Narrow Results

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.

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.

In this paper gas sensing properties of 0.5–3% polyaniline (PAni) doped SnO₂ thin films sensors prepared by chemical route have been studied towards the trace level detection of NO₂ gas. The structural, optical and surface morphological properties of the PAni doped SnO₂ thin films were investigated by performing X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Raman spectroscopy measurements. A good correlation has been identified between the microstructural and gas sensing properties of these prepared sensors. Out of these films, 1% PAni doped SnO₂ sensor showed high sensitivity towards NO₂ gas along with a sensitivity of 3.01 × 10² at 40°C for 10 ppm of gas. On exposure to NO₂ gas, resistance of all sensors increased to a large extent, even greater than three orders of magnitude. These changes in resistance upon removal of NO₂ gas are found to be reversible in nature and the prepared composite film sensors showed good sensitivity with relatively faster response/recovery speeds.

In the present work, we determined the electrical properties of octachlorinated metallophthalocyanines with Co(II) and Cu(II) ions as metal centers. We engaged them in heterojunctions, with lutetium bisphthalocyanine as a partner. Surprisingly, cobalt and copper complexes show opposite behaviors, the first being an $n$-type material whereas the latter is a $p$-type material, as deduced from the response of the heterojunctions towards ammonia; showing the unusual key role played by the metal center. While the LuPc${}_{\mathrm{\text{2}}}$/Cu(Cl${}_{\mathrm{\text{8}}}$Pc) complex exhibits a negative response to ammonia, the LuPc${}_{\mathrm{\text{2}}}$/Co(Cl${}_{\mathrm{\text{8}}}$Pc) complex exhibits a positive response to ammonia, with a sensitivity of 1.47% ppm${}^{\mathrm{\text{-1}}}$ at concentrations lower than 10 ppm and a limit of detection of 250 ppb. All the devices operate at room temperature and in real atmosphere.

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.

The adsorption interactions between ethylene oxide (EO) molecule and pristine and aluminum-doped coronene (Al-coronene) were studied in the presence and absence of perpendicular external electric fields (EFs) with strengths $1.0\times 10^{-2}$, $2.0\times 10^{-2}$ and $3.0\times 10^{-2}$ a.u. using density functional theory (DFT) calculations. The geometry optimizations and adsorption calculations were carried out by employing 6-31$++$G** basis set. The changes in geometric and electronic structures after the adsorption were investigated to characterize the sensitivity of pristine and Al-coronene toward EO molecules. For all the studied systems, adsorption energies ($E_{\mathrm{\text{ads}}})$, band gap energy ($E_g)$, Mulliken charge transfer, molecular electrostatic potential (MEP) and density of electron state (DOS) were calculated and discussed. According to the obtained results, the high impact of the applied EFs on the adsorption characteristics of EO molecules on the pristine and Al-doped coronenes showed that applying EF is a good strategy for enhancing the EO adsorption capability of the pristine and Al-doped coronenes, improving the potential application of coronene-based sensors for detection of EO in trace amounts.

Pure and Eu-doped (1.0, 3.0, 5.0wt.%) $\alpha$-Fe₂O₃ (PFO and EFO) nanotubes and nanowires have been successfully synthesized through the combination of electrospinning and calcination techniques. The structures, morphologies and chemical compositions of the as-obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric and differential scanning calorimetry (TG-DSC) and energy dispersive spectrum (EDS), respectively. To demonstrate the superior gas sensing performance of the doped nanotubes, a contrastive gas sensing study between PFO (EFO) nanotubes and nanowires was performed. It turned out that Eu doping could magnify the impact of morphology on gas sensitivity. Specifically, at the optimum operating temperature of 240${}^{\circ }$C, the response value of PFO nanotubes to 100ppm acetone is slightly higher than that of nanowires (3.59/2.20). EFO (3.0wt.%) nanotubes have a response of 84.05, which is almost 2.7 times as high as that of nanowires (31.54). Moreover, they possess more rapid response/recovery time (11s and 36s, respectively) than nanowires (17s and 40s, respectively). The lowest detection limit for acetone is 0.1ppm and its response is 2.15. In addition, both of EFO nanotubes and nanowires sensors have a good linearity (0.1–500ppm) and favorable selectivity in acetone detection.

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.

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.

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.

The synthesis and characterization of novel asymmetric zinc(II) phthalocyanines (4–9) and their linking through peripheral and nonperipheral positions on the phthalocyanine ring via click coupling to alkyne-functionalized 2,3,6,7,10,11-hexakis(prop-2-ynyloxy)triphenylene core are described for the first time. These phthalocyanines (Pcs) (4–12) were characterized by elemental analysis and different spectroscopic techniques such as UV-vis, ¹H-NMR, FT-IR and mass spectroscopy. Furthermore, the utilization of thin films of novel Pcs as a sensitive layer for detection of lung cancer from exhaled human breath at room temperature under exposure to marker volatile organic compounds (VOCs) are presented. The developed sensors were tested for acetone, ethanol, $n$-hexane, toluene, chloroform and isoprene in a range of 300–14560 ppm. The obtained results have confirmed the possibility of utilization of Pc-based Surface Acoustic Wave (SAW) sensors for medical diagnosis based on exhaled breath analysis.

Over the past decade, functionalization with bimetallic catalysts have been studied owing to their excellent catalytic activities for various reactions, whereas few studies have been performed on cofunctionalization with two different types of metal catalysts despite its simplicity. This study examined the sensing performances of Nb₂O₅ nanorods cofunctionalized with Pd and Au nanoparticles. Pd, Au-cofunctionalized Nb₂O₅ nanorods were prepared by a hydrothermal technique. The Nb₂O₅ nanorods cofunctionalized with Pd and Au nanoparticles showed far stronger response to ethanol gas than the Pd or Au-functionalized counterpart. The origin for the enhanced response of the Pd, Au-cofunctionalized Nb₂O₅ nanorods is discussed.

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.

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.

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.

To enhance the poor sensing capabilities of traditional p-type metal oxide semiconductor sensors, a novel gas sensor was designed with Co₃O₄/CuO heterostructure modified by glutathione (GSH)-reduced gold (Au), which was characterized by different analyses. The experiments showed that the 0.5wt.% Au–Co₃O₄/CuO gas sensor exhibited excellent sensing performance with a response value of up to 28.3 for 3ppm NO₂ at a relatively low operating temperature ($100^{\circ }$C). Besides, it demonstrated a linear relationship between detection concentration and response value, displayed good selectivity for NO₂, showcased stability and exhibited repeatability. Moreover, the sensor revealed the ability to resist humidity at the optimal temperature. Finally, we proposed a gas sensing mechanism to explain the enhanced NO₂ detection performance of the sensor, attributed to the heterojunction structure between Co₃O₄/CuO and the catalytic properties of Au. This led to an increase in adsorbed oxygen, as confirmed by XPS characterization. Therefore, the 0.5wt.% Au–Co₃O₄/CuO ternary nanocomposite gas sensor is deemed to be a highly effective sensing material that can be utilized to detect NO₂ gas in real-life applications.

This paper presents the performance of three different micro-electro mechanical systems (MEMS)-based surface acoustic wave (SAW) devices for sensing hydrogen gas. All three devices, namely, Device 1, Device 2 and Device 3, were constructed with the same dimensions but with varying geometries. The devices were simulated using COMSOL Multiphysics and various analyses such as deflection, electric potential, frequency shift with respect to the concentration of hydrogen gas, total capacitance of interdigital transducers (IDTs) and sensitivity were performed using finite element modeling. The devices were constructed with a lithium-niobate piezoelectric substrate and a ZnO sensing layer. The performance of MEMS-based SAW devices can be improved by doping with nanomaterials. The devices were tested with hydrogen gas at concentration from 10ppm to 100ppm. Owing to the mass loading effect, Device 3 exhibited maximum sensitivity and a close approximation of the simulated results with the theoretical results.