Selective Detection Of Ammonia Research Articles

TiO2 decorated MXene nanosheets for high-performance ammonia gas sensing at room-temperature

A room-temperature sensor with superior performance to detect traces of toxic gas molecules is highly desirable. MXenes, due to their unique planar structure, higher electrical conductivity and abundant functional groups on the surface, have emerged as leading low dimensional gas sensing materials. But, the gas sensors based on Ti3C2Tx MXene possess higher detection limit and poor long-term stability, thereby limiting their applications. However, TiO2 modified Ti3C2Tx as a gas sensing platform has displayed improved ammonia sensing performance. Here, we report a facile method to prepare Ti3C2Tx/TiO2 composite via calcination of Ti3C2Tx. The experimental results indicate that the oxidation temperature plays a key role in the morphology evolution and gas-sensing performance of Ti3C2/TiO2 composites. Compared to the as obtained Ti3C2Tx, the Ti3C2Tx/TiO2 composite obtained at 200 °C displays improved response to NH3 gas due to the formation of a heterointerface between Ti3C2Tx and TiO2. Room-temperature, selective ammonia detection down to 5 ppb has been obtained. Moreover, the device displayed a stable sensing response to 10 ppb of ammonia over the RH range of 26%–90%. It also displayed higher selectivity to NH3 over other analytes including dimethyl formamide, ethanol, isopropyl alcohol, methanol, acetone, chloroform, xylene and N-methyl pyrolidone. The results suggest that by appropriate engineering of the Ti3C2Tx/TiO2 composites, ammonia sensor with improved sensing performance can be designed.

Zinc Oxide-Loaded Cellulose-Based Carbon Gas Sensor for Selective Detection of Ammonia.

Cellulose-based carbon (CBC) is widely known for its porous structure and high specific surface area and is liable to adsorb gas molecules and macromolecular pollutants. However, the application of CBC in gas sensing has been little studied. In this paper, a ZnO/CBC heterojunction was formed by means of simple co-precipitation and high-temperature carbonization. As a new ammonia sensor, the prepared ZnO/CBC sensor can detect ammonia that the previous pure ZnO ammonia sensor cannot at room temperature. It has a great gas sensing response, stability, and selectivity to an ammonia concentration of 200 ppm. This study provides a new idea for the design and synthesis of biomass carbon-metal oxide composites.

PtS-decorated WS2 microflakes based sensors for selective ammonia detection at room temperature

In this paper, platinum sulfide decorated WS2 microflakes (PtS/WS2) heterostructure nanocomposites were prepared by an in-situ chemical reduction process. The chemiresistive-type gas sensor based on the synthesized PtS/WS2 heterostructure nanocomposites exhibited a significantly improved sensing properties compared to that of the pure WS2 microflakes at different concentration of NH3 from 1 ppm to 10 ppm at room temperature. As the concentrations of PtS nanoparticles decorated on the surface of WS2 microflakes increased, the response of the PtS/WS2 heterostructure sensor to ammonia firstly increased when the concentration of PtS increased up to 1 wt%, whereas above 1%, the response decreased instead. Moreover, it was found that the response speeds of the PtS-decorated WS2 were significantly improved compared to that pure WS2. The sensors also exhibited excellent selectivity to formaldehyde, toluene, acetone, methanol and ethanol at room temperature. The sensing mechanisms were studied by using the in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The enhanced sensing properties could be explained by “electronic sensitization” effect induced by the PtS/WS2 heterostructure, being confirmed by density functional theory (DFT) calculations.

Porous biocompatible colorimetric nanofiber-based sensor for selective ammonia detection on personal wearable protective equipment

Colorimetric sensors are economical and power-free devices for gas detection. Ammonia is used in several industries and overexposure can lead to death. In this study, we demonstrate a simple, single-step fabrication of a sensitive and selective colorimetric ammonia sensor. This sensor is based on simple pH-indicator immobilized electrospun mat and was able to detect ammonia concentrations as low as 0.5 ppm with a fast response time of 10 s. The core-shell bi-polymer nanofiber mat was produced using single nozzle electrospinning with a PDMS shell for selectivity. We overcome the main weakness of colorimetric ammonia sensing which is its response to pH liquids and aerosol by the addition of PDMS shell making it suitable for personal protective equipment (PPE) in industrial environments. The detection range is adjustable by controlling the thickness of the PDMS shell without compromising the other performances of the sensor. Smart PPEs with integrated colorimetric sensors could potentially be used by workers in industrial settings to detect the presence of toxic ammonia gas in a visual way.

Ti3C2 MXene-TiO2 hybrid-modified U-bend fiberoptic sensor for improved refractive index sensitivity and ammonia detection

This study introduces the U-shaped evanescent optical fibers (UOFEs), coated with TiO2 and Ti3C2 MXene composites, for refractive index (RI) measurement and ammonia sensing applications. The composites of Ti3C2 MXene multilayers and TiO2 were prepared using a novel preparation technique based on the liquid-phase deposition of (NH4)2TiF6. This is a safe alternative of conventional synthesis techniques in which hazardous HF acid is used. The UOFEs coated with Ti3C2 MXene/TiO2 hybrid films were 12-fold more sensitive to RI with a maximum RI response value of 943–1056%/RIU than bare fibers. In addition, UOFEs exhibited a linear response to ammonia concentrations between 0.5 and 20 ppm at 25 °C. The limit of detection (LOD) of UOFEs for detecting ammonia in water was 1.02 ppm in the detection range of 0–7.5 ppm. The response of UOFEs could be restored by immersing them in water for 5 min. Furthermore, UOFEs demonstrated selective detection of ammonia over aqueous solutions with a concentration of 300 ppm of other routinely used solvents, such as ethanol, methanol, hexane, acetonitrile, acetone, and chloroform. These results demonstrate good reversibility and reproducibility of UOFEs, indicating that UOFE-based sensor for detection of ammonia can be developed with potential biomedical applications.

Facile Electrodeposition-Based Chemosensors Using PANI and C-Hybrid Nanomaterials for the Selective Detection of Ammonia and Nitrogen Dioxide at Room Temperature

Sensor systems for monitoring indoor air quality are vital for the precise quantification of the mechanisms which lead to the deterioration of human health, with a typical person spending an average of 20 h a day in an enclosed space. Thus, a series of layered chemoresistive sensors, obtained by the facile electrodeposition of carbon nanomaterial-enhanced PANI composites, have been tested for the selective detection of two core indoor pollutants: ammonia and nitrogen dioxide. The sensors were tested with respect to sensitivity and selectivity to the target gasses, with performance being assessed based on response linearity and repeatability at room temperature. Of the tested sensors, two have been identified as having an adequate performance on ammonia, with sensitivities of up to 96.99% and resolutions of up to 0.85 ppm being observed, while on nitrogen dioxide, despite the successful sensor having a lower sensitivity, 10.71%, it has shown high resolution, 1.25 ppm, and linearity over a large concentration domain. These high performances highlight the viability of multi-layers chemosensors based on the electrodeposition of nanomaterial-enhanced conductive polymers for the detection of pollutant gasses, with finetuning of the detection layer allowing the accurate monitoring of a wide range of gasses.

Novel SnO2/PAni nanocomposites for selective detection of ammonia at room temperature

The present study aims to investigate a new method of SnO2/polyaniline (PAni) nanocomposite sensor fabrication for detection of ammonia at different temperatures including the room one. The fabrication of composite is performed by synthesis of PAni according to oxidative polymerization. Then the SnO2/PAni hybrid nanocomposites containing different percentages of polymer were fabricated by a deposition–precipitation method in presence of SnCl4 solution. The produced powders were characterized by XRD, BET, FTIR, Raman, TGA and FESEM tests. By increasing PAni contents of the nanocomposites, SnO2 crystallite sizes decrease, the surface area increases, and thermal stability improves. The sensing behavior of SnO2/0–30 wt% PAni in presence of 100–500 ppm ammonia was measured. The SnO2/8 wt% PAni shows the best sensitivity, where the response of sensor for 100 ppm NH3 at room temperature is about 187 %. Optimum heteronucleation and decoration of SnO2 on PAni surface enhances the response. Moreover, the sensor is selective in presence of interfering gases including CO, ethanol, methane, toluene and trichloroethylene.

Energy-Efficient Chemiresistive Sensor Array Based on SWCNT Networks, WO3 Nanochannels and SWCNT-Pt Heterojunctions for NH3 Detection against the Background Humidity

Recently, promising results have been achieved in improving the sensitivity to ammonia in gas sensors through the use of structures composed of heterojunctions or nanochannels. However, their sensitivity is highly dependent on the background humidity under air conditions. The sensor structures which could ensure selective ammonia detection with a low detection limit, despite interference from changing background humidity, remain highly demanded. In this work, we consider sensing units containing (i) nanochannels formed by a continuous tungsten oxide nanolayer to appear in contact between single-walled carbon nanotubes (SWCNTs) and a Pt sublayer and (ii) SWCNT-Pt junctions in frames of mass-scale microelectronic technologies. SWCNTs were deposited by spray-coating on a thin WO3/Pt/W sublayer formed by a photolithographic pattern to be accompanied by satellite samples with just SWCNTs for reference purposes. We elucidate the specific differences that appeared in the response of sensors based on SWCNT-Pt junctions and WO3 nanochannels relative to satellite SWCNT samples with a similar SWCNT network density. Particularly, while a similar response to NH3 vapors mixed with dry air is observed for each sensor type, the response to NH3 is reduced significantly in the presence of background humidity, of 45 rel.%, especially in the case of WO3 nanochannel structures even at room temperature. A multisensor array based on the four various sensing structures involving SWCNT-Pt junctions, WO3 nanochannels, and their satellite-only-SWCNT ones allowed us to determine a correct ammonia concentration via utilizing the linear discriminant analysis despite the presence of background air humidity. Thus, such an energy-efficient multisensor system can be used for environmental monitoring of ammonia content, health monitoring, and other applications.

Design and construction of core-shelled Co3O4-CoFe2O4 heterojunction for highly sensitive and selective detection of ammonia

In this study, the fabrication process and the gas sensing performance toward ammonia of core-shelled Co3O4-CoFe2O4 heterojunction composites with the abundant mesoporous structures were presented detailedly. The hierarchical Co3O4-CoFe2O4 was prepared by using Fe-Co glycerate as a precursor combined with a subsequent thermolysis method. The well-designed core-shelled heterojunction architecture was investigated through SEM and TEM. Apparently, the internal and external structure of the glycerate-derived sensing materials can be efficiently regulated by adjusting the molar ratio of the Fe and Co in the precursor. It was worth pointing out that the core-shelled heterojunction structure possessed a large specific surface area (198.6 m2/g), which not only can provide more active sites in both interior and exterior of the composites sphere, but also accelerate absorption-penetration efficiency of gas molecules. Compared with other prepared nanoparticles and hollow spheres, the sensor fabricated by Co3O4-CoFe2O4 with a core–shell structure revealed the best sensing characteristics, and the response toward 100 ppm ammonia at 220 °C was as high as 35. Moreover, it also showed excellent selectivity and long-term stability. These admirable advancements can be ascribed to the synergistic effect of unique core–shell architecture and p-p heterojunction. This work may offer a promising strategy to realize the practical application of Co3O4-CoFe2O4 p-p heterojunction in ammonia detection.

Investigation on the effect of NiO content on spray deposited ZnO for selective ammonia detection

Investigation on the effect of NiO content on spray deposited ZnO for selective ammonia detection

Selective detection of ammonia by rGO decorated nanostructured ZnO for poultry and farm field applications

Nanostructured Zinc Oxide (ZnO) was deposited by the spray pyrolysis technique. The ZnO was further functionalized by reduced Graphene Oxide (rGO) using the doctor blade method. The X-ray Diffraction (XRD) studies of bare and rGO functionalized ZnO showed multiple peaks and polycrystalline in nature. The morphological studies confirmed rGO distribution over the ZnO surface. The ammonia sensing studies of the bare and functionalized ZnO were analyzed by varying the temperature from room temperature (RT) to 450 °C. The rGO/ZnO exhibited increased sensitivity towards ammonia at a lower temperature (300 °C) compared with bare ZnO. The range of detection was found to be 0.5 ppm to 100 ppm. The selectivity studies towards 20 ppm ammonia in a mixed gas environment were also investigated.

Enhanced selective ammonia detection of spray deposited Cd-doped β-Ga2O3 thin films with low hysteresis effect

The Ga2O3 thin films at different concentrations (at %) of Cd dopant were deposited using spray pyrolysis technique. The X-ray diffraction patterns revealed Cd-doped β-Ga2O3 thin film are in monoclinic crystal structure with (2 0 1) orientation. Atomic force micrographs depict the change in morphology upon Cd dopant. At ambient temperature (∼30 °C), the results of ammonia sensing measurements of 4 at % Cd-doped Ga2O3 thin films point out the low-level detection (0.5 ppm) of ammonia with good sensing response (233 %), higher sensitivity (26 Ω/m), fast response-recovery time (3 s and 14 s), better selectivity, low hysteresis, and higher stability.

A chemiresistive sensor array based on polyaniline nanocomposites and machine learning classification.

The selective detection of ammonia (NH3), nitrogen dioxide (NO2), carbon oxides (CO2 and CO), acetone ((CH3)2CO), and toluene (C6H5CH3) is investigated by means of a gas sensor array based on polyaniline nanocomposites. The array composed by seven different conductive sensors with composite sensing layers are measured and analyzed using machine learning. Statistical tools, such as principal component analysis and linear discriminant analysis, are used as dimensionality reduction methods. Five different classification methods, namely k-nearest neighbors algorithm, support vector machine, random forest, decision tree classifier, and Gaussian process classification (GPC) are compared to evaluate the accuracy of target gas determination. We found the Gaussian process classification model trained on features extracted from the data by principal component analysis to be a highly accurate method reach to 99% of the classification of six different gases.

Au-Decorated WS2 Microflakes Based Sensors for Selective Ammonia Detection at Room Temperature

Gold nanoparticles decorated WS2 microflakes (Au/WS2) have been synthesized by an in situ chemical reducing process. A chemiresistive-type sensor using as-synthesized Au/WS2 heterostructures as sensing materials shows an improved response to different concentrations of ammonia compared to pure WS2 at room temperature. As the concentrations of gold nanoparticles increased in heterostructures, response/recovery speeds of the sensors became faster although the sensitivity of the sensor was compromised compared to the sensitivity of the sensor with lower concentrations of Au. In addition, the Au/WS2-based sensor indicated excellent selectivity to formaldehyde, ethanol, benzene and acetone at room temperature. The improved performance of the sensors was attributed to the synergistic effect of electronic sensitization and chemical sensitization between WS2 and Au.

Facile green synthesis of 2D hexagonal MoO3 for selective detection of ammonia at room temperature

A facile green synthesis of 2D MoO3 has been demonstrated for detection of ammonia at room temperature. The bulk MoO3 was exfoliated in water via ultrasonication assisted liquid exfoliation technique. Interestingly, the resulting MoO3 nanosheets exhibited metastable hexagonal phase unlike the base material (orthorhombic (α) MoO3), as confirmed by different characterization techniques. The phase stability has been confirmed by annealing studies and Thermo-gravimetric analysis (TGA) and the complete transformation back to α-MoO3 was observed at 300 °C. The phase transformation has been attributed to the intercalation of water molecules in the 2D layers of MoO3. The dispersion in organic solvents like ethanol further proves this argument as no phase transformation was observed in the later. The exfoliated hexagonal MoO3 based devices responded fairly well towards ammonia in the concentration range of 0.3 ppm to 5 ppm at room temperature and also superior to the ones prepared in Ethanol medium.

Sensors for the detection of ammonia as a potential biomarker for health screening

The presence of ammonia within the body has long been linked to complications stemming from the liver, kidneys, and stomach. These complications can be the result of serious conditions such as chronic kidney disease (CKD), peptic ulcers, and recently COVID-19. Limited liver and kidney function leads to increased blood urea nitrogen (BUN) within the body resulting in elevated levels of ammonia in the mouth, nose, and skin. Similarly, peptic ulcers, commonly from H. pylori, result in ammonia production from urea within the stomach. The presence of these biomarkers enables a potential screening protocol to be considered for frequent, non-invasive monitoring of these conditions. Unfortunately, detection of ammonia in these mediums is rather challenging due to relatively small concentrations and an abundance of interferents. Currently, there are no options available for non-invasive screening of these conditions continuously and in real-time. Here we demonstrate the selective detection of ammonia using a vapor phase thermodynamic sensing platform capable of being employed as part of a health screening protocol. The results show that our detection system has the remarkable ability to selectively detect trace levels of ammonia in the vapor phase using a single catalyst. Additionally, detection was demonstrated in the presence of interferents such as carbon dioxide (CO2) and acetone common in human breath. These results show that our thermodynamic sensors are well suited to selectively detect ammonia at levels that could potentially be useful for health screening applications.

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).

Revealing Interplay of Defects in SnO2 Quantum Dots for Blue Luminescence and Selective Trace Ammonia Detection at Room Temperature.

Defect chemistry in SnO2 is well established for resistive sensors but remains to be elusive for photoluminescence (PL) sensors. It demands a comprehensive understanding of the role of cationic and oxygen defects as well as the creation of abundant such defects to provide a selective PL signal. To accomplish it, SnO2 quantum dots (QDs ∼ 2.4 nm) are prepared without a capping agent along with other dimensions. Then, the relationship of defects with the blue-emission PL is unfolded by electron energy loss spectroscopy, lifetime measurements, X-ray absorption, and Raman spectroscopic measurements. The defects acting as Lewis acid sites are utilized for selective ammonia detection. Huge enhancements of the obscured blue luminescence at 2.77 and 2.96 eV from the SnO2 QDs are observed because of interaction with ammonia. The linear variation of PL intensities with analyte concentrations and the recovery of the sensor are elaborated with detection up to 5 ppm. The interplay of defects in SnO2 is further established theoretically for site-specific interactions with ammonia by density functional theory (DFT) calculations. Thus, the unique mechanism revealed for the superlative performance of the PL sensor with uncapped SnO2 QDs provides a novel platform for defect-engineering-based optoelectronic applications.

Fabrication of flexible polyaniline@ZnO hollow sphere hybrid films for high-performance NH3 sensors

In this study, a simple inexpensive gas sensor, which uses polyaniline@ZnO hollow sphere hybrid films, is prepared with different mole percentages of ZnO hollow spheres (5–30 mol%) and combining hydrothermal and in-situ chemical oxidative polymerization methods. Polyaniline@ZnO hollow sphere hybrids are loaded on flexible polyethylene terephthalate substrates for rapid and selective detection of ammonia at room temperature. The morphology, structure, chemical functional group information and the specific surface area are, respectively, characterized by field emission-scanning electron microscopy, X-ray diffraction, Fourier transform infrared and N2 adsorption–desorption techniques. The best sensing performance is realized for the polyaniline@20 mol% ZnO hollow sphere hybrid sensor, which is exposed to 10 ppm ammonia at room temperature. Moreover, this sensor exhibits a low detection limit of 500 ppb, excellent selectivity and good response/recovery times (140/136 s). This good sensing performance can be attributed to the hollow structure of ZnO and the p–n heterojunction between the polyaniline and ZnO hollow spheres.

Electrical conductivity and ammonia sensing studies on polythiophene/MWCNTs nanocomposites

Over the years, conducting polymer nanocomposites have been successfully utilized for the fabrication of ammonia sensors. But, fabrication of a sensor for selective detection of ammonia below 01 ppm is still a challenging task. Herein, we prepared polythiophene (PTh) and a series of PTh nanocomposites with multiwalled carbon nanotubes (MWCNTs) by in-situ chemical oxidation technique. The as-prepared samples were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). PTh/MWCNTs nanocomposites showed significantly enhanced electrical conductivity as well as ammonia sensing performance as compared to PTh. The sensor-based on PTh/MWCNTs-3 (PTh/MWCNTs nanocomposite containing 15% MWCNTs to the weight of monomers) was found to be an ultra-sensitive (detection limit of 0.1 ppm), completely reversible, highly selective and stable ammonia sensor at room temperature. The sensing response of PTh/MWCNTs-3 at 2000, 1500, 1000, 500, 400, 200, 100, 50, 1 and 0.1 ppm of ammonia was found to be 88.70%, 73.27%, 62.04%, 51.65%, 46.96%, 42.97%, 38.86%, 35.18%, 32.93% and 27.66%, respectively. The result showed that the relative humidity had only a small effect on ammonia sensing properties of PTh/MWCNTs-3. We demonstrated the sensing mechanism by electronic interaction of polarons (i.e. charge carriers) of PTh with the lone pairs of electrons of the ammonia molecule.