Natural Carbonized Sugar as a Low-Temperature Ammonia Sensor Material: Experimental, Theoretical, and Computational Studies

Conductivity-Based Gas Sensors Using Tamarindus indica Polysaccharide-Capped Gold Nanoparticles for the Detection of Volatile Gases

Gold nanoparticles (nAu) were synthesized by a sustainable approach utilizing tamarind seed polysaccharide (TSP). Polysaccharides are naturally occurring polymers derived from tamarind seeds, which function both as capping and reducing agents. Polyaniline (PANI) was subsequently capped over the as-prepared gold nanoparticles in order to facilitate the sensor property. The TSP-nAu-PANI film was fabricated by Methods I and II and utilized in the investigation of active sensor devices for the detection of organic pollutants such as benzene, toluene, and chloroform. The synthesized gold nanoparticles and the TSP-nAu-PANI films were analyzed using several analytical and spectral tools. Among the two methods, the Method II (TSP-nAu-PANI) film has a high sensing response toward benzene (105.69%), toluene (96.99%), and chloroform (74.98%). TSP is also a proton-conducting biopolymer, which enhances the conductivity of the material. The combination with the PANI layer of the film adsorbs the vapors easily and the prepared film material is more effective and ideal for sensing toxic gases.

A synergistic approach to enhance sensitivity and selectivity of room temperature operable ammonia gas sensor with humidity assistance using RGO/WO3nanocomposite

In this study, the fabrication of an ultrahigh selective NH3gas sensor based on RGO/WO3nanocomposite has been proposed. The hydrothermal method was employed to synthesize the RGO/WO3nanocomposite. The formation of RGO/WO3nanocomposite and the elemental composition, structure and morphology of the as-synthesized materials were confirmed through an array of analytical techniques, including XRD, Raman, FT-IR, XPS and TEM. For gas sensing applications, pure RGO and RGO/WO3have effectively spin-coated onto the interdigitated electrodes (IDE's) based on fluorine doped tin oxide (FTO) respectively, and their sensitivity towards NH3was tested. Gas sensing characteristics of prepared materials were analyzed at room temperature (25 °C) under different relative humidity (RH) levels. The developed RGO/WO3sensor was subjected to different NH3concentrations, demonstrating a high sensing response of 89% towards 500 ppm NH3under 11%-97%-11% RH conditions. Notably, the sensor exhibited rapid response and recovery times with an average response time of 92 s and recovery time of 26 s when exposed to 500 ppm NH3under the specified RH conditions. To gauge the material selectivity, the prepared nanocomposite was exposed to a range of volatile organic compounds and the results showcased the sensor's remarkable selectivity and sensitivity specifically toward NH3vapor. This superior performance can be attributed to the abundant active sites and the excellent electron transport properties inherent to the RGO component. Importantly, the RGO/WO3sensor displayed high reproducibility and consistent responses, with minimal degradation (1.98% degradation) over 30 d at 11%-97%-11% RH. Furthermore, we examined the sensor's response with varying levels of relative humidity to assess its potential for real-world applications. The sensor exhibited extremely low power consumption, outperforming a commercially available metal oxide sensor while operating at ambient temperature. The robust performance of RGO/WO3coupled with low power requirements and ambient temperature operation, positions it as a promising candidate for next-generation gas sensing technologies.

Porous metal-graphene oxide nanocomposite sensors with high ammonia detectability

Nickel oxide-graphene oxide (NiO-GO), zinc oxide-graphene oxide (ZnO-GO) and bismuth oxide-graphene oxide (Bi₂O₃-GO) metal oxide-graphene oxide nanocomposite (MO-GO NC) sensors, operable at room temperature, were synthesized via a simple and cost-effective microwave-assisted combustion method for chemiresistive gas sensor applications. From the measured structural, morphological, and elemental detection properties, the sensors are found capable of detecting various gases. The Bi₂O₃-GO NC sensor exhibited excellent response over NiO-GO (~20 at 50 ppm) and ZnO-GO NC (~60 at 50 ppm) sensors for detecting NH₃. The response of the Bi₂O₃-GO NC sensor at 50 ppm NH₃ in just 14 s operation duration was ~81.23, which is improved 25-fold and 13-fold compared to pristine GO sensors. Additionally, the as-developed Bi₂O₃-GO NC sensor demonstrates outstanding repeatability and recovery kinetics, attributed to porosity and the combined effects of MO and GO. The sensing mechanism of the Bi₂O₃-GO NC gas sensors is proposed herein. The superior sensing performance, including quick response and recovery of the Bi₂O₃-GO NC sensor is attributed to favorable charge transfer across the Bi₂O₃ and GO interface. The significance of relative humidity on sensing potential of the Bi₂O₃-GO NC sensor has also been studied and the sensor is confirmed to be unaffected by relative humidity.

A Reusable Polymeric Film for the Alternating Colorimetric Detection of a Nerve Agent Mimic and Ammonia Vapor with Sub-Parts-per-Million Sensitivity

Thin polymeric films were developed for the vapor-phase sequential colorimetric detection of a nerve agent mimic and ammonia with high sensitivity. N-(4-Benzoylphenyl)acrylamide (BPAm), N,N-dimethylacrylamide (DMA), and (E)-2-(methyl(4-(pyridine-4yldiazenyl)phenyl)amino)ethyl acrylate (MPDEA, M1) were copolymerized via free radical polymerization (FRP) to yield p(BPAm-co-DMA-co-MPDEA), hereafter referred to as P1. P1 exhibits selective sensing properties toward diethyl chlorophosphate (DCP), a nerve agent mimic, in pure aqueous media. Upon the addition of DCP, the pyridine groups of P1 were quaternized with DCP, accompanied by a color change from yellow to pink due to the enhancement of the intramolecular charge transfer (ICT) effect. In situ generated quaternized P1, hereafter referred to as P2, after DCP sensing was used to selectively detect ammonia via dequaternization in an aqueous medium. Ammonia detection was indicated by a color change in the solution from pink back to yellow. A surface-immobilized P1 film was prepared and employed for the vapor-phase detection of DCP, demonstrating that an amount of as low as 2 ppm was detectable. Ammonia vapor was also successfully detected by the P2 film via the ammonia-triggered removal of the quaternized phosphates. Alternating exposure of the film to DCP and ammonia resulted in the corresponding color changes, thereby demonstrating the reversibility of the system. The reusability of the polymeric film for detecting DCP and ammonia in the vapor phase was confirmed by performing four sequential colorimetric detection cycles.

Rational Design of Nanoporous MoS2 /VS2 Heteroarchitecture for Ultrahigh Performance Ammonia Sensors

2D transition metal dichalcogenides (TMDs) have received widespread interest by virtue of their excellent electrical, optical, and electrochemical characteristics. Recent studies on TMDs have revealed their versatile utilization as electrocatalysts, supercapacitors, battery materials, and sensors, etc. In this study, MoS₂ nanosheets are successfully assembled on the porous VS₂ (P-VS₂ ) scaffold to form a MoS₂ /VS₂ heterostructure. Their gas-sensing features, such as sensitivity and selectivity, are investigated by using a quartz crystal microbalance (QCM) technique. The QCM results and density functional theory (DFT) calculations reveal the impressive affinity of the MoS₂ /VS₂ heterostructure sensor toward ammonia with a higher adsorption uptake than the pristine MoS₂ or P-VS₂ sensor. Furthermore, the adsorption kinetics of the MoS₂ /VS₂ heterostructure sensor toward ammonia follow the pseudo-first-order kinetics model. The excellent sensing features of the MoS₂ /VS₂ heterostructure render it attractive for high-performance ammonia sensors in diverse applications.

In Situ Growing Double-Layer TiO2 Nanorod Arrays on New-Type FTO Electrodes for Low-Concentration NH3 Detection at Room Temperature

A novel double-layer TiO₂ nanorod array (NRA) gas sensor for room-temperature detection of NH₃ was fabricated by employing etched fluorine-doped tin dioxide (FTO) glass as the in situ growing substrate and the new-type gas-sensing electrode via the facile droplet-coating and hydrothermal methods. Due to the synergistic effect of forces, special double-layer TiO₂ NRAs with a cross-linked and bridgelike structure is formed, in which adequate point junctions can be generated to construct self-assembled electron pathways required for gas-sensing tests. Gas-sensing tests indicate that all samples obtained at different growth times have an excellent gas-sensing response to low-concentration NH₃ at room temperature. Among them, the TiO₂ NRAs obtained at 6 h (S2) exhibit the highest gas-sensing response to 100 ppm NH₃ with a value of 102%. In addition, the growth mechanism, the gas reaction mechanism, and the effect of humidity on the gas-sensing performance are also discussed in the present paper.

A Room-Temperature CNT/Fe₃O₄ Based Passive Wireless Gas Sensor

A carbon nanotube/Fe₃O₄ thin film-based wireless passive gas sensor with better performance is proposed. The sensitive test mechanism of LC (Inductance and capacitance resonant) wireless sensors is analyzed and the reason for choosing Fe₃O₄ as a gas sensing material is explained. The design and fabrication process of the sensor and the testing method are introduced. Experimental results reveal that the proposed carbon nanotube (CNT)/Fe₃O₄ based sensor performs well on sensing ammonia (NH₃) at room temperature. The sensor exhibits not only an excellent response, good selectivity, and fast response and recovery times at room temperature, but is also characterized by good repeatability and low cost. The results for the wireless gas sensor’s performance for different NH₃ gas concentrations are presented. The developed device is promising for the establishment of wireless gas sensors in harsh environments.

Low-Temperature Ionic Layer Adsorption and Reaction Grown Anatase TiO2 Nanocrystalline Films for Efficient Perovskite Solar Cell and Gas Sensor Applications

A low-temperature (90 °C) and directly grown anatase titanium dioxide (TiO₂) nanocrystalline film using successive ionic layer adsorption and reaction (SILAR) for perovskite solar cell and gas sensor applications. TiO₂ nanocrystalline electron transfer layer (ETL) improves the power conversion efficiency (PCE) of perovskite solar cells due to faster charge transport kinetics as well as slower charge recombination process. The optimized TiO₂ nanocrystalline ETL (15 L) demonstrates as high as ~10% PCE with a short circuit current density of 18.0 mA/cm², open circuit voltage of 0.81 V and fill factor of 66.3% in perovskite solar cells. Furthermore, room-temperature ammonia sensing characteristics of TiO₂ nanocrystalline film (25 L) were  demonstrated for various concentration levels of ammonia in dry air conditions. A high room-temperature response of 80% was achieved at 100 ppm of ammonia with rapid response and recovery signatures of 30 and 85 s, and nearly fifteen days stability, respectively. The response of the sensor to other gases such as formaldehyde, petrol, ethanol acetone, and ammonia etc, indicated a high selectivity towards volatile organic compounds of ammonia gas. The room temperature operation, with high selectivity, repeatability and fast transition times, suggests potentially useful in flexible and cost-effective production in optoelectrochemical device technology.

Metal-free heterogeneous and mesoporous biogenic graphene-oxide nanoparticle-catalyzed synthesis of bioactive benzylpyrazolyl coumarin derivatives

We report the preparation of graphene oxide nanoparticles (GONPs), a metal-free, heterogeneous, non-toxic, reusable and mesoporous green-(acid)-catalyst obtained by sugar carbonization through a micro-wave chemical synthesis method for the synthesis of bio-active benzylpyrazolyl coumarin derivatives (BCDs) under thermal conditions (50 °C) in ethanol solvent. The obtained products were purified by re-crystallization from ethanol, assuring usability of GONPs in multicomponent reactions (MCRs) that could find wide application in the synthesis of a variety of biologically potent molecules of therapeutic significance.

Room-temperature successive ion transfer chemical synthesis and the efficient acetone gas sensor and electrochemical energy storage applications of Bi2O3 nanostructures

Successive ion transfer synthesis, efficient chemoresistive gas sensing and asymmetric electrochemical supercapacitive properties of Bi₂O₃ nanostructures are unveiled.