NH3 Sensor Research Articles

A Review on Functionalized Graphene Sensors for Detection of Ammonia.

Since the first graphene gas sensor has been reported, functionalized graphene gas sensors have already attracted a lot of research interest due to their potential for high sensitivity, great selectivity, and fast detection of various gases. In this paper, we summarize the recent development and progression of functionalized graphene sensors for ammonia (NH3) detection at room temperature. We review graphene gas sensors functionalized by different materials, including metallic nanoparticles, metal oxides, organic molecules, and conducting polymers. The various sensing mechanism of functionalized graphene gas sensors are explained and compared. Meanwhile, some existing challenges that may hinder the sensor mass production are discussed and several related solutions are proposed. Possible opportunities and perspective applications of the graphene NH3 sensors are also presented.

Highly sensitive colorimetric detection of NH3 based on Au@Ag@AgCl core-shell nanoparticles

As an important component of the atmosphere, ammonia (NH3) plays a very important role in maintaining the balance of environment. However, it is also one of the most toxic gases that can cause damage to the human respiratory system and mucous membranes even at low concentrations. As such, development of highly sensitive and selective NH3 sensors is of high significance for environmental monitoring and health maintenance. Herein, we have synthesized Au@Ag@AgCl core-shell nanoparticles (NPs) by oxidative etching and precipitating Au@Ag core-shell NPs using FeCl3 and further used them as optical probes for the colorimetric detection of NH3. The sensing mechanism is based on the fact that the etching of NH3 on AgCl and Ag shell leads to the variations of ingredients and core-to-shell ratio of the Au@Ag@AgCl NPs, thereby inducing noticeable spectral and color changes. By replacing the outmost layer of Ag with AgCl, not only is the stability of the sensor against oxygen significantly enhanced, but also is the sensitivity of the method improved. The method exhibits good linear relationship for the detection of NH3 from 0 to 5000 μmol/L with the limit of detection of 6.4 μmol/L. This method was successfully applied to the detection of simulated air polluted by NH3, indicating its practical applicability for environmental monitoring. This method shows great potential for on-site NH3 detection particularly in remote area, where a simple, fast, low-cost, and easy-to-handle method is highly desirable.

Multifunctional Latex/Polytetrafluoroethylene-Based Triboelectric Nanogenerator for Self-Powered Organ-like MXene/Metal-Organic Framework-Derived CuO Nanohybrid Ammonia Sensor.

Self-powered sensors are crucial in the field of wearable devices and the Internet of Things (IoT). In this paper, an organ-like Ti3C2Tx MXene/metal-organic framework-derived copper oxide (CuO) gas sensor was powered by a triboelectric nanogenerator (TENG) based on latex and polytetrafluoroethylene for the detection of ammonia (NH3) at room temperature. The peak-to-peak value of open-circuit voltage and short-circuit current generated by the prepared TENG can reach up to 810 V and 34 μA, respectively. The TENG can support a maximum peak power density of 10.84 W·m-2 and light at least 480 LEDs. Moreover, a flexible TENG under a single-electrode working mode was demonstrated for human movement stimulation, which exhibits great potential in wearable devices. The self-powered NH3 sensor driven by TENG has an excellent response (Vg/Va = 24.8 @ 100 ppm) at room temperature and exhibits a great potential in monitoring pork quality. Ti3C2Tx MXene and CuO were characterized by SEM, TEM, EDS, XRD, and XPS to analyze the properties of the materials. The NH3 sensing performance of the self-powered sensor based on MXene/CuO was greatly improved, and the mechanism of the enhanced sensing properties was systematically discussed.

Fabrication of ZnO-MWCNT nanocomposite sensor and investigation of its ammonia gas sensing properties at room temperature

Ammonia is one of the most hazardous gases, which plays a vital role in industry. Detection of low concentrations of this gas in the air is of particular importance for conservation and environmental purposes. In this study, ZnO-MWCNT nanocomposite is prepared by the in-situ method inclusive magnetron sputtering and spray pyrolysis. Then, its structural properties are studied regarding XRD spectra, FESEM, and EDX images. These studies show that nanotubes fill the porous spaces between ZnO nanoparticles and make the surface of the film rough. Hence, the surface area of the sensor and the probability of contact between gas and sensor increase. Also, sensing experiments are carried out for different concentrations of CH4 and CO gases at room temperature. Then, the results of this sensor for NH3 gas are compared with ZnO sensor results, which indicates that the sensitivity of ZnO-MWCNT sensor to NH3 is higher and more stable. However, its sensitivity to CH4 and CO is too low to be taken into consideration. Therefore, it can be claimed that MWCNTs could improve the sensing properties of ZnO film to detect NH3 gas with low concentrations such as 10 and 20 ppm. The response time and recovery time of ZnO-MWCNT sensor for 10 ppm of NH3 gas are 1.022, 13.687 s, and 107.109 s. Therefore, we suggest that ZnO-MWCNT nanocomposite could be used in a new generation of NH3 sensors.

Polyfullerene Thin Films Applied as NH3 Sensors

Polyfullerene Thin Films Applied as NH3 Sensors

Thin films of tungsten oxide based on NH3 and NO2 gas sensors

In this paper, the annealing effect of tungsten oxide (WO 3 ) nanoparticles has been studied on different Si and PS substrates by spin coating technology to develop the gas sensor. WO 3 thin film was prepared at RT, and 400 ∘ C. XRD pattern shows all films are polycrystalline in nature, and have hexagonal structure. The annealed of WO 3 thin film at 400 ∘ C showed high intensity crystalline peaks with decreased in crystal size. The fine nanoparticles are fully agglomerate and their spherical shape increases upon annealing of the film. The energy gap of WO 3 was 2.8 eV at RT, and it increased with increasing annealing temperature. The annealing temperature of 400 °C was selected and employed in gas sensors prepared on different substrates of Si and PS at RT, 100 °C, and 200 °C. The sensor was further fabricated to detect of nitrogen dioxide (NO 2 ) and ammonia (NH 3 ) gas at low concentration (8 ppm). The sensing effects toward NO 2 and NH 3 gases were compared between low- and high-temperature gases. The WO 3 /PS sample exhibited the highest sensitivity (144.1%) for NO 2 gas at 200 °C. The sensitivity of both gases showed different results with regard to the response. However, the response and recovery time of both gases were moderate and decreased with increasing operating temperature.

Room temperature flexible NH3 sensor based on polyaniline coated Rh-doped SnO2 hollow nanotubes

In this work, polyaniline (PANI) coated Rh-doped SnO2 hollow nanotubes (PRS) were synthesized via electrostatic spinning and in-situ polymerization technique. The obtained samples were characterized by X-ray diffractometer, Field emission scanning electron microscopy, Transmission electron microscopy, X-ray photoelectron spectroscopy and Brunauer-Emmett-Teller. The gas sensing performances of the sensors based on PRS nanotubes were investigated systematically at room temperature. It was shown that the polyaniline coated 0.5 mol% Rh-doped SnO2 nanotube (PRS0.5) sensor exhibited the highest response value of 13.6 to 100 ppm NH3 at room temperature with excellent selectivity, acceptable repeatability and favorable flexibility. The enhanced gas sensing performances were due to the morphology structure, the heterojunction between PANI and Rh-SnO2 and the catalytic effect of Rh2O3. Thus, the PANI coated Rh-doped SnO2 hollow nanotubes could be a promising candidate for designing and fabricating flexible NH3 gas sensor at room temperature.

A flexible polypyrrole/silk-fiber ammonia sensor assisted by silica nanosphere template

Flexible polypyrrole (PPy)@silk-fiber and PPy@sponge sensors were fabricated using the silica nanosphere (SiO2 NS) template via a facile in situ chemical oxidation polymerization method. Exposed to 100 ppm NH3 gas at room temperature in 68 ± 5 % relative humidity (RH), the response of the PPy/NS@silk-fiber sensor (73.25 %) was five-fold higher than that of the PPy/NS@sponge sensor (14.51 %). Meanwhile, the recovery time (69 s) of the PPy/NS@silk-fiber sensor was reduced to two-thirds of that (98 s) of the PPy/NS@sponge sensor for 100 ppm NH3. Additionally, the PPy/NS@silk-fiber sensor exhibited excellent reproducibility, flexibility, selectivity, and long-term stability to NH3 at room temperature. The improved gas-sensing properties can be attributed to the high surface area of the flexible PPy/NS@silk-fiber with relative rough hill-like shapes. This investigation indicated that the PPy/NS@silk-fiber is promising sensing material for developing flexible and wearable NH3 sensors.

Hollow Au/Polypyrrole Capsules to Form Porous and Neural Network-Like Nanofibrous Film for Wearable, Super-Rapid, and Ultrasensitive NH3 Sensor at Room Temperature.

Wearable conducting polymer-based NH3 sensors are highly desirable in real-time environmental monitoring and human health protection but still a challenge for their relatively long response/recovery time and moderate sensitivity at room temperature. Herein, we present an effective route to fulfill this challenge by constructing porous and neural network-like Au/polypyrrole (Au/PPy) electrospun nanofibrous film with hollow capsular units for NH3 sensor. Taking the unique architecture and synergistic effect between Au and PPy, our sensor exhibits not only super-rapid response/recovery time (both ∼7 s), faster than all reported sensors, but also stable and ultrahigh sensitivity (response reaches ∼2.3 for 1 ppm NH3) at room temperature even during repeated deformation. Furthermore, good selectivity has been also achieved. These outstanding properties make our sensor hold great potential in real-time NH3-related disease diagnosis and environmental monitoring at room temperature.

Mesoporous tungsten trioxide for highly sensitive and selective detection of ammonia

The sensing performance of a mixed-potential NH3 sensor is dependent on the microstructure of its electrode, which can be optimized to enhance the adsorption and diffusion of target gases. Mesoporous tungsten trioxide was prepared using an effective hard template method and applied as a sensitive electrode in a yttria-stabilized zirconia electrolyte-based mixed-potential NH3 gas sensor. The NH3 detection of the sensor was investigated in a temperature range of 250–650 °C. The sensor exhibited a much better NH3 sensing performance than another sensor based on commercial bulk WO3 under the same conditions. Furthermore, the NH3 sensor based on mesoporous WO3 exhibited a logarithmic response to the NH3 concentration (30–250 ppm). To investigate this response, the specialized microstructure of mesoporous WO3 was observed by transmission electron microscopy. Specifically, the high surface area and well-defined mesopores of the material significantly contributed to the excellent sensing performance. This report provides the first demonstration of the excellent response and sensitivity of an NH3 sensor based on mesoporous WO3 at low temperatures (250–400 °C).

Molecular Engineering of Porphyrin‐Tapes/Phthalocyanine Heterojunctions for a Highly Sensitive Ammonia Sensor

AbstractModulating the interfacial charge alignments by molecular engineering in an organic heterojunction device is a smart strategy to improve its conductivity, which can be exploited in high‐performance gas‐sensor development. Herein, the fabrication of new organic heterojunction devices based on porphyrin tapes and phthalocyanines and their potentiality in ammonia sensing at different relative humidity (rh) are investigated. The devices are built using dry approach relying on oxidative chemical vapor deposition for simultaneous synthesis, doping, and deposition of the porphyrin tape layer and physical vapor deposition of phthalocyanine layer. The association of the porphyrin tapes with copper phthalocyanine (CuPc) or its perfluorinated analogue (Cu(F16Pc)) in a bilayer device configuration reveals a nonlinear current–voltage characteristic, assigned to the formation of organic heterojunction at the bilayer interface. Cu(F16Pc)‐based devices reveal higher response, faster sorption kinetics, stable baseline, and less interference from rh fluctuations toward ammonia than CuPc‐based devices, which are attributed to more conducting interface in the former. Moreover, depending on the porphyrin tape associated, Cu(F16Pc)‐based devices exhibit sensitivity values 6.7 or 0.4% ppm−1 and detection limit of 1 ppm or 228 ppb allowing to obtain among the best NH3 sensors reported.

Stretchable, Stable, and Room-Temperature Gas Sensors Based on Self-Healing and Transparent Organohydrogels.

Conductive hydrogels have emerged as promising candidate materials for fabricating wearable electronics because of their fascinating stimuli-responsive and mechanical properties. However, the inherent instability of hydrogels seriously limits their application scope. Herein, the stable, ultrastretchable (upon to 1330% strain), self-healing, and transparent organohydrogel was exploited as a novel gas-responsive material to fabricate NH3 and NO2 gas sensors for the first time with extraordinary performance. A facile solvent substitution method was employed to convert the unstable hydrogel into the organohydrogel with a remarkable moisture retention (avoid drying within a year), frost resistance (freezing point below -130 °C), and unimpaired mechanical and gas sensing properties. First-principles simulations were performed to uncover the mechanisms of antidrying and antifreezing effects of organohydrogels and the interactions between NH3/NO2 and organohydrogels, revealing the vital role of hydrogen bonds in enhancing the stability and the adsorption of NH3/NO2 on the organohydrogel. The organohydrogel gas sensor displayed high sensitivity, ultralow theoretical limit of detection (91.6 and 3.5 ppb for NH3 and NO2, respectively), reversibility, and fast recovery at room temperature. It exhibited the capabilities to work at a highly deformed state with nondegraded sensing performance and restore all the electrical, mechanical, and sensing properties after mechanical damage. The gas sensing mechanism was understood by considering the gas adsorption on functional groups, dissolution in the solvent, and the hindering effect on the transport of ions.

SnO2 doped In2O3 thin films as reducing gas sensors

SummeryThis research includes description of the x-ray diffraction, morphology and sensing measurements of SnO2 doped In2O3 thin films synthesized by pulsed laser deposition method on glass and silicon wafer substrates. In2O3:SnO2 powders were obtained by mixing In2O3 with SnO2 in the desired ratio, and calcination the at temperature 1273 K for 5 hours. SnO2 doped In2O3 thin films with different ratios (0, 0.01, 0.03, 0.05, 0.07, and 0.09% wt.) were prepared using pulsed laser deposition method. The structural investigation using X-ray diffraction revealed that the main peaks were compatible with the slandered cards of indium oxide and indium tin oxide. Atomic force microscope declared reduction of grain size by increasing of tin oxide ratio. The research imply details of samples preparation, experimental methods and results which are given and explained. In2O3:SnO2/n-Si film NH3 sensors were fabricated. The doping ratio that gave the highest sensitivity for NH3 was 5% wt.SnO2. SnO2 doped In2O3 thin films was found sensitive against NH3 at the working temperature 473K. The results showed that the sensors based on I2O3:SnO2 films revealed very short response time(13.5s) to NH3 at 3% SnO2 ratio at473Kworking temperature.

Study of electrical and gas sensing characteristics of (TiO2/rGO) nanocomposite to NH3 sensor application

TiO2/rGO nanocomposite is synthesized by using pulsed laser ablation in liquid method, the UV–VIS absorption spectra and Scanning electron microscopy (SEM) TiO2/rGO) nanocomposites reveal absorption spectra in ultraviolet region and that the particles were in an aggregated state shrubbery, showed AFM image the size of each image showed that the membrane materials and through the two-dimensional and three-dimensional examines are homogeneous, noting that there are no spaces in the surface. Electrical properties of the nanocomposite improved markedly with bare TiO2NPs, without significantly changing the morphology of the TiO2NPs. Ammonia-sensing acts for (TiO2/rGO) layered film tackled. Sensing behavior of the (TiO2rGO) nanocomposites examined under the 100 ppm of NH3 environment. The (TiO2/rGO-1) nanocomposite clarified a high reaction to NH3 gas (48 %) in room temperature.

Synthesis and NH3/TMA sensing properties of CuFe2O4 hollow microspheres at low working temperature

In this work, CuFe2O4 hollow microspheres assembled with nanosheets (CuFe2O4 HMANs) were synthesized using a solvothermal method followed by an annealing treatment. The effects of annealing temperature on microstructure, chemical composition and gas sensing characteristics of as-prepared samples were investigated. The results showed that annealing treatment played a crucial role in the final products. All samples demonstrated hollow spherical morphology assembled with nanosheets or nanoparticles. The CuFe2O4 HMANs annealed at 400 °C exhibited the best n-type conductometric sensing properties toward low-concentration NH3 at 100 °C and 49%RH. The sensor response to 10 × 10−6 NH3 was 4.0 with a rapid response time of 32 s, and it even showed a response of 1.2 toward 1 × 10−6 NH3 at the same condition, while a response of 3.95 to trimethylamine (TMA). The CuFe2O4 HMANs-based NH3 sensor also exhibited good selectivity and excellent reproducibility. Therefore, this work provided a novel promised sensing material of low-concentration NH3 and TMA for real-time monitoring.

PSS-PANI/PVDF composite based flexible NH3 sensors with sub-ppm detection at room temperature

Improved ammonia (NH3) sensor is proposed based on polyaniline (PANI) with poly(styrene sulfonic acid) (PSS) as an additive, which was produced by in-suit polymerization of aniline on flexible porous polyvinylidene-fluoride (PVDF) membranes and then treated with PSS aqueous solution. The whole film sensor fabrication process was low-cost and convenient in operation, suitable for large-scale commercial production. The results demonstrated that the appropriate addition of PSS could significantly improve the sensor response to NH3. The PSS-PANI/PVDF film sensor response was improved to approximately 70%, which was 2.8 times higher than that of the pure PANI/PVDF film with 25% response towards 1 ppm NH3 at room temperature. Furthermore, it still showed an excellent response of 9.4% for 0.1 ppm NH3. The fabricated film sensor showed remarkable long-term stability with response decreases less than 5% after 30 days, and excellent flexibility under 10,000 repeated bending times with a response value degradation of only 15.1% towards 1 ppm NH3. The flexible PSS-PANI/PVDF film offers potential applications in smart wearable devices for detecting sub-ppm NH3 under ambient conditions.

Conductive elastic sponge-based triboelectric nanogenerator (TENG) for effective random mechanical energy harvesting and ammonia sensing

Abstract Triboelectric nanogenerator (TENG) based on elastic materials is increasing interests for irregular and random mechanical energies harvesting. However, the conductive design of the elastic materials in TENGs often limits its applications. Herein, a new conductive and elastic sponge-based triboelectric nanogenerator (ES-TENG) is developed for random mechanical energy harvesting, which integrates the elastic material and the conductive material on a flexible sponge to realize the collection of mechanical energies, particularly for irregular and random motions. The conductive elastic sponge is prepared by a simple dilute chemical polymerization of aniline to grow conductive polyaniline nanowires (PANI NWs) on the surface of elastic sponge. Due to the flexible deformation of sponge, it can harvest the kinetic energy of disordered motion with different amplitudes and from variable directions. As the triboelectric layer of ES-TENG, the porous sponge and polyaniline nanowires on its surface can provide a large contact area and improve the triboelectric efficiency. At the same time, the conductive polyaniline coating on the surface of sponge can also be used as the electrode of ES-TENG to conduct electrons and generate an output of 540 V and 6 μA respectively, which can be used on various flexible object surfaces to collect irregular and random mechanical energy ubiquitous in daily life. In addition, based on the NH3-sensing performance and the three-dimensional reticular structure of the polyaniline nanowires on the elastic sponge, the ES-TENG can make it work as self-powered sensor for detecting toxic NH3 with the detection limit up to 1 ppm and the response time less than 3 s. In view of the microporous and nanowire structures, elasticity, conductivity and easy fabrication of the conductive elastic sponge, the ES-TENG has promising applications in various irregular and random mechanical energy harvesting and self-powered NH3 sensors.

Visible light-activated room temperature NH3 sensor base on CuPc-loaded ZnO nanorods

A one-step microwave-assisted hydrothermal synthetic approach was used to synthesize CuPc-loaded ZnO nanorods. Several characterization techniques were applied to analyze the compositional, structural and morphological information of the products, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV − vis spectrophotometer (UV-vis) and X-ray photoelectron spectroscopy (XPS). Both pure ZnO and CuPc-loaded ZnO were characterized in terms of their gas sensing performances towards various gases under light illumination. The results indicated that CuPc/ZnO sensor delivers excellent sensitivity and selectivity towards ammonia, accompanied with rapid response/recovery rate, remarkable humidity resistance and a low detection limit down to 0.8 ppm at room temperature under red light illumination. This work will open-up new vistas in the development of room temperature gas sensors based on wide-band gap semiconductors with visible-light irradiation.

A TPA-DCPP organic semiconductor film-based room temperature NH3 sensor for insight into the sensing properties

Ammonia (NH3) gas sensor is an indispensable element in human daily life, especially in the respiratory analysis, it can perform non-invasive diagnosis of kidney disorder and hepatitis. Addressing the issue of high working temperature and achieving repeatable and stable gas-sensing properties under ambient humidity is favorable for the widespread development of NH3 sensor. In this work, a planar room-temperature NH3 sensor is manufactured through spin-coated 7,10-bis(4-(diphenylamino)phenyl)-2,3-dicyanopyrazino phenanthrene (TPA-DCPP) organic semiconductor material onto Al2O3 substrate with Au interdigital electrodes. The sensor exhibits favorable sensing response of 76.4 % and ppb-level detection ability under 98 % relative humidity (RH), also exhibits good repeatability, selectivity, and 396 days of long-term stability to NH3. The sum frequency generation (SFG)/density functional theory (DFT) calculation results further demonstrate that the excellent sensing characteristics are due to the enhanced NH3 absorption to TPA-DCPP through the synergy interaction between NH3 and H2O under high RH. This study is expected to serve as a reference in the further development of room-temperature gas sensors and contribute to our understanding of the sensing mechanism.

PANI nanofibers-supported Nb2CTx nanosheets-enabled selective NH3 detection driven by TENG at room temperature

As a new member of the MXene family, two dimensional (2D) niobium carbide MXene (Nb2CTx) holds a promising potential in gas detection due to the abundant surface terminated groups and large specific surface area. In this work, a selective NH3 sensor based on polyaniline (PANI) nanofibers-supported Nb2CTx nanosheets (Nb2CTx/PANI) directly driven by a facile triboelectric nanogenerator (TENG) is proposed to provide a possible method for enhancing the NH3-sensing response. In addition, the gas sensing properties have been optimized by regulating different spray volumes of Nb2CTx nanosheets. Test results demonstrate that the NH3-sensing response and the response speed of the Nb2CTx/PANI-2 sensor have been evidently improved, indicating a good linear response toward a wide sensing range of 1–100 ppm NH3 at room temperature (∼25℃) under 87.1 % relative humidity (RH). Moreover, the influence of high humidity on gas sensing response of the Nb2CTx/PANI-2 sensor has been efficiently reduced due to the occupied active sites for water adsorption caused by intermolecular hydrogen bonds between PANI and Nb2CTx. Finally, mechanism of the enhanced gas sensing properties has been further investigated, which should be mainly attributed to the gas sensing improvement effect of p-n junction. This work is expected to offer a useful reference for the development of high-performance Nb2CTx/polymer-based gas sensors.