NO2 Gas Sensor Research Articles

Development and Performance of ZnO/MoS2 Gas Sensors for NO2 Monitoring and Protection in Library Environments

The presence of harmful oxidizing gases accelerates the oxidation of cellulose fibers in paper, resulting in reduced strength and fading ink. Therefore, the development of highly sensitive NO2 gas sensors for monitoring and protecting books holds significant practical value. In this manuscript, ZnO/MoS2 composites were synthesized using sodium molybdate and thiourea as raw materials through a hydrothermal method. The morphology and microstructure were characterized by X-ray diffraction analysis (XRD), energy dispersive spectroscopy (EDS), field emission scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The ZnO/MoS2 composite exhibited a flower-like structure, with ZnO nanoparticles uniformly attached to the surface of MoS2, demonstrating advantages such as high specific surface area and good uniformity. The gas sensitivity of the ZnO/MoS2 nanocomposites reached its peak at 260 °C, with a sensitivity value around 3.5, which represents an improvement compared to pure ZnO, while also enhancing sensitivity. The resistance of the ZnO/MoS2 gas sensor remained relatively stable in air, exhibiting short response times during transitions between air and NO2 environments while consistently returning to a stable state. In addition to increasing adsorption capacity and improving light utilization efficiency, the formation of hetero-junctions at the ZnO-MoS2 interface creates an internal electric field that effectively promotes the rapid separation of photo-generated charge carriers within ZnO, thereby extending carrier lifetime.

Carborazine doped nanographene (CBNG) sheet as a promising NO2 gas sensor: A theoretician’s approach

Nanographenes (NGs) are a distinct section of graphene in which the dangling bonds are saturated with hydrogen atoms (C42H18). This confinement in size results in unique properties and potential applications. The density functional theory (DFT) is used to investigate the reactivity and electronic sensitivity of a model carborazine (B2C2N2) ring doped nanographene (CBNG) for detecting NO2 gas. In CBNG/NO2 complex, one oxygen atom of the NO2 molecule is positioned at a distance of 2.93Ả from the center of the B2C2N2 ring, with an adsorption energy −6.2 kcal/mol. The adsorption energy of NO2 on CBNG is apparently larger than those of other gas molecules, which fall between the suitable range of strong physical adsorption and weak chemical adsorption. Upon NO2 adsorption, the band gap of CBNG sheet reaches 62.4 %. The outcome of the present study may be exploited in the industry, particularly in the synthesis of effective NO2 gas sensors.

A room-temperature NO2 gas sensor based on Zn2+ doped Cu2O/CuO composites with ultra-high response

A room-temperature NO2 gas sensor based on Zn2+ doped Cu2O/CuO composites with ultra-high response

Flexible and highly selective NO2 gas sensor based on direct-ink-writing of eco-friendly graphene oxide for smart wearable application

Nitrogen dioxide (NO2) is a major cause of respiratory disorders in outdoor and indoor environments. Real-time NO2 monitoring using nonintrusive wearable devices can save lives and provide valuable health data. This study reports a room-temperature, wearable, and flexible smart NO2 gas sensor fabricated via cost-effective printing technology on a polyimide substrate. The sensor uses alkali lignin with edge-oxidised graphene oxide (EGO-AL) ink, demonstrating a sensitivity of 1.70% ppm⁻1 and a detection limit of 12.70 ppb, with excellent selectivity towards NO2. The high sensing properties are attributed to labile oxygen functional groups from GO and alkali lignin, offering abundant interacting sites for NO2 adsorption and electron transfer. The sensor fully recovers to the baseline after heat treatment at 150 °C, indicating its reusability. Integration into lab coats showcased its wearable application, utilising a flexible printed circuit board to wirelessly alert the wearer via cell phone to harmful NO2 levels (>3 ppm) in the environment. This smart sensing application underscores the potential for practical, real-time air quality monitoring, personal safety enhancement, and health management.

Insights into the Effects of Co-doping on the Electronic Properties of Armchair Graphene Nanoribbon-based NO2 Gas Sensors

Insights into the Effects of Co-doping on the Electronic Properties of Armchair Graphene Nanoribbon-based NO2 Gas Sensors

Synthesis and Characterization of TiO2 Nanotubes for High-Performance Gas Sensor Applications

In this study, we investigated the fabrication, properties, and sensing applications of TiO2 nanotubes. A pure titanium metal sheet was used to demonstrate how titanium dioxide nanotubes can be used for gas-sensing applications through the electrochemical anodization method. Subsequently, X-ray diffraction indicated the crystallization of the titanium dioxide layer. Scanning electron microscopy and transmission electron microscopy then revealed the average diameter of the TiO2 nanotubes to be approximately 100 nm, with tube lengths ranging between 3 and 9 µm and the thickness of the nanotube walls being about 25 nm. This type of TiO2 nanotube was found to be suitable for NO2 gas sensor applications. With an oxidation time of 15 min, its detection of NO2 gas showed a good result at 250 °C, especially when exposed to a NO2 gas flow of 100 ppm, where a maximum NO2 gas response of 96% was obtained. The NO2 sensors based on the TiO2 nanotube arrays all exhibited a high level of stability, good reproducibility, and high sensitivity.

Enhanced NO2 Gas Sensing in Nanocrystalline MoS2 via Swift Heavy Ion Irradiation: An Experimental and DFT Study.

Nanostructured transition metal dichalcogenides (TMDs) like MoS2 hold promise for gas sensing applications due to their exceptional properties. However, limitations exist in maximizing sensor performance, such as limited active sites for gas interaction and sluggish response/recovery times. This study explores swift heavy ion (SHI) irradiation as a strategy to address these challenges in MoS2-based NO2 gas sensors. MoS2 nanoflakes were fabricated and subsequently irradiated with 120 MeV silver (Ag) ions to induce structural and morphological modifications. Characterization techniques confirmed the formation of Mo and S vacancies within the MoS2 lattice due to irradiation. Significantly, SHI irradiation resulted in a remarkable enhancement of approximately 3 times improvement in sensing response compared to pristine MoS2 sensors. Additionally, the irradiated sensors exhibit substantial improvements in both response and recovery times for NO2 detection. SHI irradiation resulted in the formation of self-affine nanostructures and increased grain fragmentation as fluence rises. This enhanced surface area is hypothesized to promote gas-sensor response. To gain deeper insights into the underlying mechanism, first-principles calculations were employed. These calculations suggest that electron transfer occurs from the MoS2 surface to the NO2 molecule during interaction. Furthermore, the irradiation-induced vacancies facilitate stronger NO2 adsorption on the MoS2 surface compared to the pristine sample. This work demonstrates the effectiveness of SHI irradiation in engineering defects within MoS2 nanoflakes, leading to significantly improved NO2 gas-sensing performance. This approach offers a promising avenue for developing next-generation TMD-based gas sensors with enhanced sensitivity, response times, and stability.

Highly responsive gas sensors based on grain boundary–rich polycrystalline few-layer MoS2 films for NO2 detection

Abstract This study addresses the issues of insufficient sensitivity and poor reversibility for NO2 detection by successfully fabricating a sensor based on uniform and high-quality few-layer MoS2 polycrystalline material using chemical vapor deposition. This approach aims to improve the response of the sensor by exploiting the abundance of grain boundary (GB) defects in polycrystalline MoS2 membranes. Comprehensive surface morphology analysis of the few-layer MoS2 polycrystalline films was conducted using microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy to characterize their chemical composition and properties. Subsequently, evaluation of 1–100-ppm NO2 was conducted at room temperature (25°C). The results show excellent performance of the sensor, with a response range of 11–82.24. Notably, under ultraviolet excitation at room temperature, this sensor exhibits a response time of only 41 s to 50 ppm of NO2 with complete recovery and improved sensitivity, maintaining reliable stability over eight weeks. Furthermore, the findings reveal that the sensor demonstrates high selectivity toward NO2 gas with limit of detection and limit of qualification values of 10 and 34 ppb, respectively. Owing to the abundant adsorption sites provided by GB defects in polycrystalline thin films, the response performance of the sensor is effectively enhanced. This study provides valuable insights into the future design and development of high-performance NO2 gas sensors.

Spectroscopic, structural characterization, along with DFT calculation, of a new cadmium(II) acetato meso-arylporphyrin: Theoretical study on NO2, CO2, N2, NO2, and SO2 gas-sensing and analysis of electrical conductance and dielectric properties

The paper presents a combined experimental and computational investigation of the cadmium(II) (acetato)‑meso-tetra(para-methoxyphenyl)porphyrin ion complex [Cd(TMPP)(OAc)]- (complex 1), which was prepared by the reaction of [Cd(TMPP)] with an excess of NaOAc and crysptand-222 in chloroform. This new Cd(II) meso‑arylporphyrin was characterized by elementary analysis and UV–Vis, IR, and 1H NMR spectroscopic techniques along with single crystal X-ray diffraction. This later study shows that the Cd2+center ion adopts a distorted square pyramidal geometry and is coordinated by the four nitrogens of the TMPP porphyrinate and the oxygen atom of the acetato axial ligand. The intermolecular interactions in the crystal lattice of [Cd(TMPP)(OAc)]-, determined using the PLATON program and Hirshfeld surfaces analysis, are of types O__H…O, C__H…H, C__H…Cl, C__H…Cg and C__Cl…Cg (Cg is the centroid of a phenyl or a pyrrole ring) involving the [Cd(TMPP)(OAc)]- ion complex, the [Na(crypt-222)]+ counterion, and the chloroform and water molecules found in the crystal lattice of complex 1. Using DFT calculations at the DFT/B3LYP-D3/lanL2DZ level of theory HOMO–LUMO orbitals of 1 and several global reactive parameters of this compound were calculated. The 3D-MEP plots of [Cd(TMPP)(OAc)]- were also determined. This theoretical study includes the sensing properties of complex 1 and the NO2, CO2, N2, and SO2 gas molecules. Furthermore, experimental tests have been carried out concerning the impedance and dielectric spectroscopy of the InGa/[Cd(TMPP)(OAc)]/InGa device.

N-n type In2O3@-WO3 heterojunction nanowires: enhanced NO2 gas sensing characteristics for environmental monitoring.

Solvothermal synthesis of 1D n-In2O3@n-WO3 heterojunction nanowires (HNWs) and their NO2 gas sensing characteristics arereported. The n-In2O3@n-WO3 HNWs have been well-characterised using XRD, Raman spectroscopy, XPS, SEM and HRTEManalyses. The NO2 sensing performance of n-In2O3@n-WO3 HNWs showed superior performance compared withpristine WO3 NWs. Due to the distinctive configuration of WO3-In2O3 heterojunctions, the n-In2O3@n-WO3 HNWs demonstrated remarkable sensitivity reaching 182% in response towards 500ppb of NO2 gas at operating temperature of 200°Cwhich is nearly 3.5 times greater than the response observed with pristine WO3 (50%). Moreover, the n-In2O3@n-WO3 HNWs also exhibited fast response (8-13s)/recovery (54-62s) time characteristics. A plausible sensing mechanism has been discussed. The enhancement in sensor characteristics shows that n-In2O3@n-WO3 HNWs could serve as a promising material for high-performance NO2 gas sensors for real-time environmentalmonitoringapplications. This work could provide new understandings of the sensing mechanism of n-In2O3@n-WO3-based heterojunction nanowires, which can be applied to the design of novel n-n type MOS heterojunction materials for the application of low-temperature real-time high-performance NO2 sensors.

Humidity-independent NO2 gas sensors based on ZnO-NiOFx nanocomposites and the synergistic humidity-immune effect of fluorine doped NiO

Clean, alternative energy sources, especially fuel cells, are gradually attracting global attentions while the produced toxic nitrogen dioxide (NO2) is a greatly hazardous chemical impacting their energy efficiencies. Metal oxide semiconductors (MOS) hold significant promise as NO2 sensors. However, intensive humidity interaction intensifies signal drifts and reliable response inhibitions under variable humidity conditions. In this study, we present a novel approach to address this issue by engineering in-situ F-doped NiO nanocomposites (NiOFx) decorated on ZnO snowflakes achieved through decomposition modulation of ZnOHF precursors. The optimized NO2 sensor demonstrates unparalleled humidity-independence across a wide operating temperature range with prime sensitivity, low detection limit and rapid response/recovery. Matrix algorithm is also implemented in highly precise NO2 identification under complicated atmospheric and humid conditions. Mechanism studies based on temperature programmed desorption (TPD), quasi in-situ X-ray photoelectron spectroscopy (Quasi in-situ XPS) reveal that F− dopants facilitate interfacial electron transferring and inhibit oxygen activity. In-situ diffuse reflectance infrared Fourier transform spectroscopy (In-situ DRIFTS) demonstrates that hygroscopic NiO and electronegative F− synergistically obstruct hydroxyl adsorptions on sensing materials. The innovative approach offers a promising solution for enhancing moisture resistance of MOS sensors for real-time NO2 concentration monitoring in fuel cells and provides valuable insights into anti-humidity mechanisms.

Theoretical insights of 2D Fe3GeTe2/In2Se3 multiferroic vdW heterostructure based gas sensors for high-performance NO detecting

The impact of the harmful gas NO on the atmospheric environment cannot be ignored, so it is necessary to develop efficient gas sensors to detect and absorb NO at room temperature. In this work, we systematically explored the electron transport properties and gas sensing properties of Fe3GeTe2, In2Se3 monolayers and its multiferroic van der Waals (vdW) heterostructures of Fe3GeTe2/In2Se3 for detecting NO by using density functional theory and nonequilibrium Green's function methods. The calculated adsorption energies, electron localisation functions, band structures and density of states indicate that its a chemisorption for the adsorption of NO on Fe3GeTe2 and a physisorption on In2Se3, while the specific adsorption style is highly dependent on the stacking and molecular adsorption sites of different Fe3GeTe2/In2Se3 structures. In addition, the pristine Fe3GeTe2 monolayer and Fe3GeTe2/In2Se3 based nanodevices realized a significant anisotropy for electron transport along the zigzag and armchair directions, and their anisotropic maximum current ratios in the zigzag to armchair directions were 1.90 and 1.89. Meanwhile, the NO sensitivity ratio of Fe3GeTe2 and Fe3GeTe2/In2Se3 based gas sensors can be up to 79 % and 107 %, respectively. This highlights a notably superior gas-sensitive performance of the Fe3GeTe2/In2Se3 heterostructure compared to the Fe3GeTe2 monolayer gas devices. These findings provide valuable references for the application of multiferroic heterostructures in the field of gas sensors.

TiO2@ZrO2 p-n heterostructured nanocomposites for enhanced NO2 gas sensing

Hydrothermal approach was used to synthesize pure TiO2, ZrO2 and 2.5–10 % TiO2-ZrO2 p-n type nanocomposite heterojunctions. Morphological and structural features of heterostructures were established by XRD, TEM/HRTEM and SEM investigations. Band gap energy calculations revealed a reduction in band structure from 4.96 eV of pure ZrO2 to 3.50 eV of 7.5 % TiO2-ZrO2 heterostructures. BET surface area characterization displayed large surface area of the nanocomposites which performed an essential part in the enhanced sensing activity of the nanocomposite heterostructures. 7.5 % TiO2-ZrO2 sensor exhibited enhanced response to NO2 gas possessing excellent response and recovery times. The maximum sensitivity of 991 was shown by 7.5 % TiO2-ZrO2 sensor to 100 ppm NO2 gas that was nearly four folds compared to pristine ZrO2 nanospheres (263). The improved NO2 gas sensing of the nanocomposites was stemmed to the construction of p-n heterostructures that resulted in the emancipation of more reactive sites and thus led to the better sensing result of the nanocomposites. The gas sensing mechanism and improved sensing characteristics have been also elaborated. The strategy thus suggested in this report may offer considerably to the understanding of more sensitive NO2 gas sensors.

Ultra-thin V2O5 nanowires: synthesis and gas sensing characteristics

This study presents the synthesis of vanadium oxide nanowires via a simple hydrothermal method and explores their potential as high-performance sensors for monitoring harmful gases, with a particular focus on NO2. The microstructure and morphology of the nanowires were characterized using scanning electron microscopy, powder x-ray diffraction, and Raman spectroscopy. The vanadium oxide nanowire material demonstrates outstanding NO2 gas sensing capabilities, detecting 5 ppm with a rapid response and high sensitivity at an optimal working temperature of 150 °C. It exhibits a relative resistance change of 70%, showcasing a sub-ppm detection limit. The V2O5 nanowires exhibited good stability and high gas selectivity for NO2 over other interfering gases (H2S, NH3, C2H4, and CO). The ultrathin structure of the nanowires holds promise for practical applications in developing NO2 gas sensors. The study sheds light on the superior sensitivity of the V2O5 gas sensor toward NO2 at low temperatures, emphasizing the influence of the 1D structure on the sensing mechanism.

A Janus WSi2P2As2 monolayer: A promising material for detecting NO2 with excellent sensitivity, selectivity, reversibility, and humidity resistance

Realizing highly sensitive, selective, humidity-resistant, and reversible detection of hazardous gas molecules with low detection limit in the air environment at room temperature is essential. Herein, we predict a novel two-dimensional Janus WSi2P2As2 material and propose a NO2 gas sensor with excellent response, selectivity, humidity resistance, and reversibility based on WSi2P2As2, by employing density functional theory, statistical thermodynamic modeling, and the non-equilibrium Green’s function approach. The Janus WSi2P2As2 monolayer is a stable semiconductor with a direct band gap of 0.85 eV and an intrinsic out-of-plane dipole moment. We study the sensing properties of the Janus WSi2P2As2 monolayer towards several typical toxic gases (NO, NO2, NH3, SO2, and H2S). All the gas molecules are physically adsorbed on the surface. Different adsorption energies and electronic structures are found for the top- and bottom-surface adsorptions due to the intrinsic dipole of the Janus WSi2P2As2. The experimental viability is characterized by the adsorption density and the recovery time. The statistical estimation of the adsorption density shows that the oxide gases can be adsorbed practically even at ultra-low concentration of part per billion (ppb) at room temperature. The rapid natural desorption of these toxic gases at 300 K indicates the recyclability of the WSi2P2As2 material. Furthermore, we evaluate the sensing performance of the WSi2P2As2-based gas sensor by the conductance change. The sensor exhibits ultra-response of 374 % and excellent selectivity towards NO2 molecules. Importantly, the sensor remains operating with high performance in the humid environment and air environment. These results demonstrate that the Janus WSi2P2As2 is a promising gas-sensing material for the NO2 detection.

Study on highly selective NO2 gas sensors based on (Fe, Mo)-doped monolayer WSe2

The two-dimensional (2D) material WSe2 is frequently employed in gas sensors due to its excellent electrical properties. However, the weak interaction between the pristine WSe2 and gas molecules limits its application. Therefore, in this paper, the adsorption behavior of transition metal X (X = Fe, Mo) atom-doped monolayers WSe2 on H and O atoms and molecules of NO2, HCN, and CO gases is investigated to gain insights into the physical mechanisms of adsorbent-substrate interactions. Doping significantly improves the adsorption properties between the substrate and the gas molecules, with the best adsorption showing for NO2 gas molecules and O atoms. The relationship between transition metals and the improvement of adsorption performance is explored by the center position of transition metal d orbitals in different systems, and it is found that the higher the center position of the transition metal d band, the stronger the adsorption between adsorbent and substrate. Compared to pristine WSe2, Mo atom doping in the transition metal doped system has higher adsorption sensitivity to gas molecules and exhibits highly selective adsorption and chemisorption behaviors through high adsorption energies and electron transfer to NO2 molecules. It is demonstrated that X (X = Fe, Mo) doped WSe2 can be used as a gas-sensitive material for efficient gas detection.

Single ZnO Nanowire for Electrical and Optical NO2 Gas Sensing: Origin of Reversible and Irreversible Gas Effects Investigated by Photoluminescence Spectroscopy.

In this work, the gas sensing properties of a single ZnO nanowire (NW) are investigated, simultaneously in terms of photoluminescence (PL) and photocurrent (PC) response to NO2 gas, with the purpose of giving new insights on the gas sensing mechanism of a single 1D ZnO nanostructure. A single ZnO NW sensing device was fabricated, characterized, and compared with a sample made of bundles of ZnO NWs. UV near-band-edge PL emission spectroscopy was carried out at room temperature and by lowering the temperature down to 77 K, which allows detection of resolved PL peaks related to different excitonic transition regions. Surface effects were observed in PL maps, considering different nano and microstructures. Electrical and optical measurements were acquired at the same time during the NO2 gas exposure, allowing for the comparison of PL and PC response times and signal recovery. During NO2 gas desorption, irreversible behavior in the surface-related and donor-acceptor pair (DAP) regions is interpreted as the effect of an initial transient when electronic transfer from the gas molecules to the bulk occurs through the ZnO NW surface which acts as a channel. To the best of our knowledge, this is the first work which investigates the simultaneous PL optical and PC electrical response signals of a single ZnO NW to gas exposure.

Fabrication of modified Sb2O3 nanospheres for the removal of hazardous malachite green organic pollutant and selective NO2 gas sensor

Sb2O3 and Ni modified Sb2O3 (Ni–Sb2O3) nanospheres were synthesized using low cost co-precipitation method and characterised using various instrumental methods such as X-ray Powder Diffraction (XRD), High Resolution Transmission Electron Microscopy (HR-TEM), Scanning Electron Microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), and Fourier-transform infrared (FT-IR) spectroscopy. The XRD pattern reveals cubic crystal lattice. The average size of Sb2O3 and Ni–Sb2O3 nanoparticles was calculated to be around 41 nm and 29 nm, respectively. The HR-TEM investigation of the Sb2O3 nanomaterial reveals homogeneous spherical balls with a fine dispersion. The random-shaped nanoparticles with porous surfaces and voids were revealed by SEM. EDS examination confirms the elemental composition of Sb (41.79 %) and O (58.21 %) in Sb2O3 and Sb (36.80 %), O (58.95 %), and Ni (4.25 %) in Ni–Sb2O3. Sb2O3 and Ni– Sb2O3 exhibit band gaps of 3.67 eV and 3.51 eV, respectively, according to UV–Vis analysis. The IR peaks 445.47, 642.18, and 745.18 in Sb2O3 and 438.72, 645.07, and 756.92 in Ni– Sb2O3 support the Sb–O bonding in the synthesized nanomaterials. The synthesized nanomaterials have been used for photocatalytic degradation of malachite green (MG) dye and sensing NO2, SO2, CO2, petroleum vapour and LPG gases. The MG dye was degraded 97.67 % in 120 min using Ni–Sb2O3 at optimized conditions (catalyst dose: 0.1 g/L to 0.3 g/L, pH: 7 and MG dye: 10 ppm). The gas sensing study showed that Ni–Sb2O3 sensor has greater sensitivity and selectivity for NO2 gas.

Synthesis and characterization of Fe-doped ZnO films for enhanced NO2 gas-sensing applications

Synthesis and characterization of Fe-doped ZnO films for enhanced NO2 gas-sensing applications

Chemiresistive flexible gas sensor for NO2 sensing at room-temperature using in situ constructed Au@In2S3/In2O3 hybrid microflowers

The construction of a novel Au nanoparticles loaded In2S3/In2O3 hybrid microflowers composite was conducted through a well-designed hydrothermal and partial oxidation method and used for NO2 sensing at room-temperature (RT). The characterization data confirmed the hybrid structures and demonstrated that the ratio of adsorbed oxygen species on the surface increased after partial oxidation. The sensing performance of flexible gas sensors based on In2S3/In2O3, In2O3, AuxIn2S3/In2O3 (x = 0.5, 1 and 2 wt%) were tested and compared at RT. Heterostructure construction and Au NPs loading significantly improved the sensing properties at RT. Peculiarly, the response value of 1 wt% Au NPs loaded In2S3/In2O3 (Au1In2S3/In2O3) sensor for 100 ppm NO2 at RT was 20.7, which was 9.2 times higher than that of In2O3 sensor. Meanwhile, it also possessed excellent selectivity, fast response/recovery time (12/27 s), good repeatability, long-term and mechanical stability. The outstanding sensing performance for NO2 at RT mainly associated to the heterojunction between In2S3 and In2O3 and the catalytic effect of Au NPs. Finally, density functional theory (DFT) was used to calculate and analyze the gas adsorption and charger transfer, which related to the enhanced sensing performance.