Introduction The exhaled acetone has been proved as a typical biomarker for Type-I diabetes. Normally, the acetone concentration from the exhale breath of healthy body is lower than 0.8 ppm, while the patient’s breath contains more than 1.8 ppm acetone gas [1]. Therefore, developing a reliable and accurate acetone gas sensor is of great significance. Meanwhile, traditional acetone gas sensors depend on the output power supplies, combining them with self-powered devices can fully utilize the energy of the external environment, which guarantee the normal operation of the sensors under the statues of power failure.Currently, the metal oxide semiconductor (MOS)-based acetone sensors are extensively researched owing to their high response and fast response-recovery times. However, the excessive power consumption restrains their further application. Recently, chitosan (CTS) has been proved to be an acetone sensing material working at room temperature [2]. For enhancing the gas sensing performance, fictionizing chitosan with other materials might be an effective way. Therefore, the chitosan (CTS)/zinc oxide (ZnO) bilayer sensing film based TENG as a self-powered gas sensor has been designed for detecting acetone at room temperature. Results indicated that the CTS/ZnO bilayer sensing film exhibited greater response of acetone than the CTS monolayer sensing film. Experimental ZnO were prepared by a hydrothermal method. Specifically, 3 mmol zinc acetate dihydrate and 5 mmol hexamethylenetetramine were dissolved in 30 mL of deionized water and ultrasonically treated for 30 min to form a clear solution. Next, the solution was transferred into an autoclave, and subsequently heated up to 150℃ for 210 min before cooling naturally. After that, the mixtures were centrifugated and washed by ethanol and deionized water for several times, and dried at 80℃ in an oven to obtain the ZnO.The detailed fabrication process of the self-powered gas sensor (Fig. 1a) are demonstrated as follows: First, 0.1 mm thickness of the flexible polyethylene terephthalate (PET) with the size of 3 cm×3 cm was covered by a gold electrode layer via thermal evaporation. Then, 1mL of CTS solution (4 mg/mL, dissolved in 2 vol.% of acetic acid) and 1.5 mL of ZnO aqueous solution (2 mg/mL) were deposited onto the PET substrate with gold electrode layer via spray coating method, respectively. Meanwhile, the PDMS friction layer was transferred onto the gold electrode layer mentioned above. Finally, the PET substrate with the gas-sensing materials was fixed onto a flexible silica gel film as the upper layer, while the PDMS layer was fixed at the bottom of an acrylic test chamber. The whole device was driven by the periodic force exerted on the silica gel film.All the output signals generated by the sensor were measured by a Keithley 6514 electrometer at room temperature (~25℃). By mixing a standard dry acetone gas (100 ppm, dry air was used as the balance gas) with dry air in proportion with the help of two mass flow controllers (MFC 300), the acetone gas with different concentration was generated and introduced into the test chamber. The total flow rate was kept at 200 sccm for unifying the gas-sensing measurement. The response value was calculated as follows: Response (%) = (Vpp-g−Vpp-a)/ Vpp-a×100%, where Vpp-g and Vpp-a are the peak-peak output voltage exposed in air and tested gas, respectively. Results and Conclusions Fig. 1b illustrates the output voltage of the sensor with the exposure to dry air and different concentration of acetone gas at room temperature. The output voltages increased with the increasing acetone concentration in the range of 2-50 ppm. Meanwhile, the CTS/ZnO sensor is of good linear response at 2-10 ppm (R2=0.9872) and 10-50 ppm acetone (R2=0.9030), of which the responses are 6.46-17.29% and 17.29-32.09%, respectively. Based on the above phenomenon, a possible sensing mechanism has been established: After the introduction of acetone gas, the nucleophilic addition reaction between the CTS and acetone would destroy the hydrogen bond interaction between CTS and ZnO (Eqs. (1)), leading to the interruption of electrical pathways for the effective electrons transfer [2], resulting in the decrease of surface conductivity and eventually increase the output voltage [3].CTS-NH2+CH3COCH3=CTS-N=C(CH3)2+H2O(1)In summary, we have successfully fabricated a novel triboelectric gas sensor based on CTS/ZnO bilayer membrane. After testing procedure, a possible sensing mechanism has been established. The CTS/ZnO gas sensor has a great potential in the applications of acetone detection without additional power supplies, and provides a useful strategy for the researches of novel acetone sensors.
76Enhanced specific surface area of ZIF-8 derived ZnO induced by sulfuric acid modification for high-performance acetone gas sensor
Enhanced specific surface area of ZIF-8 derived ZnO induced by sulfuric acid modification for high-performance acetone gas sensor
Read more10Synthesis of graphene oxide-cobalt oxide hybrid materials for gas sensors application
Synthesis of graphene oxide-cobalt oxide hybrid materials for gas sensors application
44High performance ethanol and acetone gas sensor based nanocrystalline MnCo2O4 using clad-modified fiber optic gas sensor
High performance ethanol and acetone gas sensor based nanocrystalline MnCo2O4 using clad-modified fiber optic gas sensor
8Comparative Studies of the Properties of ZnO Sprayed Thin Films on Different Polymer Substrates for Flexible Solar Cell Applications
Zinc oxide (ZnO) thin films have been deposited onto polyethylene terephthalate (PET) and polyimide (PI) substrates using the chemical spray pyrolysis technique in order to explore their potential use as transparent window materials for solar cells. The substrate temperature along deposition of the material was maintained at 250 °C. The effects of substrate types on the structural and optical characteristics of the formed films were studied. X-ray diffraction patterns confirm the proper phase formation of crystalline ZnO films. Films deposited on PI exhibited a larger roughness compared to those deposited onto PET substrates because of the large particles adsorbed on the former. Optical transmittance values exceeding 80% in the visible and infra-red (IR) region on both substrates were registered. Optical band gaps (Eg) from Tauc plots for ZnO films on PET achieved values of ca. 3.2 eV whilst on PI were ca. 3.3 eV. Surface reflectance shows that ZnO on PI has consistently a higher surface reflectance of ca. ~2% throughout the spectral region compared to ZnO films on PET substrates while both showed a parasitic absorbance below 10% within the region of interest.
Read more10Improving the signal resolution of semiconductor gas sensors to high-concentration gases
Improving the signal resolution of semiconductor gas sensors to high-concentration gases
Crystal facet engineering and polarity control in ZnO gas sensors: advancements in sensing performance and operando surface analysis—secondary publication
This review examines zinc oxide (ZnO) gas sensors, which are widely recognized for their high sensitivity to flammable and toxic gases and for their cost-effectiveness. It emphasizes the importance of controlling crystal facets and polarity to enhance sensor performance. The synthesis of pyramid-shaped ZnO particles with well-defined crystal facets was performed for volatile organic compound (VOC) gas sensing. Additionally, the fabrication of polarity-controlled ZnO epitaxial thin films using pulsed laser deposition is examined, along with evaluations of their sensing properties for ethanol and hydrogen. The effect of additives on improving gas selectivity is also discussed. Operando surface analysis using low-energy He+ ion scattering (LEIS) was employed to elucidate the influence of crystal facets on ZnO single-crystal gas sensors. This review demonstrates that the selection and control of crystal facets greatly affect gas adsorption behavior and sensor sensitivity, particularly through enhanced adsorption capacity and increased surface oxygen deficiencies. Advanced surface analysis techniques, such as LEIS, provide deeper insights into interaction mechanisms at near-atmospheric pressure. These findings underscore the pivotal role of Zn and O polar surfaces in enhancing sensor response and selectivity, paving the way for high-performance gas sensors tailored to specific applications, such as the detection of isoprene in breath analysis. The ability to optimize crystal face exposure is expected to further advance the development of highly selective and sensitive gas sensor technologies.
Read more176Advances in chemiresistive sensors for acetone gas detection
Advances in chemiresistive sensors for acetone gas detection
10Self‐Powered Room‐Temperature High‐Sensitivity Acetone Gas Sensing System
Acetone is widely used as a solvent in industry, which is volatile and harmful to the environment and people’ health. Hence, it is very important for real‐time detection of acetone concentration in exhaust gas or the surrounding air. Herein, a self‐powered acetone gas‐sensing system (SASS) based on passive half‐wave rectification power management circuits (HW‐PMCs), enhanced pulsed triboelectric nanogenerator (pulsed‐TENG), and Co3O4 acetone gas sensor is reported. First, HW‐PMC is developed based on the half‐wave rectifier with 470 μF capacitor and limited capacitor voltage (<5.5 V) to store energy efficiently. Results demonstrate that simulated energy storage efficiency of HW‐PMC is 42.2% and is 26.3 times higher than that of conventional PMCs. Then, the external capacitor is connected to electrodes of pulsed‐TENG, which forms enhanced pulsed‐TENG. The highest energy storage efficiency of HW‐PMC can reach 25.8% using enhanced pulsed‐TENG. The calculator is successfully powered using enhanced pulsed‐TENG and HW‐PMC. Finally, according to the characteristics of HW‐PMC, enhanced pulsed‐TENG, and Co3O4 gas sensor, SASS is developed and can detect 2 ppm of acetone at room temperature. SASS is important to environmental protection and reduction of production cost.
Read more174Acetone and ethanol solid-state gas sensors based on TiO2 nanoparticles thin film deposited by matrix assisted pulsed laser evaporation
Matrix assisted pulsed laser evaporation (MAPLE) is a new promising laser-based technique thought for polymer or biomaterial thin films deposition. In this work, the MAPLE technique has been used for the deposition of titania (TiO 2 ) nanoparticle thin films to be used for gas sensor applications. For this purpose, an aqueous solution of TiO 2 nanoparticles, synthesized by a novel chemical route, was frozen at the liquid nitrogen temperature and introduced in a vacuum chamber to be irradiated with a pulsed ArF excimer laser. The volatile solvent was pumped away while the TiO 2 nanoparticles were deposited on Si and Al 2 O 3 substrates. A uniform distribution of TiO 2 nanoparticles with an average size of about 10 nm was obtained, as demonstrated by high resolution scanning electron microscopy (SEM-FEG) inspection. We realized gas-sensing devices based on resistive transduction mechanism by using the TiO 2 nanoparticles thin films deposited by the MAPLE technique onto suitable rough alumina substrates equipped with interdigitated electrical contacts (IDC) and heating elements. Electrical characterization measurements were carried out in controlled environment. The results of the gas-sensing tests towards low concentrations of ethanol and acetone vapors are reported. Typical gas sensor parameters (gas responses, response/recovery time, sensitivity, and low detection limit) towards ethanol were extracted and compared with to the corresponding parameters towards acetone.
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272Nanostructured Metal Oxide-Based Acetone Gas Sensors: A Review.
Acetone is a well-known volatile organic compound that is widely used in different industrial and domestic areas. However, it can have dangerous effects on human life and health. Thus, the realization of sensitive and selective sensors for recognition of acetone is highly important. Among different gas sensors, resistive gas sensors based on nanostructured metal oxide with high surface area, have been widely reported for successful detection of acetone gas, owing to their high sensitivity, fast dynamics, high stability, and low price. Herein, we discuss different aspects of metal oxide-based acetone gas sensors in pristine, composite, doped, and noble metal functionalized forms. Gas sensing mechanisms are also discussed. This review is an informative document for those who are working in the field of gas sensors.
Read more1Study on the effect of growth-time and seed-layers of Zinc Oxide nanostructured thin film prepared by the hydrothermal method for liquefied petroleum gas sensor application
Gas sensors are devices that can convert the concentration of an analytic gas into an electronic signal. Zinc oxide (ZnO) is an important n-type metal oxide semiconductor which has been utilized as gas sensor for several decades. In this work, ZnO nanostructured films were synthesized by a hydrothermal route from ZnO seeds and used as a liquefied petroleum gas (LPG) sensor. At first ZnO seed layers were deposited on glass substrates by using spin coating method, then ZnO nanostructured were grown on these substrates by using hydrothermal growth method for different time duration. The effect of growth time and seed layers of ZnO nanostructured on its structural, optical, and electrical properties was studied. These nanostructures were characterized by X-ray diffraction, scanning electron microscopy, optical spectroscopy, and four probes sheet resistance measurement unit. The sensing performances of the synthetic ZnO nanostructures were investigated for LPG.XRD showed that all the ZnO nanostructures were hexagonal crystal structure with preferential orientation. SEM reviled that the size of nanostructure increased with increase in growth time. Band gap and sheet resistance for ZnO nanostructured thin film decreased with increase in growth time. ZnO nanostructured thin film showed high sensitivity towards LPG gas. The sensitivity of the film is observed to increase with increase in no of seed layers as well as growth time. The dependence of the LPG sensing properties on the different growth time of ZnO nanostructured was investigated. The sensing performances of the film were investigated by measured change in sheet resistance under expose to LPG gas. BIBECHANA 16 (2019) 145-153
Read more10Temperature and humidity effects on the acetone gas sensing of pristine and Pd-doped WO3 clusters: A transition state theory study.
The performance of pristine and Pd-doped WO3 acetone gas sensors is calculated theoretically and compared with available experimental results. Temperature, humidity, and acetone concentration variation are considered in the present work. Transition state theory calculates Gibbs free energy of transition, including its components enthalpy and entropy of transition or activation. The variation of Pd doping concentration is used to obtain the maximum response and lowest response time for the optimum performance of the gas sensor. The present theory considers the reduction of acetone gas concentration as acetone reaches its autoignition temperature. Acceptable agreement between theory and experiment is obtained. The acceptance includes the decrease of Gibbs free energy with doping percentage, variation of temperature exponent to the power twelve in the considered reactions, and reduction of response time with the increase of temperature. Density functional theory at the B3LYP level is used. 6-311G** basis set (for O atoms) and SDD (for heavy Pd and W atoms) are used to optimize the structures examined in the present work. The Gaussian 09 program and accompanying software were used to perform the current tasks.
Read more7Experimental Studies on Doped and Co-Doped ZnO Thin Films Prepared by RF Diode Sputtering
Our research on the growing and characterizing of p-type ZnO thin films, prepared by radio frequency (RF) diode sputtering, mono-doped with nitrogen, and co-doped with aluminium and nitrogen, is a response of the need from p-type ZnO thin films for device applications. The dopants determine the conductivity type of the film and its physical properties. We obtained p-type ZnO thin films by RF diode sputtering and using a nitrogen dopant source. The novelty in our approach is in the use of a plasma assisted deposition method, to increase nitrogen solubility and the concentration of the NO acceptors in the film. The structural parameters, such as preferential orientation, crystallite size and strain in the film, depend on percentage of nitrogen in the working gas and the negative bias voltage. The XRD diffraction patterns reveal more or less stronger expressed c-axis preferential orientation of the films depending on the N2 content in the sputtering gas. The diffraction lines of ZnO (100), (002), (101), and (110) are observed in the XRD diffraction patterns of all ZnO:N thin film. Aluminium- nitrogen co-doping improves the crystalline structure and all ZnO:Al:N thin films show a c-axis texture in direction declined about 16 deg from the surface normal. Three diffraction lines ((100), (002) and (101)), appear only in the XRD patterns of the films deposited at 25 % N2, indicating that their preferential orientation is more random. A strong preferential orientation of the crystallites is observed for high dopant contents (50 % and 75 % N2) and intensities of the (002) diffraction lines are almost the same.
Read moreDefect characterization of low temperature solution grown ZnO
Zinc oxide (ZnO) is a wide bandgap semiconducting oxide with many potential applications in optoelectronic devices such as light emitting diodes (LEDs) and field effect transistors (FETs). Controlling the conductivity of ZnO is a foremost concern in the optoelectronic industry. Understanding the nature of ZnO native defects is vital for the application of ZnO in the semiconductor industry. Many electronic properties depend significantly on the intrinsic defect concentration as it affects the doping efficiency and the growth of the material. These properties also depend on the type and amount of impurities and degree of crystallinity. There is a need to understand the function of native point defects and the incorporation of impurities, with the intention for a better control of the conductivity of ZnO. However, one major issue in determining whether it is zinc or oxygen deficiency that provides ZnO its unique properties remains. In this thesis, ZnO films and powders were synthesized via a low temperature aqueous solution chemical bath deposition route and its short to medium range structure order characterized. In addition, Ga-doped ZnO films and powders were also synthesized as Ga has been found to be an excellent donor, increasing the conductivity of ZnO films. All samples were post-growth thermally annealed in air in order to improve the electrical and optical properties, and correlate the annealing temperature with the defect structure. The epitaxial nature of the ZnO films (undoped and Ga-doped) were determined via high resolution X-ray diffraction (HRXRD). The morphology of the films was studied via field emission gun scanning electron microscopy (FEGSEM) showed that the films were smooth and continuous on the plane-view. Cross-sectional images showed that the films were about 2 µm thick after a growth time of 4 hours at 90°C. Visible pores were also observed in the films after post-growth thermal annealing at temperatures of above 200°C. Electrical properties were obtained via Hall measurements showed characteristic n-type conductivity and a carrier concentration of the order of 1020 cm-3 after post-growth thermal annealing at 400°C in air for 1 h for the Ga-doped ZnO films. For the ZnO powders, phase identification was determined by conventional powder XRD methods. The morphologies were obtained via FEGSEM and showed different nanorods morphologies for the different precursors used for the syntheses. Internal pores were observed in the ZnO nanorods upon thermal annealing at >300 °C and were examined using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). Three-dimensional electron tomography reconstruction shows that pores exist within the nanorods. These pores coalesce and also increase in size as the ZnO nanorods were annealed at higher temperatures or for extended periods of time, as observed by an in situ TEM study. As such, this pore formation phenomenon will significantly affect the utilisation of solution-synthesized ZnO for optoelectronic devices, but new application fronts such as gas sensors and photo/electro catalysis will benefit due to its high light absorption properties and high surface areas. Further defect characterization was performed for the all the ZnO samples, largely using synchrotron-based characterization techniques, namely X-ray absorption spectroscopy (XAS) and X-ray pair distribution function (PDF) techniques. XAS is an ideal, atom specific characterization technique that is able to probe defect structure in many materials, including ZnO. Comparative studies of commercially available ZnO and aqueous solution grown (≤ 90°C) ZnO powders using XAS and PDF has allowed for the study of short to medium range structure order. The ZnO films were studied via ex situ XAS and the ZnO powder samples were studied via ex situ and in situ XAS and in situ PDF experiments. The local structure order of the ZnO films and powders were determined. From XAS of the Ga-doped ZnO samples, it was evidently shown that Ga3+ resides tetrahedrally in the Zn2+ site within the ZnO lattice. The understanding of the role of defects and the short to medium range order and structure within the ZnO system has provided useful insight for further exploitation of the material and is invaluable for the exploitation of ZnO for further development of optoelectronic device applications.
Read moreImproved Performance of Acetone Gas Sensing through Oxygen Vacancy Formation of ZnO Nanoparticles
Introduction Recently, interest in gas sensors have been increasing in different fields of not only industry and medical applications but also development of smart city and detection of indoor air pollutants. In particular, acetone is a volatile organic compound (VOC) used as a biomarker to indicate various diseases in human exhalation, or has been importantly measured as one of the indicator gases for indoor pollution measurement [1]. Unlike industrial sensors that need to detect relatively high concentration gas, the detection of acetone for biomarkers requires highly sensitive sensing materials which can react with the gas quickly.Metal oxide semiconductor (MOS) have been widely used as gas sensors because of their thermal and chemical stability and natural abundance. A lot of researches for detecting acetone gas using metal oxide semiconductor, for instance, WO3, SnO2 and ZnO through diverse method and morphology control, have been studied in recent [2]. Among them, ZnO is in the spotlight for various reasons due to their facile size and structure control, gas reactive surface and appropriate band gap. Many papers associated gas sensing of ZnO were published in multiple ways as metal doping and quantum dot control [3, 4]. In this study, oxygen vacancy was produced by simple H2O2 surface treatment of commercial ZnO, and the amount of oxygen vacancy by the degree of surface treatment was quantified. In addition, through evaluating acetone sensing performance according to the amount of oxygen vacancy, optimal vacancy amount showing significantly superior sensitivity was found. Chemical calculation described the reason of the outstanding response [5-8]. Further information will be discussed in detail. Method Surface oxygen vacancy is generated by a variety of H2O2 treatment with 400 ˚C annealing. ZnO controlled oxygen vacancy was reacted with 10 ppm acetone at 300 – 500 ˚C, and confirm response of the material. Response of varied temperature was confirmed through three or more repeated sensor measurements, and the measurement was performed at various concentration ranging from 0.01 ppm to 10 ppm under optimized temperature conditions. And the performance was identified under various humidity conditions and long-term stability. Results and Conclusions When H2O2 was treated on commercial ZnO, ZnO2 was produced. ZnO with oxygen vacancy was formed after 400 ˚C annealing on the obtained ZnO2. Treatment with high concentrated H2O2 results in more defects, breaking crystallinity and reducing the XRD peak sharpness. Therefore, we found optimal concentration conditions that create oxygen vacancy around the surface. The deficient oxygen and lattice oxygen peaks were deconvoluted from the O 1s peaks of the XPS spectrum and the vacancy to lattice ratio was obtained. Also, the formation of oxygen vacancy could be confirmed by the peak shift of Zn 2p3/2. The oxygen vacanced ZnO had a high sensitivity of 1692.1 (Fig. 1). This results showed the world’s best sensitivity compared with previous reported outcomes such as commercial ZnO (S=107), SnO2 nanorod arrays (S=511) and In-doped ZnO quantum dots (S=424). This study shows the possibility of commercialization through a simple surface treatment method that can be widely applied to a wide range of metal oxides, and it is widely applicable to systems of diverse fields where low concentrations of acetone have to be fairly sensitive.
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