Ammonia Gas Detection Research Articles

Room-temperature ammonia gas sensor based on reduced graphene oxide nanocomposites decorated by Ag, Au and Pt nanoparticles

We report a novel and highly sensitive two-dimensional (2D) gas sensing material based on metal nanoparticles-reduced graphene oxide (rGO) nanocomposite for the detection of ammonia gas. The rGO samples decorated by Ag, Au and Pt nanoparticles (NPs) were successfully synthesized using a single-step chemical reduction process, and the effect of different metal NPs on the gas sensing performance for ammonia gas were systematically investigated. The samples were characterized by TEM and XRD methods. The gas-sensing properties of the fabricated sensors were investigated for NH3 and other target gases at room temperature. The sensor decorated by AgNPs has higher sensitivity, selectivity, better response/recovery times and great stability to ammonia gas than sensors decorated by Au and Pt NPs. AgNPs-rGO presented the highest performance, confirming a strong dependence on the metal type. The enhanced sensing properties of the samples may be attributed to the combined effect of the superior conductivity of rGO and metal nanoparticles, chemical sensitization caused from proposed production method, catalytic properties of metal nanoparticles and active oxygen species on the rGO surface.

Zinc oxide nanoparticle incorporated graphene oxide as sensing coating for interferometric optical microfiber for ammonia gas detection

A simple and reliable method by combination of sensing coating and interferometric optical microfiber to detect the concentration of ammonia is reported in this study. The sensor is fabricated by coating the tapered microfiber interferometer (MFI) with zinc oxide nanoparticle incorporated graphene oxide (GO-ZnO). GO-ZnO nanocomposites serving as an electron acceptor trap electrons after ammonia absorption and then change the surface refractive index of the optical microfiber in MFI. Subsequently, the MFI translates the tiny refractive index change into wavelength shift of the transmission spectra. As prepared sensor exhibits a good repeatability and high sensitivity to ammonia with different connections from 4ppm to 140ppm at room temperature. The gas sensor response to ammonia has been studied in different moisture level and show reliable operation in low humidity atmosphere. In addition, the gas sensor also displays an excellent selectivity to ammonia compared to several possible interfering volatile organic compounds. This may be attributed to the selective ammonia absorption at the GO-ZnO surface and the additional synergistic effects of GO-ZnO nanocomposites that are desirable and advantageous for gas sensing.

Application of TiO2/SnO2 nanoparticles in photoluminescence based fast ammonia gas sensing

In the present research work we reported the highly dispersible TiO2/SnO2 nanoparticles produced via a simple aqueous solution growth technique with ~50 nm average grain size. The surface morphology of the material have been studied by using scanning electron (SEM) and atomic force microscopes (AFM). Using photoluminescence, interaction between ammonia gas and TiO2/SnO2 (60:40 composition) nanoparticles were investigated. The material shows average significant increment in the PL intensity with no shifting in peak, which conform its tremendous applicability in optical gas sensor to detect ammonia gas (20 ppm) using photoluminescence technique. The gas sensing was systematically performed through photoluminescence spectrometer for different concentration of ammonia at room temperature. The response and recovery time of these samples are found to be in the range of 12 and 50 s respectively.

An in-line Mach-Zehnder Interferometer Using Thin-core Fiber for Ammonia Gas Sensing With High Sensitivity

Ammonia is an important indicator among environmental monitoring parameters. In this work, thin-core fiber Mach-Zehnder interferometer deposited with poly (acrylic acid) (PAA), poly (allyamine hydrochloride) (PAH) and single-walled carbon nanotubes (SWCNTs-COOH) sensing film for the detection of ammonia gas has been presented. The thin-core fiber modal interferometer was made by fusion splicing a small section of thin-core fiber (TCF) between two standard single mode fibers (SMF). A beam propagation method (BPM) is employed for the design of proposed interferometer and numerical simulation. Based on the simulation results, interferometer with a length of 2 cm of thin-core fiber is fabricated and experimentally studied. (PAH/PAA)2 + [PAH/(PAA + SWCNTs-COOH)]8 film is deposited on the outer surface of thin-core fiber via layer-by-layer (LbL) self-assembly technique. The gas sensor coated with (PAH/PAA)2 + [PAH/(PAA + SWCNTs-COOH)]8 film towards NH3 gas exposure at concentrations range from 1 to 960 ppm are analyzed and the sensing capability is demonstrated by optical spectrum analyzer (OSA). Experimental results show that the characteristic wavelength shift has an approximately linear relationship in the range 1–20 ppm, which is in accordance with the numerical simulation. Thus, this paper reveals the potential application of this sensor in monitoring low concentration NH3 gas.

Long-term stability of superhydrophilic oxygen plasma-modified single-walled carbon nanotube network surfaces and the influence on ammonia gas detection

Single-walled carbon nanotube (SWCNT) networks are subjected to a low-powered oxygen plasma for the surface modification. Changes in the surface chemical composition and the stability of the plasma-treated SWCNT (p-SWCNT) with aging in air for up to five weeks are studied using X-ray photoelectron spectroscopy (XPS) and contact angle analysis. The contact angle decreases from 120° of the untreated hydrophobic SWCNT to 0° for the superhydrophilic p-SWCNT. Similarly, the ratio of oxygen to carbon (O:C) based on the XPS spectra increases from 0.25 to 1.19, indicating an increase in surface energy of the p-SWCNT. The enhanced surface energy is gradually dissipated and the p-SWCNT network loses the superhydrophilic surface property. However, it never revert to the original hydrophobic surface state but to a metastable hydrophilic state. The aging effect on sensitivity of the p-SWCNT network-based ammonia sensor is investigated to show the importance of the aging process for the stabilization of the p-SWCNT. The best sensitivity for monitoring NH3 gas is observed with the as-prepared p-SWCNT, and the sensitivity decreases as similar as the p-SWCNT loses its hydrophilicity with time goes by. After a large performance degradation during the aging time for about two weeks, the response characteristics including sensitivity and response time of the p-SWCNT to ammonia gas are stabilized and eventually saturated.

Detection of Ammonia and Phosphine Gas using Heterojunction Biomolecular Chain with Multilayer GaAs Nanopore Electrode

This paper presents Density Functional Theory and Non-Equilibrium Green’s Function based First Principles calculations to explore the sensing property of Adenine and Thymine based hetero-junction chins for Ammonia and Phosphine gas molecules. This modeling and simulation technique plays an important and crucial role in the fast growing semiconductor based nanotechnology field. The hetero-junction chain has been passed through the multi layer GaAs nanopore electrodes. It has been found that Current-Voltage characteristics of the bio-molecular chain highly depend during the foreign gas molecules adsorption. This Current-Voltage sensitivity has been raised upto 40 and 9.3 times with the presence of single Ammonia and Phosphine molecules respectively under the ultra low bias voltage application. Adsorption of single molecule Ammonia and Phosphine increases the conductivity of the heterogeneous bio-molecular chain at room temperature. The quantum ballistic transmission through the direct band gap semi-conductor material GaAs nanopore increases during the Ammonia and Phosphine gas adsorption by the heterogeneous chain. In this paper we attempt to present the molecular model sensor with circuit elements. The attractive potential of conductivity modulation suggests this heterogeneous bio-molecular chain as an application in future generation bio-sensor technology.

Sensitivity investigation for the dependence of monolayer and stacking graphene NH3 gas sensor

The influence of various stacking chemical vapor deposition (CVD) graphene on ammonia sensing is investigated. Three interdigitated electrodes (IDEs) gas sensor with non-stacking monolayer (NSM), less stacking double layer (LSDL) and more stacking few layer (MSFL) CVD graphene were fabricated for ammonia gas detection. NSM sensor is more sensitive than LSDL and MSFL ones towards NH3. Especially for 12,500ppm NH3, the sensitivity of NSM device is more than twice the LSDL device and almost 7 times of MSFL device. Moreover, the repeatability and response time of NSM device are all much better than the other two. The simulation results show that the change ratios of integral electrons in total DOS changed 26.65% after NH3 adsorption for monolayer graphene, which is three times more than triple layer graphene of 8.29%. This is the reason why NSM has the highest sensitivity towards NH3.

Detection of sub-ppm Concentrations of Ammonia in an Ionic Liquid: Enhanced Current Density Using “Filled” Recessed Microarrays

The voltammetric detection of less than 1 ppm of ammonia gas in the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][NTf2]) is demonstrated using low-cost planar electrode devices. Three commercially available planar devices were employed, all with platinum (Pt) working electrodes: a thin-film electrode (TFE), a screen-printed electrode (SPE), and a microarray thin film electrode (MATFE), along with an "ideal" conventional Pt microdisk electrode for comparison. The microholes on the recessed MATFE were also "filled" with electrodeposited platinum, to improve radial diffusion characteristics to the microhole and generate higher current densities. Current density was lowest for the TFE and SPE surfaces (linear diffusion), higher for the MATFE (mixed radial and linear diffusion), and even higher for the filled MATFE (predominantly radial diffusion). Linear sweep voltammetry (LSV) and potential-step chronoamperometry (PSCA) at 10-100 ppm of NH3 gave linear behavior for current vs concentration. Limits of detection (LODs) were in the range of ca. 1-9 ppm, lower than the minimum exposure limit (25 ppm) for NH3. The best stability, reproducibility, and the lowest LODs were observed on the recessed and filled MATFEs. These were employed to detect lower concentrations of ammonia (0.1-2 ppm), where linear behavior was also observed, and LODs of 0.11 (recessed) and 0.02 (filled) were obtained. These are believed to be the lowest LODs (to date) reported for ammonia gas in neat ionic liquids. This is highly encouraging and suggests that RTILs and low-cost miniaturized MATFEs can be combined in amperometric sensor devices to easily and cheaply detect ammonia gas at ppb concentrations.

Development of Zinc Oxide Sensors for Detecting Ammonia Gas in the Ambient Air: A Critical Short Review

Ammonia (NH3) is emitted into the atmosphere by various industries and other sources and causes environmental pollution. Considering the hazards of ammonia, detecting leakage from vessels and pipes demands the use of sensors. Therefore, the development of NH3 gas sensors assumes considerable importance to researchers and regulators and to industry, businesses, and facilities that make, store, or use ammonia. The use of metal oxide sensors (MOS) for detecting NH3 gas, such as zinc oxide (ZnO), has been a topic of interest to researchers seeking methods to detect NH3 gas, even at low concentrations. In this article, an attempt has been made to review the research thus far published on the synthesis of ZnO‐based NH3 gas sensor materials, their characterization, and analyses of their performance. Finally, we make several recommendations regarding the scope of future research. For example, the kinetics of the sensor materials shouldbe determined. Furthermore, extensive studies of gas–solid (NH3–ZnO) adsorption are proposed to ascertain the exact adsorption mechanism in terms of isotherm, kinetics, and diffusive mass transport, and to determine “reversibility” and “recovery” of sensor materials so they can continue sensing and activating alarms when necessary for practical applications.

Structural analysis of Zr4+ doped ceria, a possible material for ammonia detection in ppm level

With the aim of application for ammonia sensing, zirconium doped ceria (Ce1−xZrxO2 for 0 ≤ x ≥ 0.7) nanopowders were synthesized by solution combustion technique using glycine as fuel in stoichiometric ratio. The calcined powders (at 500 °C) were thoroughly characterized by XRD to evaluate how the structural parameters such as lattice constant, crystallite size, cell density, cell volume, strain etc. change with the increase of Zr concentration. The crystallite size is found to reduce from 20 nm to 4 nm with the increase of doping concentration. The strain in crystal, as calculated by William Hall Plots, does not increase with the increase of Zr doping beyond 40 mol%. Micro-Raman study also indicates that beyond 40 mol% doping there exist zirconia phase in the spectra; although XRD could not resolve any segregation evidence. The optical absorption study clearly indicates how the absorption coefficient changes with doping. Incidentally, the band gap is found to reduce (3.15 eV–2.85 eV) with the increase of doping due to dominant doping level transition. In addition to near band edge emission, the photoluminescence emission spectra reveal existence of defect structure with several intra-band transitions within optical band gap. As an active electrode in electrochemical gas sensor, using lanthanum gallate as electrolyte, in amperometric mode, the synthesized Zr doped ceria was found to be highly sensitive to detect ammonia gas down to 3 ppm level in the temperature range 300–450 °C.

Electrochemical Detection of Low-Concentration Ammonia Gas on Miniaturised Electrodes in Room Temperature Ionic Liquids

The detection of ammonia (NH3) gas at low concentrations is of great importance due to its use in a wide range of industries e.g. the oil and gas industry, fertilizer industry, refrigeration industry1 and due to its high toxicity. Concentrations as low as 500 ppm can be lethal, and the current (USA) Occupational Health and Safety Permissible Exposure Limit (OSHA PEL) is 25 ppm in the gas phase. There are commercially available electrochemical gas sensors to monitor ammonia, mostly based on amperometric gas sensors (AGSs). However one problem with AGSs is that their solvent/electrolyte combinations are typically water/sulphuric acid, and can dry-up quickly, thus making the lifetime of these sensors very limited. Room Temperature Ionic Liquids (RTILs) have been attracting a great attention as replacement electrolytes in AGSs2 due to their unique physical properties such as wide electrochemical windows, high intrinsic conductivity, low volatility and negligible vapor pressure, high chemical and thermal stability and their ability to dissolve a wide range of compounds. Importantly, they do not evaporate when exposed to a high gas flow, and can function in hot and dry environments. In our work, we are investigating commercially available thin-film metal electrode surfaces as new sensing surfaces, consisting of three electrodes that are incorporated onto a small area on an inert substrate. Their small size means that only a few microliters RTIL solvent needed, and the small amount of inert metal required (e.g. platinum) minimizes the overall cost of the sensor. Four different techniques will be employed for ammonia oxidation: linear sweep voltammetry (LSV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV), and potential-step chronoamperometry (PSC) over the concentration range of 10-100 ppm NH3. The results on commercially available Pt thin-film electrodes, screen-printed electrodes, and microarray thin-film electrodes will be compared to “ideal” Pt microdisk electrodes. Calibration curves (current vs. concentration) for all voltammetric techniques on all four surfaces will be presented, showing excellent linearity with increased concentrations of NH3. The limits of detection found on all four surfaces for all four techniques are in the range of ca. 2-5 ppm, much lower than minimum exposure limit (25 ppm) for NH3. These results are highly encouraging and suggest that RTILs and low-cost miniaturised electrodes can be combined in sensor devices to detect ammonia gas at low ppm concentrations.

A Precursor Approach to Electrospun Polyaniline Nanofibers for Gas Sensors

Polyaniline (PANI) has served as one of the most promising conducting materials in a variety of fields including sensors, actuators, and electrodes. Fabrication of 1D PANI fibers using electrospinning methods has gained a significant amount of attention. Due to the extremely poor solubility of PANI in common organic solvents, fabrication of electrospun PANI fiber has been carried out either by using corrosive solvents such as H2SO4 or by electrospinning in the presence of other matrix polymers. Herein, a new approach to the fabrication of PANI fibers using tert‐butyloxycarbonyl‐protected PANI (t‐Boc PANI) as the conducting polymer precursor is reported. The t‐Boc PANI is soluble in common organic solvents (e.g., chloroform and tetrahydrofuran), and electrospinning of t‐Boc PANI in those solvents affords nano/micrometer‐sized t‐Boc PANI fibers. Treatment of the electrospun t‐Boc PANI fibers with HCl results in the removal of the acid labile t‐Boc group and the generation of conducting (≈20 S cm−1) PANI fibers. The HCl‐doped PANI fibers are successfully used in the detection of gaseous ammonia with a detection limit of 10 ppm. image

Quantitative detection of formaldehyde and ammonia gas via metal oxide-modified graphene-based sensor array combining with neural network model

This paper reports metal oxide (MOx)-decorated graphene-based sensor array combining with back-propagation (BP) neural network toward the detection of indoor air pollutant exposure. Tin dioxide (SnO2) nanospheres and copper oxide (CuO) nanoflowers-decorated graphene were used as candidates for formaldehyde and ammonia gas sensing, respectively. The as-synthesized sensing materials were characterized in terms of their nanostructural, morphological and compositional features by SEM, Raman spectra, and XRD. The sensor array was fabricated via one-step hydrothermal route and layer-by-layer (LbL) self-assembly technique on the substrate with interdigital microelectrodes. The sensing properties of MOx/graphene composite toward the mixture gas of ammonia and formaldehyde, such as dynamic response, sensitivity, response/recovery time, and stability, were investigated at room temperature. And furthermore, this work successfully achieved the recognition and quantitative prediction of components in the gas mixture of formaldehyde and ammonia through the combination of MOx/graphene-based sensor array and neural network-based signal processing technologies.

Polypyrrole/Metal Sulphide Hybrid Nanocomposites: Synthesis, Characterization and Room Temperature Gas Sensing Properties

The present research work explores the room temperature gas sensing ability of hybrid nanocomposites of metal sulphide nanoparticles with polypyrrole (PPy) matrix. Sonochemically synthesized both silver sulphide (Ag2S) and cadmium sulphide (CdS) nanoparticles were mixed in varying ratios with PPy matrix by in-situ oxidative polymerization route. The resulting PPy/(Ag2S:CdS) hybrid nanocomposites were analyzed by characterizing them using FTIR and UV-Visible spectroscopy, XRD, SEM, four-probe conductivity method and gas sensing ability by two-probe gas sensing setup. The current-voltage (I-V) characteristics of the PPy hybrid nanocomposites revealed their semiconducting nature with an electrical conductivity in the range of 10−4 to 10−3 S/cm. As compared to pure PPy, their hybrid PPy/(Ag2S:CdS) nanocomposites showed an enhancement in sensitivity towards ammonia gas detection. The results clearly indicated a synergistic effect between the Ag2S:CdS nanoparticles and the PPy matrix.

Self-assembly synthesis and ammonia gas-sensing properties of ZnO/Polythiophene nanofibers

Polythiophene nanocomposite nanofibers (70–150 nm in diameter) containing ZnO nanoparticles were synthesized through a self-assembly process in the presence of CTAB as the surfactant. Gas-sensing properties of the prepared sample have been investigated for different concentrations of ammonia gas at room temperature. A template-like model was proposed to interpret the formation of the composite nanofibers. Gas sensing tests showed that the chemiresistor based on the as-prepared hybrid has high sensitivity, excellent repeatability, long-term stability and short response time to ammonia gas at room temperature. Therefore, the ZnO/PT hybrid can be expected to be potentially used as a gas sensor material for detection of ammonia gas at room temperature. The sensing mechanism of ZnO/PT nanocomposite to ammonia gas was presumed to be the effect of p-n heterojunction between ZnO nanoparticles and PT.

Flexible Transparent Reduced Graphene Oxide Sensor Coupled with Organic Dye Molecules for Rapid Dual‐Mode Ammonia Gas Detection

Flexible chemical sensors utilizing chemically sensitive nanomaterials are of great interest for wearable sensing applications. However, obtaining high performance flexible chemical sensors with high sensitivity, fast response, transparency, stability, and workability at ambient conditions is still challenging. Herein, a newly designed flexible and transparent chemical sensor of reduced graphene oxide (R‐GO) coupled with organic dye molecules (bromophenol blue) is introduced. This device has promising properties such as high mechanical flexibility (>5000 bending cycles with a bending radius of 0.95 cm) and optical transparency (>60% in the visible region). Furthermore, stacking the water‐trapping dye layer on R‐GO enables a higher response as well as workability in a large relative humidity range (up to 80%), and dual‐mode detection capabilities of colorimetric and electrical sensing for NH3 gas (5–40 ppm). These advantageous attributes of the flexible and transparent R‐GO sensor coupled with organic dye molecules provide great potential for real‐time monitoring of toxic gas/vapor in future practical chemical sensing at room conditions in wearable electronics.

Iron Oxide-Carbon Nanotube Composite for NH3 Detection

Fabrication of iron oxide/carbon nanotube composite structures for detection of ammonia gas at room temperature is reported. The iron oxide/carbon nanotube composite structures are fabricated by in situ co-arc-discharge method using a graphite source with varying numbers of iron wires inserted. The composite structures reveal higher response signals at room temperature than at high temperatures. As the number of iron wires inserted increased, the volume of carbon nanotubes and iron nanoparticles produced increased. The oxidation condition of the composite structures varied the carbon nanotube/iron oxide ratio in the structure and, consequently, the resistance of the structures and, finally, the ammonia gas sensing performance. The highest sensor performance was realized with oxidation heat-treatment condition, in which most of the carbon nanotubes were removed from the composite and iron oxide played the main role of ammonia sensing. The response signal level was 62% at room temperature. We also found that UV irradiation enhances the sensing response with reduced recovery time.

Simple detection of food spoilage using polydiacetylene/poly(vinyl alcohol) hybrid films

Polydiacetylene (PDA)/poly (vinyl alcohol) (PVA) hybrid films are investigated for detection of ammonia gas generated by the food spoilage process. The films were obtained by mixing solutions containing diacetylene vesicles and aqueous PVA, and then drying. The films, which consist of carboxylic-acid-terminated PDA, showed a blue-to-red color transition upon reaction with ammonia gas. Through Fourier transform infrared (FTIR) analysis, we found that the observed color transition resulted from an ionic interaction between the carboxyl group of PDA and ammonia gas. In addition, patterned films were fabricated by selective UV irradiation through a photomask. Finally, the PDA/PVA hybrid films were found to show a color transition after reaction with real proteinic food at 25 °C. These results verify that the PDA/PVA hybrid films can be used for easier and more convenient real- time detection of food spoilage by the naked eye.

Enhancement of ammonia gas detection by integrating wavelength-modulated spectra across the line 992.69 cm−1

A rapid tunable diode laser (TDL) absorption sensor was developed for real-time measurements of ammonia concentration by using wavelength modulation spectroscopy (WMS) at 992.698cm−1 of the ν2 vibrational band. This line has patterns free from interference with other species in the atmosphere, and can be used for open-path detection. The 1f signal was used to normalize the 2f signal thereby eliminating the need for calibration and explaining the laser transmission variations. Using WMS with a large modulation depth and integrating the absolute value of the resulting spectra increased the limit of detection (LOD) of the sensor by a factor of seven, compared with the LOD achieved by using the maximum value of the WMS 2f signal. Furthermore, an increase by a factor of 25 compared with the direct absorption spectroscopy was achieved, which allowed obtaining LOD∼1ppb with a resolution time of <2s for the detection of NH3 in the atmosphere using a short-path cell (a 60-cm absorption cell with four passes).

Zinc(II)porphyrin-poly(lactic acid) nanoporous fiber membrane for ammonia gas detection

A functional zinc(II)porphyrin-poly(lactic acid) nanoporous fiber membrane (Zn(II)TPP-PLA NFM) for ammonia (NH3) gas detection was developed via the one-step electrospinning method. With the porous structure, Zn(II)TPP-PLA NFM overcomes the limited gas absorption and diffusion of the sensing materials and thus is beneficial to NH3 gas detection. FE-SEM and FT-IR were employed to characterize the morphology and structure of the Zn(II)TPP-PLA NFM. NH3 gas sensing properties of the Zn(II)TPP-PLA NFM were studied by UV–visible spectroscopic techniques. Results showed the Zn(II)TPP-PLA NFM with the volume ratio of dichloromethane/tetrahydrofuran (DCM/THF) 4/1 has a relatively higher porosity of 38 % and the Zn(II)TPP-PLA NFM with 2.0 mg mL−1 Zn(II)TPP content exhibits an excellent response/recovery performance toward sub-ppm levels of NH3 gas. The detection limit was found to be 0.264 ppm toward NH3 at room temperature. In addition, the performance of this sensor was highly stable after five cycles of tracing NH3 gas and recovery.