NH3 Gas Sensor Research Articles

Silicon Nanowire-Based Ammonia Gas Sensor with Enhanced Response at Elevated Humidity Levels

Abstract Ammonia (NH3) is a reductive toxic gas, and prolonged exposure can lead to severe health issues. Additionally, elevated Levels of NH3 in exhaled breath can serve as a biomarker for various diseases. Consequently, monitoring NH3 in the air and for medical diagnostics is critical for public health and safety. However, developing NH3 gas sensors that function effectively under high humidity conditions, such as those found in human breath, has proven challenging. In this study, we present a simple and cost-effective NH3 gas sensor based on an interconnected silicon Nanowire (SiNW) structure, fabricated using the metal-assisted chemical etching (MACE) method. The sensing mechanism is attributed to the formation of a hole accumulation layer in the air, whose width decreases upon exposure to NH3. Moreover, the bundling of individual nanowires enhances the sensor’s response time, achieving a rapid response of approximately 70 seconds. Our NH3 sensor demonstrates a response magnitude significantly higher—by an order of magnitude—than that of similar SiNW structures reported in the literature.

Graphene Functionalization by O2, H2, and Ar Plasma Treatments for Improved NH3 Gas Sensing.

Graphene-based materials have gained attention for their promise in various applications owing to their two-dimensional structure. Functionalizing the graphene surface can help realize materials with noble properties. In this study, graphene was functionalized by plasma treatment in O2, H2, and Ar environments, and the effects on the NH3 gas-sensing performance were evaluated. The O2 plasma treatment induced oxidation of the graphene (i.e., graphoxide), while the H2 plasma treatment induced hydrogenation (i.e., graphane). Raman scattering spectroscopy suggested that graphoxide had vacancy-type defects and graphane had sp3-type defects, while Ar-treated graphene had both types of defects. Graphane had the highest sheet resistance followed by graphoxide, Ar-treated graphene, and pristine graphene, which can be attributed to the large bandgap of 3.0 eV for graphane. In contrast, graphoxide had the best NH3 gas-sensing performance, which indicates that NH3 gas interacts more strongly with vacancy-type defects than with sp3-type defects. The results showed that functionalizing the graphene structure generated noble materials with a superior NH3 gas-sensing performance compared with pristine graphene.

Study of Structural, Morphological, Electrical, and Thermal Characteristics of PPy-Fe(ClO4)2 -Au Nanocomposite and its Application in Ammonia Gas Sensing

Objectives: The synthesis of Polypyrrole based nanocomposites using chemical techniques and then characterize using various techniques to study the Structural, morphological, and Thermal characteristics of these materials. The main objective of this research is to fabricate room temperature operative NH3 gas sensor. Methods: Turkevich method is used for the synthesis of gold nanoparticles. These Gold nanoparticles are further employed to form polypyrrole-based nanomaterials using the Chemical oxidative polymerization method. These nanocomposites were comprehensively characterized using SEM, TEM, X-ray Diffraction, FTIR, UV-vis Spectroscopy, and TGA. The two-probe approach was used to measure electrical conductivity. Synthesized PPy-Fe(ClO4)2-Au nanocomposite was then applied to fabricate room temperature operated gas sensor that can detect ammonia (NH3) gas at low ppm levels. Findings: The SEM of the PPy based nanoparticle shows its globular morphology with size in 180-250 nm. XRD shows an amorphous nature with some crystalline formation indicating Au presence. FTIR reveals prominent peaks showing significant bonds of PPy. The UV-visible spectra of pure PPy shows a peak at 349 nm while PPy-Fe(ClO4)2 and PPy-Fe(ClO4)2-Au show additional peak at 541 nm and 421 nm. The I-V characteristic of PPy-Fe(ClO4)2-Au shows enhanced conductivity of 30.58 Scm-1 which is higher than pure PPy. Novelty: A novel dopant Iron(II) per chlorate Fe(ClO4)2, was added to the nanoparticles to synthesize PPy-Fe(ClO4)2-Au nanocomposites. Since most of the sensors worked at some elevated temperature, this paper presents low ppm level NH3 gas sensing at room temperature which is the key step for this research work. Keywords: PPy; AuNPs; Polypyrrole; NH3; PPy-AuNPs-Fe(ClO4)2

Oxygen Vacancy Mediated-Bismuth Molybdate/Graphitic Carbon Nitride Type II Heterojunction Chemiresistor for Efficient NH3 Detection at Room Temperature.

Metal oxide-based chemiresistive gas sensors are expected to play a significant role in assessing human health and evaluating food spoilage. However, the high operating temperature, insufficient limit of detection (LOD), and long response/recovery time restrict their broad application. Herein, 3D Bi2MoO6/2D Eg-C3N4 heterocomposites are developed for advanced NH3 gas sensors with RT operational mode. Utilizing the synergetic engineering of micro-nanostructure, surface oxygen vacancies, and well-defined Type II n-n heterojunctions, BMOCN3 demonstrated superior NH3 sensing properties at 23 °C, including the high response (S = 13.6 at 10 ppm), fast response/recovery speed (8/30 s), excellent selectivity, and low LOD (166 ppb). Based on the experimental, DFT, and MD studies, the improved sensing performance can be ascribed to accelerated charge transfer, superior redox capacity, and improved adsorption/desorption kinetics. Moreover, the practical application in rapid exhaled NH3 biomarker detection of the as-fabricated gas sensor was preliminarily verified. This work highlights that the novel synergetic engineering can effectively modulate the electronic structure and charge transfer, offering a rational solution for room temperature chemiresistive gas sensors.

Achieving High Response of Perovskite-based (MAPbI3) NH3 Gas Sensors Using Binary Mixed Solvent Approaches

Achieving High Response of Perovskite-based (MAPbI3) NH3 Gas Sensors Using Binary Mixed Solvent Approaches

Ultrathin Copper Monosulfide Films for an Optically Semitransparent, Highly Selective Ammonia Chemosensor.

Transition-metal sulfides are emerging as promising materials for chemiresistive gas sensors─a field still dominated by semiconducting metal oxides. Despite the availability of materials with tunable electronic, optical, physical, and chemical properties, few studies have moved beyond synthesis to provide strategies for enhancing gas sensing performance through material modification. Here, we present a simple, scalable synthetic strategy for developing an optically semitransparent, flexible NH3 gas sensor with a highly uniform, ultrathin CuS (covellite) active sensing layer. The optical and chemical properties of the CuS were precisely controlled near the percolation threshold of thin-film formation by varying key experimental parameters such as the Cu film thickness (<10 nm) and the sulfurization time (∼90 s) under ambient conditions. Experimental and computational studies of CuS and its NH3 sensing characteristics identify key physicochemical properties. The controlled surface chemistry and morphology of the ultrathin CuS layer demonstrate its effectiveness in functional NH3 sensing devices, which achieve a calculated detection limit of 1.38 ppm for NH3 gas at 150 °C, along with exceptional mechanical robustness and optical semitransparency in the visible-light spectrum.

Promoted room temperature NH3 gas sensitivity using interstitial Na dopant and structure distortion in Fe0.2Ni0.8WO4.

The demand for gas-sensing operations with lower electrical power and guaranteed sensitivity has increased over the decades due to worsening indoor air pollution. In this report, we develop room-temperature operational NH3 gas-sensing materials, which are activated through electron doping and crystal structure distortion effect in Fe0.2Ni0.8WO4. The base material, synthesized through solid-state synthesis, involves Fe cations substitutionally located at the Ni sites of the NiWO4 crystal structure and shows no gas-sensing response at room temperature. However, doping Na into the interstitial sites of Fe0.2Ni0.8WO4 activates gas adsorption on the surface via electron donation to the cations. Additionally, the hydrothermal method used to achieve a more than 70-fold increase in the surface area of structure-distorted Na-doped Fe0.2Ni0.8WO4 powder significantly enhances gas sensitivity, resulting in a 4-times increase in NH3 gas response (Rg/Ra). Photoluminescence and XPS results indicate negligible oxygen vacancies, demonstrating that cation contributions are crucial for gas-sensing activities in Na-doped Fe0.2Ni0.8WO4. This suggests the potential for modulating gas sensitivity through carrier concentration and crystal structure distortion. These findings can be applied to the development of room-temperature operational gas-sensing materials based on the cations.

High-performance PANI sensor on silicon nanowire arrays for sub-ppb NH3 detection

For industrial production and disease diagnosis, real-time detection of low concentrations of NH3 is crucial, necessitating a gas-sensitive sensor compatible with integrated processes and exhibiting excellent performance. Herein, we employed wet etching and rapid in-situ polymerization on silicon nanowire substrates to grow polyaniline fibers, thereby fabricating NH3 gas sensors with p-p heterojunction and three-dimensional network structures. Characterization and gas sensing performance testing were conducted. The results demonstrate the outstanding NH3 detection capabilities of the sensor, providing stable responses down to concentrations as low as 1 ppb, which indicates its LOD is one to two orders of magnitude lower than current similar products. It also exhibits verified selectivity and long-term reliability. The excellent sensing performance is attributed to the high surface area from the silicon nanowire structure and efficient synergy of p-p heterojunction. Additionally, the influence of doping types of the substrates and annealing process were explored. This work serves as a reference for the design of silicon-based gas sensors with high sensitivity, low detection limits, and extended operational lifetimes, suitable for deployment in commercial integrated monitoring systems.

Preparation and mechanism study of highly sensitive NH3 gas sensor based on Au-modified CdS nanoparticles

A high-performance ammonia (NH3) gas sensor based on Au nanoparticles (AuNPs) modified CdS (Au/CdS) was synthesized by hydrothermal method, and the sensing mechanism of Au/CdS was studied by first-principles based on density functional theory (DFT). Experimental results show that the addition of AuNPs can effectively enhance CdS-based NH3 gas sensor performance. Au/CdS sensor exhibits high response (16580), short response/recovery time (2.25 s/1.25 s), and low limit detection (500 ppb), good repeatability and stability. Because AuNPs can effectively increase the generation of sulfur vacancies on the surface of CdS, increasing the amount of chemisorbed oxygen and providing more active sites for NH3. Furthermore, the good conductivity of AuNPs promotes the separation and transport of carriers on CdS surface, thereby improving the gas sensing performance. DFT calculations indicate that the ionization energy of Au is less than that of Cd, which causes some Cd atoms to lose their coordination with S atoms and increase sulfur vacancies on the surface of CdS. In Au/CdS sensors, sulfur vacancies accelerate the cleavage of NH3, and resulting electrons participate in charge transport, thereby enhancing the adsorption energy. This study introduces a new method for fabricating high performance NH3 sensor based on CdS rich in sulfur vacancies.

Comparison of Gas-sensitive response of three metal-doped GaNNT with Pb, Pd and Pt after adsorption of hazardous gases

In this paper, we comparatively analyze the gas-sensing ability of Pb, Pd and Pt metal-doped GaNNT (M-GaNNT) materials for the hazardous H2S, SO2, NH3 and Cl2 gases. The adsorption structure, adsorption energy (Eads), density of states (DOS), differential charge density and frontier molecular orbital of the M-GaNNT adsorbed hazardous gas have been studied based on the density functional theory (DFT) calculations. The results show that the energy gap of Pb-GaNNT performs the largest change with an increasing percentage change of 358 % after the Cl2 adsorption compared with that before the Cl2 adsorption, while the energy gap of Pt-GaNNT has the least change with an average value of 20.8 %. The doping of metal atoms can effectively improve the gas-sensitivity of M-GaNNT, and the gas-sensitivity follows the order of Pb-GaNNT> Pd-GaNNT> Pt-GaNNT. The potential applications of M-GaNNT in gas sensor and adsorbent are then predicted through the analysis of the adsorption energy, sensitive response (SR) and recovery time (τ). Pb-GaNNT performs the best Cl2 gas removal since the largest Eads (-5.883 eV), largest SR (4.4 × 1015) and largest τ (2.9 × 1087s) can be determined for Cl2 adsorption on Pb-GaNNT. Furthermore, Pb-GaNNT is a good NH3 gas sensor since the related τ is only 2.9 s at 498 K, and a small Eads (-1.232 eV) with large SR (9.7 × 105) can be determined as well. The research findings in this paper provide a new sensor material option for both the detection and the removal of harmful gases, and the systematically theoretical method can spread to other systems.

Portable and Hand-Held Ammonia Gas Sensor Enables Noninvasive Prediagnosis of Helicobacter pylori Infection.

Disease diagnosis of Helicobacter pylori (Hp) through human exhaled breath analysis has attracted considerable attention. However, conventional methods, such as carbon 13 (13C) breath test and infrared spectrometers, are facing the challenge of achieving portability and reliability synchronously. Herein, we report a portable and hand-held Hp analyzer using a bimetallic PtRu@SnO2-based gas sensor for the prediagnosis of Hp infection, which is based on detecting ammonia (NH3) as a potential biomarker in exhaled breath. Owing to the surface functionalization through highly catalytically active bimetallic PtRu nanoparticles (NPs) prepared by a photochemical reduction strategy, the PtRu@SnO2-based sensor exhibits high sensitivity and selectivity toward trace-level (200 ppb) NH3 even at high-humidity surroundings (80% RH). Consequently, the designed portable and hand-held Hp analyzer makes the accurate determination of NH3 at 800 ppb in exhaled breath. The tuning of energy band structure and electrical characteristics and the catalytic modulation of NH3 oxidation by PtRu NPs are proposed to be the reasons behind the enhanced NH3 gas-sensing performance, as confirmed by in situ analysis using an online MKS MultiGas 2030 FTIR gas analyzer. This work paves the way for the prediagnosis of Hp infection using a metal oxide gas sensor.

Detecting low-concentration ammonia with a surface acoustic wave sensor using a silver nanoparticles–graphene–polypyrrole hybrid nanocomposite film

In this study, a surface acoustic wave (SAW) resonator coated with graphene/polypyrrole hybrid nanocomposite films decorated with silver nanoparticles (AgNPs-G/PPy) is proposed for detecting ammonia (NH3) in parts-per-billion concentrations. The AgNPs-G/PPy hybrid nanocomposite film was synthesized via in situ chemical oxidative polymerization. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction were used to characterize the AgNPs-G/PPy hybrid nanocomposite film, confirming its successful synthesis and identifying a wrinkled multilayered structure. The AgNPs-G/PPy hybrid nanocomposite film was spin-coated onto the surface of a stress-compensated temperature-cut quartz SAW resonator having an operating frequency of 98.5 MHz to create an NH3 gas sensor. NH3 adsorption by the AgNPs-G/PPy hybrid nanocomposite film modulated the acoustic wave velocity, and the corresponding frequency shift served as a sensing signal. The synergistic interaction between the three constituent materials (AgNPs, graphene, and polypyrrole) enhanced the sensitivity, selectivity, and response speed of the sensor for NH3 detection. At room temperature, the proposed sensor exhibited a positive frequency shift of 568 Hz when exposed to 50 ppb of NH3 gas and a rapid response time of less than 60 s. In addition, the SAW sensor exhibited excellent selectivity.

Study the Effect of Ion Doping on ZnO Nanostructures for Room Temperature NH3 Gas Sensor

We investigated the impact of doping ion type on the performance of a ZnO-based ammonia gas sensor to show the capability of these ions to achieve high-performance gas sensing at room temperature. A sol-gel method was used to synthesize both doped and undoped ZnO nanostructures, while the gas sensor device was made by casting ZnO onto a glass substrate for a uniform thin film. Then Al electrodes were attached to the film. The characterization was carried out via field-emission scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, UV–vis, Pl luminescence, Brunnauer-Emmett-Teller, I-V characteristic, and gas sensor setup device. PL measurement shows an increase in green emission spectra with Ba ion shifting the peaks from VO to VO+ and VO+ to VO++ states. The gas sensor test at room temperature greatly enhances performance for certain ions. The Ba ions greatly influence gas sensor performance, increasing the response to 24 compared to 5 for undoped ZnO. The room-temperature enhancement achieved by the Ba ions could open the way to investigate more effective dopants for NH3 gas sensors.

Novel development of laser synthesized double orthogonal PSi surface NH3 gas sensors

Novel development of laser synthesized double orthogonal PSi surface NH3 gas sensors

Preparation and characterisation of NH3 gas sensor based on PANI/Fe-doped CeO2 nanocomposite

PANI/Fe-doped CeO2nanocomposite was synthesised by the in-situ process. The produced powders were characterised by XRD, XPS, FT-IR, Raman, HRTEM and SEM-EDS tests. The sensors' function was based on PANI/Fe-doped CeO2nanocomposite with thin film deposited on top of interdigitated electrodes (IDT). NH3 detection with PANI/Fe-doped CeO2 nanocomposite sensor could be successfully performed even at room temperature (RT) and relative humidity of 45 %. Results demonstrated that PANI/Fe-doped CeO2 might be promising sensing materials for detecting the low NH3 concentration (ppm). In addition, the sensor is selective to the interfering gases, including CO, CO2 and NO2. This sensor displays acceptable repeatability and stability over time.

Unlocking low-concentration NH3 gas sensing: An innovative MOF-derived In2O3/Co3O4 nanocomposite approach

Ammonia (NH3) is an odorless gas with a pungent smell that can affect health differently based on exposure and concentration. In this study, indium oxide was decorated with cobalt oxide (In2O3/Co3O4) flower-like nanocomposites (NFs) as gas-sensitive materials, revealing p-type semiconducting characteristics. The detection of ammonia (NH3) at low concentrations is a significant challenge for chemoresistive gas sensors. Porous Co3O4 nanoflowers were combined with In2O3 nanoparticles to form p-n heterojunctions for NH3 detection. The p-n heterojunction effect and the capability of the sub-valent band to hold vacancies within In2O3 nanoparticles effectively inhibit electron-hole recombination and extend the carrier lifetime. The In2O3/Co3O4 = 0.04 ratio-based gas sensor exhibited excellent selectivity, achieving a low detection limit of 500 ppb for NH3 at 250 °C. The rapid diffusion of gas within the porous Co3O4 NSs and In2O3 nanoparticles accounted for the high response (7.72) and fast response/recovery time (92 s/51 s) of the In2O3/Co3O4-based gas sensor to 10 ppm NH3. This study presents a method for fabricating NH3 gas sensors with trace-level detection capabilities by adjusting the band structure of nanoparticles and three-dimensional metal-oxide nanostructures.

A Flexible Ammonia Gas Sensor Based on a Grafted Polyaniline Grown on a Polyethylene Terephthalate Film.

A novel NH3 gas sensor is introduced, employing polyaniline (PANI) with a unique structure called a graft film. The preparation method was simple: polydopamine (PD) was coated on a flexible polyethylene terephthalate (PET) film and PANI graft chains were grown on its surface. This distinctive three-layer sensor showed a response value of 12 for 50 ppm NH3 in a dry atmosphere at 50 °C. This value surpasses those of previously reported sensors using structurally controlled PANI films. Additionally, it is on par with sensors that combine PANI with metal oxide semiconductors or carbon materials, the high sensitivity of which have been reported. To confirm our film's potential as a flexible sensor, the effect of bending on the its characteristics was investigated. This revealed that although bending decreased the response value, it had no effect on the response time or recovery. This indicated that the sensor film itself was not broken by bending and had sufficient mechanical strength.

Improving the gas sensing performance of halide perovskite MAPbI3 film via fractal geometry electrode structure

The first successful fabrication of metal halide Perovskite MAPbI3 Film for NH3 gas sensing using fractal electrode structure is reported. High performance NH3 gas sensor was fabricated on ITO glass substrate by laser-patterning method. Gas sensors were fabricated using Hilbert, Peano, and Gosper curve structure electrodes, and their performance is compared to conventional interdigitated electrode. Gas sensing performance on Hilbert electrode design showed the highest response of 2.82 at 10 ppm NH3 gas, which is 145 % times higher compared to conventional interdigitated structures. Simulation study demonstrates that the electric field intensity and number of nodes of the fractal electrode are higher than those of the traditional interdigitated electrode. This study demonstrates that fractal electrode is a feasible strategy for optimizing the potential performance of MAPbI3-based Perovskite gas sensor with low-cost fabrication with no extra processing.

Hf3C2O2 MXene: A promising NH3 gas sensor with high selectivity/sensitivity and fast recover time at room temperature

Owing to metallic conductivity, tunable surface chemistry, mechanical flexibility, high surface area and chemical stability, MXenes have emerged as promising candidates for room-temperature gas sensors. In this study, gas sensing performances of the newly synthesized Hf3C2 MXene with oxygen termination toward a wide range of common molecules (NH3, H2O, H2S, H2, CO2, CO, CH4, N2 and NO) were investigated by first-principles density functional calculations. With the most negative adsorption energy, the highest charge transfer and the shortest adsorption distance, the adsorption of NH3 among the investigated gases causes the most significant changes in electrical conductivity and work function of Hf3C2O2 substrate, thus holds the biggest gas response. Only the NH3 exhibits strong chemical interactions with Hf3C2O2, and other gas molecules are weakly chemisorbed or physisorbed. All these indicate that Hf3C2O2 exhibits high selectivity and sensitivity to NH3. The adsorption energy of NH3 falls within the appropriate range for room-temperature gas sensors, enabling Hf3C2O2 to maintain NH3 sensitivity while also achieving a fast recovery time. Furthermore, giving that human exhaled breath does not affect, and may even enhance, the selectivity and sensitivity of Hf3C2O2 towards NH3, Hf3C2O2 can serve effectively as an NH3 sensor in human disease detection.

Flexible NH3 gas sensors based on ZnO nanostructures deposited on kevlar substrates via hydrothermal method

Owing to their flexibility and high thermal resistance, para-aramid based Kevlar™ fabric substrates are an ideal candidate for obtaining flexible gas sensors for new-generation wearable technologies. The morphology of the surface of the substrate where the target gas comes into contact directly affects the important features of the sensor such as detection limit, selectivity, and response. In this context, a feasible technique is introduced to enhance the efficiency of flexible gas sensors utilizing ZnO/Kevlar™, entailing the modification of ZnO morphology. ZnO based gas sensing layers were deposited on Kevlar™ fabric substrates by a two-stage method. Initially, seed layer was produced on Kevlar™ fabric using the ultrasonic bath method, with five different seed layer processing times ranging from 1 min to 20 min. In the nucleation, all nanostructured layers were deposited by hydrothermal method with constant parameters and under the same conditions. As the seeding time was increased, nanorods (1D) formed on the surface became flakes (2D), leading to considerable improvement in NH3 gas sensing properties. The sensor with a 5-min seeding time showed a sensitivity of 49 % at an optimal operating temperature of 190 °C, while the sensor produced in 20 min showed the best response performance with 169 % at 130 °C for 50 ppm NH3 gas. The increase in seeding time not only reduced the operating temperature of the gas sensor through the conversion from 1D nanostructure to 2D, but also significantly increased the sensor response. Under constant hydrothermal conditions and solution concentration, the density per unit area increases. However, after 10 min of seeding, the length of nanorods shortens and turn into a rod-flake hybrid morphology. A superior sensor performance was demonstrated for the samples examined. The obtained results also showed that flexible Kevlar™ fabric could be a feasible and interesting substrate for nanostructured ZnO-based NH3 gas sensors.