Investigations of Vacancy-Assisted Selective Detection of NO2 Molecules in Vertically Aligned SnS2

GO-SELEX-enhanced dual-recognition sensor for highly specific detection of azamethiphos

Organophosphorus pesticides (OPs) have attracted attention due to their widespread application in agriculture and public health sector. Among them, azamethiphos (AZA) may pose risks to non-target organisms and human health through food chain accumulation. Therefore, establishing a highly sensitive and specific detection method of AZA is of great significance for ensuring food safety and ecological protection. In this study, based on graphene oxide-SELEX technology, an aptamer (Apt) with specific recognition for AZA (Kd=26.27±1.27 nM) was screened for the first time. This aptamer was subsequently integrated with molecularly imprinted polymers to construct a dual-recognition electrochemical sensor, leveraging the complementary advantages of both recognition elements. This dual-recognition strategy enabled the synergistic enhancement of specific recognition ability, effectively reducing interference from non-target substances and improving sensor selectivity and accuracy. Additionally, a doping strategy was adopted to modify the electrode surface with AuNPs@SnS2@ZnCo-MOF nanocomposites, improving electron transfer efficiency and providing abundant active sites, thereby significantly enhancing the electrochemical signal response. The sensor exhibited a wide detection range (1.00×10-2-1.00×104 ng/mL) and a low limit of detection (3.33×10-3 ng/mL), while also demonstrating excellent stability and specificity. In summary, this study developed a highly efficient, sensitive and selective electrochemical sensor, providing a novel strategy for the rapid detection of AZA and other organophosphorus pesticides, with broad application prospects in food safety and environmental monitoring.

CVD-grown SnS2active layers on AlGaN/GaN HEMT for arsenic (III) ions detection

The pervasive contamination of water sources by the toxic heavy metal arsenic presents a serious threat to human health and ecological systems. This raises the critical need for innovative detection platforms that can detect such contamination at low cost and as part of an onsite, distributed sensor network. In this context, we report an Arsenic (As3+) ion detection system that was fabricated using 2D SnS2functionalized AlGaN/GaN high electron mobility transistor (HEMT). SnS2layers were grown on the HEMT surface by chemical vapor deposition (CVD) which depicts hexagonal oriented nanosheets with crystal edges. The source and drain tri-metal contacts of Au/Cr/Al were fabricated by thermal evaporation using shadow mask. The sensor response was analyzed by measuring the variation in drain to source current of the device after introducing varied concentrations of As3+ions, ranging from 1 ppb to 10 ppm. The observed sensitivity of the device is 0.42μA ppb-1, with a detection limit of 0.90 ppb, and a response time of 3.2 s. Further, real-time data analysis was performed by the integration of the developed sensor with a customized printed circuit board connected with an Arduino Nano 33 Bluetooth Low Energy (BLE) module for data transmission. The concept of growing the SnS2layer as a functionalizing layer by CVD results in quick response, good repeatability, and selectivity thereby eliminating the need for any additional reference electrode. Integration of the developed AlGaN/GaN HEMT sensor with Arduino Nano 33 BLE makes it an ideal candidate for portable heavy metal ion sensing device for onsite detection.

Far-field femtosecond laser-driven λ/73 super-resolution fabrication of 2D van der Waals NbOI2 nanostructures in ambient air

The design and fabrication of ultrafine nanostructures in two-dimensional (2D) van der Waals materials are crucial for the functionalization of electronic devices. Here, we report the utilization of far-field femtosecond laser patterning to fabricate super-resolution nano-groove array (NGA) structures in 2D multilayer NbOI2 in ambient air, achieving groove widths as low as ~14.5 nm (~λ/73). The NGA structures maintain a well-defined single-crystal NbOI2 with amorphous Nb2O5 edges as narrow as 3.2 nm. The formation mechanism of NGA structure is confirmed to be associated with the coupled field of surface plasmon polariton periodic field and nano-groove-induced local near-field induced by femtosecond laser irradiation. Furthermore, the NGA-NbOI2 gas sensor exhibits NO2 sensing performance, with a rapid response time (5.1 s), which is attributed to the existence of abundant NbOI2-Nb2O5 heterojunctions. This approach will propel the further development of nano-lithography techniques for functional device applications of 2D materials.

Engineering an Ultrafast Ambient NO2 Gas Sensor Using Cotton-Modified LaFeO3/MXene Composites

This work presents a room-temperature (RT) NO2 gas sensor based on cotton-modified LaFeO3 (CLFO) combined with MXene. LaFeO3 (LFO), CLFO, and CLFO/MXene composites were synthesized via a hydrothermal method. The fabricated sensor, utilizing MXene/CLFO, exhibits a p-type behavior and fully recoverable sensing capabilities for low concentrations of NO2, achieving a higher response of 14.2 times at 5 ppm. The sensor demonstrates excellent performance with a response time of 2.7 s and a recovery time of 6.2 s, along with notable stability. The sensor's sensitivity is attributed to gas interactions on the material's surface, adsorption energy, and charge-transfer mechanisms. Techniques such as in situ FTIR (Fourier transform infrared) spectroscopy, GC-MS (gas chromatography-mass spectroscopy), and near-ambient pressure X-ray photoelectron spectroscopy were employed to verify gas interactions and their byproducts. Additionally, finite-difference time-domain simulations were used to model the electromagnetic field distribution and provide insight into the interaction between NO2 molecules and the sensor surface at the nanoscale. A prototype wireless IoT (Internet of Things)-based NO2 gas leakage detection system was also developed, showcasing the sensor's practical application. This study offers valuable insight into the development of room-temperature NO2 sensors with a low detection limit.

Recent Advances in Engineering of 2D Layered Metal Chalcogenides for Resistive-Type Gas Sensor

2D nanomaterials have triggered widespread attention in sensing applications. Especially for 2D layered metal chalcogenides (LMCs), the unique semiconducting properties and high surface area endow them with great potential for gas sensors. The assembly of 2D LMCs with guest species is an effective functionalization method to produce the synergistic effects of hybridization for greatly enhancing the gas-sensing properties. This review starts with the synthetic techniques, sensing properties, and principles, and then comprehensively compiles the advanced achievements of the pristine 2D LMCs gas sensors. Key advances in the development of the functionalization of 2D LMCs for enhancing gas-sensing properties are categorized according to the spatial architectures. It is systematically discussed in three aspects: surface, lattice, and interlayer, to comprehend the benefits of the functionalized 2D LMCs from surface chemical effect, electronic properties, and structure features. The challenges and outlooks for developing high-performance 2D LMCs-based gas sensors are also proposed.

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.

Vacancy-assisted exposed Sn atoms enhancing NO2 room temperature sensing of SnSe2 nanoflowers

NO2 is a hazardous gas extremely harmful to the ecosystem and human health, so effective detection of NO2 is critical. SnSe2 is a promising candidate for gas sensors owing to its unique layered configuration that facilitates the diffusion of gas molecules. Here, ultrathin self-assembled nanoflowers F-SnSe2 rich in defects were synthesized by a simple solvothermal method. It exhibits excellent gas sensing performances for NO2 at room temperature (25 °C), with a high gas sensing response of 8.6 for 1 ppm NO2 and a lower detection limit as low as 200 ppb, capable of sensitively detecting ppb-level NO2. DFT calculations revealed that the presence of Se vacancies assists the central Sn atoms to break through the shielding effect of the surface Se atoms and become exposed active sites. The higher reactivity leads to more charge transfer and higher adsorption energy, which strongly promoted the adsorption of NO2. This work verifies the important role of vacancies for the exposed active sites and provides new guidance for defect engineering to modulate the gas sensing performances of SnSe2.

2H-SnS2 assembled with petaloid 1T@2H-MoS2 nanosheet heterostructures for room temperature NO2 gas sensing

In this study, we explored the gas-sensing capabilities of MoS2 petaloid nanosheets in the metallic 1T phase with the commonly investigated semiconducting 2H phase. By synthesizing SnS2 nanoparticles and MoS2 petaloid nanosheets through a hydrothermal method, we achieve notable sensing performance for NO2 gas at room temperature (27 °C). This investigation represents a novel study, and to the best of our knowledge no, prior similar investigations have been reported in the literature for 1T@2HMoS2/SnS2 heterostructures for room temperature NO2 gas sensing. The formed heterostructure between SnS2 nanoparticles and petaloid MoS2 nanosheets exhibits synergistic effects, offering highly active sites for NO2 gas adsorption, consequently enhancing sensor response. Our sensor demonstrated a remarkable sensing response (R a/R g = 7.49) towards 1 ppm of NO2, rapid response time of 54 s, baseline recovery in 345 s, good selectivity and long-term stability, underscoring its potential for practical gas-sensing applications.

Catalytic synergy of WS2-anchored PdSe2 for highly sensitive hydrogen gas sensor

Hydrogen (H2) is widely used in industrial processes and is one of the well-known choices for storage of renewable energy. H2 detection has become crucial for safety in manufacturing, storage, and transportation due to its strong explosivity. To overcome the issue of explosion, there is a need for highly selective and sensitive H2 sensors that can function at low temperatures. In this research, we have adequately fabricated an unreported van der Waals (vdWs) PdSe2/WS2 heterostructure, which exhibits exceptional properties as a H2 sensor. The formation of these heterostructure devices involves the direct selenization process using chemical vapor deposition (CVD) of Pd films that have been deposited on the substrate of SiO2/Si by DC sputtering, followed by drop casting of WS2 nanoparticles prepared by a hydrothermal method onto device substrates including pre-patterned electrodes. The confirmation of the heterostructure has been done through the utilization of powder X-ray diffraction (XRD), depth-dependent X-ray photoelectron spectroscopy (XPS) and field-emission scanning electron microscopy (FE-SEM) techniques. Also, the average roughness of thin films is decided by Atomic Force Microscopy (AFM). The comprehensive research shows that the PdSe2/WS2 heterostructure-based sensor produces a response that is equivalent to 67.4% towards 50 ppm H2 at 100 °C. The response could be a result of the heterostructure effect and the superior selectivity for H2 gas in contrast to other gases, including NO2, CH4, CO and CO2, suggesting tremendous potential for H2 detection. Significantly, the sensor exhibits fast response and a recovery time of 31.5 s and 136.6 s, respectively. Moreover, the explanation of the improvement in gas sensitivity was suggested by exploiting the energy band positioning of the PdSe2/WS2 heterostructure, along with a detailed study of variations in the surface potential. This study has the potential to provide a road map for the advancement of gas sensors utilizing two-dimensional (2D) vdWs heterostructures, which exhibit superior performance at low temperatures.

Electronic Modulation of MoS2 Nanosheets by N-Doping for Highly Sensitive NO2 Detection at Room Temperature

Transition metal dichalcogenide (TMD) materials hold great promise for gas sensors working at room temperature (RT). But the low response and slow dynamics derived from pristine TMDs remain a challenge toward their real applications. In this work, we report an efficient N-doping strategy to modulate the electronic structure of MoS2 nanosheets (N-MoS2) to achieve improved detection toward NO2. The effect of N-doping on the sensor properties, which has been rarely investigated, is elucidated by both experimental and computational studies. Due to N-doping, the Fermi level of N-MoS2 decreased from -5.29 to -5.33 eV and the band gap was reduced from 1.79 to 1.65 eV. The smaller band gap indicated the reduced resistance of N-MoS2 compared to that of original MoS2. As a result, the response of the MoS2 sensor to 10 ppm of NO2 was improved from 1.23 to 2.31 at RT. The sensor also has a limit of detection (LOD) of 62.5 ppb. To explain the effect of N-doping, density functional theory (DFT) calculations were conducted to figure out the important roles played by N-doping. This work demonstrates a pathway to modulate the chemical and electronic structures of TMD materials for advanced sensors.

Ce-Ag Active Bimetallic Pairs in Two-Dimensional SnS2 for Enhancing NO2 Sensing

Developing gas sensors capable of efficiently detecting harmful gases is urgent to protect the human environment. Here, an active Ce-Ag bimetallic pair was innovatively introduced into SnS2, which successfully exhibited excellent NO2 gas sensing performance. 0.8% Ce-SnS2-Ag showed a gas sensing response of 5.18 to 1 ppm of NO2 at a low temperature of 80 °C, with a lower limit of detection as low as 100 ppb. DFT calculations revealed that Ce atoms are substituted into the main lattice of SnS2, which opens up the interlayer spacing and serves as an anchor point to fix the Ag atoms in the interlayer. The Ce-Ag bimetallic pairs successfully modulate the electronic structure of SnS2, which promotes the adsorption and charge transfer between NO2 and Ce-SnS2-Ag and thus achieves such an outstanding gas sensing performance. This work opens an avenue for the rational functional modification of SnS2 with an optimized electronic structure and enhanced gas sensing.

Highly Sensitive Gas Sensor for Detection of Air Decomposition Pollutant (CO, NOx): Popular Metal Oxide (ZnO, TiO2)-Doped MoS2 Surface

When partial discharges occur in air-insulated equipment, the air decomposes to produce a variety of contamination products, resulting in a reduction in the insulation performance of the insulated equipment. By monitoring the concentration of typical decomposition products (CO, NO, and NO2) within the insulated equipment, potential insulation faults can be diagnosed. MoS2 has shown promising applications as a gas-sensitive semiconductor material, and doping metal oxides can improve the gas-sensitive properties of the material. Therefore, in this work, MoS2 has been doped using the popular metal oxides (ZnO, TiO2) of the day, and its gas-sensitive properties to the typical decomposition products of air have been analyzed and compared using density functional theory (DFT) calculations. The stability of the doped system was investigated using molecular dynamics methods. The related adsorption mechanism was analyzed by adsorption configuration, energy band structure, density of states (DOS) analysis, total electron density (TED) analysis, and differential charge density (DCD) analysis. Finally, the practical application of related sensing performance is evaluated. The results show that the doping of metal oxide nanoparticles greatly improves the conductivity, gas sensitivity, and adsorption selectivity of MoS2 monolayer to air decomposition products. The sensing response of ZnO-MoS2 for CO at room temperature (25 °C) reaches 161.86 with a good recovery time (0.046 s). TiO2-MoS2 sensing response to NO2 reaches 3.5 × 106 at 25 °C with a good recovery time (0.108 s). This study theoretically solves the industrial challenge of recycling sensing materials and provides theoretical value for the application of resistive chemical sensors in air-insulated equipment.

Effects of Plasma Treatment on the Surface and Photocatalytic Properties of Nanostructured SnO2-SiO2 Films

In this work, we study the effects of treating nanostructured SnO₂-SiO₂ films derived by a sol-gel method with nitrogen and oxygen plasma. The structural and chemical properties of the films are closely investigated. To quantify surface site activity in the films following treatment, we employed a photocatalytic UV degradation test with brilliant green. Using X-ray photoelectron spectroscopy, it was found that treatment with oxygen plasma led to a high deviation in the stoichiometry of the SnO₂ surface and even the appearance of a tin monoxide phase. These samples also exhibited a maximum photocatalytic activity. In contrast, treatment with nitrogen plasma did not lead to any noticeable changes in the material. However, increasing the power of the plasma source from 250 W to 500 W led to the appearance of an SnO fraction on the surface and a reduction in the photocatalytic activity. In general, all the types of plasma treatment tested led to amorphization in the SnO₂-SiO₂ samples.

Synergy of S-vacancy and heterostructure in BiOCl/Bi2S3-x boosting room-temperature NO2 sensing

The special physicochemical properties of Bi₂S₃ nanomaterial endow it to be exceptional NO₂ sensing properties. However, sensors based on pure Bi₂S₃ cannot detect trace NO₂ at room temperature effectively due to the scanty active sites and poor charge transfer efficiency. Herein, vacancy defect and heterostructure engineering are rationally integrated to explore BiOCl/Bi₂S_3-x heterostructure with rich S vacancies to enhance NO₂ sensing performance. The optimized sensor based on S-vacancy-rich BiOCl/Bi₂S_3-x heterostructure exhibited a high response value (R_g/R_a = 29.1) to 1 ppm NO₂ at room temperature, which was about 17 times compared to the pristine Bi₂S₃. Meanwhile, the BiOCl/Bi₂S_3-x sensor also exhibited a short response time (36 s) towards 1 ppm NO₂ and a low theoretical detection limit (2 ppb). The superior response value of S-vacancy-rich BiOCl/Bi₂S_3-x heterostructures was ascribed to the improved electron migration at the heterointerface and the additional exposed active sites caused by the S vacancies in Bi₂S_3-x. Additionally, the sensors based on S-vacancy-rich BiOCl/Bi₂S_3-x heterostructures showed good long-term stability, outstanding selectivity, and good flexibility. This study offers an effective method for synergistically engineering defect and heterostructure to enhance gas sensing properties at room temperature.