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The rapid and skillful detection of toxic gases is a crucial requirement for the advancement of gas sensors. In this study, we fabricated undoped and In-doped (1 %, 3 %, and 5 % by weight) ZnO films using a two-step modified SILAR deposition technique. The ethanol gas sensing properties of both undoped and In-doped ZnO films were examined across a range of operating temperatures (from room temperature, 27 °C–200 °C) and concentrations (1 ppm–50 ppm). Of all the films, those doped with 5 % Indium exhibited the most stable, reproducible, and highest response, achieving 86.27 % at 50 ppm ethanol at an operating temperature of 100 °C. Compared to the undoped ZnO films, all Indium-doped ZnO films demonstrated significantly shorter response times (17 s) and recovery times (19 s). The response of all the deposited films to various gases such as acetone, methanol, toluene, xylene, and formaldehyde was lower than their response to ethanol. The mechanism behind the enhanced sensing characteristics of the Indium-doped ZnO films is explored. Additionally, the impact of humidity on sensor performance was investigated. This study reveals that 5 % In-doped ZnO films hold great potential as materials for ethanol gas sensing applications. [ABSTRACT FROM AUTHOR]

We present the results of gas sensing using the fluctuation-enhanced sensing method in selected two-dimensional materials (2DMs). We claim that gas sensing selectivity can be improved further by considering semiconducting two-dimensional materials doped by noble metal nanoparticles. The 2DMs’ structures exhibit some imperfections defined by their structure, occurring repeatedly there. These imperfections are adsorption–desorption centers responsible for gas-sensing properties and generating flicker noise of various intensities. We consider how these imperfections can be modulated and utilized for fluctuations-enhanced gas sensing. We propose the decoration of 2DMs by noble metal nanoparticles that impact flicker noise. Additionally, we consider utilizing localized surface plasmonic resonance induced by irradiation at selected wavelengths. [ABSTRACT FROM AUTHOR]

Since its first application in the 1950s, the laser has become an indispensable tool in scientific research and manufacturing. Laser manufacturing includes traditional methods such as cutting and engraving and emerging methods such as laser‐induced surface modification, laser‐induced materials transfer, and laser ablation synthesis. Laser manufacturing is widely applied in the fabrication of multifunctional sensing systems. Compared with other manufacturing methods such as lithography, vacuum deposition, and etching processes, laser manufacturing technology has several advantages, including maskless patterning, high precision, non‐contact processing, minimum heat affected zone, high throughput, ability to work with multiple materials, and ease of automation and integration. Here, this review aims to present a comprehensive analysis of the applications of laser manufacturing in various components of health and gas monitoring systems. Emphasis is placed on the application of laser manufacturing in various components of biosensors, including microchannels, sensing circuits, and working electrodes. Subsequently, laser manufacturing of physical and gas sensors is introduced. Meanwhile, traditional laser manufacturing methods, laser surface modification, laser‐induced material transfer, and laser ablation synthesis are introduced. Finally, the challenges and prospects of laser manufacturing in sensing systems are discussed. [ABSTRACT FROM AUTHOR]

We are proposing a novel self-assembled monolayer (SAM) functionalized ZnO nanowires (NWs)-based conductometric sensor for the selective detection of hydrogen (H2). The modulation of the surface electron density of ZnO NWs due to the presence of negatively charged terminal amine groups (−NH2) of monolayers leads to an enhanced electron donation from H2 to ZnO NWs. This, in turn, increases the relative change in the conductance (response) of functionalized ZnO NWs as compared to bare ones. In contrast, the sensing mechanism of bare ZnO NWs is determined by the chemisorbed oxygen ions. The functionalized ZnO NWs exhibit an eight times higher response compared to bare ZnO NWs at an optimal working temperature of 200 °C. Finally, in comparison to studies in the literature involving strategies to enhance the sensing performance of metal oxides toward H2, like decoration with metal nanoparticles, heterostructures, and functionalization with a metal–organic framework, etc., SAM functionalization showed superior sensing results. [ABSTRACT FROM AUTHOR]

Improving the gas‐sensing properties of sensors is important for the detection of ultralow‐concentration gases. As sensor signals are generated from the reactions on the surface of the sensor material, improving the surface structure of the sensor material can enhance the sensing properties. In this study, nanosheet‐type tin oxide with a metastable (101) crystal facet surface was used as the gas sensor material. To enhance the sensing properties, crystal facet‐controlled cerium oxide with superior oxygen storage capacity at moderate temperatures was decorated on the surface of the nanosheet‐type tin oxide material. An investigation of the sensor properties revealed that the decorated sensor exhibited improved gas selectivity and enhanced sensitivity to all tested gases. Prior to decoration, selectivity was observed for acetone and ethanol, whereas the decorated sensor exhibited high selectivity for acetaldehyde. The limits of detection of the decorated sensors were 245, 459, and 934 ppt for acetone, ethanol, and acetaldehyde, respectively. Thus, the proposed material can effectively enhance the sensing of extremely low‐concentration gases. [ABSTRACT FROM AUTHOR]

With recent trends moving towards sustainable approaches in adherence to environmental, social, and governance (ESG) standards, research is actively focused on sustainable production of high-potential materials. In this study, a successful synthesis pathway was demonstrated for a graphene/tungsten carbide (WC) nanocomposite via pulsed arc discharge in liquid medium, utilizing crude palm oil and commercial cooking palm oil as liquid precursors. The synthesis of the graphene/WC nanocomposites was carried out by applying current with amplitude of 80 A and 100 A to the tungsten electrode immersed in the liquid palm oil, subjected to 150 arc discharges. A comparative investigation was performed to examine the morphological and functional characteristics of the materials synthesized from the different types of palm oil under different current conditions. In addition, the synthesized nanocomposites were assessed with respect to their gas sensing performance. Impressively, the CRG100(150) nanocomposite (produced from crude palm oil with current of 100 A) exhibited gas sensing response of 4.853% upon injection of 200 ppm of ethanol. The CRG100(150) nanocomposite also demonstrated short response and recovery time of 43 s and 182 s, respectively. Thus, the successful synthesis of CRG100(150), utilizing a natural precursor via arc discharge in liquid, paves the way for the development of sustainable gas sensing materials. [ABSTRACT FROM AUTHOR]

In this study, pristine silver-doped zinc oxide (Ag–ZnO) and Plumbago zeylanica leaf extract (PZE) incorporated with Ag–ZnO, along with the additional material of cetyltrimethylammonium bromide (CTAB)-assisted Ag–ZnO nanorods, were synthesized and extensively characterized. The basic properties of the samples were studied and optimized. Gas sensing measurements were conducted, and the obtained results were thoroughly interpreted. The study includes demonstrating and examining pure Ag–ZnO, PZE-added Ag–ZnO, and CTAB-assisted Ag–ZnO. Notably, the presence of CTAB exhibited a favorable effect on the Ag–ZnO, indicating an enhanced isopropyl alcohol gas sensing response time of 20 s at 15 ppm within an ambient temperature. Additionally, improvements in selectivity and reduced sensor resistance in current (nanoampere - nA) were observed in CTAB-assisted Ag–ZnO. The sensing mechanism was investigated, focusing on the depletion layer of Ag–ZnO with the surfactant. The work emphasizes the sensing abilities of PZE-assisted Ag–ZnO and CTAB Ag–ZnO, highlighting the significance of these noble metals in systematic gas sensing applications. [ABSTRACT FROM AUTHOR]

The MXene Ti3C2Tx was synthesized using hydrofluoric acid and an improved multilayer method in this study. Subsequently, a Bi2O3/Ti3C2Tx composite material was produced through hydrothermal synthesis. This composite boasts a unique layered structure, offering a large surface area that provides numerous contact and reaction sites, facilitating the adsorption of ammonia on its surface. The prepared Bi2O3/Ti3C2Tx-based sensor exhibits excellent sensing performance for ammonia gas, including high responsiveness, good repeatability, and rapid response–recovery time. The sensor's response to 100 ppm ammonia gas is 61%, which is 11.3 times and 1.6 times the response values of the Ti3C2Tx gas sensor and Bi2O3 gas sensor, with response/recovery times of 61 s/164 s at room temperature, respectively. Additionally, the gas sensitivity mechanism of the Bi2O3/Ti3C2Tx-based sensor was analyzed, and the gas sensing response mechanism was proposed. This study shows that the sensor can effectively enhance the accuracy and precision of ammonia detection at room temperature and has a wide range of application scenarios. [ABSTRACT FROM AUTHOR]

Real‐time monitoring of carbon dioxide (CO2) is imperative for medical diagnosis and effective environmental preservation. Despite the formidable challenge posed by the inherent chemical inertness of CO₂ molecules, a pioneering CO2 sensor based on MOF‐804 cofunctionalized with ionic liquid (IL) and m‐cresol purple (mCP) is successfully developed. By ingeniously integrating hydrogen bonding, electrostatic interactions, and hydrophobic properties within the sensitive layer, the sensor achieves a state‐of‐the‐art sensitivity (Δf = 384 Hz), an exceptionally vast detection range spanning 400–80 000 ppm, and remarkable stability with minimal sensitivity drift even at relative humidity (RH) levels exceeding 80%. Furthermore, the inherent gasochromic property, stemming from the zwitterionic mechanism, paves the way for innovative self‐sustaining CO2 test strips and groundbreaking applications, including CO2 tracking and CO2‐encrypted security labeling technology. Collectively, the realization of this ultra‐sensitive and robust CO2 monitoring approach, coupled with its CO2‐triggered visual and multifunctional capabilities, opens up novel avenues for dynamic CO2 detection, advanced military encryption strategies, and enhanced health management systems. [ABSTRACT FROM AUTHOR]

In this study, we developed and validated an improved tuning method for a nonlinear scanning laser diode in methane gas sensing, using wavelength modulation spectroscopy - tunable diode laser absorption spectroscopy (WMS-TDLAS). This approach combines cubic nonlinear scanning with high-frequency modulation to precisely target the methane absorption peak at 6046.96 cm−1. The method enhances absorption time, thus increasing system sensitivity and stability. Our results show that this nonlinear scanning, optimized for peak absorption, significantly improves the slope of the methane concentration relationship curve by 76.9%. It also reduces the standard deviation by 61.1% and the limit of detection by 60% compared to linear scanning. The limit of detection the system is 4.2 ppm, and the optimal integration time is 48s. This novel modulation strategy significantly enhances the WMS-TDLAS system's efficiency, offering significant benefits for various applications. • Cubic nonlinear scanning method (CNSM) was proposed and CH 4 detection was verified. • Scanning central wavenumber of LD obtained a longer absorption time. • CNSM significantly improved the slope of the methane concentration curve. • The sensing sensitivity and stability were improved by 45% and 49%, respectively. [ABSTRACT FROM AUTHOR]

The construction of heterojunctions is generally considered as one of the effective strategies to improve gas sensing performance. Herein, the NiO/Al 2 O 3 (NAO) hybrid structure is constructed by calcining Ni–Al layered double hydroxides (NiAl-LDHs). The specific surface area and pore size of NAO are effectively regulated by changing the content of NaOH. The XPS and BET characterization results indicate that NAO-5 exhibits a high oxygen vacancy content, a large specific surface area (468.524 m2 g−1), and abundant pore size. The hydrogen (H 2) sensitivity property of NAO was investigated, and NAO-5 exhibited outstanding gas sensing performance to 500 ppm H 2 at 370 °C, including high response (10.524), fast response recovery speed (21 and 30 s), and wide detection range (0.1–5000 ppm). The improved gas property is mainly attributed to the increased oxygen vacancies and specific surface area. This study provides a feasible approach for NiAl-LDHs in H 2 monitoring and early warning. [Display omitted] • NAO-based sensor was prepared by controlling the amount of NaOH to induce Ni–Al hydrotalcite derivatives. • NAO-based sensor exhibited remarkably enhanced response toward H 2. • NAO-based sensor displayed short response and recovery time to H 2 (21/30 s). • NAO-based sensor showed a wide detection range (5000-0.1 ppm) and a low detection limit (100 ppb). [ABSTRACT FROM AUTHOR]

In residential buildings that are private, autonomous, and occupied spaces for most of the time, it is necessary to maintain good indoor air quality (IAQ), especially when there are children, elderly, or other vulnerable users. Within the development of sensors, their low-cost features with adequate accuracy and reliability, as well as Internet of Things applications, make them affordable, flexible, and feasible even for ordinary occupants to guarantee IAQ monitoring in their homes. This systematic review searched papers based on Scopus and Web of Science databases about the Low-Cost Sensors (LCS) and IoT applications in residential IAQ research, and 23 studies were included with targeted research contents. The review highlights several aspects of the active monitoring strategies in residential buildings, including the following: (1) Applying existing appropriate sensors and their target pollutants; (2) Applying micro-controller unit selection; (3) Sensors and devices' costs and their monitoring applications; (4) Data collection and storage methods; (5) LCS calibration methods in applications. In addition, the review also discussed some possible solutions and limitations of LCS applications in residential buildings based on the applications from the included works and past device development experiences. [ABSTRACT FROM AUTHOR]

Graphene and MXenes have emerged as promising materials for gas sensing applications due to their unique properties and superior performance. This review focuses on the fabrication techniques, applications, and sensing mechanisms of graphene and MXene-based composites in gas sensing. Gas sensors are crucial in various fields, including healthcare, environmental monitoring, and industrial safety, for detecting and monitoring gases such as hydrogen sulfide (H2S), nitrogen dioxide (NO2), and ammonia (NH3). Conventional metal oxides like tin oxide (SnO2) and zinc oxide (ZnO) have been widely used, but graphene and MXenes offer enhanced sensitivity, selectivity, and response times. Graphene-based sensors can detect low concentrations of gases like H2S and NH3, while functionalization can improve their gas-specific selectivity. MXenes, a new class of two-dimensional materials, exhibit high electrical conductivity and tunable surface chemistry, making them suitable for selective and sensitive detection of various gases, including VOCs and humidity. Other materials, such as metal-organic frameworks (MOFs) and conducting polymers, have also shown potential in gas sensing applications, which may be doped into graphene and MXene layers to improve the sensitivity of the sensors. [ABSTRACT FROM AUTHOR]

This paper presents a novel technique for extracting the alveolar part of human breath. Gas exchange occurs between blood and inhaled air in the alveoli, which is helpful in medical diagnostics based on breath analysis. Consequently, the alveolar portion of the exhaled air contains specific concentrations of endogenous EVOC (exogenous volatile organic compound), which, among other factors, depend on the person's health condition. As this part of the breath enables the screening for diseases, accurate sample collection for testing is crucial. Inaccurate sampling can significantly alter the composition of the specimen, alter the concentration of EVOC (biomarkers) and adversely affect the diagnosis. Furthermore, the volume of alveolar air is minimal (usually <350 mL), especially in the case of people affected by respiratory system problems. For these reasons, precise sampling is a key factor in the effectiveness of medical diagnostic systems. A new technique ensuring high accuracy and repeatability is presented in the article. It is based on analyzing the changes in carbon dioxide concentration in human breath using a fast and compensated non-dispersive infrared (NDIR) sensor and the simple moving adjacent average (SMAA) algorithm. Research has shown that this method accurately identifies exhalation phases with an uncertainty as low as 20 ms. This provides around 350 ms of breath duration for carrying out additional stages of the diagnostic process using various types of analyzers. [ABSTRACT FROM AUTHOR]

Due to the non-selective behavior of gas sensors in electronic nose (e-nose) systems, the provided signals in exposure to target analytes contain un-needed information. These are considered as noise reducing the detection accuracy. Feature selection, as a pre-processing step in data analysis, removes extra information from the sensors' signals and provides a more relevant data matrix with lower dimensionality to enhance the system selectivity. In the high-dimensional sensor array response spaces, it is however essential to improve the conventional algorithms to be able to cope with complicated feature selection problem. In this study, in order to acquire optimal responses from the gas sensor array of an e-nose system and increase its selectivity for detection of rice type and its storage duration (freshness), the feature selection problem was formulated in an optimization framework. For this reason, a particle swarm optimization (PSO) with an automatic stagnation detecting system was enhanced by genetic operators of differential evolution. This helped acquiring more exploration ability through providing oriented jumps. It was revealed that the system's detection accuracy was improved when smaller subset of features was utilized instead of the whole response, indicating that the sensor array signals included large amount of irrelevant information. The improved PSO could significantly present lower error values than the standard PSO and other examined conventional algorithms. It was concluded the developed algorithm has the potential to be applied as a promising feature selection algorithm in high-dimensional signals of the e-nose systems. [ABSTRACT FROM AUTHOR]

In recent years, the development of efficient and environmentally friendly synthesis methods for nanomaterials has gained significant attention in various research fields, particularly in gas‐sensing applications. Among these methods, ultrasonic synthesis stands out for its simplicity, cost‐effectiveness, and ecofriendly nature. Herein, a simple and green ultrasonic synthesis process is used to synthesize the SnO2 nanoparticles‐decorated rGO nanosheets. The obtained X‐ray diffraction reveals the tetragonal rutile‐type crystal structure. The transmission electron microscopy images reveal the decoration of SnO2 nanoparticles on the surfaces of the rGO sheets. SnO2 nanoparticles of size 4–8 nm are identified on the surfaces of the rGO sheets. Furthermore, the optical absorbance and photoluminescence spectra of the nanocomposites validate charge migrations occurring at the interface of SnO2 and the rGO sheets. Compared to the pristine SnO2 nanoparticles, the green ultrasonically synthesized SnO2 nanoparticles‐decorated SnO2/rGO nanocomposite exhibits better sensing performance against NO2 gas and shows selectivity for NO2 gas at 200 °C. The SnO2/rGO nanocomposite demonstrates high NO2 sensing with appealing sensing properties such as excellent responsiveness (67% at 400 °C), rapid reaction time (18 s), and short recovery time (25 s). [ABSTRACT FROM AUTHOR]

Bimetallic PtPd nanostructures were synthesized via a facile one-step coreduction method at room temperature and loaded on the In 2 O 3 nanoparticles (NPs) through self-assemblies. Among the PtPd-functionalized In 2 O 3 NPs with different PtPd alloy compositions, the sample with the Pt/Pd molar ratio of 3.0 exhibits the highest response value of 232.7 in the detection of 100 ppm triethylamine at 130 °C and a detection threshold as low as 5 ppm. Besides, the optimal working temperature was reduced by 30 °C and the selectivity coefficient under the interference of ammonia and some common VOCs elevated from 2.54 to 4.85 compared with the pristine counterpart. Eventually, the sensitization mechanism referring to the pristine In 2 O 3 and monometal-functionalized In 2 O 3 is explained by oxygen vacancy, the metal/metal oxide-semiconductor junctions and the synergistic catalytic effect of the PtPd nanostructure with the help of density functional theory simulations. [ABSTRACT FROM AUTHOR]

Helicobacter pylori (HP), a common microanaerobic bacteria that lives in the human mouth and stomach, is reported to infect ≈50% of the global population. The current diagnostic methods for HP are either invasive, time‐consuming, or harmful. Therefore, a noninvasive and label‐free HP diagnostic method needs to be developed urgently. Herein, reduced graphene oxide (rGO) is composited with different metal‐based materials to construct a graphene‐based electronic nose (e‐nose), which exhibits excellent sensitivity and cross‐reactive response to several gases in exhaled breath (EB). Principal component analysis (PCA) shows that four typical types of gases in EB can be well discriminated. Additionally, the potential of the e‐nose in label‐free detection of HP infection is demonstrated through the measurement and analysis of EB samples. Furthermore, a prototype of an e‐nose device is designed and constructed for automatic EB detection and HP diagnosis. The accuracy of the prototype machine integrated with the graphene‐based e‐nose can reach 92% and 91% in the training and validation sets, respectively. These results demonstrate that the highly sensitive graphene‐based e‐nose has great potential for the label‐free diagnosis of HP and may become a novel tool for non‐invasive disease screening and diagnosis. [ABSTRACT FROM AUTHOR]

Developing room temperature (RT) gas sensor based on metal oxide semiconductor material has long been challenging. Herein, a 1D hierarchical Ag‐modified Cu@Cu2O/CuO nanocomposite has been designed by low‐temperature etching self‐assembly combined with photochemical deposition method based on Cu nanowires (NWs). After a step of alkaline solution etching, the surface of Cu NWs is self‐assembled to form a hierarchical Cu@Cu2O/CuO, and then Ag nanoparticles are modified on its surface by photochemical deposition to obtain the desired material. All the preparation processes are carried out at RT and have good controllability. When applied as sensing material, the optimal Cu@Cu2O/CuO/Ag nanocomposite exhibits high response of ≈337.0 to 10 ppm NO2 with excellent selectivity and fast response/recovery (60/400 s) at 25 °C. It is worth noting that such a strategy of loading Ag nanoparticles improves its gas sensitivity by about 42.4 times, and the resulting sensor shows good sensitivity and screening ability to NO2 in the low concentration range. Finally, the nanostructure of the material is characterized systematically and the sensing mechanism is discussed. [ABSTRACT FROM AUTHOR]

Air pollutants generated from volatile toxic chemicals pose significant public health concerns. Density functional theory (DFT) computations were used in this research to explore the efficiency and mechanism of harmful gas sensing over the reduced graphene oxide-polypyrrole (rGO-PPy) composite. Volatile molecule sensing was investigated for the NH3, H2CO, CH3OH, and C2H5OH gas molecules over three PPy orientations on the rGO substrate. Results showed that PPy orientation over rGO plays a crucial role in the sensing efficiency of the investigated gas molecules. The rGO-PPy composite, with PPy in a vertical orientation, demonstrated higher stability and enhanced sensing than other orientations. The results indicate that the strong hydrogen bonding of NH3 and CH3OH with both PPy and rGO significantly enhanced the sensing of these gas molecules on rGO by influencing the charge transfer with adsorption energy values of − 0.84 and − 0.92 eV, respectively. The lack of a direct hydrogen bonding with rGO and the weak hydrogen bonding with PPy caused a weak adsorption of H2CO and C2H5OH over rGO as indicated by the adsorption energy values of − 0.60 and − 0.78 eV, respectively. Selectivity analysis for the NH3 and C2H5OH gas molecules showed that NH3 can maintain hydrogen bonding with PPy in the presence of C2H5OH while C2H5OH cannot sustain this interaction. This study highlights the importance of the structural and electronic properties of the rGO-PPy composite in volatile pollutant sensing, providing insights for designing high-performance gas sensors. [ABSTRACT FROM AUTHOR]

Optical fiber sensor emerges as a highly promising technology for trace gas detection due to their high sensitivity, remote capability, and immunity to electromagnetic interference. However, the state‐or‐the‐art fiber‐optic gas sensors typically use lengthy optical fibers as gas absorption cells or coatings with functional materials to achieve more sensitive gas detection, which poses challenges such as slow response and/or poor selectivity, as well as limitations on their use in confined spaces. Here, an ultraminiature optical fiber‐tip photothermal gas sensor via direct 3D micro‐printing of a Fabry‐Pérot cavity on the end face of a standard single‐mode optical fiber is reported. It enables not only direct interaction between light and gas molecules at the fiber output but also remote interrogation through an interferometric read‐out scheme. With a low‐finesse microcavity of 66 µm in length, a noise equivalent concentration of 160 parts‐per‐billion acetylene gas is demonstrated with an ultra‐fast response time of 0.5 s. Such a small high‐performance photothermal gas sensor offers an approach to remotely detecting trace gases for a myriad of applications ranging from in‐reactor monitoring to medical diagnosis. [ABSTRACT FROM AUTHOR]

The possibility of Fe loaded on BP (Fe@BP) as an efficient gas sensor for the detection of toxic gases such as NO2, NO, and CO is studied by the first‐principles calculation, and it is proposed that Fe@BP is an excellent gas‐sensitive material. The adsorption behaviors of gases on Fe@BP were analyzed in terms of adsorption configurations and electronic properties. It is found that all gases adsorbed on Fe@BP exhibit significantly enhanced interactions, and the adsorption intensity is much larger than that of molecules adsorbed on the surface of pure BP. Fe@BP has high selectivity for toxic and ambient gas molecules. In addition, the adsorption strength of NO2 and NO molecules on Fe@BP increases after compression strain is applied (within −3%), while the adsorption strength of CO decreases gradually. After the tensile strain is applied, the adsorption intensity of NO2 and NO is decreased, but that of CO is increased gradually. It is speculated that the strain causes changes in the electronic structure, which affects the adsorption behavior. The adsorption of NO has a stronger strain sensitivity. For these reasons, Fe@BP with high adsorption strength and strain selection is the ideal gas‐sensitive material. [ABSTRACT FROM AUTHOR]

Buildings worldwide are becoming more thermally insulated, and air circulation is being reduced to a minimum. As a result, measuring indoor air quality is important to prevent harmful concentrations of various gases that can lead to safety risks and health problems. To measure such gases, it is necessary to produce low-cost and low-power-consuming sensors. Researchers have been focusing on semiconducting metal oxide (SMOx) gas sensors that can be combined with intelligent technologies such as smart homes, smart phones or smart watches to enable gas sensing anywhere and at any time. As a type of SMOx, p-type gas sensors are promising candidates and have attracted more interest in recent years due to their excellent electrical properties and stability. This review paper gives a short overview of the main development of sensors based on copper oxides and their composites, highlighting their potential for detecting CO2 and the factors influencing their performance. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials have emerged as a promising candidate in the chemoresistive gas sensor field to overcome the disadvantages of conventional metal-oxide semiconductors owing to their strong surface activities and high surface-to-volume ratio. This review summarizes the various approaches to enhance the 2D-material-based gas sensors and provides an overview of their progress. The distinctive attributes of semiconductor gas sensors employing 2D materials will be highlighted with their inherent advantages and associated challenges. The general operating principles of semiconductor gas sensors and the unique characteristics of 2D materials in gas-sensing mechanisms will be explored. The pros and cons of 2D materials in gas-sensing channels are discussed, and a route to overcome the current challenges will be delivered. Finally, the recent advancements to enhance the performance of 2D-material-based gas sensors including photo-activation, heteroatom doping, defect engineering, heterostructures, and nanostructures will be discussed. This review should offer a broad range of readers a new perspective toward the future development of 2D-material-based gas sensors. [ABSTRACT FROM AUTHOR]

In this paper, a room-temperature NO2 sensor based on a polyaniline (PANI)/black phosphorus (BP) composite material was proposed to solve the power consumption problem of traditional metal-oxide sensors operating at high temperatures. PANI was synthesized by chemical oxidative polymerization, whereas BP was synthesized by low-pressure mineralization. The PANI/BP composite materials were prepared via ultrasonic exfoliation and mixing. Various characterization techniques, including scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), confirmed the successful preparation of the PANI/BP composites and their excellent structural properties. The sensor demonstrated outstanding gas sensitivity in the NO2 concentration range of 2–60 ppm. In particular, the sensor showed a response exceeding 2200% at 60 ppm NO2 concentration when using a 1:1 mass ratio of PANI to BP in the composite material. [ABSTRACT FROM AUTHOR]

The field of gas sensors has been developing for the last year due to the necessity of characterizing compounds and, in particular, volatile organic compounds whose detection can be of special interest in a vast range of applications that extend from clinical evaluation to environmental monitoring. Among all the potential techniques to develop sensors, magnetron sputtering has emerged as one of the most suitable methodologies for the production of large-scale uniform coatings, with high packing density and strong adhesion to the substrate at relatively low substrate temperatures. Furthermore, it presents elevated deposition rates, allows the growth of thin films with high purity, permits a precise control of film thickness, enables the simple manufacturing of sensors with low power consumption and, consequently, low costs involved in the production. This work reviewed all the current applications of gas sensors developed through magnetron sputtering in the field of VOCs assessment by gathering the most relevant scientific works published. A total of 10 compounds were considered for this work. Additionally, 13 other compounds were identified as promising targets and classified as future trends in this field. Overall, this work summarizes the state-of-the-art in the field of gas sensors developed by magnetron sputtering technology, allowing the scientific community to take a step forward in this field and explore new research areas. [ABSTRACT FROM AUTHOR]

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Nitrogen group oxide is one of the major pollutants in the air, and its accurate and rapid detection is essential for environmental protection and human health. Therefore, it is of great significance to develop high-performance new line sensor for Nitrogen group oxide. Here, we investigate the potential of monolayer 2D MoSH materials as candidates for NO gas sensing using a combination of density functional theory and non-equilibrium functions to construct nanodevices based on MoSH monolayer, and theoretically study the adsorption behavior of MoSH monolayer to NO, NO 2 , and NH 3 gas molecules. The results indicate that MoSH monolayer exhibit metallicity, and nanodevices based on 2D MoSH monolayer exhibit anisotropic transport properties and significant negative differential resistance effects(NDR). More interestingly, gas sensors based on MoSH monolayers exhibit typical chemical adsorption of NO, NO 2 , and NH 3 gas molecules, and the anisotropic transport properties still maintain, but significant differences of sensitivity appear for these three gas molecules. Specifically, the MoSH based gas sensor has the highest sensitivity to NO, reaching 93.1 % and 76.3 % along the armchair and zigzag directions, respectively. These results show that 2D MoSH monolayer is an excellent gas-sensing material with excellent application prospects for NO gas detection. The electronic structures and the electronic transport performance of MoSH based gas sensor are systemically studied using density functional theory and non-equilibrium Green's function method. MoSH gas sensors have good gas adsorption capacity. Among them, MoSH gas sensors exhibit typical chemical adsorption for NO, NO 2 , and NH 3 , and have the highest sensitivity to NO, the maximum sensitivity is 93.1 %. In summary, MoSH gas sensors provide a theoretical basis for detecting NO gas in the future. [Display omitted] [ABSTRACT FROM AUTHOR]

ZnO–TiO2 thin films containing 0.5 mol%, 1.0 mol%, and 5.0 mol% ZnO were synthesized by oxidative solid-phase pyrolysis. The materials contained anatase and rutile phases with particle size of 6–13 nm, as confirmed using X-ray phase analysis and scanning electron microscopy. When a certain number of ZnO crystallites appeared in the TiO2 film structure in the temperature range of room temperature to 220 °C, a two-level response of the film resistance was observed, differing by approximately 10%, as obtained by electrophysical measurements. The two-level response correlates with the formation of two donor energy levels of 0.28 and 0.33 eV in the band structure of the ZnO–TiO2 films. The donor level with a higher activation energy corresponded to the Ti vacancy (V−Ti), and that with a lower activation energy corresponded to the Zn vacancy (V−Zn). Two levels of gas-sensitive properties were noted for 0.5ZnO–TiO2, 1ZnO–TiO2, and 5ZnO–TiO2 under the influence of 50 ppm NO2 at 250 °C. Such two-level responses can be ascribed to the pinning of the Fermi level on ZnO and TiO2 nanocrystallites. The mechanism of the beak-shaped and two-level responses of sensors based on composite nanomaterials when exposed to various gases was elucidated.

Abstract This research presents a compact portable electronic gas sensor that can be monitored through a smartphone application. The smart sensor utilizes three state-of-the-art sensors. The sensors integrate an ESP8266 microcontroller within the same device. This facilitates their integration with the electronics and enhances their performance. Herein, primarily focuses on utilizing the sensor to detect carbon monoxide. This article outlines the fabrication process of a gas sensor utilizing a P–N heterojunction, eliminating the need for a binder. The sensor consists of CuO/copper foam nanowires and hierarchical In2O3. In order to verify the system’s functionality, it underwent testing with various levels of CO concentrations (10–900 ppm), including particular tests designed to examine the device’s performance in different humidity and temperature circumstances. A mobile application for the provision of monitoring services has been developed at last. To process the information obtained from the gas sensor, an algorithm has been constructed, trained, and integrated into a smartphone for this purpose. This research demonstrated that a smartphone-coupled gas sensor is a viable system for real-time monitoring and the detection of CO gas.

While metal‐organic frameworks (MOFs) and covalent organic frameworks (COFs) have been widely investigated as porous conductive materials, the research on the electrical properties of HOF materials has been limited. Moreover, the electrical conductivity of HOF materials is typically several orders of magnitude lower than that of MOFs and COFs. In this work, a HOF material based on naphthalene diimide is designed and achieved a remarkable electrical conductivity of 2.9 × 10−2 S cm−1 after hydrazine doping, which represents the highest value reported in the HOF system to date. In addition, this material exhibits a reversible change of its electrical conductivity under exposure to ammonia which is promising for gas‐sensor applications. The demonstration reveals a new dimension of HOFs as conductive materials and opens up possibilities for new HOF‐based devices. [ABSTRACT FROM AUTHOR]

Molecular identification of volatile organic compounds (VOCs) plays an important role in various applications including environmental monitoring and smart farming. Mid‐infrared (MIR) fingerprint absorption spectroscopy is a powerful tool to extract chemical‐specific features for gas identification. However, the detection and recognition of trace VOC gas mixtures remain challenging due to their intrinsic weak light–matter interaction and highly overlapped absorption spectra. Here, an artificial intelligence‐enhanced “photonic nose” for MIR spectroscopic analysis of trace VOC gas mixtures is proposed. To enhance the sensing performance by increasing bandwidth and sensitivity, the “photonic nose” is designed to employ coupled multi‐resonant plasmonic nanoantennas to cover MIR molecular fingerprints, coated with metal–organic frameworks as the gas enrichment layer. Low limits of detection are achieved (IPA: 1.99 ppm, ethanol: 3.43 ppm, and acetone: 9.82 ppm). With machine learning, a high classification accuracy of 100% is realized for 125 mixing ratios (IPA, ethanol: both 5 concentrations, 0–130 ppm; acetone: 5 concentrations, 0–201 ppm), and low‐deviation component concentration predictions of root‐mean‐squared error within 10 ppm are achieved for IPA and ethanol (both 0–130 ppm) under interference from 50 ppm acetone. The work paves the way for intelligent sensing platforms for environmental monitoring and smart framing. [ABSTRACT FROM AUTHOR]

In this study, a cladding-modified fiber-optic sensor is reported for NO2 gas detection. Monitoring the purity of air is the need of the hour, with the growing technologies. Hence, in this work, Ag-doped CdS is coated over the cladding-removed region of 3cm length by Chemical Bath Deposition (CBD) which acts as the gas-sensing medium. Ag–CdS is coated over four fibers each with a different coating duration of 10min, 20min, 30min and 40min. Characterization of Ag–CdS is done by Scanning Electron Microscope (SEM), UV-visible absorption spectroscopy and UV-visible reflectance spectroscopy. The spectral response for different concentrations of NO2 is studied on the four fibers separately, and it is analyzed and compared. The minimum detection limit is 100ppm and the response time is 10min. Out of the four fibers, Ag–CdS-30 exhibited the best response with a sensitivity of 15.5%. The results are compared with cladding-modified fiber coated with CdS, which was reported previously. The effect of Ag-doping is analyzed. [ABSTRACT FROM AUTHOR]

Artificial olfaction, also known as an electronic nose, is a gas identification device that replicates the human olfactory organ. This system integrates sensor arrays to detect gases, data acquisition for signal processing, and data analysis for precise identification, enabling it to assess gases both qualitatively and quantitatively in complex settings. This article provides a brief overview of the research progress in electronic nose technology, which is divided into three main elements, focusing on gas-sensitive materials, electronic nose applications, and data analysis methods. Furthermore, the review explores both traditional MOS materials and the newer porous materials like MOFs for gas sensors, summarizing the applications of electronic noses across diverse fields including disease diagnosis, environmental monitoring, food safety, and agricultural production. Additionally, it covers electronic nose pattern recognition and signal drift suppression algorithms. Ultimately, the summary identifies challenges faced by current systems and offers innovative solutions for future advancements. Overall, this endeavor forges a solid foundation and establishes a conceptual framework for ongoing research in the field. [ABSTRACT FROM AUTHOR]

Due to serious harm of triethylamine (TEA) to environmental safety and human health, it is significant to synthesize gas-sensitive materials with high performance for TEA detection. However, it is still a challenge to achieve high-sensitivity detection of TEA at low temperature for a sensor synthesized through an economical and efficient method. In this work, hollow-structured SnO 2 (HS-SnO 2) nanospheres have been fabricated by a facile, low-cost hydrothermal method in one step, which exhibit superior TEA-sensing properties, including not only ultrahigh response (127.75) for 100 ​ppm TEA, good selectivity, but also fast response and recovery time (17/28 ​s), low detection threshold (1 ​ppm) and robust stability at a relatively low optimum operational temperature of 225 ​°C. The excellent gas-sensitizing performances are ascribed to porous hollow structures with rich oxygen vacancies that provide abundant active sites for raising O 2 adsorption and reaction of TEA and oxygen species. This work offers an effective and economical strategy for fabricating high-performance TEA sensors for industrial applications. [ABSTRACT FROM AUTHOR]

It is well known that two metal oxides can form depletion layers at the interface by constructing heterojunctions due to the different Fermi energy levels of each metal oxide, which can improve the carrier mobility and provide significant advantages for gas sensing. In this work, NdFeO 3 nanoparticles were grown on ZnO with hexagonal cone structure by secondary hydrothermal method to successfully construct n-ZnO/p-NdFeO 3 heterojunctions, and the crystal structures, oxygen vacancies, microstructures, optical properties, and gas-sensing properties of the ZnO/NdFeO 3 composites were investigated. The ZnO/NdFeO 3 sensors showed good ethanolamine (EA) The response characteristics of the ZnO/NdFeO 3 sensor to ethanolamine (EA) with a concentration of 100 ppm EA at 240 °C (R g /R a) is about 25, which improves the response by a factor of 1.6 and 1.32 compared with that of NdFeO3 and ZnO. Meanwhile, it has excellent selectivity, good cyclic reproducibility, and durable long-term stability with response/recovery times of 19 s/49 s. The improved EA sensing performance of NdFeO 3 -modified ZnO, in addition to its large specific surface area due to its unique rough inhomogeneous structure, is also related to the higher concentration of oxygen vacancies at the ZnO/NdFeO 3 interface after the composite. In addition, the construction of ZnO/NdFeO 3 heterostructure brings more efficient carrier migration, which is favorable to the surface reaction and diffusion of EA molecules, and lowers the ZnO operating temperature, thus reducing the energy consumption. The ZnO/NdFeO 3 composite sensor based on n-p heterojunction provides a valuable strategy for the detection of volatile organic compounds. [ABSTRACT FROM AUTHOR]

Humidity is a well-known interference factor in metal oxide (MOX) gas sensors, significantly impacting their performance in various applications such as environmental monitoring and medical diagnostics. This study investigates the effects of adsorbed water on MOX conductivity using two different materials: pure tin oxide (SnO2) and a tin–titanium–niobium oxide mixture (SnTiNb)xO2 (STN). The results reveal that (SnTiNb)xO2 sensors exhibit reduced sensitivity to humidity compared to pure tin oxide, rendering them more suitable for applications where humidity presence is critical. We aimed to shed light on a still controversial debate over the mechanisms involved in the water surface interactions for the aforementioned materials also by exploring theoretical studies in the literature. Experimental analysis involves varying temperatures (100 to 800 °C) to understand the kinetics of surface reactions. Additionally, a brief high-temperature heating method is demonstrated to effectively remove adsorbed humidity from sensor surfaces. The study employs Arrhenius-like plots for graphical interpretation, providing insights into various water adsorption/desorption phenomena. Overall, this research contributes to a deeper understanding of the role of humidity in MOX gas sensor mechanisms and offers practical insights for sensor design and optimization. [ABSTRACT FROM AUTHOR]

Recently, a new class of two-dimensional (2D) materials known as MXenes, such as Ti3C2Tx, have received significant attention due to their exceptional structural and physiochemical properties. MXenes are widely used in a variety of applications, including sensors, due to their excellent charge transport, high catalytic, and conducive properties, making them superior materials for sensing applications. Sensing technology has attracted significant interest from the scientific community due to its wide range of applications. In particular, gas sensing technology is essential in today's world due to its vital role in detecting various gases. Gas sensors have an essential role in real-time environmental monitoring health assessment, and the demand for air quality monitoring is driving the gas sensor market forward. Similarly, optical sensors are a related technology that can rapidly detect toxic substances and biomaterials using optical absorption spectroscopy. MXenes are highly desirable for gas and optical sensing applications due to their abundant active sites, metallic conductivity, optical properties, customizable surface chemistry, and exceptional stability. In this review article, we compile recent advancements in the development of gas sensors and optical sensors using MXenes and their composite materials. This review article would be beneficial for researchers working on the development of MXenes-based gas sensors and optical sensors. [ABSTRACT FROM AUTHOR]

Air pollution has been associated with several health problems. Detecting and measuring the concentration of harmful pollutants present in complex air mixtures has been a long-standing challenge, due to the intrinsic difficulty of distinguishing among these substances from interferent species and environmental conditions, both indoor and outdoor. Despite all efforts devoted by the scientific and industrial communities to tackling this challenge, the availability of suitable device technologies able to selectively discriminate these pollutants present in the air at minute, yet dangerous, concentrations and provide a quantitative measure of their concentrations is still an unmet need. Thermal conductivity detectors (TCDs) show promising characteristics that make them ideal gas sensing tools capable of recognising different gas analytes based on their physical fingerprint characteristics at the molecular level, such as their density, thermal conductivity, dynamic viscosity, and others. In this paper, the operation of TCD gas sensors is presented and explored using a finite element simulation of Joule heating in a sensing electrode placed in a gas volume. The results obtained show that the temperature, and hence, the resistance of the individual suspended microbridge sensor device, depends on the surrounding gas and its thermal conductivity, while the sensitivity and power consumption depend on the properties of the constitutive metal. Moreover, the electrode resistance is proven to be linearly dependent on the applied voltage. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) potentially harms human health, the ecosystem, industrial and agricultural production, and other fields. Therefore, the detection of NH3 has broad prospects and important significance. Ti3C2Tx is a common MXene material that is great for detecting NH3 at room temperature because it has a two-dimensional layered structure, a large specific surface area, is easy to functionalize on the surface, is sensitive to gases at room temperature, and is very selective for NH3. This review provides a detailed description of the preparation process as well as recent advances in the development of gas-sensing materials based on Ti3C2Tx MXene for room-temperature NH3 detection. It also analyzes the advantages and disadvantages of various preparation and synthesis methods for Ti3C2Tx MXene's performance. Since the gas-sensitive performance of pure Ti3C2Tx MXene regarding NH3 can be further improved, this review discusses additional composite materials, including metal oxides, conductive polymers, and two-dimensional materials that can be used to improve the sensitivity of pure Ti3C2Tx MXene to NH3. Furthermore, the present state of research on the NH3 sensitivity mechanism of Ti3C2Tx MXene-based sensors is summarized in this study. Finally, this paper analyzes the challenges and future prospects of Ti3C2Tx MXene-based gas-sensitive materials for room-temperature NH3 detection. [ABSTRACT FROM AUTHOR]

A method for the formation of nanostractured coatings from ZnO nanorods for use in adsorption gas sensors is presented. It has been shown that ultrasonic spray pyrolysis provides the formation of local growth centers for the formation of ZnO nanorods by the low-temperature hydrothermal synthesis. The obtained ZnO nanorods with a small diameter demonstrate a high concentration of oxygen vacancies in the near-surface region of the nanorods and a high surface concentration of hydroxyl groups. An additional method is proposed for testing seed layers by resistance using a liquid probe based on an indium-gallium melt without the need to apply top contacts. The presented technique is suitable for mass production of sensor coatings. The obtained nanostructured coatings from ZnO nanorods demonstrate a high gas analytical response. [ABSTRACT FROM AUTHOR]

An investigation on a single mode optical fiber sensor-based surface plasmon resonance was carried out in this work. A titanium dioxide (TiO2) coated gold Nano-column (Au) are deposited on the proposed sensor and theoretically analyzed using COMSOL Muliphysics software 5.3. Presence of TiO2 over the Au Nano-column can improve the sensitivity of the sensor and tune the resonance peak of transmission spectrum from visible region to near-infrared region. The size effect of TiO2 nanoparticles on the sensor performance is studied. The optimum parameters of such as Au size and separation width between the Au Nano-column have been selected to enhance the performance of the sensor. In comparison, the sensor with TiO2 over Au Nano-column is significantly improve the sensitivity and develop the sensor performance. The greater sensitivity of 5243.76 nm/RIU (refractive index unit) is obtained of sensor with TiO2 over Au Nano-column when the external refractive index of analyte is varying from 1.33 to 1.39, while sensitivity of the sensor coated with Au Nano-column is obtained to be 4643.17 nm/RIU for the same analyte range. Above results can be used to predict the best parameters values of the sensor that corresponding to the greatest sensitivities of detection and finally opening new study in the field of gas sensors. [ABSTRACT FROM AUTHOR]

Highly sensitive, and versatile metal oxide semiconductors, including perovskites, are used in gas sensors for environmental, and safety applications. This study described the substitution of Cu for Fe in LaFe 1-x Cu x O 3 nanostructured perovskites, denoted as C x 's, using Pechini sol-gel method at 600 °C, to detect the volatile organic compounds (VOCs). Characterization techniques, including TGA/DTA, XRD, BET, FE-SEM/EDS, Raman, PL, XPS, UV-DRS, FTIR, TPD-O 2 and ethanol chemisorption showed significant enhancements in physicochemical, and gas sensing properties of LaFeO 3 perovskites, upon copper doping in its structure. The responses to ethanol improved, the average crystallite and nanoparticle sizes decreased, and the electrical conductivity increased as the perovskite copper content increased to x = 0.6. The crystallite size of 20.5 nm for LaFeO 3 decreased to 12.7 nm for LaFe 0.4 Cu 0.6 O 3. The SC 0.6 thick film gas sensor showed high potential in the VOCs detection, with best responses of 17 for ethanol, 18 for acetone, and 16 for acetaldehyde when exposed to each of 300 ppm at 300 °C. At these conditions, the response and recovery times of highly stable SC 0.6 sensor for ethanol gas were 4 and 11 min, respectively. [Display omitted] • Cu-doped LaFe 1-x Cu x O 3 (x = 0.0–0.8) perovskites were synthesized by Pechini sol-gel method. • By adding up to x = 0.6 Cu into LaFeO 3 , XRD peaks shift to higher angles, and smaller nanoparticles form. • Both Fe4+ and Fe3+, and oxygen vacancies are present in the structure of LaFe 0.4 Cu 0.6 O 3. • 10% of surface Cu is active Cu1+ for strong interaction with target gases. • As compared to LaFeO 3 , LaFe 0.4 Cu 0.6 O 3 shows 6.5 times higher response to 300 ppm ethanol at 300 °C. [ABSTRACT FROM AUTHOR]

ZnO--TiO2 thin films containing 0.5 mol%, 1.0 mol%, and 5.0 mol% ZnO were synthesized by oxidative solidphase pyrolysis. The materials contained anatase and rutile phases with particle size of 6-13 nm, as confirmed using X-ray phase analysis and scanning electron microscopy. When a certain number of ZnO crystallites appeared in the TiO2 film structure in the temperature range of room temperature to 220 °C, a two-level response of the film resistance was observed, differing by approximately 10%, as obtained by electrophysical measurements. The two-level response correlates with the formation of two donor energy levels of 0.28 and 0.33 eV in the band structure of the ZnO--TiO2 films. The donor level with a higher activation energy corresponded to the Ti vacancy (V-Ti), and that with a lower activation energy corresponded to the Zn vacancy (V-Zn). Two levels of gas-sensitive properties were noted for 0.5ZnO--TiO2, 1ZnO--TiO2, and 5ZnO--TiO2 under the influence of 50 ppm NO2 at 250 °C. Such two-level responses can be ascribed to the pinning of the Fermi level on ZnO and TiO2 nanocrystallites. The mechanism of the beak-shaped and two-level responses of sensors based on composite nanomaterials when exposed to various gases was elucidated. [ABSTRACT FROM AUTHOR]

In recent decades, various pollutants have been released into the environment in substantial amounts due to human activities. Oil pollution is one of these pollutants and can be harmful to both humans and the environment, making its detection and cleanup highly important. Considering the applicability of the electronic nose methods in various domains, including the food industry, environment, etc, this research aims to measure the feasibility of using electronic nose technology to detect soil contaminated with crude oil. An electronic nose system with eight metal oxide semiconductor sensors was used in this research. The soil used in this research was from one of the farms surrounding Karaj province, which, in the laboratory of the University of Tehran, was contaminated with crude oil at four concentrations: 200 ppm, 500 ppm, 1000 ppm, and 5000 ppm, and then the samples evaluated. This system was examined along with pattern recognition methods such as principal component analysis (PCA), linear discriminant analysis (LDA), and support vector machine (SVM). The results from the pattern recognition methods showed an accuracy of 92% for principal component analysis, 100% for linear discriminant analysis, and 100% for the support vector machine method. Moreover, by employing statistical data analysis using a factorial experiment method within a randomized block design and using decision tree regression, support vector regression, gradient boosted regression, and random forest regression, which has the pollutant detection rate with an average accuracy of 95.5% for the MQ3 sensor, showed the best performance, and detect the difference between the contaminated concentrations. In conclusion, by comparing the results of selected electronic nose sensors with the results obtained by the gas chromatography system on the soil contaminated with crude oil, they have had an acceptable sensitivity. [ABSTRACT FROM AUTHOR]

Langmuir–Blodgett (LB) film technology is an advanced technique for the preparation of ordered molecular ultra-thin films at the molecular level, which transfers a single layer of film from the air/water interface to a solid substrate for the controlled assembly of molecules. LB technology has continually evolved over the past century, revealing its potential applications across diverse fields. In this study, the latest research progress of LB film technology is reviewed, with emphasis on its latest applications in gas sensors, electrochemical devices, and bionic films. Additionally, this review evaluates the strengths and weaknesses of LB technology in the application processes and discusses the promising prospects for future application of LB technology. [ABSTRACT FROM AUTHOR]

The current study, accurately designed and created a two-dimensional (2D) structure of SnO 2 nano-flowers and In 2 O 3 nanoparticles using a simple hydrothermal technique and sol-gel method, respectively. On the outer surface of SnO 2 nanoflowers the In 2 O 3 nanoparticles were uniformly growing, clearly revealed by field emission scanning electron microscopic. Besides, crystal phase structure, surface area and elementals composition were characterized by XRD, BET, TEM, EDS, XPS and the gas sensing properties of In 2 O 3 @SnO 2 NFs. The results exhibited that 2 wt% In 2 O 3 @SnO 2 NFs sensor is highly sensitive to NO 2 , the response (R g /R a) to 30 ppm NO 2 is 94.5, and at 50 ppb the response measured 0.61 at 150 °C, the response time is 32 and 51s, respectively, along with good moisture resistance. Besides along with excellent selectivity, long-term stability, and relative humidity (RH) in high-humidity environment, the 2 wt% In 2 O 3 @SnO 2 NFs still maintain high response 91 at 30 ppm. More importantly, at room temperature the response was (Rg/Ra = 1.01) at detection limit 300 ppb towards NO 2 , which could use be for trace NO 2 gas detection. The large specific surface areas of SnO 2 , the abundance of oxygen species adsorbed on the surface, the distinctive electron transformation between heterojunction materials, and high electron transmission channel of SnO 2 and In 2 O 3 transition layer were all considered to have a synergistic effect thatin2 contributed to excellent sensing properties of In 2 O 3 @SnO 2 NFs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

For the first time, nanostructured thin films of the β-Ga2O3−GaN system have been obtained by plasma-enhanced chemical vapor deposition (PECVD) on c-plane sapphire substrates. High-purity gallium metal, as well as high-purity gaseous nitrogen and oxygen, were used as sources of macrocomponents. Low-temperature nonequilibrium plasma of an inductively coupled RF (40.68 MHz) discharge at reduced pressure (0.01 torr) was the initiator of chemical transformations between the reactants. A mixture of oxygen and nitrogen was used as a plasma-forming gas. The plasma-chemical process was studied using optical emission spectroscopy (OES). The resulting β-Ga2O3−GaN thin films with a GaN content of 2 to 7% were characterized by various analytical methods. [ABSTRACT FROM AUTHOR]

Gas sensors exhibit significant potential due to their widespread use in various applications, such as food packaging, indoor air quality assessment, and real-time monitoring of man-made gas emissions to mitigate global warming. The utilization of nanostructured materials for sensor and adsorbent surfaces has seen remarkable growth over time, though substantial efforts are still needed to develop more efficient adsorbents. Consequently, this study investigates the viability of metal-doped quantum dots (QDs) as prospective gas-sensing and adsorption materials. Density functional theory (DFT) calculations employing the 6-311 + G(d,p) basis set and three functionals (B3LYP, B3LYP-GD3(BJ), and ɷB97XD) were utilized for this investigation. Three environmentally and health-significant gases (C6H6, CO2, and H2S) were chosen as adsorbates on arsenic (As) and cobalt (Co) functionalized QDs to assess the performance and sensing capabilities of resulting QD surfaces. The analysis encompassed computation of adsorption energy, thermodynamic properties, non-covalent interactions, natural bond orbital analysis, and other topological aspects for both the surfaces and gases. The outcomes indicate that the GP_As functionalized surface exhibits a lower energy gap, rendering it more reactive and sensitive toward the respective gases (C6H6, CO2, and H2S). Moreover, the calculated adsorption energies of the investigated systems indicate thermodynamic favorability and spontaneity. Notably, our findings suggest that QD_As surfaces possess superior adsorption potential for H2S compared to the other gases examined; nonetheless, all studied QD surfaces demonstrate significant adsorption capacities for C6H6, CO2, and H2S gases. [ABSTRACT FROM AUTHOR]