Highly Selective Ethyl Mercaptan Sensing Using a MoSe2/SnO2 Composite at Room Temperature

TiO2 Nanosphere/MoSe2 Nanosheet-Based Heterojunction Gas Sensor for High-Sensitivity Sulfur Dioxide Detection

With the growing severity of air pollution, monitoring harmful gases that pose risks to both human health and the ecological environment has become a focal point of research. Titanium dioxide (TiO2) demonstrates significant potential for application in SO2 gas detection. However, the performance of pure TiO2 is limited. In this study, TiO2 nanospheres and MoSe2 nanosheets were synthesized using a hydrothermal method, and the gas-sensing properties of TiO2/MoSe2 nanostructures for SO2 detection were investigated. The TiO2/MoSe2 composites (with a TiO2-to-MoSe2 volume ratio of 2:1) were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The TiO2/MoSe2 sensor exhibited high sensitivity to SO2; the response to 100 ppm of SO2 reached as high as 59.3, with a significantly shorter response and recovery time (15 s/13 s), as well as excellent repeatability, selectivity, and long-term stability. The experimental results suggest that the enhanced SO2 adsorption capacity of the TiO2/MoSe2 composite can be attributed to the formation of an n-n heterojunction and the unique microstructural features of TiO2/MoSe2. Therefore, the TiO2/MoSe2 sensor represents a promising candidate for rapid SO2 detection, providing a theoretical foundation for the development and application of high-performance SO2 sensors.

MoSe2-Layered Nanosheet Decorated SnO2 Hollow Nanofiber-Based Highly Sensitive and Selective Room Temperature H2S Gas Sensor

In this work, we successfully demonstrated a MoSe2@SnO2 nanocomposite-based room temperature H2S gas sensor. A sensing mechanism was proposed based on experimental results and density functional theory calculations. The FESEM micrographs of the heterostructure formed by hydrothermally grown MoSe2-layered nanosheets and SnO2-hollow nanofiber result in a high surface area for H2S gas adsorption. On exposure to calcination, the electro-spun PVP/SnO2 nanofiber undergoes the Kirkendall phenomenon, resulting in 94.6 nm thick hollow nanofibers. The combination of TMD@SMO shows an abundance of charge transfer, resulting in an excellent response toward H2S gas. The MoSe2@SnO2 detects a low concentration of 500 ppb with a relative response of ∼19.9% at room temperature (RT). The simulation, using density functional theory (DFT), discloses that the adsorption energies ranged from -0.3645 to -0.5193 eV, indicating reduced bond lengths and significant H2S interactions. The sensor proves an excellent sensitivity toward H2S gas, ranging from 100 ppm to 500 ppb, with a LoD of ∼15 ppb at RT. As the sensor worked at RT with accuracy and reliability, consistent performance was observed upon exposure to various humidity levels, making it suitable for exhaled breath gas sensors. The sensor, as developed, also exhibited a good selectivity toward H2S gas in contrast to other gases as well as stability and longevity over time.

van der Waals ZnO/HfSn2N4 Heterojunction with Exceptional Photoresponse for Photodetectors

Two-dimensional van der Waals heterojunctions represent a promising avenue for a spectrum of optoelectronic endeavors. Nonetheless, their deployment has been somewhat constrained by the suboptimal efficiency of the photocurrent generated. In this article, a ZnO/HfSn2N4 heterojunction is proposed to achieve high photoresponse efficiency. First-principles calculations are utilized to confirm that this heterojunction possesses thermal stability with a direct bandgap (1.36 eV). It exhibits a high light absorption coefficient and high carrier mobility (2.51 × 103 cm2 V-1 s-1), and biaxial strain has a significant effect on the modulation of the band structure. As the tensile strain increases, the bandgap changes nonlinearly, transitioning from a type-II to a type-I heterojunction. When compressive strain increases, the bandgap decreases. Quantum transport simulations are employed to calculate the density of states and transmission spectrum of the ZnO/HfSn2N4 model, verifying its excellent photoresponse (a photocurrent peak reaching 4.93 a02/photon and an extinction ratio peak of 75.1). It shows that the ZnO/HfSn2N4 heterojunction is a potentially efficient photodetector.

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

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

A three-in-one versatile sensor for concise detecting biogenic amines and beef freshness

Biogenic amines (BAs), as important indicators for evaluating food spoilage caused by fermentation processes or microbial activities, present significant risks of food safety. Consequently, the development of a simple, sensitive, and selective detection method for amines is of great importance. In this study, we proposed a three-in-one sensor 3,6-bis(dimethylamino)-9-(ethylthio)xanthylium (PSE) for high sensitivity and selectivity detecting BAs with multimodal responses, including olfactory, colorimetric, and fluorescent signals, thus facilitating convenient real-time detection of BAs. Mechanism study indicated that the nucleophilic substitution of PSE with BAs induced such rapid multi-responses with a low detection limit (LOD = 0.03 μM). We further fabricated PSE loaded paper for portable detection of BAs vapors. And the accurate determination of BAs levels is achieved through analyzing the RGB color mode. Finally, we successfully applied these test strips for non-destructive assessing meat beef freshness with the assistance of a smartphone in on-site scenarios.

Phase-Dependent Dual Discrimination of MoSe2/MoO3 Composites Toward N,N-Dimethylformamide and Triethylamine at Room Temperature

Herein, we present, a chemiresistive-type gas sensor composed of two-dimensional 1T-2H phase MoSe2 and MoO3. Mixed phase MoSe2 and MoSe2/MoO3 composites were synthesized via a facile hydrothermal method. The structure analysis using X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy revealed the formation of different phases of MoSe2 at different temperatures. With increase in synthesis temperature from 180 to 200 °C, the relative percentage of 1T and 2H-MoSe2 phases changed from 80 to 48%. On the other hand, at 220 °C, 2H-MoSe2 was obtained as a major component. The gas sensing properties of individual MoSe2 and composites were investigated at room temperature toward various analytes. The obtained results revealed that composites possess improved sensing features as compared with individual MoSe2 or MoO3. Data also revealed that the composite with dominating 1T-phase exhibits relatively higher response (10%, at 10 ppm) for dimethylformamide (DMF) compared to triethylamine (TEA) (3%, at 10 ppm). In contrast, the composite with larger 2H-phase exhibited affinity toward TEA and had a relative response of about 2%. Therefore, selectivity of a sensor device can be tuned by an appropriately designed MoSe2/MoO3 composite. These results signify the importance of MoO3-based composites with dual-phase MoSe2 for successfully discriminating between DMF and TEA at room-temperature.

Ultrasensitive Room-Temperature NO2 Detection Using SnS2/MWCNT Composites and Accelerated Recovery Kinetics by UV Activation

High performance with lower power consumption is one among the essential features of a sensing device. Minute traces of hazardous gases such as NO₂ are difficult to detect. Tin disulfide (SnS₂) nanosheets have emerged as a promising NO₂ sensor. However, their poor room-temperature conductivity gives rise to inferior sensitivity and sluggish recovery rates, thereby hindering their applications. To mitigate this problem, we present a low-cost ultrasensitive NO₂ gas sensor with tin disulfide/multiwalled carbon nanotube (SnS₂/MWCNT) nanocomposites, prepared using a single-step hydrothermal method, as sensing elements. Relative to pure SnS₂, the conductivity of nanocomposites improved significantly. The sensor displayed a decrease in resistance when exposed to NO₂, an oxidizing gas, and exhibited p-type conduction, also confirmed in separate Mott-Schottky measurements. At a temperature of 20 °C, the sensor device has a relative response of about ≈5% (3%) for 25 ppb (1 ppb) of NO₂ with complete recovery in air (10 min) and excellent recovery rates with UV activation (0.3 min). A theoretical lower limit of detection (LOD) of 7 ppt implies greater sensitivity than all previously reported SnS₂-based gas sensors, to the best of our knowledge. The improved sensing characteristics were attributed to the formation of nano p-n heterojunctions, which enhances the charge transport and gives rise to faster response. The composite sensor also demonstrated good NO₂ selectivity against a variety of oxidizing and reducing gases, as well as excellent stability and long-term durability. This work will provide a fresh perspective on SnS₂-based composite materials for practical gas sensors.

Facile hydrothermal synthesis of layered 1T′ MoTe2 nanotubes as robust hydrogen evolution electrocatalysts

Layered transition metal dichalcogenides (TMDs), such as molybdenum ditelluride (MoTe₂), have attracted much attention because of their novel structure-related physicochemical properties. In particular, semi-metallic-phase MoTe₂ (1T′) is considered as a competitive candidate for low-cost electrocatalysts for water splitting. However, there are few reports on the simple hydrothermal synthesis of MoTe₂ nanostructures compared with other layered TMDs. In this study, a facile one-step hydrothermal process was developed for the fabrication of layered MoTe₂, in which uniform nanotubes with a few layers of 1T′ MoTe₂ were fabricated at a lower temperature for the first time. The as-obtained MoTe₂ nanotubes were fully characterized using different techniques, which revealed their structure and indicated the presence of layered 1T′ nanocrystals. The efficient activity of MoTe₂ nanotubes for the electrocatalytic hydrogen evolution reaction (HER) in 0.5 M H₂SO₄ was demonstrated by the small Tafel slope of 54 mV/dec⁻¹ and endurable ability, which is attributed to the abundant active sites and remarkable conductivity of 1T′ MoTe₂ with a few-layer feature. This provides a facile method for the design and construction of efficient layered MoTe₂ based electrocatalysts.

Humidity-Tolerant Room-Temperature Selective Dual Sensing and Discrimination of NH3 and NO Using a WS2/MWCNT Composite

Continuous detection of toxic and hazardous gases like nitric oxide (NO) and ammonia (NH₃) is needed for environmental management and noninvasive diagnosis of various diseases. However, to the best of our knowledge, dual detection of these two gases has not been previously reported. To address the challenge, we demonstrate the design and fabrication of low-cost NH₃ and NO dual gas sensors using tungsten disulfide/multiwall carbon nanotube (WS₂/MWCNT) nanocomposites as sensing channels which maintained their performance in a humid environment. The composite-based device has shown successful dual detection at temperatures down to 18 °C and relative humidity of 90%. For 0.1 ppm ammonia, it exhibited a p-type conduction with response and recovery times of 102 and 261 s, respectively; on the other hand, with NO (10 ppb, n-type), these times were 285 and 198 s, respectively. The device with 5 mg MWCNTs possesses a superior selectivity along with a relative response of ≈7% (5 ppb) and ≈5% (0.1 ppm) for NO and NH₃, respectively, at 18 °C. The response is less affected by relative humidity, and this is attributed to the presence of MWCNTs that are hydrophobic in nature. Upon simultaneous exposure to NO (5-10 ppb) and NH₃ (0.1-5 ppm), the response was dominated by NO, implying clear discrimination to the simultaneous presence of these two gases. We propose a sensing mechanism based on adsorption/desportion and accompanied charge transfer between the adsorbed gas molecules and sensing surface. The results suggest that an optimized weight ratio of WS₂ and MWCNTs could govern favorable sensing conditions for a particular gas molecule.