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Gas detection and monitoring are critical to protect human health and safeguard the environment and ecosystems. Chemiresistive sensors are widely used in gas monitoring due to their ease of fabrication, high customizability, mechanical flexibility, and fast response time. However, with the rapid development of industrialization and technology, the main challenges faced by chemiresistive gas sensors are poor selectivity and insufficient anti-interference stability in complex application environments. In order to overcome these shortcomings of chemiresistive gas sensors, the pattern recognition method is emerging and is having a great impact in the field of sensing. In this review, we focus systematically on the advancements in the field of data processing methods for feature extraction, such as the methods of determining the characteristics of the original response curve, the curve fitting parameters, and the transform domain. Additionally, we emphasized the developments of traditional recognition algorithms and neural network algorithm in gas discrimination and analyzed the advantages through an extensive literature review. Lastly, we summarized the research on chemiresistive gas sensors and provided prospects for future development. [ABSTRACT FROM AUTHOR]

As a stable, low-cost, environment-friendly, and gas-sensitive material, semiconductor metal oxides have been widely used for gas sensing. In the past few years, single-atom catalysts (SACs) have gained increasing attention in the field of gas sensing with the advantages of maximized atomic utilization and unique electronic and chemical properties and have successfully been applied to enhance the detection sensitivity and selectivity of metal oxide gas sensors. However, the application of SACs in gas sensors is still in its infancy. Herein, we critically review the recent advances and current status of single-atom catalysts in metal oxide gas sensors, providing some suggestions for the development of this field. The synthesis methods and characterization techniques of SAC-modified metal oxides are summarized. The interactions between SACs and metal oxides are crucial for the stable loading of single-atom catalysts and for improving gas-sensitive performance. Then, the current application progress of various SACs (Au, Pt, Cu, Ni, etc.) in metal oxide gas sensors is introduced. Finally, the challenges and perspectives of SACs in metal oxide gas sensors are presented. [ABSTRACT FROM AUTHOR]

Relative humidity (RH) is an important physical quantity in industry, agriculture, and medical treatment. However, it is still challenging to exploit high-performance humidity sensors that can meet the detection requirement for responding to both high humidity variation and low humidity variation. In this work, ternary graphitic carbon nitride (g-C3N4) nanosheet/TiO2 nanoparticle/Ti3C2Tx nanosheet composites were synthesized by in situ oxidation and thermal polymerization. The response of the g-C3N4/TiO2/Ti3C2Tx sensor reaches 531 from 11–95% RH, which enhances 4, 11, and 450 times compared with that of TiO2, g-C3N4, and TiO2/Ti3C2Tx sensors. Moreover, the ternary g-C3N4/TiO2/Ti3C2Tx sensor demonstrates excellent reproducibility, fast response speed, low hysteresis loop, and good anti-interference ability. The as-fabricated g-C3N4/TiO2/Ti3C2Tx sensor is further utilized in practical applications for human respiration detection and evaluation of waxing of fruits. The test results show that our fabricated sensor is capable of precisely sensing breathing status and distinguishing the waxing of fruits. In addition, our sensor can be used in most application scenarios and accelerate the integration of the Internet of Things (IoT). [ABSTRACT FROM AUTHOR]

The high-operating temperature and poor selectivity of metal oxide semiconductor (MOS)-based chemiresistive-type gas sensors severely limit their application in the future Internet of Things (IoT), which need a lower power consumption and a higher accurate molecular recognition ability. Here, a simple and effective modification strategy is proposed for the incorporation of Cu2O and the two-dimensional (2D) material MoS2via a facile hydrothermal and wet chemical method. The sensing characteristics of a series of (p–p) Cu2O/MoS2 nanohybrids towards ammonia (NH3) are systematically investigated. The nanohybrid based sensor shows an excellent NH3 sensing performance compared with the pristine Cu2O nanoparticles in the 25–325 °C temperature range. Under an optimal low-operating temperature of 75 °C, the sensing performance for 20–100 ppm NH3 is studied and the sensing response of the Cu2O/MoS2 sensor (at ∼872%) with an optimized composition for 100 ppm NH3 is increased more than 8 times compared with the pristine Cu2O (∼103%) under the same conditions. Furthermore, excellent selectivity for NH3 is observed against other interferent gases. The Cu2O/MoS2 sensor belongs to a surface-controlled type and the enhanced sensing property of nanohybrid benefits from the superimposed effect of the p–p heterojunction formation and the elevated specific surface area at the interface between Cu2O and MoS2. [ABSTRACT FROM AUTHOR]

In this work, SnS1−xSex ternary nanobelts were synthesized by a facile hydrothermal method without the assistance of surfactants. The structure, morphology, microstructure, compositions, chemical valences, phonon modes, and optical band gaps of the SnS1−xSex nanobelts were characterized in detail. The results indicate that the SnS1−xSex nanobelts have uniform one-dimensional morphology and are single crystals with high crystallinity. Se is incorporated into the SnS lattice to substitute for S-forming ternary SnS1−xSex alloy. With the increase of Se doping concentration, the optical band gaps of the nanobelts gradually decrease from 1.15 to 1.01 eV, confirming the tunable optical property achieved here. [ABSTRACT FROM AUTHOR]

It is still challenging to control the crystallization and morphologies of molecular crystal nanostructures with excellent photocatalytic activities. In this study, single-crystalline melem (C6N10H6) nanorods (MNRs) were prepared by a facile thermal polymerization route under a flowing argon atmosphere. Compared with the bulk melem counterpart and g-C3N4, the MNRs exhibited substantially improved efficiency and stability towards the photodegradation of diverse organic pollutants including methyl orange, rhodamine B, and methylene blue. Moreover, the average photocatalytic hydrogen evolution rate of MNRs was about 2.6 folds higher than that of bulk melem under the same conditions. The enhanced photocatalytic redox performance of MNRs arises from the single-crystal nature and novel one-dimensional (1D) nanorod morphology, contributing to elevated conduction band potentials and promoting charge transport dynamics. This study not only reports single-crystalline melem 1D nanostructures as novel highly efficient and stable molecular-crystal photocatalysts, but also reveals the important roles of synergetic tuning of charge potentials and dynamics in enhancing the photocatalytic activity of molecular-crystal photocatalysts. [ABSTRACT FROM AUTHOR]

Explosives can be analyzed for their content by detecting the photolytic gaseous byproducts. However, to prevent electrostatic sparking, explosives are frequently preserved in conditions with low temperatures and high humidity, impeding the performance of gas detection. Thus, it has become a research priority to develop gas sensors that operate at ambient temperature and high humidity levels in the realm of explosive breakdown gas-phase detection. In this work, 3-aminopropyltriethoxysilane (APTES) self-assembled monolayer-functionalized tin diselenide (APTES-SnSe 2 ) nanosheets were synthesized via a facile solution stirring strategy, resulting in a room-temperature NO 2 sensor with improved sensitivity and humidity tolerance. The APTES-SnSe 2 sensor with moderate functionalization time outperforms the pure SnSe 2 sensor in terms of the response value (317.51 vs 110.98%) and response deviation (3.11 vs 24.13%) under humidity interference to 500 ppb NO 2 . According to density functional theory simulations, the stronger adsorption of terminal amino groups of the APTES molecules to NO 2 molecules and stable adsorption energy in the presence of H 2 O are the causes of the improved sensing capabilities. Practically, the APTES-SnSe 2 sensor achieves accurate detection of photolysis gases from trace nitro explosives octogen, pentaerythritol tetranitrate, and trinitrotoluene at room temperature and various humidity levels. This study provides a potential strategy for the construction of gas sensors with high responsiveness and antihumidity capabilities to identify explosive content in harsh environments.

Metal-oxide-based chemiresistive hydrogen sensors exhibit high sensitivity, long-term stability, and low cost and have been extensively applied in safety monitoring of H 2 . However, the sensing performances are dramatically affected by the water vapor, resulting in reduced response value and increased response/recovery time. To improve the anti-humidity property of sensors, coating the breathable and hydrophobic membrane on the surface of the sensing film is an effective strategy. In this work, the poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole- co -tetrafluoroethylene] (Teflon AF-2400) was dip-coated on the surface of SnO 2 in a commercial hydrogen sensor (TGS2615) as a breathable and hydrophobic membrane. For safety, He instead of H 2 was used to test the gas permeability of membranes. The Teflon membrane shows a high He permeability of up to 40,700 Barrer and an excellent He/H 2 O selectivity of 99. Moreover, Teflon shows high processability to form a defect-free coating on the rough surface of the sensing film and high chemical stability under the operando condition of the sensor. Thus, the Teflon-modified sensor possesses excellent selectivity with a value of 5, and the resistance is stable at 10,554 ± 3% Ω for 20 days in 80% RH. The modified sensor shows an improved anti-humidity property with a 75% response to 200 ppm H 2 at 80% RH and has a low coefficient of variation value of 7.23% that shows advances than other reported sensors modified by coatings. The commercially available Teflon and the simple coating technology make the strategy easily scale up and show promising applications.

Bi 2 Te 3 -based compounds are important near room temperature thermoelectric materials with commercial applications in thermoelectric modules. However, new routes leading to improved thermoelectric performance are highly desirable. Incorporation of superparamagnetic nanoparticles was recently proposed as a means to promote the thermoelectric properties of materials, but its feasibility has rarely been examined in mainstream thermoelectric materials. In this study, high quality single-crystalline Bi 2 Te 2.7 Se 0.3 nanoplates and Ni nanoparticles were successfully synthesized by solvothermal and thermal decomposition methods, respectively. Bulk nanocomposites consisting of Bi 2 Te 2.7 Se 0.3 nanoplates and superparamagnetic Ni nanoparticles were prepared by spark plasma sintering. It was found that incorporation of Ni nanoparticles simultaneously increased the carrier concentration and provided additional scattering centers, which resulted in enlarged electric conductivities and Seebeck coefficients. The greatly improved ZT was achieved due to the increase in power factor. Spark plasma sintered bulk nanocomposites of Bi 2 Te 2.7 Se 0.3 nanoplates incorporated by 0.4 mol %Ni nanoparticles (in molar ratio) showed a figure-of-merit ZT of 0.66 at 425 K, equivalent to 43% increase when compared to pure Bi 2 Te 2.7 Se 0.3 nanoplates. The results revealed that incorporation of magnetic nanoparticles could be an effective approach for promoting the thermoelectric performance of conventional semiconductors.