a response of 28 was witnessed for SnO2 nanorods. A response of 59 was observed for SnO2 nanoparticle-based sensor toward C2H5OH at 150 °C. This variation in the optimal temperature with respect to variations in the sensor morphology implies that the vapor selectivity and sensitivity are morphology-dependent. The relation between the intrinsic sensing performance and vapor selectivity originated from the nonstoichiometry of SnO2, which resulted in excess oxygen vacancies (VO) and higher surface areas. This characteristic played a vital role in the enhancement of the target gas absorptivity and the charge transfer capability of SnO2 hollow sphere-based sensor.

Selective detection of propanol vapour at low operating temperature utilizing ZnO nanostructures

Abstract We report on the propanol vapour (C3H8O) gas sensing characteristics of ZnO nanostructures prepared via hydrothermal assisted method. The ZnO-4h sensor showed a high response (i.e. resistance ratio), sensitivity and selectivity toward C3H8O gas at low operating temperature of 125 °C. A response and recovery times of approximately 190 and 200 s were recorded. The response of ZnO-4h based sensor to 40 ppm C3H8O was approximately 2 times higher than that of other sensing materials in dry air, while in the presence of 40% RH the response was 5 times higher. The exceptional C3H8O-sensing performance of ZnO-4h is related to more C3H8O adsorption sites provided by VO. The ZnO-04h based sensor showed a clear repeatability towards 40 ppm C3H8O for four successive cycles in the presence of various RH of 40 and 60% at 125 °C. The sensor response improved in the presence of RH humidity showing that the water vapour was not competing with the C3H8O for the pre-adsorbed oxygen ions, thus its interfering effect in the C3H8O sensing was considerably minimized. The ZnO-4h based sensor was further tested for long-term stability and the sensor was very stable after 45 days. The fundamental sensing mechanism towards C3H8O vapour is also discussed.

Effect of noble metal functionalization and film thickness on sensing properties of sprayed TiO2 ultra-thin films

In this paper, the effect of the thickness of nano-structured TiO2 thin films (12–40 nm) and successive deposition of different noble metal nanoparticles on the performances of propanol vapor and H2 gas sensors was investigated. The obtained titania thin films were integrated into a device for UV, gas, and gas/vapor sensing studies at different operating temperatures. Qualitative analysis revealed that the sensor selectivity and its response could be altered by film thickness and type of noble metal nanoparticles. The results indicate that the sensor with 40 nm TiO2 film has the highest response to H2 gas (˜ 650%). The fastest response time and the most rapid recovery however were achieved by the sensors made of 12 nm sprayed TiO2 ultra-thin films, which also offered the highest selectivity to H2 gas.The best UV detection performances were demonstrated by films functionalized with Au nanoparticles (the IUV/Idark ≈ 80). The structural, chemical, electrical, UV, and gas sensing properties of such films were investigated using SEM, AFM, Raman spectroscopy, electrical characterization, and sensing experiments. It has been clearly demonstrated that films are nanostructured and have mixed phases that contain mostly anatase (annealed at 450 °C) and small amounts of rutile after thermal annealing at higher temperatures (more than 600 °C), as improved materials for sensor applications. Our combined study analyzes the relationship between thickness, electrical properties and the gas/vapor sensing performance of such thin film based TiO2 gas sensors as well as the effect of different types of noble metal nanoparticles (Au, Ag, Ag-Au and Ag-Pt) deposited on the surface. The enhanced response was attributed to the involvement of noble nanoalloy or nanoparticle interface to titania forming nano-junctions in the gas sensing mechanism. Highly selective and sensitive sensors towards specific gas or vapor molecules are essential for environmental monitoring, and for health and safety issues.

Influence of CuO nanoparticles and graphene nanoplatelets on the sensing behaviour of poly(vinyl alcohol) nanocomposites for the detection of ethanol and propanol vapors

Poly(vinyl alcohol)/copper oxide/graphene nanoplatelets (PVA/CuO/Gr-NPls) nanocomposite based chemiresistive alcohol sensors were fabricated using colloidal blending method. The PVA/CuO/Gr-NPls nanocomposite films were characterized using Fourier transform infrared spectroscopy, X-ray diffraction, UV–Vis spectroscopy, thermogravimetric analysis, scanning electron microscopy, atomic force microscopy and the sensing behaviour of PVA/CuO/Gr-NPls nanocomposite films was evaluated for volatile organic compounds (VOCs). The improvement in the thermal, mechanical and VOCs sensing properties of nanocomposite film was observed attributing to the homogeneity of the nanocomposites and strong interfacial interaction between Gr-NPls, CuO and PVA matrix. The sensors were analyzed in the concentration range from 1800 to 4000 ppm. It was observed that PVA/CuO/Gr-NPls nanocomposite film exhibited excellent propanol sensing at a room temperature, typically at an applied voltage of 10 V when compared with other VOCs. Thus, the strong interaction between CuO and Gr-NPls helps in achieving excellent reinforcement effect in a PVA matrix for fabrication of high performance nanocomposite films for VOC’s sensing applications.

Response of a Zn₂TiO₄ Gas Sensor to Propanol at Room Temperature.

In this study, three different compositions of ZnO and TiO2 powders were cold compressed and then heated at 1250 °C for five hours. The samples were ground to powder form. The powders were mixed with 5 wt % of polyvinyl butyral (PVB) as binder and 1.5 wt % carbon black and ethylene-glyco-lmono-butyl-ether as a solvent to form screen-printed pastes. The prepared pastes were screen printed on the top of alumina substrates containing arrays of three copper electrodes. The three fabricated sensors were tested to detect propanol at room temperature at two different concentration ranges. The first concentration range was from 500 to 3000 ppm while the second concentration range was from 2500 to 5000 ppm, with testing taking place in steps of 500 ppm. The response of the sensors was found to increase monotonically in response to the increment in the propanol concentration. The surface morphology and chemical composition of the prepared samples were characterized by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The sensors displayed good sensitivity to propanol vapors at room temperature. Operation under room-temperature conditions make these sensors novel, as other metal oxide sensors operate only at high temperature.

Sensing of 0.1 ppm of methanol, ethanol, and propanol vapors at 130°C by SnO2 thin film

ABSTRACTSnO2 thin film was synthesized by spray pyrolysis. The sensing properties of the same for detecting volatile organic compounds (VOCs) were investigated. It was observed that the sensing was maximum for methanol vapor (96.82%) in case of both experimental and theoretical results. The gas was detected for as low as 0.08 ppm, which has not been reported till date. The Levenberg–Marquardt (LM) algorithm was used for the theoretical analysis using the Electrochemical Impedance Spectroscopy (EIS) Spectrum analyzer. Theoretical calculation revealed that the resistance due to the grain boundary reduces when gases were introduced into the chamber.

Synergistic effect of tungsten on gas sensing characteristics of chromium oxide based gas sensor

Enhancement of gas sensing response due to addition of tungsten into Cr2O3 has been reported. Pure and W-doped Cr2O3 nanoparticles, prepared by a chemical method, have been characterized by X-ray diffraction and field emission scanning electron microscopy. X-ray diffraction studies have revealed the substitution of Cr3+ ions by W6+ ions. The concentration of tungsten, used as dopant, has been varied from 1 to 5 wt% and its effect on structural and gas sensing properties has been studied. Synthesized samples have been deposited as a thick film onto alumina substrate and tested for methanol, ethanol and propanol at different operating temperatures. All the sensors have exhibited optimum response at 250 °C. Fabricated sensors have exhibited best response towards propanol vapour. The activation energy of conduction for all the samples has been estimated using Arrhenius plots and it has been observed that sample doped with 3 wt% W possesses minimum activation energy and interestingly this sample gives the best sensing response amongst fabricated sensors.

Electrical and gas-sensitive properties of a SnO2-based nanocomposite with multiwalled carbon nanotubes

This paper presents the results of study of the electrophysical and gas-sensitive properties of a SnO2-based film nanocomposite with the addition of multiwalled carbon nanotubes (to 7 wt %), produced by the hydrolysis of aqueous-alcoholic solutions of tin salts. The dependences of the free carrier mobility and concentration on the number of nanotubes in the composite, and the temperature dependences of the gas sensitivity to ethanol, acetone, and propanol vapors in air are studied. It is shown that the gas sensitivity of the nanocomposite containing ∼1.75 wt % of nanotubes is 10–15 times higher in comparison with that of the pure SnO2 film.

Aqueous chemical route deposition of nanocrystalline ZnO thin films as acetone sensor: Effect of molarity

Nanocrystalline ZnO thin films were deposited onto glass substrate using a simple and inexpensive aqueous chemical method at low temperature (90°C). The concentration of precursor solution was varied in order to study its effect on structural, morphological, and gas response properties. Field-emission scanning electron microscopy (FESEM) images indicate the growth of ZnO with hexagonal shaped nanostructure. Further these films were used to explore gas response properties towards acetone, propanol and ethanol vapors. The sensor response was found to be decreased with increase in precursor concentration. The highest sensor response of 92% was observed towards acetone for the film deposited at 0.05M at an operating temperature of 350°C. The higher vapor response towards acetone is attributed to size and surface morphology of the film deposited at 0.05M.

Effect of pH on the morphology and gas sensing properties of ZnO nanostructures

Morphology dependent gas sensing behaviour of zinc oxide has been reported in this paper. Nanostructures of zinc oxide have been synthesized by following a precipitation route at various pH values of the precursor solution. Structural and morphological analyses were carried out by using XRD and FESEM techniques. The XRD pattern confirmed wurtzite hexagonal structure of ZnO. The FESEM study revealed that ZnO synthesized at pH 8 developed nanorod like structure, rods got fused together when synthesized at pH 9 and 10, whereas synthesis at pH 11 resulted in transformation of rods into nanoparticles. The thick films of synthesized samples were deposited on alumina substrate and their sensing response to methanol, ethanol and propanol was investigated at different operating temperatures. It was observed that all the sensors exhibited optimum sensing response at 400°C. It has also been observed that sample prepared at pH 11, constituting nanoparticles, exhibited high sensing response than an assembly of nanorods prepared at pH 8–10. Sensing response of all the samples tested was significantly higher towards propanol vapour than towards that of methanol and ethanol.

Soluble mass, hygroscopic growth, and droplet activation of coated soot particles during LACIS Experiment in November (LExNo)

The LACIS Experiment in November (LExNo) campaign was conducted in November 2005 at the Atmospheric Composition Change the European Network of Excellence (ACCENT) site Leipzig Aerosol Cloud Interaction Simulator (LACIS). The goal of LExNo was to provide deeper insight into the activation properties of coated soot particles imitating aged combustion aerosol particles. The aerosols were prepared by starting with spark‐generated soot particles. In some experiments the soot particles were compacted by exposure to propanol vapor; in others this step was bypassed. The soot was thermally coated with ammonium sulfate, levoglucosan, or a mixture of both ammonium sulfate and levoglucosan. The synthesized particles were investigated using aerosol mass spectrometry, a Hygroscopicity Tandem differential mobility analyzer, two Wyoming static diffusion cloud condensation nuclei (CCN) instruments, a Droplet Measurement Technologies continuous flow CCN instrument, and LACIS. A close correlation between the hygroscopic growth factor at 98% relative humidity and the critical supersaturation of CCN activation was observed. Closure between hygroscopic growth, CCN activation, and chemical composition of the investigated particles was achieved with two different single‐parameter Köhler model approaches and with a third approach, a standard Köhler model using as input parameter the soluble mass as determined by aerosol mass spectrometry.

Influence of the Poly(Vinyl Butyral) Binder in Screen-Printed Thick-Film Gas Sensors Containing ${\rm NiO}{\hbox{-}}{\rm TiO}_{2}$ Oxides

This study investigates gas sensitive resistors fabricated by screen-printing inks created from a mixture of NiO-TiO2 and containing a poly(vinyl butyral) binder for the detection of alcohol vapors at room temperature. It was found that these films exhibited a significant resistance change in response to the vapors, while also displaying an inherent selectivity, proving most sensitive to toluene and propanol vapor; with comparatively low responses exhibited towards ethanol and methanol vapors. It is proposed that swelling of the polymer binder used in the fabrication of the NiO-TiO2 thick-films, rather than oxygen ion induced majority carrier modulation in the oxides, is the significant factor in causing the electrical resistance of the films to increase upon exposure to the organic solvent vapors. Very fast response and recovery times of 9 s and 16 s, respectively were recorded for the devices upon exposure to 4000 ppm step changes in propanol concentration. For comparative analysis, poly(vinyl butyral)/carbon black composites were fabricated from a by a drop-coating technique. The superior sensitivities and response times of the screen-printed sensors were attributed to the (SEM confirmed) highly porous structure attained by the thick-film devices, caused by the excessive free-volume induced in the polymer-binder matrix by the oxide materials. The results suggest that the effects of the polymer binder, even when present in comparatively small amounts, cannot be ignored in certain sensing applications

Simultaneous measurement of temperature and chemicalspecies concentrations with a holographic interferometer and infrared absorption

What is believed to be a new technique that allows for the simultaneous measurement of 2D temperature and chemical species concentration profiles with high spatial resolution and fast time response was developed and tested successfully by measuring a thin layer of fuel vapor created over a volatile fuel surface. Normal propanol was placed in an open-top rectangular container, and n-propanol fuel vapor was formed over the propanol surface in a quiescent laboratory environment. An IR beam with a wavelength of 8-13 mum emitted from a heated plate and a He-Ne laser beam with a wavelength of 632 nm were combined and passed through the n-propanol vapor layer, and both beams were absorbed by the vapor layer. The absorption of the IR beam was recorded by an IR camera, and the He-Ne laser was used to form a holographic interferogram. Two-dimensional temperature and propanol vapor concentration profiles were, respectively, determined by the IR absorption and the fringe pattern associated with the holographic interferogram. This new measurement technique is a significant improvement over the dual wavelength holographic interferometry that has been used previously to measure temperature and fuel concentration, and it is ready for application under different types of fire and flame conditions.

Excess noise in a drop-coated poly(vinyl butyral)\\carbon black nanocomposite gas sensitive resistor

Presented are the results of excess noise measurements on poly(vinyl butyral)\\carbon black nanocomposite gas sensitive resistors. The devices were prepared by a drop-coating technique in which a microlitre syringe was used to deposit the materials onto Cu thin-film parallel electrodes. Noise power spectra of the devices under bias currents ranging from 80 to 150 μA were obtained. The detection limits were found to be 6.3 ppm, 5.2 ppm and 68 ppb for methanol, propanol and hexanol vapour, respectively. The noise index was also evaluated for the devices, with a value of approximately 29 dB being measured.

Screen-Printed Fe2O3/ZnO thick films for gas sensing applications

This paper investigates iron-oxide and zinc-oxide thick-films for gas sensing applications. The films were printed onto glass substrates with silver electrodes. The effects of propanol, methanol and ethanol vapor on the devices at room temperature (in the concentration range 500–2000ppm) were investigated. The percentage relative resistance change, ΔR = ((Rgas − Rair)/Rair) ×100, was seen to increase linearly with increasing gas vapor concentration. The sensitivity of the films to the gas vapor was determined from the slope of the graphs. It was observed that various film compositions showed a higher sensitivity to propanol than to methanol and ethanol. Moreover, the sensitivity to propanol increased from 0.077 to 0.166 to 0.173%/ppm for the three samples with molecular weight composition ratios of: 90%/10%, 80/20% and 70%/30% of Fe2O3 to ZnO respectively. The response times of sensors 1, 2 and 3 (to 1000ppm step changes in propanol concentration) were 48.6 seconds, 86.4 seconds and 76.5 seconds, while the recovery times were 117 seconds, 186 seconds and 153 seconds respectively.

Nucleation probability in binary heterogeneous nucleation of water-n-propanol vapor mixtures on insoluble and soluble nanoparticles.

Nucleation probabilities for binary heterogeneous nucleation have been measured quantitatively. Heterogeneous nucleation of binary n-propanol-water vapor mixtures on partially soluble 6.9-nm NaCl particles and on nonsoluble oxidized and nonoxidized 8-nm Ag particles at a constant nucleation temperature of 288 K (NaCl) or 285 K (Ag) has been investigated experimentally and theoretically. An expansion chamber was applied to generate supersaturated vapor mixtures. Number concentrations of particles activated to condensational growth were determined optically for various vapor phase activities at constant temperature. Nucleation probabilities have been measured as functions of the vapor phase activities for several n-propanol-water vapor mixing ratios. Beyond certain vapor phase activities a sharp onset of heterogeneous nucleation was observed both for NaCl and for Ag particles. For insoluble particle surfaces the theoretical slopes of the nucleation probability versus vapor phase activity curves were found to be somewhat steeper as compared to the experiment. On the other hand, for soluble particles the experimental slopes were found to be in satisfactory agreement with theory. The onset of the nucleation process is defined at an activity value where 50% of the particles were activated to condensational growth. Onset activities were obtained for various mixing ratios of the binary vapor mixtures. In the case of NaCl nuclei for n-propanol rich mixtures, the heterogeneous nucleation calculations based on a thermodynamically consistent version of Fletcher theory and an experimentally determined contact angle provide a reasonable approximation of the experimental data. However, it appears that the Fletcher theory is not applicable in the region of transition from n-propanol rich to water rich mixtures. Based on the Köhler theory of activation of soluble particles, a theory was formulated accounting for the presence of two condensable vapors and limited solubility of NaCl in water-propanol liquid mixtures. This approach provides a satisfactory description of the transition from activation of soluble particles to nucleation of vapors on insoluble particles. In the case of silver particles Fletcher theory with macroscopic experimental contact angles as well as with contact angle zero results in strong deviations from experimental data. A significant improvement was achieved by introducing fit contact angles, which are substantially lower than the macroscopic experimental values and may be considered as approximate values of the microscopic contact angles.

Transient infrared temperature measurements of liquid-fuel surfaces: results of studies of flames spread over liquids

An infrared thermograph technique with an 8-12-microm spectral range was used to measure transient two-dimensional profiles of liquid (1-propanol) surface temperatures. An IR camera was placed over the liquid, allowing us to observe the fuel surface through propanol vapor. To use this technique, one must know the emissivity of the liquid surface and the IR absorption of both the liquid propanol and the propanol vapor. The emissivity of the liquid propanol was determined with a fine thermocouple temperature measurement, IR absorption with the propanol vapor was calibrated with a blackbody source, and IR absorption with a liquid propanol was theoretically estimated. The accuracy of our infrared thermograph technique proved to be better than 97% in detecting the liquid-surface temperature with a temperature sensitivity of 0.1 degrees C and a time response of 30 ms.