Ppm NH3 Research Articles

Ni-doped (MoO3/MoS2) heterostructure chemiresistive sensor for dual selective detection of NH3 and NOx at room temperature

The transition metal dichalcogenide heterostructures are emerging as promising candidates for room-temperature gas sensors. This work presents a Ni-doped (MoO3/MoS2) heterostructure, synthesized via hydrothermal methods with varying Ni concentrations, for the dual selective detection of NH3 and NOx gases. The electronic sensitization of Ni improves the sensitivity of heterostructure. The heterostructure was characterized by using X-ray diffractometer, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM), with Ni incorporation confirmed by X-ray photoelectron spectroscopy (XPS). The 10 % Ni-doped MoO3/MoS2 heterostructure showed high sensitivity, achieving responses of 15 % and 18.3 % towards 10 ppm NH3 and NOx, respectively, with detection limits of 0.13 ppm and 0.11 ppm. Furthermore, the sensor demonstrated outstanding cyclic stability, device-to-device reproducibility, and long-term stability, with a retained response of 98.1 % and 98.5 % towards NH3 and NOx, respectively. These findings highlight the potential of Ni-doped (MoO3/MoS2) heterostructures for dual gas sensing applications at room temperature.

Transition from p-type to n-type semiconductor in V₂O₅ nanowire-based gas sensors: Synthesis and understanding of the sensing mechanism

Vanadium pentoxide (V2O5) nanowires (NWs) were grown via hydrothermal method, followed by annealing treatment at 500 °C in air. Morphological characterization showed that the V2O5 material consists of nanowires with a diameter of 200 nm and an average length of 2.5 μm. The nanowires were used to make an NH3 sensor that operates at room temperature (28 °C) and relative humidity of 40 % RH, giving a relative response of 6.0 % to 500 ppm. The V2O5 nanowires show a change in behavior from p-type semiconductor to n-type semiconductor when the temperature exceeds 50 °C. The maximum response (35 %) was recorded at a working temperature of 200 °C (when the semiconductor behaves as an n-semiconductor) and showed good response and recovery speed over 500 ppm NH3. The performance of the sensor was studied and a sensing mechanism that takes into account the change of majority charge carriers in the semiconductor was hypothesized.

Electrochemical Impedance Spectroscopy Study of Ceria- and Zirconia-Based Solid Electrolytes for Application Purposes in Fuel Cells and Gas Sensors.

In this study, the structural and electrochemical properties of commercial powders of the nominal compositions Ce0.8Gd0.2O1.9, Sc0.1Ce0.01Zr0.89O1.95, and Sc0.09Yb0.01Zr0.9O1.95 were investigated. The materials are prospective candidates to be used in electrochemical devices, i.e., gas sensors and fuel cells. Based on a comparison of the EIS spectra in different atmospheres (synthetic air, 3000 ppm NH3 in argon, 10% H2 in argon), the reactions on the three-phase boundaries were proposed, as well as the conduction mechanisms of the electrolytes were described. The Ce0.8Gd0.2O1.9 material is a mixed ionic-electronic conductor, which makes it suitable for anode material in fuel cells. Moreover, it exhibits an apparent and reversible response for ammonia, indicating the possibility of usage as an NH3 gas-sensing element. In zirconia-based materials, electrical conduction is realized by oxygen ion carriers. Among them, the most promising from an applicative point of view seems to be Sc0.09Yb0.01Zr0.9O1.95, showing a high, reversible reaction with hydrogen.

Multi-Stimuli Responsive Viologen-Imprinted Polyvinyl Alcohol and Tricarboxy Cellulose Nanocomposite Hydrogels.

Photochromic inks have shown disadvantages, such as poor durability and high cost. Self-healable hydrogels have shown photostability and durability. Herein, a viologen-based covalent polymer was printed onto a paper surface toward the development of a multi-stimuli responsive chromogenic sheet with thermochromic, photochromic, and vapochromic properties. Viologen polymer was created by polymerizing a dialdehyde-based viologen with a hydroxyl-bearing dihydrazide in an acidic aqueous medium. The viologen polymer was well immobilized as a colorimetric agent into a polyvinyl alcohol (PVA)/tricarboxy cellulose (TCC)-based self-healable hydrogel. The viologen/hydrogel nanocomposite films were applied onto a paper surface. The coloration measurements showed that when exposed to ultraviolet light, the orange layer printed on the paper surface switched to green. The photochromic film was used to develop anti-counterfeiting prints using the organic hydrogel composed of a PVA/TCC composite and a viologen polymer. Reversible photochromism with strong photostability was observed when the printed papers were exposed to UV irradiation. A detection limit was monitored in the range of 0.5-300 ppm for NH3(aq). The exposure to heat (70 °C) was found to reversibly initiate a colorimetric change.

Two-dimensional p-n heterojunctions of black phosphorus nanosheet-sensitized α-MoO3 nanoflake for low-temperature chemiresistive NH3 recognition

Of diverse NH3 gas-detection strategies applied in the fields of individual healthcare and industrial production, chemiresistive gas sensors gain the most popularity owing to the superior merits of low cost, convenient signal processing and high sensitivity. However, severe challenges still exist such as elevated operation temperature (>200 °C), limited sensitivity and unsatisfactory selectivity especially under low-concentration and high-humidity conditions. To overcome these hindrances, a sensing layer of black phosphorus nanosheets (BP)-modified α-MoO3 nanoflakes was prepared in this work. After subtle optimization of ingredient composition and operation temperature, the composite sensor S2 could recognize NH3 gas with the concentration spanning from 0.4 to 25 ppm at 40 °C. In particular, a larger mean response (27 % vs. ∼ 2.3 %) with a response/recovery speed of 275/388 s toward 10 ppm NH3 and lower detection of limit (LoD, 0.4 ppm vs. 10 ppm) was achieved with respect to pure BP counterpart. In addition, excellent repeatability, selectivity, long-term stability and humidity-tolerant features were demonstrated for Sensor S2. The improved sensing performance after α-MoO3 incorporation was primarily ascribed to abundant p-n heterojunctions, excellent conductivity of BP and hydrophilic MoO3 that mitigated the water corrosion effect on susceptible BP nanosheets. This work offers an alternative strategy for sensitive and low-temperature NH3 detection, and well cater for the demanding requirements of high sensitivity and low-power consumption in the field of novel gas sensors applicable in the future Internet of Things and exhaled breath-oriented medical diagnosis.

Fe(OH)3/Ti3C2Tx nanocomposites for enhanced ammonia gas sensor at room temperature

Two-dimensional material (2D material) MXene has great application potential in gas sensors because of its excellent controllable performance and vast specific surface area. In this study, we used a straightforward in-situ electrostatic self-assembly technique to create Fe(OH)3/Ti3C2Tx nanocomposites, which were then used to fabricate gas sensors for ammonia detection at room temperature (25 ℃). Several characterization methods were performed aimed at determining the surface appearance and construction of the nanocomposites, and the sensing characteristics and mechanism were also systematically examined. The findings demonstrate the effective incorporation of amorphous Fe(OH)3 nanoparticles on the surface of Ti3C2Tx. Additionally the nanocomposites of Fe(OH)3/Ti3C2Tx have considerably higher specific surface area than pure Ti3C2Tx, hence offering more active NH3 adsorption sites. The response of the sensor to 100 ppm NH3 was 48.6% at room temperature, which was 9.3 times more higher than that of pure Ti3C2Tx. The sensors also have the advantages of long-term stability (33 days), low NH3 detection limit (500 ppb), and rapid recovery time (85 s) and response times (78 s). It is anticipated that this work will be helpful for developing the new generation of wearable ammonia sensors at room temperature.

High‐Performance Flexible Gas Sensor Using Natural Rubber/MXene Composite for Selective and Stable VOC Detection

AbstractFlexible gas sensors are gaining interest for real‐time volatile gas monitoring. A natural rubber (NR)/MXene nanocomposite sensor is developed. Among the six selected target volatile gases, the composite sensor exhibited a strong response value (82% toward 100 ppm NH3) with the fastest response/recovery time (12.3 s/15.5 s) to NH3. The sensitivity showed a clear dependence of gases, suggesting a good selectivity to varying gases. Ti3C2Tx MXene gas sensors exhibited a very low limit of detection of 50–100 ppb for volatile organic compounds (VOCs) at room temperature. In addition, the NR/MXene sensor allows detection of the mixture of ammonia (NH3), dimethyl sulfoxide (DMSO), and acetone (C3H6O) and it shows good response depending on the total concentration of VOC gases. Furthermore, the flexible nanocomposite sensor exhibits stable sensing performance at different bending states (0‐120°) and shows 20‐day atmospheric stability. This sensor's ability extends to alcohol breath analysis, useful for drunk driving detection. This work paves the way to the possibility of using robust MXene‐based toward practical realization of electronic devices.

Wool powder assisted colorimetric sensing yarn with high sensitivity for NH3 monitoring

Colorimetric sensors have applications in gas monitoring due to their simple and quick detection through visible color changes. However, it remains challenging to prepare colorimetric sensors with high sensitivity. Herein, this work fabricated a biomass-based colorimetric sensing yarn with high sensitivity using anthocyanins as the colorimetric dye and wool powder as an effective ammonia (NH3) adsorbent. The sensitivity of the prepared yarns was evaluated for detection limit and response time. Surprisingly, the addition of 3% wool powder greatly improved the sensitivity of the prepared yarns, with a reduction of both detection limit and responsive time from 100 ppm to 20 ppm, and 2 min to 20 s, respectively when exposed in 150 ppm NH3. The prepared yarns also showed good selectivity and reusability. An example of the practical use of colorimetric yarns was presented. This work provides a facile strategy for fabricating wearable devices for toxic gas monitoring with visual output.

Flexible, Multifunctional, and Durable MXene/CeO2/Cellulose Nanofibers for Efficient Energy Conversion‐Storage Capacity Toward Self‐Powered Monitoring of Ammonia

AbstractThe appeal of wearable gas sensors for Internet of Things (IoTs) necessitates flexible sensory units along with sustainable source of energy supply. The key factors required for emergence of these devices are choice of electroactive materials, flexibility, skin‐compatibility, and robustness against harsh environment. Considering this, the multifunctional MXene/CeO2 composites reinforced with electrospun cellulose nanofibers are constructed and investigated for energy conversion, energy storage, and gas sensing applications. Among the synthesized composites, MXene/CeO2 (10 wt%) coated onto cellulose nanofibers outperformed triboelectric nanogenerator (TENG) with open‐circuit voltage of 160 V and supercapacitor (SC) specific capacitance of 388.98 F g−1 and sensing response of 212% toward 10 ppm NH3. The fabricated devices show promising outlooks against practical challenges of influence of humid conditions and different bending states. Lastly, the self‐chargeable device is integrated and the practical implications of charging of SC through TENG and its utilization in sensor powering is demonstrated. The above findings are expected to contribute significantly in envisioning development of wearable health monitors, combining the flexibility features and facilitating autonomous measurements of NH3 pollutant and biomarker.

Fabrication of TPU-Supported Au-Bi2S3/Ti3C2Tx electrospun mat: Towards flexible and Multi-functional sensors for human motion and NH3 detection at room temperature

The potential applications of wearable sensors in health monitoring, micro-environment detection, and advanced soft electronic noses have attracted widespread attention. However, due to the inherent limitations of traditional organic flexible substrates, simultaneously achieving excellent flexibility, high sensitivity, robustness, and breathability remains a significant challenge. Herein, using the electrospinning method, a flexible TPU substrate film was prepared, and Bi2S3/Ti3C2Tx nanocomposite materials were synthesized through a simple one-step hydrothermal method. Au nanoparticles were attached to the surface of the composite material using sodium borohydride, and finally, the surface impregnation method was used to successfully prepare the Au-Bi2S3/Ti3C2Tx-TPU flexible electrospun mat. The as-prepared sensor demonstrated an outstanding response of 154 % to 100 ppm NH3 at room temperature, coupled with high selectivity, repeatability, and long-term stability. The strain properties of the sensor were also evaluated, showcasing its potential for human motion and physiological feature detection, such as breathing, swallowing, and limb movements. The study’s findings indicated that the Au-Bi2S3/Ti3C2Tx-TPU electrospun mat sensor has promising applications in flexible electronics, wearable environmental monitoring devices, and human healthy monitoring.

Enhanced air filtration and ammonia sensing with cellulose nanofibers-based triboelectric nanogenerators under harsh environments

Fire accidents often occur in environments characterized by severe air pollution, toxic gas emissions, and microbial growth, creating significant challenges for developing multifunctional portable healthcare devices. These devices must achieve high filtration efficiency, minimal pressure drop, and the capability to provide early warnings of toxic gas leaks. Triboelectric nanogenerators present a sustainable solution as self-powered energy converters for advanced healthcare applications. In this study, we grafted Ti3C2Tx/MoS2 nanohybrid materials, which form Schottky heterojunctions, onto cellulose diacetate using tetraethyl orthosilicate, followed by electrospinning to produce nanofibrous films. When paired with a negatively charged material, the resulting device achieved an optimal balance with a low-pressure drop (52 Pa) and high filtration efficiency (98.72 % for PM0.3). It also demonstrated exceptional stability under high-temperature and high-humidity conditions. Notably, the device maintained rapid sterilization within 15 min and consistent filtration performance even after multiple washes. Furthermore, the device exhibited precise detection of trace amounts of NH3 (0.1 ppm) and demonstrated a rapid response, achieving an 86 % response rate within 2 s for 100 ppm NH3, providing an early warning 28 s faster than commercial NH₃ monitors. This study introduces a novel approach to the development of multifunctional, self-powered, wearable medical devices that offer high-efficiency air filtration and sterilization, breath monitoring, and rapid toxic gas leakage detection in harsh environments.

Highly sensitive room-temperature ammonia sensor based on PbS quantum dots modified SnS2 nanosheets and theoretical investigation on its sensing mechanism by DFT calculation

Real-time accurate detection of hazardous gases is an urgent issue for industrial development and safeguarding public health. However, large-scale application of gas sensors in the network requires low-power consumption of sensing device for successful integration in smart platform. Although traditional ammonia (NH3) sensors based on semiconductor materials possess various advantages, it still remains the challenge in high operating temperature. Herein, PbS quantum dots (QDs) with higher adsorption energy were used to sensitize SnS2 nanosheets with electron transport capacity to achieve excellent NH3 sensing performance. PbS QDs with an approximately diameter of 10 nm were dispersed on SnS2 nanosheets with an average thickness of 14 nm. Impressively, the optimal sensor employing PbS QDs/SnS2 nanocomposites exhibited high sensor response of 8.5 to 100 ppm NH3, good response/recovery times of 9 s/720 s, as well as excellent selectivity, repeatability, and long-term stability at room temperature of 25 °C. The adsorption behavior and electronic structure of PbS QDs/SnS2 nanocomposites before and after NH3 adsorption were investigated based on density functional theory calculation. Moreover, the sensing mechanism of PbS QDs/SnS2 nanocomposites was also discussed. The designed PbS QDs/SnS2 nanocomposites hold considerable promise as a candidate in realizing superior NH3 sensing performance at room temperature.

Room-temperature NH3 sensor with ppb detection via AACVD of nanosphere WO3 on IO SnO2

The room temperature gas sensor has attracted sufficient attention due to the fact that low-power products are more suitable for practical environments. However, developing gas sensors with low detection limits remains challenging. In this paper, a room-temperature sensor was prepared by in situ growth of WO3 nanospheres on SnO2 inverse opal (IO) by aerosol assisted chemical vapor deposition (AACVD) method, detecting ppb level of ammonia. The WO3 nanospheres are directly fabricated on IO, and their elemental composition, morphology and structure is characterized using XRD, SEM and TEM. The results show that WO3 nanospheres have been prepared on SnO2 IO successfully. It showes that the WO3/SnO2(WS) type sensor has a detection limit as low as 1 ppb at room temperature from the gas sensitivity data. In addition, the sensor's response value to 100 ppm NH3 reached 65 %. Its excellent sensing performance depends on the distinctive morphology features of WO3 and SnO2. The hierarchical characteristic effectively enhances the sensing performance for NH3. Consequently, this presents a feasible solution for fabricating the room temperature NH3 sensor.

High-Yield WS2 Synthesis through Sulfurization in Custom-Modified Atmospheric Pressure Chemical Vapor Deposition Reactor, Paving the Way for Selective NH3 Vapor Detection.

Nanostructured transition metal dichalcogenides have garnered significant research interest for physical and chemical sensing applications due to their unique crystal structure and large effective surface area. However, the high-yield synthesis of these materials on different substrates and in nanostructured films remains a challenge that hinders their real-world applications. In this work, we demonstrate the synthesis of two-dimensional (2D) tungsten disulfide (WS2) sheets on a hundred-milligram scale by sulfurization of tungsten trioxide (WO3) powder in an atmospheric pressure chemical vapor deposition reactor. The as-synthesized WS2 powders can be formulated into inks and deposited on a broad range of substrates using techniques like screen or inkjet printing, spin-coating, drop-casting, or airbrushing. Structural, morphological, and chemical composition analysis confirm the successful synthesis of edge-enriched WS2 sheets. The sensing performance of the WS2 films prepared with the synthesized 2D material was evaluated for ammonia (NH3) detection at different operating temperatures. The results reveal exceptional gas sensing responses, with the sensors showing a 100% response toward 5 ppm of NH3 at 150 °C. The sensor detection limit was experimentally verified to be below 1 ppm of NH3 at 150 °C. Selectivity tests demonstrated the high selectivity of the edge-enriched WS2 films toward NH3 in the presence of interfering gases like CO, benzene, H2, and NO2. Furthermore, the sensors displayed remarkable stability against high levels of humidity, with only a slight decrease in response from 100% in dry air to 93% in humid environments. Density functional theory and Bayesian optimization simulations were performed, and the theoretical results agree with the experimental findings, revealing that the interaction between gas molecules and WS2 is primarily based on physisorption.

Cu3(HHTP)2 decorated over rGO nanocomposites for flexible NH3 and H2S dual sensing at room temperature

Ammonia (NH3) and hydrogen sulfide (H2S) are both poisonous and corrosive gases, and timely detecting their leakage is thus required. Ideally, employing individual flexible sensor to simultaneously detect NH3 and H2S dual gases at room temperature would contribute to their miniaturization and integration, however, remains challenging. Here, flexible NH3 and H2S dual sensing at room temperature has been developed by utilizing Cu3(HHTP)2 decorated over reduced graphene oxide nanocomposites {Cu3(HHTP)2//rGO NCPs, HHTP=2,3,6,7,10,11-hexahydroxytriphenylene}, which have been synthesized via oxidation–reduction reaction of GO and Cu3(HHTP)2 metal–organic frameworks (MOFs). Typically, the Cu3(HHTP)2 MOFs are observed with spiny surface, and as-synthesized Cu3(HHTP)2//rGO NCPs present amorphous crystallization. Beneficially, Cu3(HHTP)2//rGO NCPs exhibit the NH3 and H2S dual sensing with the resistance-increasing response toward 10–50000 ppm NH3 and resistance-decreasing response to 0.1–20 ppm H2S. Further, the sensor prototype shows 40 days-long stability and 75 % high relative humidity tolerance, respectively. Remarkably, the ternary-NCPs show excellent flexibility, along with excellent sensing performance against various bendings. Theoretically, rGO with high specific surface ratio and Cu3(HHTP)2 MOFs with enriched adoption sites might contribute to NH3 and H2S diffusion and adsorption. Practically, the simulation utilizing Cu3(HHTP)2//rGO NCPs to monitor H2S and NH3 has been conducted with reliable sensing.

NH3 gas sensing and NH3-induced anti-counterfeiting based on nontoxic ternary copper halide

Lead-free ternary copper halides are emerging environmentally friendly materials, which have recently received great attention for their favorable optoelectronic properties. However, few attention was paid to their applications in gas sensing and gas-triggered fluorescence anti-counterfeiting. In this work, we demonstrate an effective Cs3Cu2I5 halide for NH3 sensing and NH3-triggered fluorescence anti-counterfeiting applications. The Cs3Cu2I5-based electrical NH3 sensor exhibits exceptional sensing performance, in which a resistance response of 77.8 % is achieved at 50 ppm NH3 with a rapid response time (9 s). To elucidate the NH3 sensing mechanism, we investigated the NH3-induced optical and structural evolutions including absorption, photoluminescence (PL), and Raman spectra. Our findings suggest that NH3 molecules, acting as electron donors, adsorb on the Cs3Cu2I5 surface, inducing the decomposition of Cs3Cu2I5 into CsCu2I3 and CsI. During this process, the CsCu2I3·NH3 intermediate phase is generated as a shell layer onto the surface of Cs3Cu2I5 grain, leading to an increase in electrical conductivity (or decrease in resistance), and an emission of bright yellow-red fluorescence from CsCu2I3. Inspired by NH3-induced fluorescence emission, we also explored a novel gas-triggered anti-counterfeiting method using Cs3Cu2I5-paper, demonstrating favorable reversibility and convenience, compared to previously reported water-triggered anti-counterfeiting techniques. This work will promote the development of design of Cs3Cu2I5 for gas sensing and gas-triggered fluorescence anti-counterfeiting applications in the future.

Phase-Engineered MoSe2/CeO2 Composites for Room-Temperature Gas Sensing with a Drastic Discrimination of NH3 and TEA Gases.

Detecting and distinguishing between hazardous gases with similar odors by using conventional sensor technology for safeguarding human health and ensuring food safety are significant challenges. Bulky, costly, and power-hungry devices, such as that used for gas chromatography-mass spectrometry (GC-MS), are widely employed for gas sensing. Using a single chemiresistive semiconductor or electric nose (e-nose) gas sensor to achieve this objective is difficult, mainly because of its selectivity issue. Thus, there is a need to develop new materials with tunable and versatile sensing characteristics. Phase engineering of two-dimensional materials to better utilize their physiochemical properties has attracted considerable attention. Here, we show that MoSe2 phase-transition/CeO2 composites can be effectively used to distinguish ammonia (NH3) and triethylamine (TEA) at room temperature. The phase transition of nanocomposite samples from semimetallic (1T) to semiconducting (2H) prepared at different synthesis temperatures is confirmed via X-ray photoelectron spectroscopy (XPS). A composite sensor in which the 2H phase of MoSe2 is predominant lacks discrimination capability and is less responsive to NH3 and TEA. An MoSe2/CeO2 composite sensor with a higher 1T phase content exhibits high selectivity for NH3, whereas one with a higher 2H phase content (2H > 1T) shows more selective behavior toward TEA. For example, for 50% relative humidity, the MoSe2/CeO2 sensor's signal changes from the baseline by 45% and 58% for 1 ppm of NH3 and TEA, respectively, indicating a low limit of detection (LOD) of 70 and 160 ppb, respectively. The composites' superior sensing characteristics are mainly attributed to their large specific surface area, their numerous active sites, presence of defects, and the n-n type heterojunction between MoSe2 and CeO2. The sensing mechanism is elucidated using Raman spectroscopy, XPS, and GC-MS results. Their phase-transition characteristics render MoSe2/CeO2 sensors promising for use in distributed, low-cost, and room-temperature sensor networks, and they offer new opportunities for the development of integrated advanced smart sensing technologies for environmental and healthcare.

Synthesis of CuO Thin Film Incorporated with Nanostructured Nd2O3 Deposited by Pulsed Laser Deposition for Ammonia Sensing Applications

This study involved depositing thin films of copper oxide (CuO) and copper oxide films incorporated with neodymium oxide (Nd2O3) in various weight ratios using the pulsed laser deposition technique to fabricate an ammonia gas sensor. The characteristics of the developed films were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and photoluminescence spectroscopy (PL) techniques. The study investigated the impact of incorporating Nd2O3 into the CuO film on its sensing characteristics. The X-ray analysis revealed a polycrystalline structure of CuO with a crystal size of 19 nanometers. Furthermore, incorporating CuO and Nd2O3 formed a mixed phase comprised of both CuO and Nd2O3. The average crystallite size varied with the Nd2O3 incorporation rate from 19[Formula: see text]nm to 14.7[Formula: see text]nm. With increasing Nd2O3 incorporation ratios, the surface morphology changed from smooth to spherical-like nanostructures, and the average particle sizes varied from 28[Formula: see text]nm to 130[Formula: see text]nm. The PL spectrum analysis results confirmed that the incorporation of Nd2O3 resulted in a change in the peak intensity of the PL spectrum, with a significant increase in the peak associated with oxygen vacancies, contributing to the improvement of the sensor response. The incorporation of Nd2O3 greatly enhanced the sensitivity of the as-deposited CuO film. The sample with 5 wt.% Nd2O3 exhibited the maximum sensitivity, reaching 180% against 79 ppm NH3 at a working temperature of 50[Formula: see text]C.

Novel flexible chemiresistive ammonia sensors based on rGO/ZIF-8 composites deposited on conductive graphite sheets

This work presents novel investigations on room temperature chemiresistive ammonia (NH3) gas sensing capability of composite materials based on reduced graphene oxide (rGO) and ZIF-8 metal organic framework (MOF), deposited on flexible graphite substrate. These rGO/ZIF-8 composites synthesized via a facile one-pot wet chemical route were found to exhibit a fast, highly sensitive and reversible response over successive exposure cycles towards various concentrations of NH3. The enhanced response is attributable to the synergistic performance of the appreciably conductive rGO and the highly porous ZIF-8. ZIF-8 with its high specific surface area, microporous structure and hydrophobicity, serves to provide greater gas adsorptive capacity as well as resistance to effects of ambient moisture. rGO, on the other hand, has limited specific surface area due to π-π restacking of its sheets but it is capable of providing a conductive template to the hybrid material. Consequently, the NH3 gas sensing performance parameters of rGO/ZIF-8 were measured to be exceedingly better than those of bare rGO and ZIF-8 synthesized separately. A response of 15.98 % was recorded towards 10 ppm NH3 with response/recovery times as 2.8/6 s for the rGO/ZIF-8 composites. The enhanced gas sensing performance is credited to the formation of hierarchical pore structure which allows for greater adsorption at the micropore sites and faster diffusion through the mesopores. The effect of rGO loading in the hybrid materials was also assessed. The composite materials exhibited appreciable stability with respect to ambient aging. The adsorption behaviors and the resultant gas sensing mechanisms have also been discussed for the investigated materials.

A novel electrochemical ammonia sensor based on Pt NPs@MIL101(Cr)-NH2 for chemical leaks detection at room temperature

Achieving the real-time, low-cost, portable and accurate NH3 detection is of great importance in industry owing to the toxicity of NH3. In this paper, Pt NPs@MIL-101-NH2 composites modified screen-printed electrodes (SPEs) were prepared by solvothermal method and ionic liquids [BMIM][BF4] were used as electrolytes. Finally, the prepared Pt NPs@MIL-101-NH2/SPEs were combined with a miniature electrochemical workstation to construct a novel electrochemical NH3 sensor. The experimental results showed that Pt NPs@MIL-101-NH2 has excellent adsorption capacity for NH3, and the sensor has good linearity in the range of 0.7–600 ppm with low limit of detection (0.58 ppm) and fast response time for 10 ppm NH3 (8.0 s). Furthermore, this sensor also possesses excellent stability, reproducibility, anti-interference and accuracy. The synthesized Pt NPs@MIL-101-NH2 nanocomposite was proved to be an excellent candidate for constructing high-performance NH3 sensor for industry.