Temperature and humidity effects on the acetone gas sensing of pristine and Pd-doped WO3 clusters: A transition state theory study.

CONTEXT: 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. METHODS: 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.

The reaction of pristine and Rh-doped SnO2 clusters with acetone: Application of Evans-Polanyi principle to transition state theory.

CONTEXT: Using transition state theory, acetone sensing by pristine and rhodium-doped tin dioxide is discussed. The Evans-Polanyi principle is modified from its original formulation commensurate with the Arrhenius equation to be more suitable for transition state theory. The new formalism for the activation energy replaces enthalpy with Gibbs free energy in the original Evans-Polanyi principle. The new formalism considers reaction entropy, which is not considered previously in Evans-Polanyi principle. Response and response time of interaction of acetone with both pristine and Rh-doped SnO2 clusters is calculated. Variations of response in terms of acetone concentration and temperature are calculated and compared to the experiment. Acceptable agreement between theory and experiment that calls for more comparisons to demonstrate the modified approach. METHODS: The pristine and Rh-doped clusters and their interaction with acetone are simulated using density functional theory at the B3LYP level. 6-311G** and SDD (for heavy atoms) basis sets are used to optimize the structures examined in the present work. Gaussian 09 program and accompanying software performed the current tasks.

Flexible Sensor Film Based on Rod-Shaped SWCNT-Polypyrrole Nanocomposite for Acetone Gas Detection.

A nanocomposite rod-shaped structure with a single-walled carbon nanotube (SWCNT) embedded in polypyrrole (PPy) doped with nonafluorobutanesulfonic acid (C4F), SWCNT/C4F-PPy, was synthesized using emulsion polymerization. The hybrid ink was then directly coated on a polyimide film interdigitated with the Cu/Ni/Au electrodes via a screen-printing technique to create a flexible film sensor. The sensor film showed a response of 1.72% at 25 °C/atmospheric pressure when acetone gas of 5 ppm was injected, which corresponds to almost 95% compared to the Si wafer-based array interdigitated with the Au electrode. Additionally, C4F was used as a hydrophobic dopant of PPy to improve the stability of humidity and to produce a highly sensitive film-type gas sensor that provides stable detection even in humid conditions.

A Study of High-Sensitivity Electro-Resistance Type Pre-Annealing ZnO-Doped CsPbBr3 Perovskite Acetone Sensors.

In this work, acetone gas sensors were fabricated using pre-annealing metal oxide zinc oxide (pa-ZnO)-doped perovskite cesium lead bromide (CsPbBr3). The ZnO nanopowder, before it was doped into CsPbBr3 solution, was first put into a furnace to anneal at different temperatures, and formed the pa-ZnO. The properties of pa-ZnO were different from ZnO. The optimized doping conditions were 2 mg of pa-ZnO nanopowder and pre-annealing at 300 °C. Under these conditions, the highest sensitivity (gas signal current-to-air background current ratio) of the ZnO-doped CsPbBr3 perovskite acetone sensor was 1726. In addition, for the limit test, 100 ppm was the limit of detection of the ZnO-doped CsPbBr3 perovskite acetone sensor and the sensitivity was 101.

Growth and Characterization of Sputtered InAlN Nanorods on Sapphire Substrates for Acetone Gas Sensing.

The demand for highly sensitive and selective gas sensors has been steadily increasing, driven by applications in various fields such as environmental monitoring, healthcare, and industrial safety. In this context, ternary alloy indium aluminum nitride (InAlN) semiconductors have emerged as a promising material for gas sensing due to their unique properties and tunable material characteristics. This work focuses on the fabrication and characterization of InAlN nanorods grown on sapphire substrates using an ultra-high vacuum magnetron sputter epitaxy with precise control over indium composition and explores their potential for acetone-gas-sensing applications. Various characterization techniques, including XRD, SEM, and TEM, demonstrate the structural and morphological insights of InAlN nanorods, making them suitable for gas-sensing applications. To evaluate the gas-sensing performance of the InAlN nanorods, acetone was chosen as a target analyte due to its relevance in medical diagnostics and industrial processes. The results reveal that the InAlN nanorods exhibit a remarkable sensor response of 2.33% at 600 ppm acetone gas concentration at an operating temperature of 350 °C, with a rapid response time of 18 s. Their high sensor response and rapid response make InAlN a viable candidate for use in medical diagnostics, industrial safety, and environmental monitoring.

Highly Sensitive Acetone Gas Sensors Based on Erbium-Doped Bismuth Ferrite Nanoparticles.

The acetone-sensing performance of BiFeO3 is related to structural phase transformation, morphology and band gap energy which can be modulated by rare-earth ions doping. In this work, Bi1-xErxFeO3 nanoparticles with different amounts of Er doping were synthesized via the sol-gel method. The mechanism of Er doping on acetone-sensing performance of Bi1-xErxFeO3 (x = 0, 0.05, 0.1 and 0.2) sensors was the focus of the research. The optimal working temperature of Bi0.9Er0.1FeO3 (300 °C) was decreased by 60 °C compared to BiFeO3 (360 °C). The Bi0.9Er0.1FeO3 sample demonstrated the optimal response to 100 ppm acetone (43.2), which was 4.8 times that of pure BFO at 300 °C. The primary reason, which enhances the acetone-sensing performance, could be the phase transformation induced by Er doping. The lattice distortions induced by phase transformation are favorable to increasing the carrier concentration and mobility, which will bring more changes to the hole-accumulation layer. Thus, the acetone-sensing performance of Bi0.9Er0.1FeO3 was improved.

Acetone Gas Sensor Based on SWCNT/Polypyrrole/Phenyllactic Acid Nanocomposite with High Sensitivity and Humidity Stability.

We synthesized core-shell-shaped nanocomposites composed of a single-walled carbon nanotube (SWCNT) and heptadecafluorooctanesulfonic acid-doped polypyrrole (C8F-doped-PPy)/phenyllatic acid (PLA), i.e., C8F-doped-PPy/PLA@SWCNT, for detecting acetone gas with high sensitivity and humidity stability. The obtained nanocomposites have the structural features of a sensing material as a C8F-doped-PPy layer surrounding a single-stranded SWCNT, and a PLA layer on the outer surface of the PPy as a specific sensing layer for acetone. PLA was chemically combined with the positively charged PPy backbone and provided the ability to reliably detect acetone gas at concentrations as low as 50 ppb even at 25 °C, which is required for medical diagnoses via human breath analysis. When C8F was contained in the pyrrole monomer in a ratio of 0.1 mol, it was able to stably detect an effective signal in a relative humidity (RH) of 0-80% range.

Highly sensitive and stable MEMS acetone sensors based on well-designed α-Fe2O3/C mesoporous nanorods.

Highly sensitive and stable acetone gas sensors based on MEMS substrate supported carbon nanoparticles decorated mesoporous α-Fe2O3 (C-d-mFe2O3) nanorods (NRs) derived from Fe-MIL-88B-NH2 NRs were first synthesized via a sequential process including a facile hydrothermal reaction and one-step pyrolysis at a moderate temperature in air. The MEMS architecture ensures low power consumption, small size, and high integration of the sensor. The obtained C-d-mFe2O3 NRs exhibit good thermal stability and superior acetone sensing performance with excellent response (Ra/Rg = 5.2 to 2.5 ppm) and selectivity, fast response/recovery speed (10/27 s), and low detection limit of 500 ppb at 225 °C. Furthermore, the acetone sensor exhibits remarkable long-term stability and repeatability even after being stored in air for over 10 months. The enhanced acetone sensing performance could be attributed to the large specific surface area of mesoporous α-Fe2O3 NRs, highly conductive carbon nanoparticles on the surface, and the formation of α-Fe2O3/C heterojunction. Density functional theory (DFT) calculations help to further confirm the superior acetone sensing performance. The competitive performance makes C-d-mFe2O3 NRs gas sensor a great potential for practical application in environmental harmful acetone gas monitoring.

Selectivity of a ZnO@ZIF-71@PDMS Nanorod Array Gas Sensor Enhanced by Coating a Polymer Selective Separation Membrane.

It is important for noninvasive diagnosis of diabetes to develop acetone gas sensors with high selectivity. ZnO@ZIF-71 has been reported as a highly sensitive and selective gas sensor on acetone detection. However, it is difficult to exclude the interference with similar molecular sizes gas in the gas-sensing process, like ethanol. To solve this problem, polydimethylsiloxane (PDMS) was synthesized on the surface of ZnO@ZIF-71 to form a ZnO@ZIF-71@PDMS sensor by vapor deposition. The new sensor shows inert response to ethanol and effective response to acetone simultaneously. The PDMS membrane acts as a molecular sieve, which shows the acetone selectivity performance and can totally eliminate the response to low concentration ethanol at low temperature. Theory calculations and solubility test are also employed to prove the role PDMS plays in this process. It demonstrated that the acetone selectivity performance comes from the hydrogen bond interaction between the ethanol gas molecules and PDMS, which increases difficulty for ethanol gas molecules to penetrate the PDMS membrane. Further, this work provides a new method for enhancing gas-sensing selectivity and promoting for miniaturization of gas sensors.

Novel quaternary oxide semiconductor for the application of gas sensors with long-term stability.

In this paper, quaternary oxide semiconductor was applied as sensing material for the fabrication of gas sensors. One-step solvothermal method was utilized to synthesize the sensing material. Various characterization methods including XRD, XPS, SEM, HRTEM were employed to analyze the composition and structure of the sensing material. Composite composed of CuInW2O8 and CuWO4 was successfully prepared at last characterized by XRD result. The SEM result revealed the structure of the sensing material: nanoparticles assembled spindle-like nanostructure with ~200 nm long axis and ~60 nm short axis. Sensor based on the spindle-like nanostructures was systemically tested to acquire the information about the sensing properties. The sensor exhibited responses to acetone at the operating temperatures from 190 to 275 °C. The results showed that the sensor was more sensitive to acetone compared with other gases at the optimal operating temperature of 210 °C. The response of the sensor was also tested under the relative humidity from 25 RH% to 95 RH% at the operating temperature of 210 °C. The response variation was only 13.9%, demonstrating that the sensor possessed strong anti-humidity ability. It was worth noting that the sensor showed acceptable long-term stability compared with other acetone sensors. The gas sensing mechanism was also discussed here. This work might provide ideas for the development of novel sensitive materials for the application of gas sensors.

Catalytic Activation of Cobalt Doping Sites in ZIF-71-Coated ZnO Nanorod Arrays for Enhancing Gas-Sensing Performance to Acetone.

Developing acetone gas sensors with high sensitivity is crucially important for many applications including nonevasive diagnosis of diabetes. In the present work, cobalt doping is used to catalyze acetone gas-sensing reactions and hence to promote the sensitivity of acetone gas sensors. In order to achieve this, ZIF-71 metal-organic framework (MOF) is synthesized onto ZnO nanorod arrays with various concentrations of Co doping to form composite ZnO@ZIF-71(Co) sensors, which are then evaluated as sensing materials for acetone detection. Such sensors are shown to be sensitive to a trace amount of acetone (50 ppb) and have a massively enhanced response of about 100 times that for the undoped sensor at an optimal Co/Zn ratio and operating temperature. Fourier-transform infrared spectroscopy and temperature-programmed desorption with density functional theory calculations are also made to assist in elucidating the catalytic gas-sensing mechanism for the Co-doped composite sensors ZnO@ZIF-71(Co). It demonstrated that the introduced Co site in ZIF-71(Co) can activate oxygen catalytically and increase active oxygen released to the ZnO surface. Meanwhile, the Co sites also promote the decomposition of acetone. These two steps together affect the catalytic oxidation of gases and finally enhance the sensitivity. This work introduces the catalytic effect of the MOF into the gas-sensing mechanism and provides an idea for broadening the application of MOF catalysis.

Fabrication of a Micro-Electromechanical System-Based Acetone Gas Sensor Using CeO2 Nanodot-Decorated WO3 Nanowires.

Preparation of reliable, stable, and highly responsive gas-sensing devices for the detection of acetone has been considered to be a key issue for the development of accurate disease diagnosis systems via exhaled breath. In this paper, novel CeO2 nanodot-decorated WO3 nanowires are successfully synthesized through a sequential hydrothermal and thermolysis process. Such CeO2 nanodot-decorated WO3 nanowires exhibited a remarkable enhancement in acetone-sensing performance based on a miniaturized micro-electromechanical system device, which affords high response (S = 1.30-500 ppb, 1.62-2.5 ppm), low detection limit (500 ppb), and superior selectivity toward acetone. The improved performance of the acetone sensor is likely to be originated from the fast carrier transportation of WO3 nanowires, the formation of WO3-CeO2 heterojunctions, and the existence of large amounts of oxygen vacancies in CeO2. The improved reaction thermodynamics and sensing mechanisms have also been revealed by the specific band alignment and X-ray photoelectron spectroscopy analysis.

Ultrafine Tungsten Oxide Nanowires: Synthesis and Highly Selective Acetone Sensing and Mechanism Analysis.

By using WCl6 as a precursor and absolute ethanol as a solvent, ultrafine W18O49 nanowires (UFNWs) were synthesized by a one-pot solution-phase method and used as gas sensing materials. Their crystal structure, morphology, and specific surface area can be regulated by controlling precisely the content of the WCl6 precursor in the solution. It has been found that, when the content of the precursor is 4 mg/mL, the formed products are UFNWs with a diameter of about 0.8 nm, only one crystal plane [010] is exposed, and the specific surface area is 194.72 m2/g. After the gas sensing test, we found that they have excellent selectivity to acetone. The response of 50 ppm acetone reaches 48.6, the response and recovery times are 11 and 13 s, respectively. In order to evaluate the interaction between W18O49 surfaces and different volatile organic compound (VOC) molecules, we simulated and calculated the adsorption energy (EAds) among different W18O49 surfaces and different VOCs by DFT. The calculated results are in agreement with the experimental results, further confirming the ultrahigh selectivity of W18O49 UFNWs to acetone. The above results demonstrate that the high selectivity of W18O49 UFNWs to acetone is due to the exposure of its single crystal plane [010]. This work has practical significance for better detection of acetone.

Incorporating N Atoms into SnO2 Nanostructure as an Approach to Enhance Gas Sensing Property for Acetone.

The development of high-performance acetone gas sensor is of great significance for environmental protection and personal safety. SnO2 has been intensively applied in chemical sensing areas, because of its low cost, high mobility of electrons, and good chemical stability. Herein, we incorporated nitrogen atoms into the SnO2 nanostructure by simple solvothermal and subsequent calcination to improve gas sensing property for acetone. The crystallization, morphology, element composition, and microstructure of as-prepared products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Electron paramagnetic resonance (EPR), Raman spectroscopy, UV⁻visible diffuse reflectance spectroscopy (UV⁻vis DRS), and the Brunauer⁻Emmett⁻Teller (BET) method. It has been found that N-incorporating resulted in decreased crystallite size, reduced band-gap width, increased surface oxygen vacancies, enlarged surface area, and narrowed pore size distribution. When evaluated as gas sensor, nitrogen-incorporated SnO2 nanostructure exhibited excellent sensitivity for acetone gas at the optimal operating temperature of 300 °C with high sensor response (Rair/Rgas - 1 = 357) and low limit of detection (7 ppb). The nitrogen-incorporated SnO2 gas sensor shows a good selectivity to acetone in the interfering gases of benzene, toluene, ethylbenzene, hydrogen, and methane. Furthermore, the possible gas-sensing mechanism of N-incorporated SnO2 toward acetone has been carefully discussed.

Self-Assembly Template Driven 3D Inverse Opal Microspheres Functionalized with Catalyst Nanoparticles Enabling a Highly Efficient Chemical Sensing Platform.

The design of semiconductor metal oxides (SMOs) with well-ordered porous structure has attracted tremendous attention owing to their larger specific surface area. Herein, three-dimensional inverse opal In2O3 microspheres (3D-IO In2O3 MSs) were fabricated through one-step ultrasonic spray pyrolysis (USP) which employed self-assembly sulfonated polystyrene (S-PS) spheres as a sacrificial template. The spherical pores observed in the 3D-IO In2O3 MSs had diameters of about 4 and 80 nm. Subsequently, the catalytic palladium oxide nanoparticles (PdO NPs) were loaded on 3D-IO In2O3 MSs via a simple impregnation method, and their gas sensing properties were investigated. In a comparison with pristine 3D-IO In2O3 MSs, the 3D-IO PdO@In2O3 MSs exhibited a 3.9 times higher response (Rair/Rgas = 50.9) to 100 ppm acetone at 250 °C and a good acetone selectivity. The detection limit for acetone could extend down to ppb level. Furthermore, the 3D-IO PdO@In2O3 MSs-based sensor also possess good long-term stability. The extraordinary sensing performance can be attributed to the novel 3D periodic porous structure, highly three-dimensional interconnection, larger specific surface area, size-tunable (meso- and macroscale) bimodal pores, and PdO NP catalysts.