Ppm NH3 Research Articles

Enhanced NH3 sensing performance at ppb level derived from Ti3C2Tx-supported ZnTi-LDHs nanocomposite with similar metal-semiconductor heterostructure

Layered double hydroxides (LDHs) are attracting increased attention in the field of gas sensor owing to their high specific surface and interlayer modifiability. However, the general tendency to restacking and poor conductivity significantly affect the performance of the gas sensor based on LDHs towards rarefied gas. To resolve these problems, we successfully constructed the MXene (Ti3C2Tx)-supported ZnTi-LDHs (LDHs/Ti3C2Tx) nanocomposite with loose heterostructure by one-step hydrothermal method based on electrostatic ordered self-assembly. The LDHs uniformly wrapped on Ti3C2Tx nanosheets form a highly synergistic similar metal-semiconductor contact with Ti3C2Tx, and the formed anti-barrier layer (ABL) has a trapping effect on the electrons generated by NH3-sensing. Meanwhile, the formation of tiny LDHs might be ascribed to the effect of Ti atoms in Ti3C2Tx, which is confirmed by first-principles calculations. Benefiting from similar metal-semiconductor heterostructure and the effect of Ti atoms in Ti3C2Tx, the electrical conductivity and the adsorption active sites are prominently improved, which are essential for the enhancement of sensitivity to rarefied gas. The gas sensor based on ZnTi-LDHs/Ti3C2Tx nanocomposite exhibits about 5 and 9-fold enhancement in response value to 50 ppm NH3 at room temperature (RT) compared with the pure LDHs and Ti3C2Tx, respectively. Notably, the as-fabricated gas sensor could detect as low as 100 ppb NH3 with a response of 1.26 at RT. Furthermore, the LDHs/Ti3C2Tx sensor exhibits fast response/recovery time, high selectivity, acceptable humidity tolerance and outstanding long-term stability towards NH3. Above all, this work provides a feasible route to develop excellent gas-sensing materials of sensor via interfacial design.

Enhanced performance of room temperature ammonia sensors using morphology-controlled organic field-effect transistors

Developing electronic sensors for ammonia (NH3) is very useful for environmental monitoring and diagnostic purposes. In this work, a highly sensitive, organic field-effect transistor (OFET) based, room temperature sensor for NH3 has been fabricated using dinaphtho [2,3-b:2′,3′-f]thieno [3,2-b]thiophene (DNTT), which showed a fast response to low concentration of the analyte down to 100 ppb. A thin film of solution-processed polymethyl methacrylate (PMMA) has been used as the gate dielectric material and its hydrophobic surface promoted structured growth of organic semiconductor, DNTT, by inducing mass transfer. By controlling the thickness and thereby exploiting the growth dynamics of the semiconductor film, the sensor performance was improved. The sensitivity of the device towards 1 ppm of NH3 was almost doubled with a thinner and porous film of DNTT as compared to that with a thick film. Morphological studies of the sensing layers, using atomic force microscopy (AFM), have established this structure-property relation. The variations in different transistor parameters have been studied with respect to different analyte concentrations. The p-channel devices in the enhancement mode showed depletion upon exposure to NH3. The devices exhibited a fast response and good recovery to the initial state within 2 min.

NiWO4 Microflowers on Multi-Walled Carbon Nanotubes for High-Performance NH3 Detection.

NiWO4 microflowers with a large surface area up to 79.77 m2·g-1 are synthesized in situ via a facile coprecipitation method. The NiWO4 microflowers are further decorated with multi-walled carbon nanotubes (MWCNTs) and assembled to form composites for NH3 detection. The as-fabricated composite exhibits an excellent NH3 sensing response/recovery time (53 s/177 s) at a temperature of 460 °C, which is a 10-fold enhancement compared to that of pristine NiWO4. It also demonstrates a low detection limit of 50 ppm; the improved sensing performance is attributed to the porous structure of the material, the large specific surface area, and the p-n heterojunction formed between the MWNTs and NiWO4. The gas sensitivity of the sensor based on daisy-like NiWO4/MWCNTs shows that the sensor based on 10 mol % (MWN10) has the best gas sensitivity, with a sensitivity of 13.07 to 50 ppm NH3 at room temperature and a detection lower limit of 20 ppm. NH3, CO2, NO2, SO2, CO, and CH4 are used as typical target gases to construct the NiWO4/MWCNTs gas-sensitive material and study the research method combining density functional theory calculations and experiments. By calculating the morphology and structure of the gas-sensitive material NiWO4(110), the MWCNT load samples, the vacancy defects, and the influence law and internal mechanism of gas sensitivity were described.

The Room Temperature Highly Sensitive Ammonia Gas Sensor Based on Polyaniline and Nitrogen-Doped Graphene Quantum Dot-Coated Hollow Indium Oxide Nanofiber Composite.

Hollow indium trioxide (In2O3) nanofibers fabricated via an effectively combined method of electrospinning and high-temperature calcination were coated with nitrogen-doped graphene quantum dots (N-GQDs) prepared by a hydrothermal process through electrostatic interaction. The N-GQD-coated hollow In2O3 nanofibers served as a core for the synthesis of polyaniline (PANI)/N-GQD/hollow In2O3 nanofiber ternary composites using in situ chemical oxidative polymerization. The chemical structure and morphology of the fabricated ternary composites were characterized using Fourier transform infrared, field-emission scanning electron microscopy, and transmission electron microscopy. The gas-sensing performances of the ternary composites were estimated by a homemade dynamic test system which was supplied with a real-time resistance acquisition platform at room temperature. The response value of the PANI/N-GQD/hollow In2O3 nanofiber sensor with a loading of 20 wt% N-GQD-coated hollow In2O3 nanofiber and an exposure of 1 ppm NH3 was 15.2, which was approximately more than 4.4 times higher than that of the PANI sensor. This ternary composite sensor was proved to be very sensitive in the detection of NH3 at a range of concentration between 0.6 ppm and 2.0 ppm at room temperature, which is crucial in the detection of hepatic or kidney disease in human breath. The PANI/N-GQD/hollow In2O3 nanofiber sensor also revealed higher selectivity and repeatability when exposed to 1.0 and 2.0 ppm NH3 at room temperature. Because of the excellent selectivity and repeatability in the detection of 1.0 and 2.0 ppm NH3 at room temperature achieved in this study, it is considered that the PANI/N-GQD/hollow In2O3 nanofiber composite sensor will be a favored gas-sensing material applied on human breath for the detection of hepatic or kidney disease.

Twistable and tailorable V2O5/PANI/GO nanocomposites textile for wearable ammonia sensing

Gaseous ammonia (NH3) under high concentration (e.g., larger than 25 ppm) is usually harmful to human organs. Instead, lower - concentration NH3 that is generated from human metabolism may serve as a biomarker for exhaled diagnosis of kidney disease. Ideally, wearable NH3 sensors integrated over cloths are highly desired for real-time monitoring. Here, twistable and tailorable nanocomposites (NCPs) textile has been developed for yielding wearable NH3 sensing, by which graphene oxide was firstly mixed with aniline monomer, and subsequently this mixture was in-situ polymerized by vanadium pentoxide to obtain a ternary NCPs of vanadium oxide, polyaniline and graphene oxide (V2O5/PANI/GO NCPs). Benefiting from the incorporation of PANI, V2O5 and GO, the V2O5/PANI/GO NCPs textile shows enhanced response (Rg/Ra −1 = 31.2 ± 1.8% @10 ppm NH3, room temperature), high stability that maintains 91.5% response after 56 days and excellent interfering selectivity. Remarkably, the V2O5/PANI/GO NCPs textile displays excellent twistability and tailorability. This strategy to V2O5/PANI/GO NCPs textile might be extended to nanosensing materials that could be integrated onto other textiles.

Studies on the Effects of NH3 in H2 and Air on the Performance of PEMFC

The effect of NH3 in H2 and in air was investigated at various concentrations ranging from 1.0 ppm to 100 ppm in air and ranging from 0.25 ppm to 10 ppm in fuel. The effect of NH3 on cathode caused an instantaneous decrease in cell voltage which dropped from 0.734 V to 0.712 V in 30 h and drop rates was 0.73 mV/h for 1 ppm; however, the cell voltage dropped to 0.415 V in 1 h for 100 ppm of NH3. The voltage could not be recovered after the polarization test (V-I test) but could be recovered to 84.4% after operation with neat air for 1.5 h and 98.4% after cycle voltammogram (CV). It was found that the voltage drop was obvious, and the drop rate increased with the NH3 concentration in H2. The voltage drop rates at 500 mA/cm2 were 0.54 mV/h for 0.5 ppm of NH3, 0.8 mV/h for 1 ppm, and 2 mV/h for 10 ppm. The voltage could be recovered from 70.6% to 77.3% after discharged with high purity H2 for 24 h, to 92.8% after being purged with clean air for 10 h and to 98.4% after CV scan. The tolerance concentration of NH3 in H2 for 1000 h was 40 ppb, for 2000 h was 20 ppb, and for 5000 h was 9 ppb.

Layered amorphous a-SnO2 gas sensors by controlled oxidation of 2D-SnSe2

2D-layered amorphous a-SnO2 is utilized for the first time to detect NO2, H2 and NH3 gases at 100 °C operating temperature opening new perspectives for the exploitation of amorphous metal-oxides interfaces for gas sensing applications. Liquid-phase exfoliated 2D-SnSe2 flakes have been subjected to controlled oxidation in air (from 1 h to 170 h) at temperatures below the crystallization temperature of SnO2 (200 °C) yielding template self-assembled, amorphous a-SnO2 thin-layers (10–40 nm thick) grown over 2D-SnSe2. A suitable oxidation process has been optimized by “in operando” monitoring the base line resistance (BLR) while changing the annealing conditions, demonstrating that at least 48 h at 200 °C are required to stabilize BLR, corresponding to the formation of a self-terminating a-SnO2 oxide with excellent BLR and sensor’s signal reproducibility over one year. Humidity cross-response on gas sensing demonstrated that increasing the relative humidity (RH@25 °C) from dry air to 80%, (Rg/Ra) to 1 ppm NO2 increases from 2.2 to 5.7 while (Ra/Rg) to 100 ppm H2 and NH3 decreases from 2.7 to 1.7 and from 1.8 to 1.6 (σ ± 0.2). A preliminary ab-initio DFT modeling of water adsorption over amorphous a-SnO2 highlighted that dissociative adsorption is thermodynamically favored. The thin film sensor’s conduction model, comprising stacked layers of a-SnO2/SnSe2 flakes, is explained by the formation of Schottky barriers between the flakes. The seamless texture of amorphous a-SnO2 skin with no grain-boundaries, no crystal-planes orientations, greatly simplify gas sensing mechanisms assumptions, paving the way for a new class of “layered amorphous metal-oxides gas-sensors” (LAMOS).

Doubly ionized oxygen vacancies dominated Co3O4 nanoparticles for highly selective NH3 sensing application at room temperature

Polycrystalline Co3O4 nanoparticles were synthesized using a hydrothermal method with calcination. The microstructure and surface defects of these materials were investigated systematically. Room temperature gas sensing properties of Co3O4 nanoparticles were tested towards ammonia (NH3). The response value of Co3O4-2 h gas sensor to 200 ppm NH3 is 102.8 with response and recovery time of 65 s and 208 s, respectively. The Co3O4-2 h sensor also exhibited high selectivity, good repeatability and long-term stability. After excluding the impact of specific surface area and grain-size effect on sensitivity, the boosted sensing performance of Co3O4-2 h nanoparticles is mainly attributed to the high Co3+ concentration and the abundant doubly ionized oxygen vacancies (VO¨). This work provides a promising strategy to enhance gas sensing properties of p-type oxides by adjusting charge states of oxygen vacancy.

Facile Fabrication of Hybrid Carbon Nanotube Sensors by Laser Direct Transfer.

Ammonia is one of the most frequently produced chemicals in the world, and thus, reliable measurements of different NH3 concentrations are critical for a variety of industries, among which are the agricultural and healthcare sectors. The currently available technologies for the detection of NH3 provide accurate identification; however, they are limited by size, portability, and fabrication cost. Therefore, in this work, we report the laser-induced forward transfer (LIFT) of single-walled carbon nanotubes (SWCNTs) decorated with tin oxide nanoparticles (SnO2 NPs), which act as sensitive materials in chemiresistive NH3 sensors. We demonstrate that the LIFT-fabricated sensors can detect NH3 at room temperature and have a response time of 13 s (for 25 ppm NH3). In addition, the laser-fabricated sensors are fully reversible when exposed to multiple cycles of NH3 and have an excellent theoretical limit of detection of 24 ppt.

In situ polymerized polyaniline/MXene (V2C) as building blocks of supercapacitor and ammonia sensor self-powered by electromagnetic-triboelectric hybrid generator

This paper reports in situ polymerization of polyaniline (PANI)/MXene (V 2 C) composites as building blocks of supercapacitor and ammonia sensor self-powered by electromagnetic-triboelectric hybrid generator. The high accessible surface of MXene produced abundant high reactivity and electronegativity sites, which could promote or induce the polymerization of aniline on its surface and the polymerization of aniline on its surface could prevent its re-stacking and enhance its electrochemical activity, which could significantly improve the performance of ammonia sensor and supercapacitor. The working principle of the integrated self-power system is to use the hybrid nanogenerator of triboelectric nanogenerators (TENGs) and electromagnetic generator (EMGs) to charge the supercapacitor for driving the ammonia sensor. The supercapacitor utilized PANI/MXene as anode and active carbon as cathode, which displays a capacitance of 337.5 F/g at the current density of 1 A/g, a considerable energy density of 11.25 Wh/kg and a power density of 415.38 W/kg. The sensing material of PANI/MXene nanosheets have an eye catching response value ((R g -R a )/R a = 14.9% @ 1 ppm NH 3 ), good stability (more than 60 days) and fast response/recovery time (9 s/9 s @ 1 ppm NH 3 ), which is much better than the pristine PANI and MXene nanosheets. This work provided a candidate of PANI/MXene for constructing supercapacitor and sensing elements, which opened up an avenue for the integration of self-power gas sensing for industrial and agricultural pollution. • In situ polymerization of PANI/MXene composites as building blocks of supercapacitor and ammonia sensor. • The PANI/MXene composite film-based NH 3 sensor was self-powered by a hybrid power generation system. • The hybrid power generation system is constructed by triboelectric nanogenerators and electromagnetic generator. • A series of detection and alarm systems are designed to realize the real-time transmission and sharing of data.

Facile, Low‐Cost and Flexible Ammonia Sensor Arrays Based on Metallic Ion Charge Carriers and Polymer Matrices

AbstractWith the development of industrial and medical technology, chemical sensors based on electron charge carriers are difficult to meet the upping requirements on excellent sensitivity, good selectivity, and portability. Herein, a new type of sensing material is developed via facile preparation method. Metal ions, instead of electrons, are used as charge carriers and distributed in the polymer matrix. As a representative, the ionic conductive gas sensor based on polyacrylic acid and copper ions (PAA‐Cu(II)) is fabricated. The PAA‐Cu(II) sensor exhibits excellent linear response to ammonia (NH3), together with high sensitivity (50.3% for 50 ppm NH3), good selectivity, and fast response/recovery time (10/10.5 s). The sensor also displays high transparency, long‐term air stability, and excellent flexibility. In addition, sensor arrays based on various metal ions (Cu2+, Co2+, Ni2+, Ag+, Fe3+, Mg2+) and polymers (polyacrylic acid, polyvinyl alcohol, polyethyleneimine) are also developed, and the sensing properties are investigated. The results suggest that metal ions‐based capacitive flexible sensors have great potential for low‐cost chemical sensors and provide a promising strategy for developing new sensing materials.

Conductometric room temperature ammonia sensors based on titanium dioxide nanoparticles decorated thin black phosphorus nanosheets

Ammonia gas (NH3) as a harmful and toxic gas species severely threatens ecological harmony and human health, thus necessitating its sensitive detection at very low dose. In this regard, two-dimensional (2D) nanomaterials have been extensively harnessed as the sensing layers due to the unique merits of large surface area, intriguing layer-dependent electrical behaviors and versatile modifications. Of these 2D candidates, black phosphorus (BP) as a rising representative has attracted considerable attention, whereas undesirably hindered by sluggish response/recovery kinetics and fragile stability. To circumvent these obstacles, we employed titanium dioxide (TiO2) nanoparticles decorated BP nanosheets as the sensing layer to selectively discern 0.5–30 ppm NH3 at room temperature (18 ± 2 °C) for the first time. The constituent ratio-optimized BP-TiO2 sensors exhibited higher response, less baseline drift, shorter response/recovery times, and stronger long-term stability when compared with pure BP counterparts. Enlarged specific surface area, numerous p-n BP-TiO2 heterojunctions and TiO2 nanoparticles involved passivation were primarily responsible for these improvements. In summary, the proposed composite sensors have expanded BP-related gas sensing to NH3 gas for the first time in the experimental perspective simultaneously enriching feasible strategies to improve the operation stability of BP nanosheets.

Mixed-potential ammonia sensor using Ag decorated FeVO4 sensing electrode for automobile in-situ exhaust environment monitoring

High-performance YSZ-based mixed potential NH3 sensor has been developed and utilized with the prospect of excellent applications in in-vehicle SCR (Selective Catalytic Reduction) systems. In order to further lower the detection limit and improve the sensitivity to NH3, we prepared Ag decorated FeVO4 as sensing electrode material through the NaBH4 reduction method in this work. Electrochemical methods such as cyclic voltammetry (CV), linear sweep voltammetry (LSV) and I-t curves are used to explore and compare the electrochemical catalytic activity of electrode materials. 3 mol% Ag decorated FeVO4 was considered as the best sensing electrode material because of its highest electrochemical catalytic activity and reliable stability. Also, the reaction product under the sensor’s working condition was confirmed by the online mass spectrometer. The sensor attached with 3 mol% Ag decorated FeVO4-SE could give a response of − 57 mV to 50 ppm NH3 in 3s and recover to base line in 16s, exhibiting its rapid detection ability at high temperature of 550 °C. Moreover, it displayed good selectivity and a low detection limit of 200 ppb. Additionally, the stability of the sensor under different oxygen concentration and humidity was studied in detail.

Copper Fluoride Doped Polypyrrole for Portable and Enhanced Ammonia Sensing at Room Temperature

AbstractPoint‐of‐care (POC) monitoring of breath ammonia has emerged as a great approach for non‐invasive chronic kidney disease (CKD) diagnosis. Polypyrrole (PPy) is recognized as a suitable polymer material for breath ammonia sensing. Here we describe the copper fluoride (CuF2) doping effect on sensing performance of the ammonia gas sensor based on PPy. At first, PPy was synthesized by chemical oxidative polymerization and characterized by scanning electron microscopy, energy dispersive X‐ray analysis, and Fourier Transform Infrared Spectroscopy techniques. The CuF2 was doped to the polymer by an aqueous ion exchange process. A portable sensing system was developed for portable ammonia detection by measuring the resistance variation of the fabricated electrode from synthesized materials. The gas‐sensing results disclose that the CuF2‐PPy based sensor displays the highest response to 2 ppm NH3, which is 3 times higher than that of the pure PPy sensor. The low limit of detection (LOD) value for pure PPy was found to be 0.19 ppm, which has been decreased to 0.02 ppm for CuF2 doped PPy. The CuF2‐PPy resistive sensor exhibits a sustainable, selective, and stable sensing response to ammonia even in the presence of 60 % humidity. Moreover, the fabricated setup is low‐cost, user‐friendly, and suitable enough to be used at the point of care and CKD diagnosis applications.

Design of p–p heterojunctions based on CuO decorated WS2 nanosheets for sensitive NH3 gas sensing at room temperature

Tungsten disulfide (WS2) nanosheets (NSs) have become a promising room-temperature gas sensor candidate due to their inherent high surface-to-volume ratio, tunable electrical properties, and high on-state current density. For further practical applications of WS2-based gas sensors, it is still necessary to overcome the insensitive response and incomplete recovery at room temperature. In this work, we controllably synthesized high-performance ammonia (NH3) gas sensor based on CuO decorated WS2 NSs. The optimized p–p WS2/CuO heterojunctions improve the surface catalytic effect, thereby enhancing the gas-sensing performance. The pure WS2 NSs-based gas sensors showed a low response and an incomplete recovery in the case of NH3 sensing. After the functionalization of CuO nanoparticles, the WS2/CuO heterostructure-based gas sensor exhibits an improved response value of 40.5% to 5 ppm NH3 and full recoverability without any external assistance. Density functional theory calculations illustrate that the adsorption of CuO for NH3 is much superior to WS2. The p–p heterojunctions strategy demonstrated in this work has great potential in the design of sensitive materials for gas sensors, and provides useful guidance for enhancing the room-temperature sensitivity and recoverability.

Selective catalytic oxidation of ammonia to nitrogen over zeolite-supported Pt-Au catalysts: Effects of alloy formation and acid sites

The selective catalytic oxidation of ammonia (NH3-SCO) to N2 and H2O at low temperatures was studied to remove low-concentration (50 ppm) NH3 from the air. A series of mordenite (M20)-supported Pt-Au alloy catalysts with different Pt:Au ratios were synthesized and tested in the NH3-SCO. The NH3 conversion and N2 selectivity both depended on the ratio of Pt to Au. The 0.52 wt% Pt84Au16/M20 catalyst showed the highest NH3 conversion (90% at 144 °C) even better than Pt100/M20, which was ascribed to the combination of electron-deficient Pt and electron-rich Au in the alloy nanoparticles. The effects of acid sites on the NH3-SCO were investigated by NaOH treatment of Pt84Au16/M20 catalyst. Results suggested that the acid sites could help to increase NH3 conversion, and that Brønsted acid sites are essential for the selective formation of N2.

Rapid synthesis of rhombohedral In2O3 nanoparticles via a microwave-assisted hydrothermal pathway and their application for conductometric ethanol sensing

Rhombohedral In2O3 exhibits high gas sensing potential. However, its rapid synthesis remains challenging, and it is yet to be revealed whether it has a higher gas sensing capability than the cubic counterpart. Herein, we report a facile and rapid synthesis of rhombohedral In2O3 nanoparticles (NPs) via a microwave-assisted hydrothermal pathway, and compare their gas sensing characteristics with those of other In2O3 polymorphs (i.e., cubic NPs and mixed rhombohedral and cubic phases). To investigate the polymorphs for optimized gas sensing, the gas sensing properties of rhombohedral In2O3 NPs are compared with those of mixed-phase In2O3 NPs prepared via a conventional hydrothermal pathway and commercial cubic In2O3 NPs. The pure cubic In2O3 NPs and the mixed-phase In2O3 NPs show similar gas responses (resistance ratios) to 100 ppm ethanol in the temperature range of 150–400 °C. In contrast, the rhombohedral In2O3 NPs exhibit much higher ethanol responses at all the sensor temperatures. In particular, their ethanol response at 300 °C (43.1) is four times higher than the values obtained for the other polymorphic NPs (9.44–11.6) at the same temperature. Furthermore, the rhombohedral In2O3 NPs possess excellent ethanol selectivity with low cross-responses to 100 ppm NH3, CH4, H2, CO, CO2, and NO2 and long-term stable ethanol sensing properties for 21 days. The excellent gas sensing characteristics of rhombohedral In2O3 NPs are strongly related to their gas adsorption, particle sizes, and electrical conductivity. The rhombohedral In2O3 NPs can be potentially used in high-performance breathalyzers for screening drunk drivers.

High performance ammonia gas detection based on TiO2/WO3·H2O heterojunction sensor

In this study, a gas sensor based on TiO2/WO3·H2O (TW) heterojunction with high sensitivity, excellent selectivity and long-term stability for ammonia (NH3) detection was successfully prepared by hydrothermal method. Compared with WO3·H2O and TiO2, TW heterojunction shows excellent selective to NH3 and the response varies by 3 orders of magnitude to 500 ppm NH3 at room temperature (RT, 25 ± 3 °C). The lowest response limit of TW is 0.5 ppm and the response/recovery time is 2.35 s/1.95 s. The main reason for improving the performance of TW heterojunction to NH3 detection is that TiO2 nanoparticles cause more oxygen free radicals on the surface of TW heterojunction, which can react with more NH3 molecules to release more electrons. Therefore, heterojunction structure increases the electrons and reduces the width of electron depletion layer in TW gas sensor. In addition, TW heterojunction has small and uniform particle size which can provide more active sites for the reaction between NH3 and oxygen free radicals to release more electrons. This work provides a heterojunction structure composed of TiO2 and WO3·H2O to effectively improve the performance of sensor for NH3 detection at RT, which is beneficial to the development of high-performance gas sensors.

Dynamic ammonia adsorption by FAU zeolites to below 0.1 ppm for hydrogen energy applications

Hydrogen can be released from ammonia (NH3) by cracking, but the residual ammonia is harmful to polymer exchange membrane fuel cells and should be less than 0.1 ppm (μmol/mol). In this paper, the adsorption of NH3 by commercial faujasite (FAU) zeolites to below 0.1 ppm have been investigated. The results show that the Si/Al ratio of zeolite is inversely proportional to the adsorption capacity, and the strength of ammonia adsorption by cation Li+ is more than that of Na+, thus the ammonia adsorption capacity of LiLSX zeolite is greater than that of 13X–HP zeolite. However, the small granule size of crystalline microspheres and the rough surface of 13X–HP zeolite were the factors that lead to the dynamic NH3 adsorption capacity of 13X–HP zeolite close to LiLSX zeolite. In the dynamic 1700 ppm NH3 adsorption, with a breakthrough point of 0.1 ppm, the adsorption capacity is 9.27 wt% for LiLSX zeolite and 8.73 wt% for 13X–HP zeolite.

One-pot wet chemical synthesis of reduced graphene oxide-zinc oxide nanocomposites for fast and selective ammonia sensing at room temperature

The present study focuses upon the response of nanocomposites of reduced graphene oxide (rGO) and zinc oxide (ZnO) towards ammonia gas at room temperature. We have synthesized reduced graphene oxide-zinc oxide nanocomposites (rGO-ZnO) by wet chemical route via in-situ one-pot method. The as-synthesized samples were characterized using FT-IR spectroscopy, Raman spectroscopy, X-ray Diffraction, Scanning Electron Microscopy (SEM) and high resolution Transmission Electron Microscopy (HR-TEM) techniques. The average crystallite size of the ZnO sample and rGO-ZnO sample, determined by Williamson-Hall analysis of the XRD results, were calculated to be 20.62 nm and 13.21 nm respectively. The TEM analysis suggests that these nanocomposites comprise of ZnO nanoparticles of average size about 10.8 nm, anchored on rGO sheets. At 300 K, the chemiresistive gas sensing response of pure rGO and rGO-ZnO towards subsequently increasing concentrations (from 20 ppm to 200 ppm) of ammonia gas has been studied. rGO-ZnO samples were prepared by varying the concentration of precursor GO dispersion (0.5, 0.75, 1, 1.25, 1.5 mg/mL). The optimal nanocomposite material (1 mg/mL) is found to exhibit excellent selectivity towards ammonia with a response of 8.92 % towards 20 ppm NH3 and a response time of 8 s. The response is found to increase with increase in ppm level of gas. The selectivity of the synthesized nanocomposite towards ammonia has been confirmed by exposing it to 20 ppm of various other gases such as methanol, ethanol, acetone, propanol and chloroform. The response towards these gases was lower as compared to that towards NH3. To assess the potential of the material in practical applications, the effect of ambient humidity on the sample’s surface resistance was studied. The ammonia sensing response in the presence of humidity was found to vary only by 1.5 % from 10 % RH to 70 % RH, beyond which it saturated. The rGO-ZnO nanocomposite sensing material also displayed good reversibility over subsequent exposure cycles and efficient stability of response with aging. The mechanism of NH3 sensing is understood on the basis of heterojunction interactions between rGO and ZnO in the nanocomposites.