Nitric Oxide Gas Sensor Research Articles

Adsorption of NO on ZnO monolayer doped with transition metal (Ti, V, Cr, Mn, Co, and Zr): The first-principles study

Nitric oxide (NO) is a harmful gas produced by fuel combustion in the petrochemical industry. In this paper, the gas sensitivity of NO molecule on ZnO monolayer (ZnO-ML) doped with transition metal (TM = Ti, V, Cr, Mn, Co, and Zr) is systematically investigated by the first-principles calculation. The results show that the adsorption mode of NO molecule on the doped system (TM-ZnO-ML) changes from physisorption to chemisorption, and adsorption energies range from −1.59 eV to −3.12 eV, which are 8–16 times the origin adsorption energy (−0.19 eV) on the pristine ZnO-ML. Meanwhile, the charge transfer between NO molecule and substrates increases by 4–13 times compared with the pristine ZnO-ML. Furthermore, under the applied electric field of −0.4 V/Å, the charges transferred from V-ZnO-ML to the NO increase to 0.54 e. All of the results reveal the broad application prospect of TM-ZnO-ML in NO gas sensors.

Gold Nanoparticle Sensitized Zinc Oxide Nanorods-Based Nitric Oxide Gas Sensors with High Sensitivity, Selectivity and Low Detection Limit

Development of a low-cost hand-held nitric oxide (NO) sensor with high selectivity, sensitivity and low detection limit is attractive for environment and health monitoring applications. NO gas sensor was fabricated using hydrothermally grown ZnO nanorods (ZnO NRs). The sensing performance like sensor response, sensitivity, detection limit has been improved significantly by attaching gold nanoparticles (Au NPs) with ZnO NRs. Au NPs were synthesized by chemical reduction method from gold chloride trihydrate. The attachment of Au NPs on nanorods was done by spin coating method. The maximum sensor response and sensitivity were obtained at [Formula: see text]C operating temperature with [Formula: see text]l gold loading. The interference study of the sensor was carried out with acetone, ammonia, carbon monoxide, hydrogen peroxide and propanol. It demonstrated high selectivity towards the interfering gases and high humid condition. Au-decorated ZnO NRs exhibited very low detection limit [Formula: see text][Formula: see text]ppb, which is attractive for biomedical applications.

Performance improvement of MOCVD grown ZnGa2O4 based NO gas sensors using plasma surface treatment

Gas sensors are essential devices in various industrial and environmental monitoring applications. Nitric oxide (NO) is a harmful gas that is produced in various combustion processes and is associated with air pollution and respiratory diseases. Zinc gallate (ZnGa2O4) has shown promising results as a material for NO gas sensing applications. Previously, the performance of NO gas sensors based on ZnGa2O4 epilayers was not substantial. However, there is potential for further improvement by optimizing their surface properties. Plasma surface treatment has been widely utilized to modify the surface characteristics of materials, including semiconductors, for various applications. We have investigated the impact of plasma surface treatment on the performance of metal–organic chemical vapor deposition grown ZnGa2O4 based NO gas sensors in this work. An inductive coupled plasma reactive ion etching was used to apply Ar plasma to successfully optimize the sensing response of the ZnGa2O4 based gas sensor for NO gas. The sensor response for ZnGa2O4-based NO gas sensors is 159.5%, which is enhanced by 8 times and reached 1276.1% under 5 ppm NO gas concentration after 10 min Ar plasma treatment. The limit of detection is found to be 2.4 ppb. These results demonstrate that Ar plasma treatment significantly improved the ZnGa2O4-based NO gas sensor’s response. The cross-selectivity of this sensor is tested among NO, CO2, CO, and SO2 gases, which indicated that ZnGa2O4 gas sensor possess highly selectivity towards NO gas. This study provides valuable insights into the surface modification techniques for enhancing the performance of gas sensors, which can have a significant impact on the development of advanced sensing technologies for environmental and industrial applications.

Growth and Characterization of Sputtered ZnO:ZnGa2O4 Dual-Phase Films on Sapphire Substrates for NO Gas-Sensing Applications

Nitric oxide (NO) released from combustion facilities and automobiles adversely affects the respiratory systems and environment. Hence, the development of a NO gas sensor with high sensing response to measure NO gas levels is significantly commendable. Herein, we report the growth of ZnO:ZnGa2O4 dual-phase films on the c-plane sapphire substrates using radio-frequency magnetron sputtering for NO gas sensors. The microstructures and morphology of ZnO:ZnGa2O4 films were systematically investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy. The XRD patterns revealed the polycrystalline nature of the ZnO:ZnGa2O4 film with (222) preferred orientation. The SEM micrographs showed the presence of grain boundaries in the nanostructures over the surface of the film due to the recrystallization of grains upon annealing the film at 700 °C. This ZnO:ZnGa2O4 film was employed to fabricate the NO gas sensor, which demonstrates significantly high sensor response of 28.6 at 400 °C operating temperature with the quick response time of 8 s and recovery time of 140 s upon exposure to 100 ppm NO gas concentration. The ZnO:ZnGa2O4-based gas sensor is found to be highly selective for NO gas among NO, CO2, and SO2 gases. The gas-sensing mechanism behind the high response of ZnGa2O4-based NO gas sensors is described. The results achieved in this study are particularly important in terms of the development of technologies for the early detection of poisonous and hazardous gases from polluting industries and metropolises, which is crucial for environmental security.

Ultrasensitive nitric oxide gas sensors based on Ti-doped ZnO nanofilms prepared by RF magnetron sputtering system

It is aimed to explore the advantages of titanium doping and magnetron sputtering as opposed to chemical-based methods on the surficial and electrical characteristics of ZnO films and their gas sensing performance in particular. RF magnetron sputtering was employed to synthesize a pure ZnO nanofilm as a reference and Ti-doped ZnO nanofilms with various Ti contents. The doping process was done by sputtering Ti-doped ZnO targets developed through solid-state reaction, and doping content was determined by EDS analysis. All nanofilms exhibited pure hexagonal wurtzite structure and relatively flat and homogenous surfaces with a clear distribution of nanoparticles in the Ti-doped samples. The observed enhancement in the properties of the nanofilms was reflected in the ultimate performance of the gas sensor. In this regard, the sensor with 1 wt% Ti content showed the best gas sensing performance with an ultra-sensitivity of 1.72 for 1 ppm and 0.9 for 1 ppb NO gas at a relatively low working temperature of 167 °C. The sensor also acquired outstanding stability, quick responsivity, reproducibility and superior selectivity required for NO monitoring.

Synthesis and Application of Doped Metal-Organic Framework (MOF) Nanomaterials

In recent years, MOF has been widely studied as new material. Due to its structure’s diversity, flexibility, and tunability, it is favoured by many scholars and has been used in many fields. However, due to the diversity of MOF types and the wide range of applications, there is a lack of systematic description of the application of MOF materials at present. This paper concluded several aspects of the application of MOF to close this loophole. In this paper, the preparation method including the gas-phase method, hydrothermal method, and liquid-phase epitaxy method of the MOF is introduced, then followed by the method of bringing metal nanoparticles into the prepared frame to make the doped MOF including the impregnation method and double solvent method, and then by adsorption, catalysis, and gas sensor, three aspects are briefly introduced MOF in these fields of application are introduced in these areas in different refining branch such as carbon monoxide adsorption, catalytic hydrogenation, and alkanes as nitric oxide gas sensor. Meanwhile, the challenges for this kind of material are long-term stability, heat resistance, and high cost. This paper is expected to summarize the application of MOF and hope it can bring more economic benefits and scientific value.

Gas detection and recovery characteristics at room temperature observed in a Zr3N4-based memristor sensor array

One of the major challenges with a nitric oxide (NO) gas sensor is the development of a facile and robust room temperature gas sensor for fast recovery and high response in an NO ambient, especially below ppb-level. In order to detect an NO gas in ppb-level, a Zr3N4 based gasistor with very sensitive conducting filaments was investigated. The proposed gasistor showed a high response of 25.8 for the NO of 500 ppb, a fast recovery within 1.6 μs in a pulse mode, and a measurement limit of 37 ppb for NO gas at 21°C. In addition, in the NO, O2, and C2H6 mixture gas test, we observed the feasibility of the selective detection of NO gas of the proposed gasistor. Therefore, we believe that the proposed gasistor has huge potential for NO gas sensing, which will revolutionize in the NO gas-sensor industries.

Structure Effect on the Response of ZnGa2O4 Gas Sensor for Nitric Oxide Applications.

We fabricated a gas sensor with a wide-bandgap ZnGa2O4 (ZGO) epilayer grown on a sapphire substrate by metalorganic chemical vapor deposition. The ZGO presented (111), (222) and (333) phases demonstrated by an X-ray diffraction system. The related material characteristics were also measured by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. This ZGO gas sensor was used to detect nitric oxide (NO) in the parts-per-billion range. In this study, the structure effect on the response of the NO gas sensor was studied by altering the sensor dimensions. Two approaches were adopted to prove the dimension effect on the sensing mechanism. In the first approach, the sensing area of the sensors was kept constant while both channel length (L) and width (W) were varied with designed dimensions (L × W) of 60 × 200, 80 × 150, and 120 ×100 μm2. In the second, the dimensions of the sensing area were altered (60, 40, and 20 μm) with W kept constant. The performance of the sensors was studied with varying gas concentrations in the range of 500 ppb~10 ppm. The sensor with dimensions of 20 × 200 μm2 exhibited a high response of 11.647 in 10 ppm, and 1.05 in 10 ppb for NO gas. The sensor with a longer width and shorter channel length exhibited the best response. The sensing mechanism was provided to explain the above phenomena. Furthermore, the reaction between NO and the sensor surface was simulated by O exposure of the ZGO surface in air and calculated by first principles.

Negative Effects of Annealed Seed Layer on the Performance of ZnO-Nanorods Based Nitric Oxide Gas Sensor.

Nitric oxide (NO) is a toxic gas, which is dangerous for human health and causes many respiratory infections, poisoning, and lung damage. In this work, we have successfully grown ZnO nanorod film on annealed ZnO seed layer in different ambient temperatures, and the morphology of the nanorods sensing layer that affects the gas sensing response to nitric oxide (NO) gas were investigated. To acknowledge the effect of annealing treatment, the devices were fabricated with annealed seed layers in air and argon ambient at 300 °C and 500 °C for 1 h. To simulate a vertical device structure, a silver nanowire electrode covered in ZnO nanorod film was placed onto the hydrothermal grown ZnO nanorod film. We found that annealing treatment changes the seed layer’s grain size and defect concentration and is responsible for this phenomenon. The I–V and gas sensing characteristics were dependent on the oxygen defects concentration and porosity of nanorods to react with the target gas. The resulting as-deposited ZnO seed layer shows better sensing response than that annealed in an air and argon environment due to the nanorod morphology and variation in oxygen defect concentration. At room temperature, the devices show good sensing response to NO concentration of 10 ppb and up to 100 ppb. Shortly, these results can be beneficial in the NO breath detection for patients with chronic inflammatory airway disease, such as asthma.

Flexible NO gas sensor fabricated using graphene/silver nanoparticles stacked electrode structures

The study presents micro- and nano-structures forming a flexible gas sensor based on combinative coating and ultrashort-pulse laser techniques in graphene/silver nanoparticles (G-Ag) thin film electrodes on polyimide (PI) substrate. The prepared silver nanoparticles (AgNPs) revealed the nano-microstructures retain the characteristics of graphene (G). The irregularly distributed AgNPs were deposited on the surface of G sheets, promoting the formation of stacked porous structures with high specific surface area between the AgNPs and G sheets. Under temperature-assisted control, G-Ag composite structures with high sensitivity (response) and selectivity increase gas detection of nitric oxide (NO). This is due to the high adsorption capacity and stability of AgNPs for NO gas molecules, and therefore G-Ag thin film on flexible substrate is a potential sensor for gas detection.

In Situ TiO2-rGO Nanocomposite for Low Concentration NO Gas Sensor

A novel room temperature-based Nitric Oxide (NO) gas sensor of TiO2-rGO composite nanofibers was prepared using electrospinning and solvothermal synthesis. The composite’s physicochemical properties were investigated using various analytical methods such as SEM, TEM, EDS, XRD, Raman spectroscopy, and XPS. When the composite was exposed to the NO gas sensor, it exhibits an excellent gas sensing property at room temperature (30 °C). This composite sensor sensitivity is 7.1 when exposed to 2.75 ppm of NO gas, with a 440 s response time. The possible gas sensing mechanism of TiO2-rGO was also proposed. This study demonstrates that TiO2-rGO composite nanofibers have capability application possibilities in gas sensing, thereby imparting another perspective to create and develop sensors.

Characteristics of highly sensitive and selective nitric oxide gas sensors using defect-functionalized single-walled carbon nanotubes at room temperature

One of the most important trends in modern medicine is the development of non-invasive methods that diagnose diseases by analyzing specific gases from human exhalation. Examination of such gases helps monitor various diseases. The ability of nanosensors to potentially detect conditions such as Rhinitis digestive diseases, liver transplant rejection, inflammation in the stomach, cystic fibrosis, encephalopathy, helicobacter pylon digestive cancer, respiratory diseases, and COVID-19, by examining nitric oxide (NO), has been discussed as well as studied increasingly in recent years. In this paper, we have proposed a low-cost detector that can measure NO gas from the exhaled air, which is applied to the ppb level at room temperature. A sensor that detects NO gas with high sensitivity by using single-walled carbon nanotubes (SWNTs) as nanomaterials, has been fabricated. The semiconductor-type gas sensors using SWNTs showed characteristics such as rapid detection, long-term reliability, reproducibility, and miniaturization at room temperature. To improve the selectivity for NO gas, SWNT network channels were formed between the Au electrodes, and SWNTs were functionalized with en-APTAS. A new rinse process was introduced to solve the problem of low sensitivity in SWNT-based NO sensors. With the introduction of the improved rinsing process, the recovery of the fabricated sensor increased from less than 20% to 90.34% when the device was rinsed ten times under optimized conditions. The improved rinsing process effectively straightened the rearrangement of the large amount of amine-functionalized SWNTs attached during the electrostatic self-assembled deposition. In addition, a 28.64% response for a 100 ppb concentration of NO gas was measured at room temperature. We also confirmed that the fabricated sensor does not react with carbon monoxide (CO) and volatile organic compounds (VOCs) gases owing to its high selectivity to NO gas.

Sensing performance of gas sensors fabricated from controllably grown ZnO-based nanorods on seed layers

ZnO nanorods (NRs) grown on different ZnO seed layers deposited at various Ar–O2 ambient conditions, and the morphologies of the seed layers that affect their response to nitric oxide (NO) gas were investigated. The sensing performance of the devices fabricated with the seed layers deposited under an O2-rich condition tends to deteriorate. We believe that the surface roughness, grain size, and defect concentration of the seed layer are responsible for this phenomenon. Despite the response to the gas was found to be less dependent on NR length, the gas sensing response is significantly dependent on the oxygen vacancy concentration and the exposure of the NR structure to the NO gas ambient surface. Excellent gas response (57.5% at 1 ppm and 7.1% at 100 ppb of NO gas) was achieved at room temperature—superior to the response presented by other proposed methods. This study not only proposes the potential of ZnO-NRs for high-performance NO gas sensor devices but also offers a simple and low-cost method to optimize the response without using any catalyst and additional treatment.

Feedback-controlled photolytic gas phase nitric oxide delivery from S-nitrosothiol-doped silicone rubber films

Constant therapeutic gas phase nitric oxide (NO) delivery is achieved from S-nitrosothiol (RSNO) type NO donor doped silicone rubber films using feedback-controlled photolysis. For photo-release of the NO gas, the intensity of the LED light source is controlled via a PID (proportional–integral–derivative) controller implemented on a microcontroller. The NO concentration within the emitted gas phase is monitored continuously with a commercial amperometric NO gas sensor. NO release was accurately adjustable up to 10 ppm across a broad range of setpoints with response times of roughly 1 min or less. When NO is generated into an air recipient stream, lower NO yields and a comparable level of toxic nitrogen dioxide (NO2) formation is observed. However, NO gas generated into an N2 recipient gas stream can be blended into pure O2 with very low NO2 formation. Following scale-up, this technology could be used for point-of-care gas phase NO generation as an alternative for currently used gas cylinder technology for treatment of health conditions where inhaled NO is beneficial, such as pulmonary hypertension, hypoxemia, and cystic fibrosis.

Ultrasensitive NO Gas Sensor Based on the Graphene Oxide-Coated Long-Period Fiber Grating.

An ultrasensitive nitric oxide (NO) gas sensor based on the graphene oxide (GO)-coated long-period fiber grating (LPFG) was constructed successfully because of its excellent sensitivity to the surrounding refractive index (SRI) change. The surface morphology and structure of GO coated on LPFG were characterized by the scanning electron microscope (SEM), scanning probe microscope (SPM), and Raman spectroscopy, respectively. The adsorption principle of NO molecules by GO was calculated in detail by density functional theory (DFT) and further characterized by Fourier transform infrared spectrometry (FT-TR) and X-ray photoelectron spectroscopy (XPS). Our studies demonstrate that the adsorption principle of NO molecules by GO was the combined effect of physical adsorption and chemical adsorption because of the formation of C-N bonds between GO and NO and the oxidization of NO to NO2. The NO sensor exhibits excellent sensing performance in the NO concentration range of 0 to 400 ppm.

Low operating temperature NO gas sensors based hydrogen peroxide treated GaN nanorods

Abstract In recent days, surface treatment strategies have employed to enhance the active sites for chemisorption of gas molecules in gas sensors. In this work, the simple and effective hydrogen peroxide (H2O2) treatment is used to enhance the active sites on the surface of gallium nitride (GaN) nanorods (NRs) for nitric oxide (NO) gas detection. The surface treatment was carried out by immersing the GaN NRs into a hydrogen peroxide (H2O2) solution at different temperatures for 10 min. The X-ray photoelectron spectroscopy (XPS) is used to find the physicochemical properties of GaN NRs. XPS studies revealed that the active sites (O2 species) on GaN NRs were increased by H2O2 treatment. NO gas sensing measurements revealed that response of the H2O2 treated GaN NRs enhanced by 4-times than that of pristine GaN NRs to 100 ppm of NO gas concentration at 50 °C. Further, H2O2 treated GaN NRs exhibited high response under UV illuminations (λ = 382 nm, P = 1.45 mW/cm2) compared to dark conditions. Under UV illumination, the H2O2 treated GaN NRs generated a large amount of electron-hole pairs, indicating additional defect states on the surface of GaN NRs induced by the H2O2 treatment and these are accountable for the high NO gas response.

ZnO/Si nanowires heterojunction array-based nitric oxide (NO) gas sensor with noise-limited detectivity approaching 10 ppb

We report a ZnO/Silicon nanowire (ZnO/Si NWs) heterojunction array-based NO gas sensor operating at room temperature with an extremely high response (noise limited response ∼10 ppb). The sensor shows very high selectivity towards NO gas sensing and limited perturbation in response due to the presence of moisture. The sensor has been fabricated by using cost-effective chemical processing that is compatible with wafer-level processing. The vertically aligned Si NWs array has been made by an electroless etching method and the ZnO nanostructure was made by chemical solution deposition and spin-coating. Extensive cross-sectional electron microscopy and composition analysis by line EDS allowed us to make a physical model. The electrical characteristic of the model was to fit the I–V data before and after exposure to gas and essential changes in electrical parameters were obtained. This was then explained based on a proposal for the mechanism of gas sensing. We observe that the heterostructure leads to a synergetic effect where the sensing response is more than the sum total of the individual components, namely the ZnO and the Si NWs. The response is much enhanced in the p-n junction when the n-ZnO nanostructure interfaces with p-Si NW compared to that in the n-n junction formed by ZnO on n-Si NW.

Highly sensitive nitric oxide gas sensor based on ZnO-nanorods vertical resistor operated at room temperature

We successfully demonstrated a simple and low-cost nitric oxide (NO) gas sensor to deliver parts-per-billion (ppb) regime detection at room temperature operation. A vertical-channel ZnO nanorods resistor is fabricated by putting silver nanowire electrode onto the hydrothermal ZnO nanorods film. With suitable process condition, the nanorods film exhibits a uniform morphology to enable the formation of gas-permeable nanowire top electrode while also the nanorods provide good surface-to-volume ratio to deliver strong reaction with NO gas. A detection limit to 10 ppb NO is observed while the sensing dynamic range from 10 ppb to 100 ppb is obtained. The sensor is reversible and the real-time sensing response is within 30 s. The results benefit the NO breath detection for patients with chronic inflammatory airway disease, such as asthma.

High Sensitivity of NO Gas Sensors Based on Novel Ag-Doped ZnO Nanoflowers Enhanced with a UV Light-Emitting Diode.

An ultraviolet-enhanced (UV-enhanced) nitric oxide (NO) sensor based on silver-doped zinc oxide (ZnO) nanoflowers is developed using a low-cost hydrothermal method. The results indicate that silver (Ag) ions were doped into the ZnO nanostructure successfully, thus changing the morphology. In the high-resolution transmission electron microscopy images, we also found that some Ag ions were separated out onto the surface of the ZnO nanoflowers and that the Ag-doped and Ag nanoparticles improved the sensing property. The NO sensing property increased from 73.91 to 89.04% through the use of a UV light-emitting diode (UV-LED). The response time was approximately 120 s without the UV-LED, and the UV-enhanced Ag-doped ZnO nanoflower sensor exhibited a reduced response time (60 s). The best working temperature could be reduced from 200 to 150 °C using UV light illumination, and it was found that the NO response increased by 15.13% at 150 °C. The UV photoresponse of the Ag-doped ZnO nanoflowers and the mechanisms by which the improvement of NO sensing property occurred through the use of UV light illumination are discussed. The property of the gas sensor can be calibrated using a self-photoelectric effect under UV light illumination. These interesting UV-enhanced Ag-doped ZnO nanoflowers are viable candidates for practical applications.

Functionalized Carbon Nanotube Sensors for the Detection of Sub-ppm Nitric Oxide Gas

In this paper, we demonstrate the highly sensitive carbon nanotube (CNT) sensors for the detection of sub-ppm nitric oxide (NO) gas operating at room temperature. Such achievement can be realized by functionalizing CNT thin films with amine-based polymers through a solution-process technology at low temperature. In addition to high sensitivity, functionalized CNT sensors exhibit high selectivity towards NO gas, which is an effective and practical factor for health-care monitoring nano-electronics. We also investigated the effect of a post-cleaning treatment on the sensing performance of functionalized CNT thin films for sub-ppm NO gas sensors. We believe that this work can open-up new routes to realize high performance human-interactive electronics for respiratory diseases detection in exhaled air.