NH3 Gas Sensor Research Articles

Enhanced and selective ammonia detection using In2O3/reduced graphene oxide hybrid nanofibers

Over the last few decades, there has been an increasing interest in ammonia gas detection for a wide range of applications, including food and environmental sectors and medical diagnostics. Herein, a useful NH3 gas sensor based on a hybrid nanocomposite (NFI-rGO) combining In2O3 ceramic nanofibers (NFI) and reduced graphene oxide (rGO) is proposed. The NFI was obtained by electrospinning technique followed by calcination treatment. The hybrid nanostructure was achieved by covering of the as-prepared NFI with rGO. The structure, surface morphology, and elementary composition of the NFI-rGO were characterized by X-ray diffraction, X-ray photo-electron spectroscopy, scanning and transmission electron microscopies. The ammonia sensing performance of the NFI-rGO was investigated at room temperature by exposing the sensor to a variable gas concentration in the range from 1 up to 60 ppm. The hybrid nanocomposite exhibited superior electrical sensing properties and selectivity when compared with each individual material as sensing layer, indicating the synergistic effect between NFI and rGO. The NFI-rGO nanocomposite sensor showed a fast response with sensitivity 10 times higher than the individual NFI and rGO, a low detection limit of 44 ppb and an outstanding selectivity to NH3 against other nitrogenated compounds and organic solvents. The enhanced sensing performance could be ascribed to the p-n heterojunction and the synergistic effect between the nanofibrous structure and the 2D rGO sheets, paving the way for the development of novel room temperature ammonia sensors employing hybrid nanocomposites.

A high-performance NH3 gas sensor based on TiO2 quantum dot clusters with ppb level detection limit at room temperature

Nanometer sized aggregates of titanium dioxide quantum dot clusters (QDs) were used with a convenient low temperature (80 °C) hydrolysis method to prepare a high performance NH3 gas sensor. Using transmission electron microscopy, the synthesized material was found to consist of massive anatase TiO2 QDs (66 nm) with excellent stability and dispersibility (the individual QDs were formed from 2 to 5 nm diameter anatase crystals). The unique preparation method yielded a highly porous TiO2 QDs structure with a huge specific surface area (315.74 m2/g). This provides more potential reaction sites on the surface potential enhancing the performance of the sensor. Testing revealed these NH3 (g) sensors demonstrated excellent gas sensing properties (0.2–10 ppm, room temperature), high sensitivity, selectivity, stability, low detection limit (0.2 ppm), rapid response recovery (88 s/23 s for 0.2 ppm), and a linear response to concentration.

Ultrathin semiconductor films for NH3 gas sensors prepared by vertical phase separation

Vertical phase separation of the polymer blendsis a facile method to prepare double-layered polymer films. In this study, ultrathin P3HT films prepared by the vertical phase separation of the P3HT and PMMA blends were reported. The film thickness of P3HT is simply controlled by varying the P3HT/PMMA blend ratio. The thickness of the as-formed ultrathin P3HT films can be as low as around 2.0 nm. The relationship between the P3HT film thickness and charge transport performance was studied. It was found that the mobility decreased slightly with the decrease of P3HT film thickness. The ultrathin P3HT films exhibit good organic field-effect transistor performance with a mobility of 2.3 × 10−2 cm2V-1s-1. The gas sensors based on the ultrathin P3HT films was also investigated. The performance of ammonia sensor improved rapidly as the film thickness decreased and the response of the P3HT ultrathin film with 2.0 nm thickness reaches 31.1%.

Reduced graphene oxide-CuFe2O4 nanocomposite: A highly sensitive room temperature NH3 gas sensor

Sensitive and selective detection of NH3 at room temperature is required for proper environmental monitoring and also to avoid any health hazards in the industrial areas. Towards this objective, a low-cost, one-step and combustion route mediated reduced graphene oxide (rGO)-CuFe2O4 nanocomposite was exploited as a high–performance NH3 gas sensor by combining the excellent electrical properties of rGO and sensing capabilities of CuFe2O4. This nanocomposite was characterized using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM) and N2 adsorption-desorption analysis. The TEM images demonstrate the uniform distribution of the nanoparticles on the rGO surface and high-resolution transmission electron microscopy (HRTEM) confirms an average particle size of 15–20 nm. The designed sensor can detect NH3 at low concentrations up to 5 ppm at room temperature. Besides high sensing ability, the designed nanocomposite showed good recyclability suggesting its potential applications for the detection of environmentally toxic gases. The enhanced sensing behavior can be attributed to the synergistic behavior between individual rGO and CuFe2O4 component.

NH3 sensing properties and mechanism of Ru-loaded WO3 nanosheets

In this paper, WO3 nanosheets were prepared by an acidification method and Ru catalyst was loaded on the surface of nanosheets through a conventional impregnation process. NH3 gas sensors based on the neat and Ru-loaded WO3 nanosheets were fabricated by the scree-printing technique and their sensing properties to NH3 were investigated. The morphologies and surface structures of neat and Ru-loaded WO3 nanosheets were analyzed. It is revealed that WO3 nanosheets have an irregular flake shape and Ru catalyst is found on the surface of nanosheets with an oxided state. It is also found that the sensor response of WO3 is greatly improved by the loading of Ru. Based on the power-law response of oxygen and TPR results, the sensitization mechanism of Ru is explained. It is proposed that the introduction of Ru promotes the catalytic activity of WO3 and in turn modulates the reaction route of NH3 with oxygen adsorbates on the surface, which inhibit the generation of nitrogen oxides and consequently reduces the competitive adsorption with oxygen during the sensor responses.

Synthesis and characterization of highly selective and sensitive Sn/SnO2/N-doped carbon nanocomposite (Sn/SnO2@NGC) for sensing toxic NH3 gas

In the present study, a facial synthesis of Sn/SnO2 nanoparticles embedded in nitrogen doped carbon based nanocomposites has been disclosed which was used as a fast and high-performance NH3 gas sensor. The prepared nanocomposite was characterized by various analytical technique including FTIR, TGA/DTA, Raman, XRD, FESEM, TEM/HRTEM and XPS. The presence of both Sn and SnO2 nanoparticles in carbon matrix are supported by FTIR, Raman and XRD. The XRD analysis showed the tetragonal crystal phase of SnO2 nanoparticles, and the BET results revealed 148.9 m2 g−1 surface area of the nanocomposite. Furthermore, SEM image showed that Sn and SnO2 nanoparticles were well dispersed in the nitrogen doped carbon matrix. The fabricated sensor was characterized against various concentration of NH3 and the results indicated that the prepared sensor showed excellent responses at 65 °C working temperature, with 300 ppm concentration of NH3 and the sensitivity was observed 172.70. Additionally, the fabricated sensor also showed quick response and the recovery time of 60 s and 55 s, respectively. The fabricated sensor with its quick response and recovery time, good repeatability, excellent selectivity, and slight humidity effects has the potential and could be used as NH3 sensor on industrial scale.

High-selective sensitive NH3 gas sensor: A density functional theory study

P-type metal oxide semiconductor with extraordinary surface reactions is highly active for gas sensing reactions. However, presenting large active sites in materials surface for sensing reactions is a great challenge. Here, we report a strategy to fabricate Co3O4 hexagonal platelets and characterize the adsorption of ammonia (NH3) by using density-functional theory (DFT) calculations. The as-prepared Co3O4 hexagonal platelets exposed by (112) crystal plane shows high selectivity and sensitivity to NH3 at room temperatures. In addition, fantastic reproducibility of the device is also demonstrated. Such alluring sensing performances can be attributed to unique size, structure, and surface arrangement on the Co3O4 platelets that facilitate the NH3 adsorption and interface interaction. The present studies provided a new insight into improving the selectivity of gas sensors by designing special crystal-facets exposure in the nanomaterials surface matrix.

Enhanced room-temperature NH3 gas sensing by 2D SnS2 with sulfur vacancies synthesized by chemical exfoliation

Recently, tin sulfide (SnS2) with different structures has been widely used for NH3 detection. However, the low sensitivity and high operating temperatures severely limit its potential application. Here, we demonstrate enhanced room temperature NH3 sensing using scalable SnS2 nanosheets, which are facily synthesized by chemical exfoliation. Structural and morphological characterization revealed that the as-prepared two-dimensional (2D) SnS2 is composed of 1–3 layers (0.6 nm–1.8 nm). Compared with the bulk SnS2 that shows none response to NH3, the gas sensors based on the as-prepared 2D SnS2 exhibit excellent ammonia gas sensing performance at room temperature. When exposed to 500 ppm ammonia, the response time, i.e., 16 s, is the shortest among all the NH3 gas sensors based on transition metal dichalcogenides (TMDs). We attribute this enhanced sensitivity mainly to the effective NH3 gas adsorption is dominated by the high energy defect sulfur vacancies on the surface of 2D SnS2. The easily synthesized 2D SnS2 with sulfur vacancies are expected to find a vast application in gas sensing.

Synthesis and characterization of polypyrrole thin film by MW-CBD method for NH3 gas sensor

The microwave-assisted chemical bath deposition method is used for synthesis of polypyrrole (Ppy) thin film. The structural, morphological, optical absorption and wettability properties of deposited Ppy thin films are studied using various characterization techniques. The X-ray diffraction pattern shows amorphous nature of Ppy thin film. To confirm the formation of Ppy compound, Fourier transform infrared spectroscopic study is used. The scanning electron microscopy study shows porous structure of Ppy thin film. The optical study revealed that Ppy thin film exhibits band gap of 3.5 eV. The Ppy film exhibited hydrophilic nature with contact angle of 41°. The Ppy films show 85% response to ammonia (NH3) gas at room temperature.

Influence of Different Aluminum Sources on the NH3 Gas-Sensing Properties of ZnO Thin Films

Herein we report Al-doped ZnO films (AZO) deposited on the ZnO seed layer by chemical bath deposition method. Al powder, Al oxide and Al chloride were used as sources for the deposition process and investigated for their different effects on the NH3 gas-sensing performance. The morphological and microstructural properties were investigated by employing x-ray powder diffraction, scanning electron microscopy analysis and energy-dispersive x-ray spectroscopy. The characterization studies showed that the AZO thin films are crystalline and exhibit a hexagonal wurtzite structure. Ammonia (NH3) gas-sensing measurements of AZO films were performed at different concentration levels and different operation temperatures from 50°C to 210°C. The sample based on powder-Al source showed a higher response, selectivity and short response/recovery time than the remaining samples. The powder Al sample exhibited 33% response to 10-ppm ammonia gas at 190°C, confirming a strong dependence on the dopant source type.

Highly sensitive NH3 gas sensor based on the porous Ce0.94Zr0.06O2 nano-sheets with ppb level detection limit

Porous Ce0.94Zr0.06O2 nano-sheets sensing material was synthesized using a facile sol-hydrothermal process. The average thickness of the Ce0.94Zr0.06O2 nano-sheets was about 8 nm, and the nano-sheets were found to have a mesoporous structure with an average pore size around 2.1 nm. The mesoporous structure of Ce0.94Zr0.06O2 nano-sheets resulted in larger specific surface areas of 185.4 m2/g and more pore volumes of 0.51 cm3/g than those of CeO2, which was beneficial to the absorption of target gas. Due to the special mesoporous structures in the nano-sheets and the plenty of hydroxyl groups on the surface, the NH3 sensors made of the porous Ce0.94Zr0.06O2 nano-sheets showed a higher sensitivity (87–100 ppm NH3) and a lower detection limit (100 ppb) at room temperature than the sensors made of pure CeO2 nano-sheets prepared using the similar process. And they exhibited good selectivity, reproducibility and long-term stability to NH3 detection at room temperature.

Potential application of doped hexa-peri-hexabenzocoronene as NH3 gas sensor: a computational investigation

In this study, density functional theory calculations were carried out to investigate the adsorption of NH3 gas on the pristine and B- and Al-doped hexa-peri-hexabenzocoronenes (HBCs). The results indicated that the adsorption of NH3 molecule on pristine HBC is quite weak, while both B- and Al-doped HBCs can strongly adsorb NH3 molecule. The significant increase in band gap was observed in the B-doped HBCs, which confirms the high sensitivity of the B-doped HBCs towards NH3 molecule. Also, our calculations show that pristine HBC cannot detect the presence of NH3 gas. The nature of interactions was characterized by the non-covalent interaction (NCI) and quantum theory of atoms in molecules (QTAIM) analyses. Based on the overall results, B-doped HBCs are promising candidates for sensing ammonia molecules.

Influence of Ag NPs on Silicon Nanocolumns NH3 Gas Sensors

Two NH3 gas sensor devices, Al/Si nanocolumns/n-Si/Al and Al/Ag NPs/Si nanocolumns/n-Si/Al hybrid structures, have been fabricated and tested. A bare silicon nanocolumns layer was synthesized by a laser-assisted electrochemical etching process in HF solutions. The surface morphology of bare Si nanocolumns was modified by incorporating Ag NPs into Si nanocolumns by simple and fast immersions methods in an aqueous solution of AgNO3 to synthesize a hybrid structure. Characteristic features of bare Si nanocolumns and hybrid structure were investigated using scanning electron microscopy, EDS analysis, FTIR spectra, X-ray diffraction, and photoluminescence spectra (PL). The electrical characteristics of sensors with and without NH3 gas were measured at room temperature. The results showed that the nanoparticles grain size, nature, specific surface area (S.S.A) of Ag NPs, and morphological structure of the Si nanocolumns strongly affected the property characteristics. A significant enhancement in sensitivity, response, and recovery times of gas sensor for a hybrid structure was realized after compared with Al/Si nanocolumns/n-Si/Al gas sensor due to the high specific surface area.

Sensing of low concentration of ammonia at room temperature by cadmium sulphide nanoparticle decorated multiwalled carbon nanotube: fabrication and characterisation

A chemical approach to fabricate a CdS-attached multiwall carbon nanotube (CdS/MWCNT) based on NH3 gas sensor is presented. During chemical assemblage the formation of the chemical composition and chemical state of CdS/MWCNT, evaluated through XPS, is also enumerated in this work. Results on NH3 gas sensitivity at room temperature with theoretical interpretation make this work noticeable. The overall finding is that the CdS/MWCNT sensor senses NH3 at room temperature as low as 10 ppb concentration. The sensor shows good reproducibility and stability, construed on the performance of the sensor over a period of six months.

Controlled synthesis of manganese tungstate nanorods for highly selective NH3 gas sensor

In this paper, single-crystalline MnWO4 nanorods were prepared through a facile single-step hydrothermal approach and used for gas sensing. The morphology and phase of the products were characterized in detail through transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and elemental dispersive spectrum analyses. Results showed that the as-prepared MnWO4 nanorods possess uniform shape with their length of 250–300 nm and width of 20–30 nm. The nanorods were used to fabricate sensors for detecting reducing gases such as NH3, H2 and CO and evaluate gas sensing properties. The sensors exhibit not only good response and fast response time, but also almost full recovery and good stability, to NH3 gas.

One-step Synthesis of Ordered Pd@TiO2 Nanofibers Array Film as Outstanding NH3 Gas Sensor at Room Temperature

The one dimensional (1D) ordered porous Pd@TiO2 nanofibers (NFs) array film have been fabricated via a facile one-step synthesis of the electrospinning approach. The Pd@TiO2 NFs (PTND3) contained Pd (2.0 wt %) and C, N element (16.2 wt %) display high dispersion of Pd nanoparticles (NPs) on TiO2 NFs. Adding Pd meshed with C, N element to TiO2 based NFs might contribute to generation of Lewis acid sites and Brønsted acid sites, which have been recently shown to enhance NH3 adsorption-desorption ability; Pd NPs could increase the quantity of adsorbed O2 on the surface of TiO2 based NFs, and accelerated the O2 molecule-ion conversion rate, enhanced the ability of electron transmission. The response time of PTND3 sensor towards 100 ppm NH3 is only 3 s at room temperature (RT). Meantime, the response and response time of the PTND3 to the NH3 is 1 and 14s even at the concentration of 100 ppb. Therefore, the ordered Pd@TiO2 NFs array NH3 sensor display great potential for practical applications.

Effect of PEG on the Morphology and NH3 Gas Sensing Properties of WO3 Nanostructures

WO3 nanostructures were obtained by hydrothermal method using sodium tungstate dihydrate (Na2WO4•2H2O), hydrochloric acid(HCl). Polyethylene glycol (PEG-1000) was added in the initial precursors. The phase of WO3 nanostructures are characterized by X-ray diffraction (XRD). The morphology of WO3 are characterized by scanning electron microscopy (SEM). The morphology of WO3 was nanorods, however became nanoparticles with PEG-1000 adding. The effect of PEG on the formation of WO3 nanoparticles was studied. The NH3 gas sensing properties of WO3 nanostructures were also studied. The result showed that the sensitivity was increased with PEG -1000 adding.

Electronic and transport properties of silicene-based ammonia nanosensors: an ab initio study

Using density functional theory (DFT) and non-equilibrium Green’s function (NEGF) formalism, the electronic and transport properties of ammonia (NH3) molecule adsorbed on armchair silicene nanoribbons (ASiNRs) are calculated. Different variants of ASiNR have been considered viz. pristine, defective, Al-doped, and P-doped. It has been observed that though the pristine ASiNR is not much sensitive to this gas molecule, but its sensitivity can be drastically enhanced by introducing defects and dopants. NH3 gas molecule exhibits stronger adsorption on ASiNRs with addition of defect and dopants. The findings are suggestive of defective and Al-doped ASiNRs being more suitable as sensors for NH3 owing to the strong adsorption and large charge transfer of the gas molecule with these ASiNR variants whereas NH3 exhibits physisorption on pristine and P-doped ASiNRs possessing minimal adsorption energy and charge transfer as well. Defective ASiNRs are found to exhibit the strongest adsorption of all resulting in higher current as well. The study indicates that modified ASiNRs are potential candidates for nanoelectronic NH3 gas sensors.

Enhanced NH3 gas-sensing performance of silica modified CeO2 nanostructure based sensors

The silica modified CeO2 gas sensing nanomaterials are synthesized using a sol-hydrothermal route. The 8%silica-CeO2 has larger specific surface areas of 83.75m2/g and smaller crystalline size of 11.5nm than pure CeO2, respectively. Compared to pure CeO2, the 8%silica-CeO2 based gas sensor exhibits significant enhancement NH3 gas-sensing performance. At room temperature, it shows much better gas response of 3244% to 80ppm of NH3 gas and lower detection limit (0.5ppm) towards NH3 gas. It is also found that the gas response of the NH3 gas sensors increases linearly with the increase of NH3 gas concentration. Moreover, the NH3 gas sensor have good reversibility, stability and selectivity. The reason of enhanced NH3 gas-sensing performance is not only because of the increased specific surface areas, but also due to the electrolytic conductivity of NH4+ and OH− on the surface.

Bilayer SnO2–WO3 nanofilms for enhanced NH3 gas sensing performance

Bilayer SnO2–WO3 nanofilm sensors with high sensitivity and selectivity for NH3 gas were developed. The sensitized WO3 nanofilms (5–15nm) were deposited on the top of SnO2 nanofilms without vacuum break via reactive sputtering. The SnO2 nanofilm sensitized with 10-nm-thick WO3 nanofilm exhibited the best performance for sensing NH3 gas. The gas response (Ra/Rg) value of SnO2–WO3 nanofilm sensor to 250ppm NH3 was as high as 7.1 at 300°C and increased by approximately threefold compared with that of the bare SnO2 nanofilm sensor. At 300°C, the cross-gas responses of the SnO2–WO3 nanofilm sensor to 250ppm H2 (Ra/Rg=1.5) and C2H5OH (Ra/Rg=1.4) were negligibly low. The catalytic effect of WO3 nanofilm on NH3 gas molecules mainly enhanced the NH3-gas-sensing performance of the SnO2 nanofilm sensor. This work proposes an effective platform for the mass-fabrication of miniaturized, cost-effective, and highly sensitive NH3 gas sensors.