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Recently, graphyne-based gas sensors have drawn a lot of interest. One kind of graphene with acetylene bonds connecting its hexagons is graphyne. In this study, the density functional theory (DFT) method was used to investigate the physical parameters of the surface adsorption of carbon monoxide on the $\alpha$- and $\gamma$-graphyne nanosheet, taking into account van der Waals (vdW) interactions through the use of the SIESTA computational code. CO molecule adsorbed and optimized in two vertical and horizontal states from the side of carbon and oxygen atoms, at different distances and sites relative to the graphyne sheet. After optimization and finding the adsorption energy, the best adsorption sites, equilibrium distance of the molecule from the surface, electronic structure, charge transfer rate, and bandgap changes were calculated. It was observed that the changes in the electronic structure after the adsorption of CO molecule are insignificant and the $\alpha$- and $\gamma$-graphyne nanosheets remained zero-gap and narrow-gap semiconductors, respectively. The adsorption of CO molecule on the $\alpha$- and $\gamma$-graphyne nanosheets is physisorption. The results show that the $\gamma$-graphyne nanosheet has a good potential for adsorbing and detecting CO molecules and sensor applications.

Inorganic photocatalytic materials exhibiting a highly efficient response to ultraviolet-visible light spectrum have become a subject of widespread global interest. Nanocomposite metal oxides, particularly Nickel Oxide (NiO) and Zinc Oxide (ZnO), have gained attention for their diverse applications in gas sensing and photocatalytic processes. In this work, ZnO-NiO (ZnO_0.6NiO_0.4 and ZnO_0.4NiO_0.6) binary nanocomposites were synthesized by hydrothermal technique. The binary nanocomposites were analyzed by UV-Visible spectrophotometer, X-ray diffraction (XRD), photoluminescence (PL), Fourier transform infrared spectrophotometer (FTIR), energy dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The XRD pattern revealed that the nanocomposites, the peaks of both ZnO and NiO are present indicating the presence of both crystal structures hexagonal wurtzite and cubic. The miller indices, crystallite size, microstrain and dislocation density were determined from the XRD plot. FESEM and TEM analyses showed the spherical morphology of the synthesized composites with an approximate size of 10nm. The detailed analysis of ZnO–NiO binary nanocomposite sensor characteristics in terms of sensitivity, selectivity, response and recovery time were carried out and the nanocomposites were found to be highly sensitive to CO₂ 100 ppm at 350^∘C and Cl₂ at 200^∘C. The photocatalytic degradation outcome showed 52% degradation of methylene blue at 10 ppm and 90w/m². These results suggest the potential utility of these binary nanocomposites in photocatalytic applications for the degradation of organic pollutants.

Exploring the morphogical and structural properties along with gas sensing applications both pure and Ti-doped SnO₂ ultra-thin films, were meticulously crafted on micromachined silicon substrate heater devices using a combination of classical soft chemical processes and hydrothermal techniques (SCPHTP). The fabrication process involved a two-step approach: initially, a 20nm layer of tin oxide was hydrothermally deposited onto the substrates, followed by annealing in wet air at 600^∘C for 5h using a standardized temperature variation protocol. Subsequently, secondary layers with thicknesses of 20, 40 and 60nm were sequentially deposited onto the tin dioxide devices and oxidized in wet air at 550^∘C and 600^∘C for 20h each, using the same temperature modulation scheme. Throughout this process, the hydrothermal deposition temperature remained constant at 180^∘C for both the initial and secondary layers of tin dioxide deposition. Additionally, Ti layers with thicknesses of 4 and 8nm were deposited onto the 20nm + 40nm system, subjected to annealing at 550^∘C for 20h, followed by 1-min annealing in dry O₂ at 700^∘C and 800^∘C, respectively, using a Rapid Thermal Annealing (RTA) system. Characterization of the crystalline and surface structures of the devices revealed a transformation of the soft chemical tin dioxide solution into the cassiterite structure of SnO₂, resulting in uniform large surface areas for the sensor devices. Moreover, Ti metal layers of 4 and 8nm thicknesses were fully converted into TiO₂ on the surface of the devices. Subsequent testing showcased higher current values in sandwich systems of 20nm + 60nm and 20nm + 40nm compared to the 20nm + 20nm configuration. Sensitivity and stability assessments for various volatile organic compounds (VOCs) and CO gases at a constant DC temperature of 400^∘C indicated excellent performance, with sensitivity to CO gas being contingent on relative humidity (RH). Notably, RTA-annealed and Ti-8 nm-doped sensor devices exhibited superior sensitivity and reproducibility, particularly when treated at 800^∘C in dry O₂ for 1min. This heightened performance can be attributed to the occupation of chloride ions in the oxygen sites of the as-synthesized SnO₂, resulting in enhanced sensing capabilities for VOC gases.

In this work, we have investigated and compared three important parameters: resistance, absorbance, and sensitivity of the sensitive layer in the ammonia gas sensor made of conductive polymers. Using a simulation based on the Langmuir absorption model, we have examined the changes in resistance, absorbance, and sensitivity of both the pure conducting polymer and the layer doped with carbon nanotubes. We analyzed the results using Matlab software. The findings demonstrate that the addition of carbon nanotubes reduces the resistance and enhances the absorbance and sensitivity.

WO₃ is a promising candidate material for gas sensors due to its simple preparation, convenient operation, diverse structure and high electron mobility. However, WO₃ gas sensors often have problems such as high operating temperature, high-energy consumption and sensitive characteristics easily affected by environmental humidity. In this paper, an effective method to improve the gas sensitivity of WO₃ gas sensor by using composite carbon nanomaterials is explored. The results show that the composite of WS₂/WO₃ and carbon spheres, C@WS₂/WO₃ composite gas-sensitive material shows good sensing performance for triethylamine (TEA) at low temperatures. In addition, excellent TEA selectivity, good stability, and good response recovery characteristics are also achieved. Compared with pure WS₂/WO₃ material, the sensor response of C@WS₂/WO₃ composite is as high as 24.6 at the optimal operating temperature of 240${}^{\circ }$C, compared with 21.81 of pure WS₂/WO₃ material.

Gas sensors based on 2,9,16,23-tetra(2,6-dimethylphenoxy)metallophthalocyanine (TDMP-MPc) films on interlocking silver electrodes were fabricated by solvent casting from chloroform solutions containing 2,9,16,23-tetra(2,6-dimethylphenoxy)copper, cobalt or nickel phthalocyanine (TDMP-CuPc, TDMP-CoPc or TDMP-NiPc). The sensitivity of the gas sensors to the presence of NO₂ and the depletion of O₂ was investigated. It was confirmed that the gas sensors based on TDMP-CuPc and TDMP-CoPc films could detect 1 ppm NO₂ at room temperature and that the current responses to the presence of NO₂ and the depletion of O₂ were considerably quick. These results indicate that adsorption and desorption of NO₂ and O₂ on the surfaces of TDMP-MPc films are easily achieved at room temperature.

Optical gas sensors play an increasingly important role in many applications, particularly for the detection of toxic gases. A novel Goos–Hänchen (GH) shift optical gas sensing scheme based on subwavelength hyperbolic metamaterials (HMMs) is proposed. The GH shift intensity, direction and the critical wavelength characteristics were revealed. By virtue of the GH shift and subwavelength HMMs characteristics, we designed an ultra-sensitive gas sensor to detect helium (He), hydrogen (H₂), carbon monoxide (CO) and methane (CH₄). The study shows that the sensitivities of the gas sensor can reach as high as $S_{\mathrm{\text{He}}}=3.06\times {10}^6\mu \mathrm{\text{m/RIU}}$, $S_{{\mathrm{\text{H}}}_2}=2.86\times {10}^6\mu \mathrm{\text{m/RIU}}$, $S_{\mathrm{\text{CO}}}=1.81\times {10}^6\mu \mathrm{\text{m/RIU}}$, and $S_{\mathrm{\text{C}}{\mathrm{\text{H}}}_4}=9.58\times {10}^5\mu \mathrm{\text{m/RIU}}$. With proper surface chemical modification, this GH shift gas sensor would be a powerful tool for high-sensitive gas sensing applications.

To form a tungsten disulfide film, a tungsten trioxide film is deposited first and then hydrogen sulfide is injected into the furnace tube to sulfide the tungsten trioxide film in a high-temperature environment. Due to the need to accurately control the thickness of tungsten trioxide, the power of the RF sputtering machine was reduced as much as possible in a stable condition in the experiment and the bias voltage during each process was monitored. In this experiment, a sapphire substrate and a silicon substrate with 200nm silicon dioxide are used. Then use optical instruments such as Raman optics, ellipsometers and high-resolution electron transmission microscopes, atomic force microscopes and other instruments for further measurement. The analysis results show that we have successfully made tungsten disulfide films of different thicknesses. Moreover, two-dimensional tungsten disulfide thin film has a response to light, gas and pH and related devices have been successfully fabricated in experiments. Among them, comparing the single-layer film and the double-layer film, the film quality of the double-layer film is better. The quality of the film grown on the sapphire substrate is also better than the quality of the film grown on the silicon dioxide substrate.

In this work, different from the typical gas sensors responding by gas adsorption on their surface, a new gas sensor using carbon nanotubes (CNTs) as electron emitters is introduced for detecting inert gases which hardly possess chemical or electrical adsorption in normal conditions. The proposed sensor works by figuring out the variation of the dark current and the initial breakdown voltage on Paschen's law under applied high voltage. As they depend on the gas composition and the pressure in a sealed chamber, it is possible to detect the identity and the concentration of unknown inert gas species.

Polyaniline (PANI) was prepared by chemical oxidative polymerization of aniline monomers as emeraldine salt form. By the same method, polyaniline–cadmium sulfide nanocomposites were synthesized in the presence of different percentages (10–50 wt.%) of cadmium sulfide (CdS) which was prepared by using sol–gel method. The optical band gap was decrease with increasing of CdS concentration, that is obtained from UV-VIS measurements. From SEM and AFM, there is uniform distribution for cadmium sulfide nanoparticles in the PANI matrix. The electrical measurements of nanocomposites exhibit the effect of crystallite size and the high resistivity of CdS on the resistivity of nanocomposites. Emeraldine salt PANI, CdS and PANI–CdS nanocomposites were investigated as gas sensors. From this investigation, the sensitivity of PANI–CdS for NO₂ gas increase with the increasing of operation temperature and the optimum sensitivity was obtained at 200${}^{\circ }$C. The sensitivity of nanocomposites at best temperature (200${}^{\circ }$C) was increased and faster response time with the increasing of CdS contents.

The two-dimensional (2D) plane of graphene has many active sites for gas adsorption. It has broad application prospects in the field of MEMS gas sensors. At present, there are many experimental studies on graphene gas sensors, but it is difficult to accurately control various influencing factors in the experiments. Therefore, this paper applies the first principle based on density functional theory to study the adsorption and detection characteristics of graphene on CO and CO₂. The first-principles analysis method was used to study the adsorption characteristics and sensitivity of graphene. The results show that the inductive graphene has a sensitivity of 1.55% and 0.77% for CO and CO₂, respectively. The Stone–Wales defects and multi-vacancy defects have greatly improved the sensitivity of graphene to CO, which is 35.25% and 4.14%, respectively. Introduction of defects increases the sensitivity of detection of CO and CO₂, but also improves the selective gas detection material of these two gases. Thus, the control and selectively introducing defects may improve the detection accuracy of the graphene CO and CO₂.

H₂S is a gas that can cause poisoning with a composition starting from 2.5 ppm. This study investigated the ability of gas sensors to detect H₂S gas at below 1 ppm. The primary material used for the gas sensor was ZnO. To increase sensor response, Au was used as a decorated metal. These materials were dissolved using deionized water with ultrasonication and were deposited by solution deposition method onto the Pt electrode. Powder and film characterizations were made using XRD, SEM, and TEM. The characterization results show high crystallinity of the annealed ZnO. The coating material shows a highly porous interconnected structure that can absorb gas quickly. There are Au spots attached to the ZnO particles, which are spherical and homogeneous. Based on these results, the device sensor can detect H₂S gas with a high sensing response even at low gas concentration.

Gas sensors are essential devices to detect harmful gases that are present in the environment. Metal oxide semiconductors (MOSs) are used as sensing materials to detect harmful gases. Some of the metal oxides, like ZnO, SnO₂, WO₃, NiO, etc. have been used to detect the gases. This paper provides a theoretical study of gas sensing using MOSs. Many programs are available for the theoretical Density Functional Theory (DFT) approach. The theoretical calculation provides many properties about the sensing material, like electronic properties, magnetic properties, charge difference calculation, and Vander wall interaction between the sensing material surface and adsorbing molecule. The nanostructure provides better gas sensing performance due to its high surface-to-volume ratio. This paper is based on the DFT study and provides gas-sensing results using electronic properties.

Studying toxic gases is more important because it is related to the health of humans. Therefore, it is appropriate to make some theoretical calculations to cover this topic. This study selectivity tunes the graphene derivatives’ ability to sense the most common gases in the atmosphere such as carbon monoxide, carbon dioxide, and oxygen. This involves a pristine and doped Gr-sheets complex with three gases. Density Functional Theory (DFT) was employed to investigate the electronic structures of 12 graphene-based sheets. The bandgap simulations demonstrate the effect of doping and complexing graphene sheets with different segments, that result in a sensing signature. The bandgap calculations also prove that the studied graphene derivatives selectively bind to different gases and this characteristic is in good agreement with the total energy calculations. Our results show that the electrical properties of graphene are improved with doping by Ni and As.

We investigated a gas sensor that makes use of the surface plasmon resonance (SPR) effect in a thick layer of gold (Au), copper (Cu), ZnO, and multilayer black phosphorous (BP). The suitability of the proposed gas sensor was investigated for a range of analyte gases recognized for their toxicity, greenhouse effect, or flammability. The proposed gas sensor obtains a maximum sensitivity of 258.77°/RIU with a remarkable full width at half maximum (FWHM) of 7.12°, detection accuracy (DA) of 0.14/°, and Figure of merit (FoM) of 36.22. The result of our enhanced numerical analysis indicates that the performance of a multilayer BP is enhanced when compared to a conventional gas sensor. As a result, using a SiO₂ prism to sense different gases at a wavelength of 633nm, the suggested gas sensor may be more advantageous. Moreover, the maximum sensitivity of 374.31/RIU is obtained with a remarkable DA of 0.11° and FoM of 37.63/RIU to detect NO₂ gas sensing to maintain the $R_{\text{min}}$value. The gas sensor performance is high at different refractive indices for gas analyte (1–1.07). The performance of the proposed gas sensor is superior to that of the existing gas sensors.

Temperature modulation has been proved to be an efficient technique for improving the selectivity and stability of gas sensors. In this paper, a new signal processing approach is proposed for metal oxide gas sensor signals under the modulation of its operating temperature, which combined a novel global feature extraction method based on the Hilbert–Huang Transform with a pattern recognition method based on neural network. By using the empirical mode decomposition method, the dynamic signals are decomposed into the intrinsic modes that coexist in the sensor system, and a better understanding of the nature of the gas sensing response information contained in the sensor response signals is approached. The method is demonstrated by an application in the identification and quantification of gas mixtures containing three flammable species using a micro gas sensor. The three gas analytes are methane (CH₄), ethanol (C₂H₆O) and carbon monoxide (CO). And the relative average quantification errors for the three gases are about 7%, 8% and 12%, respectively.

A silver-loaded one-dimensional (1D) vertical ZnO nanowires (NWs) array synthesized by a facile seed mediated hydrothermal-RF magnetron sputtering method has been investigated for the fabrication of a highly stable and reproducible acetylene (C₂H₂) gas sensor. Successful immobilization of silver nanoparticles (NPs) as a sensitizer on the ZnO NWs array significantly enhanced the C₂H₂ sensing properties and showed a stable sensing performance. The grown structure exhibited high response magnitude (30.8 at 1000ppm), short response time (43s) and excellent selectivity at 220${}^{\circ }$C. The enhanced performance can probably be accounted for the effect of combining the highly orientated ZnO NWs and catalytically active silver-based network. The superior sensing features toward C₂H₂ along with broad detection range (1–1000ppm), outstanding stability and excellent reproducibility indicate that the sensor is a promising candidate for practical applications.

The gas nanosensor of indium oxide nanowires in laser assisted approach, doped with tin and zinc for gas sensing and 1D growth purposes respectively, was reported. The nanowires were very sensitive to H₂S gas in low concentration of 20ppb gas at room temperature. The fast dynamic intensive and sensitive response to gas was in a few seconds with an on/off sensitivity ratio of around 10. The square cross-section indium oxide nanowires were fabricated through physical vapor deposition (PVD) mechanism and annealing approach. The field emission scanning electron microscopy (FESEM) observations indicated that the annealing temperature was vital in nanostructures’ morphology. The fabricated nanowires for the optimized annealing temperature in applied growth technique were around 60nm in diameter.

In this study, GO and GO-PEDOT:PSS nanocomposite films were prepared by using the modified Hummer method and spin-coating, respectively. GO-PEDOT:PSS films with different weight ratios of GO (0.015, 0.03, 0.045 and 0.06) were prepared to study the effect of the GO additive on nitrogen dioxide (NO₂) sensing performance. XRD and AFM were used to determine the crystal structure and the topography of the GO-PEDOT:PSS films. The effects of GO concentration and temperature on electrical conductivity and the change in activation energy of PEDOT:PSS films were also investigated. The findings show that as the temperature rises, the electrical resistance reduces, and as the concentration increases, the activation energy decreases.

In this work, palladium nanoparticles (Pd NPs) are synthesized by laser ablation in liquid (PLAL) with wavelength 532nm (second harmonic Nd:YAG laser) at different laser energies 360, 660, and 800mJ with 200 pulses and an electric coil is used to generate a magnetic field. The resulting nanosolution was deposited on the previously prepared PS. The morphological and structural properties of the prepared substrates (Pd NPs/PS) are calculated by X-ray diffraction (XRD) pattern, Atomic Force Microscope (AFM), and Transmission Electron Microscopy (TEM). Their results showed that with the increase in the energy of laser pulse, the average particle size was 30.73, 22.60, and 18.01nm. Optical properties of Photoluminescence (PL) spectra show decrease of energy band gap at 2.38, 2.43, and 2.47eV with an increase in the energy. The sensitivity of application samples Pd NPs/PS/Si gas sensors for NO₂ and H₂S gas was also investigated with respect to temperature variations. Pd NPs/PS/Si gas sensors have a maximum sensitivity of NO₂ gas around 52.6% at $25^{\circ }$C for sample prepared at energy 360mJ but the highest sensitivity of H₂S gas was 31.2% at $25^{\circ }$C for energy of 660mJ. The effects of the operating temperature on reaction and recovery durations for various laser ablation energies are also discussed.