NH3 Sensor Research Articles

Preparation and freshness detection of tofu based on In-doped CeO2 ammonia gas sensor

An ammonia (NH3) sensor with high sensitivity based on indium-doped cerium oxide (In/CeO2) was prepared by hydrothermal method, and its sensing mechanism was revealed by first-principles. Experimental results show that indium ion (In3+) doping can effectually increase the sensitivity of NH3 sensor based on CeO2, which is mainly attributed to the enhancement in the number of oxygen vacancies and oxygen free radicals on the surface of In/CeO2. In/CeO2 sensor for NH3 with a response value of 5412.93 at a concentration of 1000 ppm, which is 65 times that of CeO2 sensor. Moreover, the low detection limit (LOD) of In/CeO2 is 0.433 ppm and its response/recovery time to 5 ppm NH3 is 1.1 s/1.4 s. Furthermore, the density functional theory (DFT) calculation confirmed that NH3 has higher adsorption-induced charge transfer and adsorption energy on the surface of In/CeO2 than other gases. This makes it easier for In/CeO2 to adsorb NH3 molecules and release more conduction electrons, thus improving the performance of In/CeO2. In addition, In/CeO2 sensor can be effectively used to detect the freshness of tofu through the concentration of NH3 released by the tofu in different storage environments. This work is beneficial to the safety monitoring of high protein food.

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

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

Heterostructured Ti3C2Tx/carbon nanohorn-based gas sensor for NH3 detection at room temperature

In this study, a two-dimensional Ti3C2Tx MXene compounded with carbon nanohorn (CNH) by an electrostatic self-assembly method was proposed and then fabricated as room temperature ammonia (NH3) gas sensors. The successful preparation of the Ti3C2Tx/CNH nanocomposite has been characterized in detail. The NH3 sensing performance based on Ti3C2Tx/CNH also has been tested at room temperature. The optimal Ti3C2Tx/CNH sensor has a response value of 21.6% to 100 ppm NH3 at room temperature, which is 10 times higher than that of the pure Ti3C2Tx sensor. Furthermore, this sensor is endowed with excellent selectivity, reliable long-term stability, and reproducibility. The enhanced sensing performance is associated with the interconnected structure and the synergistic effect of Ti3C2Tx and CNH. This work provides an effective way to prepare MXene-based sensitive materials for NH3 sensors, which shows excellent NH3 detection potential at room temperature.

An amperometric high-temperature ammonia sensor based on a BaCo0.4Fe0.4Zr0.1Y0.1O3-δ triple conductor

Selective catalytic reduction (SCR) utilizing urea hydrolysis to generate ammonia (NH3) is the most efficient technology to reduce the emission of nitrogen oxides (NOx). NH3 detection is crucial in the closed-loop feedback system for the precise urea injection. In this work, a high-temperature NH3 sensor using a BaZr0.8Y0.2O3-δ (BZY) proton conductor as the electrolyte and a BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) H+/e–/O2– triple conductor as the sensing electrode (SE) is reported. The effect of the micromorphology of the BCFZY SE on the sensing performance is investigated by varying the sintering temperature of SE. The sensor shows high sensitivity to NH3 with response currents of 0.39, 1.31, 3.03, and 1.81 μA/ppm at 350, 400, 450, and 500 °C, respectively. Furthermore, the sensor shows excellent selectivity and repeatability. This work demonstrates that the BCFZY-based sensor has great potential for the high-temperature NH3 detection.

An impedancemetric NH3 sensor based on Ag nanoparticle decorated NiFe2O4 sensing electrode prepared by electrochemical exsolution method

An impedancemetric NH3 sensor was prepared using Yttria-stabilized zirconia (YSZ) as the solid electrolyte and Ag nanoparticle decorated NiFe2O4 (NiFe2O4/Ag) prepared by electrochemical exsolution as the sensing electrode (SE). The feasibility of electrochemical exsolution was confirmed by XRD and TEM characterization. After a voltage of −2 V was applied across the sensor based on NiFe2Ag0.05O4.025 for 1000 s, a large number of Ag nanoparticles as the second phase appear on the surface of the NiFe2O4 particles and attached to the matrix. The effects of exsolution time, temperature, and voltage on the sensing performance of the sensor were investigated. After electrochemical exsolution, the response value and sensitivity of the sensor are significantly improved compared to the sensor before exsolution and the limit of detection (LOD) of the sensor is reduced from 50 ppm to 10 ppm at 500 °C. In addition, the reproducibility of the electrochemical exsolution is good, and the sensor exhibits good stability. More importantly, the immunity of the sensor to NOx is significantly improved using the electrochemical exsolution SE.

Fe2O3 nanoplate/TiO2 nanoparticles supported by 2D Ti3C2Tx MXene conductive layers for sensitive detection of NH3 at room temperature

Ti3C2Tx MXene, a novel 2D material, has shown promise in the field of room temperature ammonia (NH3) sensors through theoretical calculations and experimental. However, the disadvantage of low response hinders its practical application. In this study, we fabricate a gas sensor based on Fe2O3 nanoplate/TiO2 nanoparticles supported by 2D Ti3C2Tx MXene to enhance NH3 sensing capabilities. Results reveal that the S2 sensor (with 3 mL FeCl3) exhibits a significantly larger response value (3.23 times) and shorter response/recovery times (62 s and 74 s) compared to the pure Ti3C2Tx MXene sensor when exposed to 100 ppm NH3 at room temperature (25℃). Additionally, the S2 sensor exhibits a good linear response (R2 = 0.95) within the range of 1–100 ppm NH3. The enhanced gas sensing properties can be mainly attributed to the Fe2O3/TiO2/Ti3C2Tx MXene heterogeneous structure and unique microstructure. This study is anticipated to serve as a valuable reference for the advancement of high-performance MXene-based NH3 sensors.

SrMoO4-based mixed-potential gas sensor for NH3 sensing in direct ammonia-fed fuel cells

Direct ammonia-fed fuel cells (DAFCs) are well known for sustainable energy production. However, the issue is a certain amount of unreacted NH3 fuel is obtained at the outlet. Thus, real-time monitoring and quantification are of utmost importance, nevertheless, this is troublesome due to the harsh thermodynamic conditions. This work aims to develop a mixed-potential sensing electrode for the detection of NH3 under reducing conditions (H2 atmosphere) at high temperatures. In this regard, a strontium molybdate (SrMoO4) sensing electrode (SE) is a potential solution due to its physical and chemical stability, along with its sensitivity to NH3 under reducing conditions. Therefore, an SrMoO4-based mixed-potential sensor is fabricated herein using yttria-stabilized zirconia (YSZ) as the electrolyte and platinum (Pt) as the reference electrode (RE) and is operated at 400–650 ℃. The maximum response exhibits about –21.57 mV toward 80 ppm NH3 at 500 ℃. Further, the sensitivity is –17.19 mV/decade towards 10–60 ppm and –45.33 mV/decade towards 60–320 ppm NH3 under 75% H2 balanced by N2 at 500 ℃. The as-fabricated sensor also has good selectivity towards NH3 and good cross-sensitivity towards other interfering gases and is stable in long-term repeated operation. The direct current (DC) polarization curves and electrochemical impedance spectroscopy (EIS) results demonstrate the sensing mechanism in accordance with the mixed-potential theory.

Unraveling Ammonia and Trimethylamine Uptake on Conductive Doped Polyaniline.

Polyaniline (PAni)-based sensors are a promising solution for ammonia (NH3) detection at the ppb level. However, the nature of the NH3-PAni interaction and underlying drivers remain unclear. This paper proposes to characterize the interaction between doped PAni (dPAni) sensing material and NH3 by using a Knudsen cell. First, to characterize the dPAni interface, the probe-gas method, i.e., titration of surface sites with a gas of specific properties, is deployed. The dPAni interface is found to be homogeneous with more than 96% of surface sites of acid nature or with hydroxyl functional groups. This result highlights that basic gases such as amines might act as interfering gases for NH3 detection by polyaniline-based sensors. Second, the adsorption isotherms of NH3 and trimethylamine (TMA) on dPAni are reported at ambient temperature conditions, 293 K. The uptake of NH3 and TMA on dPAni follows a Langmuir-type behavior. This approach allows for the first time to quantify the uptake of NH3 and TMA on gas-sensor materials and determine typical Langmuir adsorption parameters, i.e., the partitioning coefficient, KLang, and the maximum surface coverage, Nmax. The corresponding values obtained for NH3 and TMA are Klang (NH3) = 19.7 × 10-15 cm3 molecules-1 Nmax (NH3) = 11.6 × 1014 molecules cm-2, KLang (TMA) = 7.0 × 10-15 cm3 molecules-1 Nmax (TMA) = 5.0 × 1014 molecules cm-2. KLang and Nmax values of NH3 are higher than those of TMA, suggesting that NH3 is more efficiently taken up than TMA on dPAni. The results of this work suggest that strong hydrogen bonding drives the performance of a polyaniline-based gas sensor for NH3 and amines. In conclusion, the Knudsen cell approach allows reconsidering the fundamentals of NH3 interactions with dPAni and provides new insights on drivers to enhance sensing properties.

Meta-Analysis of the Effect of Inorganic Micro/Nanomaterial Additives on Polyaniline Based NH<sub>3</sub> Gas Sensor Performance

Nowadays conducting polymer based nanocomposites become promising materials for various field of applications like energy harvesting, electronics, and gas sensing devices. This work focuses on the meta-analysis of the effect of different inorganic micro/nano-material additives on polyaniline (PAni) based nanocomposite for ammonia (NH3) gas sensor application at room temperature. The considered NH3 sensors performance parameters are sensitivity, limit of detection (LOD), response time, and recovery time. These parameters show a significant change when inorganic materials like graphene, metal oxides and ternary hybrid materials are mixed with PAni as compared to pure PAni due to the synergetic effect of the micro/nano hybrid combination. The changes in the sensitivity, LOD, response time, and recovery time are elaborated by considering different inorganic micro/nano-material additives in PAni in the framework of pure PAni as a reference point. It is found from analysis that a micro/nano additive in the PAni matrix serve as catalyst and create more active sites in the system, which improves the sensitivity in the range of 23-130 times and LOD is highly reduced by 10-1 to 10-3 order when compared with the sensitivity and LOD of pure PAni. Hence these additives in PAni-based nanocomposite are very crucial and make nanocomposite cost-effective compared to conventional NH3 gas sensors while working at room temperature.

Development of flexible PVDF/ BaTiO3-MoS2 polymer nanocomposites for energy harvesting and gas sensing applications

The need for flexible and wearable devices is quite great in the modern era of advanced electronics and the Internet of Things (IoT). Here, we present a poly(vinylidene fluoride) (PVDF)/Barium Titanate–Molybdenum Disulfide (BaTiO3–MoS2) composite-based flexible piezoelectric nanogenerator (PENG) with an improved electroactive phase. The electroactive, β-phase of the PVDF is shown to increase with the addition of BaTiO3–MoS2 fillers as a result of the filler’s good interfacial interaction with the polymer matrix. The improved electroactive phase in the PVDF matrix was confirmed by the X-ray diffraction method and FTIR analysis of the composite films. The uniform dispersion of filler particles in the polymer matrix was confirmed by a scanning electron microscopy analysis. The developed piezoelectric nanogenerator device generated peak-to-peak output voltage of 4.9 V with a high dielectric constant of 22 and a low dielectric loss of 4.7. The fabricated gas sensor can perform at room temperature and exhibits good gas sensing performance toward the NH3 gas. It was found that, compared to all other samples, the composite PVDF/BaTiO3–MoS2 films had a high level of sensitivity. Additionally, the composite films showed response and recovery times of 11 and 17 s. The composite based on PVDF/BaTiO3–MoS2 is a suitable material for NH3 sensor applications.

High conductivity of 2D hydrogen substituted graphyne nanosheets for fast recovery NH3 gas sensors at room temperature

The current two-dimensional (2D) material based NH3 sensors generally suffer from low response values and sluggish recovery dynamics, which is resulted from their inferior conductivity. Herein, high conductivity (0.045 S/m) of 2D hydrogen substituted graphyne (HsGY) nanosheets are successfully synthesized employing aqueous/organic interface method and using them for the first time for the detection of NH3 at room temperature. The resultant gas sensing performance shows that the 2D HsGY nanosheets exhibit a high gas response value (4.9) to 100 ppm NH3 and fast recovery time (108 s) at the room temperature. The NH3 gas sensing mechanism is discussed by utilizing density functional theory (DFT) calculations. The present study provides novel gas sensing material for the development of high-performance room temperature NH3 sensors.

UV-promoted NH3 sensor based on Ti3C2Tx/TiO2/ graphene sandwich structure with ultrasensitive RT sensing performances for human health detection

Gases produced by human respiration can effectively forewarn physiological health, and developing high-performance gas sensors for breath detection can help in the early diagnosis of many diseases. In this paper, Ti3C2Tx/TiO2/graphene composite with a unique sandwich structure was fabricated by hydrothermal method for resistive NH3 sensor, which is composed of the staggered interlayer of graphene, Ti3C2Tx, and in situ grown TiO2 nanosheets. The results indicate that the Ti3C2Tx/TiO2/graphene composite sensor has a response value of 35.8 at 50 ppm NH3 at room temperature and in a dark environment, which is 12.8 times higher than that of the single Ti3C2Tx and can detect dilute NH3 at ppb level with a calculated limit of 26 ppb. The sensor also possesses a fast response/recovery time of 19/29 s and excellent humidity resistance. Furthermore, with the assistance of UV illumination, the sensor response value for 50 ppm NH3 is increased to 45.18, the response/recovery time is accelerated to 18/25 s, and the calculated limit of detection is 22.23 ppb. Additionally, simulated breath detection demonstrates the potential application of the sensor for early respiratory warning in patients with renal failure. Finally, the NH3 gas sensing mechanism is discussed in terms of heterogeneous structure, morphology promotion, and energy band theory. It is believed that the sensing material with this structure has great potential for human health applications.

Transition metals doped Zr2CF2 as promising sensor and adsorbent for NH3

The effective adsorption and treatment of toxic gases have attracted great attention amongst researchers, particularly the use of new two-dimensional materials for achieving the adsorption of toxic gases. We applied the density functional theory to investigate the stability, geometric structural, electrical, and magnetic properties of NH3 molecules adsorbed on pristine, F-vacancy defected, and transition-metals (V, Cr, Mn, Y, Nb, and Mo) doped Zr2CF2. The charge transfer and adsorption energy of the original substrate were low, indicating that the interaction between NH3 and Zr2CF2 was primarily physical adsorption. After introducing F-vacancy and TM-doping, the adsorption stability was enhanced, with the large charge transfer and high adsorption energies indicating that the adsorption of NH3 transitioned to chemisorption. Electronic density of state diagrams suggested that the enhanced interaction was mainly caused by the hybridization of the d orbitals of dopants and p orbitals of the adsorbed NH3 molecules. The adsorption energy of NH3 molecules on Y-doped Zr2CF2 was the highest at a value of −1.425eV, and the material was also explored as an adsorbent for NH3 gas. After adsorbing six NH3 molecules, the Y-doped substrate had an average adsorption energy of −1.350eV and still maintained a good thermal stability at a temperature of 300 K. These results can provide insights into the development of sensors and adsorbents based on MXenes.

A flexible ammonia sensor based on MXene membrane with high sensitivity

AbstractAmmonia (NH3) of high concentration will pose a threat to ecological environment or human health, and exhaled NH3 is significant in disease monitoring and diagnosis. Thus, developing a highly sensitive gas sensor is significant to monitor NH3 concentration in complex environments. However, traditional NH3 sensors either need high working temperature, or face the challenge of poor conductivity/ sensitivity. In this work, NH3 sensors based on self‐assembled MXene membrane have been fabricated. As‐prepared sensors show a high sensitivity of 2.10 ppm−1 towards extremely low concentrations of NH3 (ppb level) at room temperature, attributed to large surface area and high conductivity. In addition, the sensors also display low detection limit (50 ppb), fast response time (41 s), good recoverability, long‐term stability (15 days) and excellent flexibility (1000 bending cycles) towards NH3. The results provide insights into the development of highly sensitive NH3 sensors for industrial or biomedical applications.

Highly sensitive detection of ammonia based on light-induced thermoelastic spectroscopy with hollow waveguide

In this paper, an ammonia (NH3) sensor based on light-induced thermoelastic spectroscopy (LITES) with hollow waveguide (HWG) is proposed for the first time. HWG has many advantages, such as small size, simple structure, high system stability and fast filling speed. The sensor used HWG with a length of 22 cm and an inner diameter of 4 mm as the light transmission medium and gas chamber. The interior of the HWG is covered with silver (Ag) and silver iodide (AgI). The reflectivity is increased and the transmission losses is reduced in the infrared region of the HWG. A diode laser with an output wavelength of 1.53 μm was employed, which can cover the two NH3 absorption lines of 6534.6 cm−1 and 6533.4 cm−1. The amplitude of the second harmonic signal (2f) showed a good linear response to the gas concentration. The experiments demonstrated that the NH3 sensor's minimum detection limit (MDL) under this system was 9.896 parts per million (ppm).

Room-temperature NH3 sensor based on CoFe2O4/PANI composite with porous structure

Development of chemo-resistive room-temperature ammonia (NH3) sensor with high performance remains a great challenge to this day. In this paper, we demonstrate a room-temperature NH3 sensor based on organic-inorganic cobalt ferrite (CoFe2O4)/polyaniline (PANI) composite. The CoFe2O4 porous nanosheets were firstly prepared by using a direct precipitation method, and then the PANI were anchored onto the surfaces of the CoFe2O4 porous nanosheets through an in-situ polymerization process to form the CoFe2O4/PANI composite. The crystal structure, morphology, and surface chemistry of the CoFe2O4/PANI composite were characterized by combined techniques of X-ray diffraction, electron microscopy, and spectroscopy. Due to the porous feature of the composite and the formation of p-p heterojunctions between the CoFe2O4 and PANI, the CoFe2O4/PANI gas sensor exhibited excellent NH3-sensing performance with high response (13 to 100 ppm NH3), good selectivity, wide detection range (10–500 ppm), and rapid response/recovery rate (18/31 s to 100 ppm NH3) at room temperature. Additionally, the CoFe2O4/PANI gas sensor owned outstanding repeatability and long-term stability. This study offered a promising candidate of CoFe2O4/PANI composite for constructing room-temperature NH3 sensor.

Pd-Decorated ZnO Hexagonal Microdiscs for NH3 Sensor

The NH3 sensor is of great significance in preventing NH3 leakage and ensuring life safety. In this work, the Pd-decorated ZnO hexagonal microdiscs are synthesized using hydrothermal and annealing processes, and the gas sensor is fabricated based on Pd-decorated ZnO hexagonal microdiscs. The gas-sensing test results show that the Pd-ZnO gas sensor has a good response to NH3 gas. Specifically, it has a good linear response within 0.5–50 ppm NH3 at the optimal operating temperature of 230 °C. In addition, the Pd-ZnO gas sensor exhibits good repeatability, short response time (23.2 s) and good humidity resistance (10–90% relative humidity). This work provides a useful reference for developing an NH3 sensor.

Fully Transient 3D Origami Paper-Based Ammonia Gas Sensor Obtained by Facile MXene Spray Coating.

Developing high-performance chemiresistive gas sensors with mechanical compliance for environmental or health-related biomarker monitoring has recently drawn increasing research attention. Among them, two-dimensional MXene materials hold great potential for room-temperature hazardous gas (e.g., NH3) monitoring regardless of the complicated fabrication process, insufficient 2D/3D flexibilities, and poor environmental sustainability. Herein, a Ti3C2Tx MXene/gelatin ink was developed for patterning electrodes through a facile spray coating. Particularly, the patterned Ti3C2Tx-based coating exhibited good adhesion on the paper substrate against repeated peeling-off and excellent mechanical flexibility against 1000 cyclic stretching. The porous morphology of the coating facilitated the NH3 sensing ability. As a result, the 2D kirigami-shaped NH3 sensor exhibited a good response of 7% to 50 ppm of NH3 with detectable concentrations ranging from 5-500 ppm, decent selectivity over interferences, etc., which could be well-maintained even at 50% stretched state. In addition, with the help of mechanically guided compressive buckling, 3D mesostructured MXene origamis could be obtained, holding promise for detecting the coming direction and height distribution of hazardous gas, e.g., the NH3. More importantly, the as-fabricated MXene/gelatin origami paper could be fully degraded in PBS/H2O2/cellulase solution within 19 days, demonstrating its potential as a high-performance, shape morphable, and environmentally friendly wearable gas sensor.

Improved NH3 Gas Sensing Performance of Femtosecond‐Laser Textured Silicon by the Decoration of Au Nanoparticles

The escalating environmental concerns have stimulated the demand for NH3 gas sensors, which are indispensable for real‐time data collection in pollution monitoring. To address this need, optimized NH3 sensor based on femtosecond‐laser textured silicon decorated with Au nanoparticles (Au‐NP) is designed. The morphologies and microstructures of the fabricated samples are characterized by scanning electron microscopy (SEM) and X‐ray diffraction (XRD) technologies. The gas‐sensing results demonstrated that the modification of Au‐NPs significantly enhances the NH3 gas‐sensing performances. Specifically, the sensor based on the textured silicon decorated with Au NPs exhibits a remarkable response of 16.02% toward 20 ppm NH3, which is 4.7 times higher than that of the pristine textured silicon gas sensor at room temperature. In addition, it also demonstrates shortened response and recovery time (26 s/98 s), showing good selectivity and long‐term availability. The enhanced NH3‐sensing mechanism of the sensor is elucidated, mainly due to the synergistic effect of textured silicon and Au NPs. These contribute to the development of portable, wearable, and intelligent sensor equipment.

Efficient detection of 45 ppb ammonia at room temperature using Ni-doped CeO2 octahedral nanostructures

To meet the requirements in air quality monitors for the public and industrial safety, sensors are required that can selectively detect the concentration of gaseous pollutants down to the parts per million (ppm) and ppb (parts per billion) levels. Herein, we report a remarkable NH3 sensor using Ni-doped CeO2 octahedral nanostructure which efficiently detects NH3 as low as 45 ppb at room temperature. The Ni-doped CeO2 sensor exhibits the maximum response of 42 towards 225 ppm NH3, which is ten-fold higher than pure CeO2. The improved sensing performance is caused by the enhancement of oxygen vacancy, bandgap narrowing, and redox property of CeO2 caused by Ni doping. Density functional theory confirms that O vacancy with Ni at Ce site (VONiCe) augments the sensing capabilities. The Bader charge analysis predicts the amount of charge transfer (0.04 e) between the Ni-CeO2 surface and the NH3 molecule. As well, the high negative adsorption energy (≈750 meV) and lowest distance (1.40 Å) of the NH3 molecule from the sensor surface lowers the detection limit. The present work enlightens the fabrication of sensing elements through defect engineering for ultra-trace detection of NH3 to be useful further in the field of sensor applications.