NO2 Gas Sensor Research Articles

Two-dimensional Janus B2P6 as potential gas sensors for NO and NO2 detection: A first-principles study

The adsorption properties of novel Janus B2P6 nanosheet with NO and NO2 on both sides are researched by DFT calculation. The results show that the (001) surface exhibits moderate adsorption energies of −0.38 eV for NO and −0.42 eV for NO2. It is found that the electronic properties of Janus B2P6 are affected obviously by NO2 adsorption on the (001) surface, where the bandgap energy is decreased by 1.14 eV and the magnetic moment of 0.93 μB is induced, indicating Janus B2P6 exhibits better sensitivity to NO2. Note that the recovery times of NO and NO2 are found to be 2.4 and 11.0 μs, facilitating the reuse of devices. And a large diffusion energy barrier is found to ensure the stable transmission of signal. Moreover, under biaxial strain of −2%, the adsorption energy of NO on the (001) surface is greatly reduced to −0.24 eV, favoring the desorption of gas molecules. Verifiably, the combined variation of the electrostatic potential difference and the bonding environment leads to differences in the adsorption behavior. These findings demonstrate the potential of Janus B2P6 as ultra-sensitive strain gas sensors.

Bioinspired supramolecular arrayed heterojunction-based room-temperature sensor for high-performance gas detection

Nitrogen dioxide (NO2) has been severely polluting the atmosphere and deteriorating human beings’ sustainable lives. Therefore, development of gas sensors for high-selectivity and high-sensitivity detection of NO2 has been attracting increasing attention. The state-of-the-art inorganic NO2 gas sensors require harsh fabrication conditions or toxic materials, making the devices intrinsically eco-unfriendly. Furthermore, in most cases the sensors work at high temperatures. These disadvantages severely impede their practical applications. Herein, we report a room-temperature and highly-integrated NO2 sensor composed of p-type self-assembled peptide fibrillar nanoforests (SPNFs) scaffolded with n-type SnO2 nanoparticles (NPs) heterojunctions. The p-n conformations provide efficient access to target gases and allow reliable electron transformations, while the SPNFs afford a large specific surface area and multiporous structures for gas adsorption and SnO2 NPs dispersion, resulting in an ultrahigh selectivity for NO2 detection. Especially, the sensing performance can be optimized by modulating the thickness and density of the SPNFs, showing a high response, short response and recovery times, along with a low detection limitation. Our strategy demonstrates the development of a bioinspired platform by utilizing peptide self-assemblies to fabricate integrated sensors for polluting gas detections.

Polymer-Based Thermally Stable Chemiresistive Sensor for Real-Time Monitoring of NO2 Gas Emission.

We present a thermally stable, mechanically compliant, and sensitive polymer-based NO2 gas sensor design. Interconnected nanoscale morphology driven from spinodal decomposition between conjugated polymers tethered with polar side chains and thermally stable matrix polymers offers judicious design of NO2-sensitive and thermally tolerant thin films. The resulting chemiresitive sensors exhibit stable NO2 sensing even at 170 °C over 6 h. Controlling the density of polar side chains along conjugated polymer backbone enables optimal design for coupling high NO2 sensitivity, selectivity, and thermal stability of polymer sensors. Lastly, thermally stable films are used to implement chemiresistive sensors onto flexible and heat-resistant substrates and demonstrate a reliable gas sensing response even after 500 bending cycles at 170 °C. Such unprecedented sensor performance as well as environmental stability are promising for real-time monitoring of gas emission from vehicles and industrial chemical processes.

ZnO/GaN n-n heterojunction porous nanosheets for ppb-level NO2 gas sensors

The development of NO2 gas sensors with lower operating temperature and good thermal stability is always a challenge to solve. In this work, 2D loose porous ZnO/GaN heterogeneous nanosheets were synthesized by ultrasonic mixing, in which ZnO nanosheets and GaN nanoparticles were prepared by hydrothermal method and solid-state pyrolysis, respectively. BET characterization result showed that the specific surface area of loose porous ZnO nanosheets was 57.24 m2/g, and XPS tests proved that the formation of heterogeneous interface between ZnO and GaN can effectively increase the number of negative oxygen ion species on the surface. Noticeably, 15 mol % ZnO/GaN composites (Ga:Zn) exhibited the highest response of 134.5–2 ppm of NO2 at 125 °C and lower limit of detection of 20 ppb. Furthermore, it showed outstanding selectivity, repeatability and long-term stability. The excellent gas-sensing properties can be attributed to the loose porous structure of ZnO and the formation of n-n heterojunction between ZnO and GaN. The gas-sensing mechanism of ZnO/GaN composites to NO2 was also discussed in detail.

Interfacial oxygen vacancies and energy-level engineering on CeO2-PPy-rGO nanocomposites towards boosted NO2 sensor performance

Monitoring of harmful nitrogen dioxide (NO2) gases is imperative for our health and environmental protection. The room-temperature operating NO2 gas sensors still suffer a limited sensitivity and slow response/recovery rate. In this work, novel CeO2-PPy-rGO nanocomposites were synthesized for improved NO2 sensing performance. The decoration of rGO introduced additional oxygen vacancies on CeO2 for enhancing the sensor response. PPy acted as a buffer layer of energy level connecting CeO2 and rGO components and promoted the response and recovery rate. The designed sensor demonstrated ppb-level NO2 detection in p-type sensing behaviors with rapid response/recovery characteristics as expected at room temperature (RT). The hybrid sensor also showed excellent selectivity, long-term stability and extremely low detection limit toward NO2. The significantly enhanced sensing properties to NO2 could be attributed to activity enhancement, a gently gradient energy level and π-π stacking between rGO and PPy. This study offers a perspective on the design of CeO2-based gas sensors for NO2 detection at RT.

Pt nanoparticle-functionalized Fe2(MoO4)3 hollow microspheres for parts-per-billion NO2 sensors operated at 80 °C

Conductometric NO2 sensors with easy preparation, low operating temperature, ultralow limits of detection, high response, and long-term stability are highly required. In pursuing this concept, the Pt nanoparticle-functionalized Fe2(MoO4)3 hollow microsphere sensors were designed based on the synergistic effect of noble metal additives and a non-agglomerated hierarchical structure. Herein, a promising NO2 gas sensor with high sensitivity at 80 °C and good long-term stability was designed and prepared by a modified facile impregnation method, which is free of reductants, surfactants, and stabilizers. The 5 wt% Pt functionalized Fe2(MoO4)3 shows superior sensing performance over pristine Fe2(MoO4)3, including a 100 °C decrease in optimal operating temperature, 19 times increase in gas response, and realized an ultralow parts-per-billion level detection of limit, as well as good selectivity and reproducibility. The synergistic effect was validated by comparing the sensing performance with Pt-decorated non-agglomerated hollow microspheres and agglomerated nanoparticles.

Simple synthesis of hydrangea-like CuO structure constructed by porous nanosheets for rapid detection of NO2 at low temperature

It is of great significance to develop gas sensors with fast and high response under low energy consumption for practical monitoring of harmful gases in industrial production and environment. In this work, hydrangea-like CuO material constructed by porous nanosheets with a specific surface area of 42.45 m2 · g−1 was synthesized by a simple one-step solution method without the addition of surfactant. It has good sensing performance to 10 ppm NO2 (S = 133.6) and short response time (4 s) at near room temperature (50 ℃), which is significantly superior to most CuO based NO2 gas sensors reported so far. The good gas sensing properties may be attributed to the synergistic effect of large specific surface area and two-dimensional porous structure. Therefore, hydrangea-like CuO may become a popular sensitive material capable of rapid detection of NO2, and the synthesis method of this material can also meet large-scale production.

Thickness dependent p-n switching in SnSe2/SnOx/SnSe heterojunction-based NO2 gas sensor as well as photodetector

SnSe2/SnOx/SnSe heterojunction thin films with different thicknesses 137, 241 and 297 nm were fabricated via the thermal evaporation technique. XRD, FESEM, Raman spectroscopy, XPS, and U–V visible spectroscopy were used to study the structural, morphological, chemical, and optical properties of the deposited thin films, which revealed that the heterojunction thin films had a microcrystalline structure and a mixed SnSe2, SnSe, SnO, and SnO2 phases. Only the sample with the lower thickness (137 nm) exhibited the p-n type behaviour when concentration (1–5 ppm) and temperature (RT-75 °C) increased. Furthermore, the SnSe2/SnOx/SnSe heterojunction thin-film gas sensor demonstrated good NO2 detecting selectivity. The development of SnSe2/SnOx/SnSe p–n junctions at the thin-film surface may be responsible for the improved NO2-sensing capability of the constructed gas sensor at low operating temperatures. For five ppm NO2, the device response was 151% at RT. Response/recovery times were 134/494 s, respectively. The estimated detection limit (LOD) was 515 ppb. NO2 gas had a higher response than SO2, NO, H2S, CO, H2, C2H5OH, and NH3. The mechanism of concentration, temperature-dependent p–n switching, selective detection of NO2 at RT, and complete response and recovery have been deliberated based on physisorption and charge transfer. The lower thickness (137 nm) sample exhibits good photo response in visible light with power (32 mW). It has good responsivity, detectivity and external quantum efficiency. This research will give 2D materials a new dimension of selective gas sensors and photodetection at room temperature.

Influence of DC Magnetron Sputtering Power on Structural, Topography, and Gas Sensor Properties of Nb2O5/Si Thin Films.

This study focuses on synthesizing Niobium pentoxide (Nb2O5) thin films on silicon wafers and quartz substrates using DC reactive magnetron sputtering for NO2 gas sensors. The films undergo annealing in ambient air at 800 °C for 1 hr. Various characterization techniques, including X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDS), Hall effect measurements, and sensitivity measurements, are employed to evaluate the structural, morphological, electrical, and sensing properties of the Nb2O5 thin films. XRD analysis confirms the polycrystalline nature and hexagonal crystal structure of Nb2O5. The optical band gap values of the Nb2O5 thin films demonstrate a decrease from 4.74 to 3.73 eV as the sputtering power is increased from 25 to 75 W. AFM images illustrate a progressive increase in particle size ranging from (41.86) to (45.56) nm, with varying sputtering power between 25 and 75 W. Additionally, EDS analysis validates the rise in Nb content, increasing from 12.2 at. % to 20.1 at. %, corresponding to the increase in sputtering power. Hall effect measurements show that all films exhibit n-type charge carriers, and increasing sputtering power leads to decreased carrier concentration and enhanced mobility. The gas sensor's sensitivity, response, and recovery time were evaluated at various operating temperatures. The NO2 sensor exhibited an optimal sensitivity of 28.6% at 200 °C when the sputtering power was set to 50 W.

Adsorption and Sensing of NO2, SO2, and NH3 on a Janus MoSeTe Monolayer Decorated with Transition Metals (Fe, Co, and Ni): A First-Principles Study.

This paper reports the adsorption of toxic gases (NO2, SO2, and NH3) on a MoSeTe structure based on first principles. It was found that the gas (NO2, SO2, and NH3) adsorption on a pure MoSeTe monolayer was weak; however, the adsorption performance of these gas molecules on transition-metal-atom-supported MoSeTe monolayers (TM-MoSeTe) was better than that on pure MoSeTe monolayers. In addition, there was more charge transfer between gas molecules and TM-MoSeTe. By comparing the adsorption energy and charge transfer values, the trend of adsorption energy and charge transfer in the adsorption of NO2 and SO2 was determined to be Fe-MoSeTe > Co-MoSeTe > Ni-MoSeTe. For the adsorption of NH3, the effect trend was as follows: Co-MoSeTe > Ni-MoSeTe > Fe-MoSeTe. Finally, by comparing their response times, the better gas sensor was selected. The Ni-MoSeTe system is suitable for NO2 gas sensors, and the Fe-MoSeTe and Co-MoSeTe systems are suitable for SO2 gas sensors. The Fe-MoSeTe, Co-MoSeTe, and Ni-MoSeTe systems are all suitable for NH3 gas sensors. Janus transition-metal dichalcogenides have the potential to be used as gas-sensing and scavenging materials.

NO2 Adsorption Sensitivity Adjustment of As/Sb Lateral Heterojunctions through Strain: First Principles Calculations

Strain engineering is an effective way to adjust the sensing properties of two-dimensional materials. In this paper, lateral heterojunctions (LHSs) based on arsenic and antimony have been designed along the armchair (AC) or zigzag (ZZ) edges. The adsorption and sensing characteristics of As/Sb LHSs to NO2 before and after applying different types of strain are calculated by first principles. The band gaps of all As/Sb heterostructures are contributed by As-p and Sb-p orbitals. In addition, the adsorption energy of As/Sb ZZ-LHS with −4% compression strain is the largest. Furthermore, its work function changes significantly before and after the adsorption of NO2. Meanwhile, strong orbital hybridizations near the Fermi level are observed and a new state is yielded after applying compressive strain. These results indicate that the As/Sb LHS with ZZ interface under −4% compression strain possesses the best sensing properties to NO2. This work lays the foundation for the fabrication of high-performance NO2 gas sensors. High-performance gas sensors can be used to track and regulate NO2 exposure and emission, as well as to track NO2 concentrations in the atmosphere and support the assessment of air quality.

NO Gas Sensor Based on Ti-Doped ZnO Thin Films Prepared by SILAR Method

In this study, Ti-doped ZnO films with flower-rod-like nanostructures were synthesized by the SILAR method for enhanced NO gas sensing applications. The stoichiometric ratio of Ti in the host ZnO lattice was confirmed by atomic absorption and energy-dispersive X-ray spectroscopies. All the synthesized films exhibited a pure wurtzite hexagonal structure that seemed to deteriorate at high Ti doping contents as it was manifested by the measured X-ray diffraction patterns. Scanning electron microscopy images of ZnO revealed the coexistence of porous flower- and rod-like structures, and became finer, denser and more compact with Ti doping. By UV-Vis measurements, the transmittance of the synthesized pure ZnO thin film in the visible region (~75%) increased by about 10% with Ti doping, and the energy bandgap seemed to decrease up to a some limit of Ti content. Among the fabricated sensors (based on pure ZnO, 1% Ti-doped, 3% Ti-doped and 5% Ti-doped ZnO films), the best sensing performance was observed for the 1% Ti-doped ZnO film. At first, this was associated with its high density of oxygen vacancies present on the surface of the film and ionized oxygen vacancies present in the ZnO lattice (confirmed respectively by X-ray photoelectron and photoluminescence spectroscopies). Nonetheless, this may be also due to its increased crystallinity (confirmed by X-ray diffraction and photoluminescence spectroscopy), high area-to-volume ratio (confirmed by scanning electron microscopy images), high specific surface area (confirmed by Brunauer-Emmett-Teller measurements) as well as high mobility and carrier concentration (confirmed by Hall measurements). The sensor was highly selective to NO gas and showed notable stability as well as very short response and recovery times which makes it eligible for the early detection of any indoor or outdoor NO gas leakages. Keywords : SILAR, Ti-doped ZnO, Structural properties, Optical properties, Electrical properties, Gas sensor. Acknowledgement This research was supported by the research grant 021220FD2201 “Development of highly sensitive MOS based nano-film gas sensors” from Nazarbayev University. Figure 1

HEXAGONAL HONEYCOMB PL-GaN NANOSHEET AS ADSORBENT SURFACE FOR GAS MOLECULES SENSING: A QUANTUM CHEMICAL STUDY

Regarding two-dimensional (2D) nanomaterials as gas sensors, we have studied the adsorption of gas molecules (NH3, NO2, NO) on the graphitic GaN sheet (PL-GaN) using density functional theory calculations. “Langmuir” adsorption of gas molecules of NH3, NO2, and NO on the graphitic GaN sheet has been accomplished using density functional theory. The changes in charge density have shown a more important charge transfer on the hexagonal honeycomb nanosheet of gallium nitride (GaN) which acts as the electron acceptor while gas molecules act as the stronger electron donors through adsorption on the graphitic-like GaN surface. The adsorption of NH3, NO[Formula: see text] and NO, respectively, on GaN nanosheet has more contribution with high expansion curves of hydrogen, nitrogen and oxygen. The results extracted from PDOS curves after optimization show the electron transferring from nitrogen and oxygen of gas molecules (adsorbate/donor) towards gallium in the active site of GaN surface (adsorbent/acceptor). GaN nanosheet represents enough capability for adsorbing gases of NH3, NO2, and NO through charge transfer from nitrogen and oxygen atoms to the gallium atom regarding the intra-atomic and interatomic interactions. Concerning the change of physicochemical properties of the PL-GaN sheet before and after molecule adsorption, the PL-GaN nanosheet can be applied as an appropriate selective gas sensor for NH3, NO2 and NO detection.

Confinement of 1D Chain and 2D Layered CuI Modules in K-INA-R Frameworks via Coordination Assembly: Structure Regulation and Semiconductivity Tuning.

Herein, we present a new series of CuI-based hybrid materials with tunable structures and semiconducting properties. The CuI inorganic modules can be tailored into a one-dimensional (1D) chain and two-dimensional (2D) layer and confined/stabilized in coordination frameworks of potassium isonicotinic acid (HINA) and its derivatives (HINA-R, R = OH, NO2, and COOH). The resulting CuI-based hybrid materials exhibit interesting semiconducting behaviors associated with the dimensionality of the inorganic module; for instance, the structures containing the 2D-CuI module demonstrate significantly enhanced photoconductivity with a maximum increase of five orders of magnitude compared to that of the structures containing the 1D-CuI module. They also represent the first CuI-bearing hybrid chemiresistive gas sensors for NO2 with boosted sensing performance and sensitivity at multiple orders of magnitude over that of the pristine CuI. Particularly, the sensing ability of CuI-K-INA containing both 1D- and 2D-CuI modules is comparable to those of the best NO2 chemiresistors reported thus far.

Fast-response/recovery In2O3 thin-film transistor-type NO2 gas sensor with floating-gate at low temperature

Metal-oxide (MOX)-based gas sensors have various advantages such as high response, fast sensing dynamics, and ease of fabrication. However, MOX-based gas sensors require high temperature for gas response and recovery, which requires large power consumption. Therefore, low-temperature operation in the MOX-based gas sensor is an important feature in terms of power-efficiency. In this work, In2O3 thin film transistor (TFT)-type NO2 gas sensor with floating-gate (FG) is fabricated, which is capable of fast response and recovery at low temperature (75 ℃). The sensor is designed to enable modulating its gas sensing properties by engineering the quantity of charge stored in FG. Specifically, the response characteristics of the sensor are significantly improved at 75 ℃ by operating the sensor in erase state. Furthermore, to quickly recover the sensor, pulsed bias recovery method is proposed. By applying pulsed negative bias to the gate electrode, NO2- molecules adsorbed to In2O3 sensing layer are desorbed quickly. Therefore, the sensor is recovered rapidly within a second even at 75 ℃. The proposed methods enhance the gas sensing properties including the response and recovery at low temperature, significantly improving the power-efficiency in MOX-based TFT-type gas sensor.

Chemiresistive room temperature NO2 sensor based on nitrogen doped zinc oxide nanowires

The prevalence of nitrogen dioxide (NO2) in the atmosphere is causing a steady increase in air pollution. As such, there is an urgent need to create a sensitive and energy-efficient NO2 gas sensor to ensure environmental and health safety. In this study, we explore the effectiveness of nitrogen-doped zinc oxide nanowires in detecting harmful NO2 gas. Through the hydrothermal method, we synthesized zinc oxide (NW-0) and nitrogen-doped zinc oxide nanowire sensors (NW-1, NW-2 & NW-4). The introduction of nitrogen induced changes in both the crystallite size and nanowire density in ZnO. Additionally, an increase in oxygen vacancy concentration was observed with nitrogen doping. At room temperature, the NW-2 sensor exhibited exceptional NO2 sensing performance (response of 110) compared to NW-0 sensor (response of 1.9) for 10 ppm of gas. The NW-2 sensor also demonstrated a rapid response/recovery time of 50 s/5 s for a 10 ppm NO2 concentration. Moreover, the sensor showed stability over an extended period, minimal response variation with changes in relative humidity, and selectivity towards NO2 over other gases. Complementing the experimental findings, density functional theory (DFT) calculations were employed to estimate the adsorption energies of NO2 on the sensor surface.

Metal doping fabricated heterobimetallic nickel-zinc composites and its performance-enhancing sensitivity towards nitrogen dioxide

Monitoring and detecting poisonous nitrogen dioxide (NO2) is greatly challenged by ambiguous knowledge about the sensing mechanism and structures of sensitive materials and reaction intermediates. In particular, synthetic strategies like doping and coupling, although do improve gas-sensing activity, have made the structural identification rather difficult. In the work, we have comprehensively examined nickel-doped zinc oxide (marked as ZON) and its material-coupled composites (ZON/Y) for sensing NO2 by density functional theory. The material (Y) varies from graphitic carbon nitride (CN), graphene (Gr) to cellulose (Cel). It is revealed that the metal doping greatly promotes the NO2 adsorption over the material coupling. This well reproduces the experimental findings that the Ni-doped ZnO has much faster response time than ZnO, ZnO/g-C3N4 and ZnO/graphene. Of all the studied SMs, ZON/CN exhibits superior NO2 gas-sensing performance. Along the reaction pathway, it gives NO2 adsorption free energy of − 0.860 eV, followed by the mildest uphill process of catching the second NO2 (0.320 eV) and the modest downhill process of forming nitrate (−0.680 eV). The large adsorption energy of the initial step is attributed to the fabricated heterobimetallic Ni-Zn sensing active sites. The better sensitivity of ZON/CN is further evidenced by analyses of structures and interfacial bondings.

Ocimum sanctum Leaf Extract-Assisted Green Synthesis of Pd-Doped CuO Nanoparticles for Highly Sensitive and Selective NO2 Gas Sensors.

In view of facile, cost-effective, and environmentally friendly synthetic methods, palladium-doped copper oxide (Pd-CuO) nanoparticles have been synthesized from Ocimum sanctum (commonly known as "Tulsi") phytoextract for gas-sensing applications. The structural, morphological, and compositional properties of Pd-doped CuO nanoparticles were studied using various techniques such as XRD, FESEM, XPS, and EDX. The characterization results confirmed the doping of Pd on CuO nanoparticles, and Pd-CuO nanostructures appear as nanoflakes in FESEM analysis. The gas-sensing response of Pd (1.12 wt %)-CuO nanoflake-based sensor was measured at 5-100 ppm concentration of different gases, NO2, H2S, NH3, and H2, at 125 °C. Gas-sensing tests reveal that the sensitivity of the sensor were 81.7 and 38.9% for 100 and 5 ppm concentrations of NO2, respectively, which was significantly greater than that of pure CuO. The response and recovery times of the sensor were 72 and 98 s for 100 ppm of NO2 gas, while they were 90 and 50 s for 5 ppm NO2. The calculated limit of detection (LOD) value of the sensor is 0.8235. This appealing LOD is suitable for real-time gas detection. The gas sensor was found to exhibit excellent selectivity toward NO2 gas and repeatability and stability in humid (80%) conditions. The Pd doping in CuO nanostructures plays a significant role in escalating the sensitivity and selectivity of CuO-based NO2 gas sensor suitable to work at low operating temperatures.

Experimental realization of Au:TiO2 via magnetic field-assisted laser ablated on porous silicon for H2S and NO2 gas sensors applications

Experimental realization of Au:TiO2 via magnetic field-assisted laser ablated on porous silicon for H2S and NO2 gas sensors applications

A study of the optical and structural properties of the PbS films that affect the sensitivity of the NO2 gas sensor

A study of the optical and structural properties of the PbS films that affect the sensitivity of the NO2 gas sensor