Yanqiong Li

This study presents a straightforward and efficient methodology for augmenting the gas sensing capabilities of Nickel Oxide (NiO)-based sensors, achieved through the fabrication of novel flower-shaped NiO nanomaterials characterized by a distinctive nanoneedle structure. The resulting gas sensors exhibited a remarkable enhancement in performance, showcasing heightened sensitivity, rapid response and recovery rates, and exceptional reproducibility. The superior gas sensing attributes are ascribed to the unique structural features inherent in the flower-like NiO spheres, which contribute to an increased surface area and the optimization of oxygen vacancies (O_V) and oxygen complexes (O_C). Beyond addressing the imperative for heightened gas sensing in NiO-based sensors, this study offers a comprehensive analysis of the growth mechanism underlying the formation of the distinct flower-like structure. This research not only represents a significant advancement in gas sensing technology but also contributes a novel solution for the improvement of air quality monitoring within the confined spaces of car cabins. The findings elucidate the intricate relationship between the morphology of NiO nanomaterials and their gas sensing properties, providing insights that extend beyond conventional approaches. The synthesis and characterization of the flower-shaped NiO nanomaterials were meticulously conducted using various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), elemental mapping, and X-ray photoelectron spectroscopy (XPS). These analyses yielded specific parameters crucial for understanding the gas sensing performance of the fabricated NiO nanomaterials. The research findings not only contribute to the fundamental understanding of NiO-based gas sensors but also hold promise for practical applications in the context of air quality monitoring, particularly within the enclosed environments of vehicular cabins.

This work characterized the microstructure of stainless steel before and after adsorption. At the same time, the adsorption experiments at different temperatures and the adsorption characteristic experiment were carried out. The results show that chemical adsorption has taken place on the surface of stainless steel. The change of temperature has little effect on the functional groups of the stainless-steel surface after adsorption. Hydrogen sulfide showed the largest adsorption capacity and fastest rate, while methyl and ethyl mercaptan performed second. Carbonyl sulfide exhibited the smallest adsorption capacity and slowest rate.

In recent years, substantial advancements have been made in the development of enzyme-free glucose sensors utilizing pristine metal-organic frameworks (MOFs) and their combinations. This paper provides a comprehensive exploration of various MOF-based glucose sensors, encompassing monometallic MOF sensors as well as multi-metal MOF combinations. These approaches demonstrate improved glucose detection capabilities, facilitated by the augmented surface area and availability of active sites within the MOF structures. Furthermore, the paper delves into the application of MOF complexes and derivatives in enzyme-free glucose sensing. Derivatives incorporating carbon or metal components, such as carbon cloth synthesis, rGO-MOF composites, and core–shell structures incorporating noble metals, exhibit enhanced electrochemical performance. Additionally, the integration of MOFs with foams or biomolecules, such as porphyrins, enhances the electrocatalytic properties for glucose detection. Finally, this paper concludes with an outlook on the future development prospects of enzyme-free glucose MOF sensors.

Firstly, ZnO nanorods were prepared by a relatively simple method, and then self-sacrificed by a water bath heating method to generate a commonly used porous ZIF-8 and firmly attached to the ZnO surface. The successful synthesis of synthetic composites was demonstrated with various detection methods. The gas-sensing results show that the ZIF-8-coated ZnO with a core-shell structure exhibits better response than the raw ZnO because of the increased specific surface area and active sites.

In this work, we reported a novel core–shell NiO spheres with a three-layer structure for gas sensor. The obtained gas sensors exhibited a higher response, rapid response/recovery rate and nice reproducibility. The gas sensitivity test results showed that NiO-12 h with a three-layer structure obtained a gas response of 35.4, a response/recovery time of 13/9.8 s, to 200 ppm ethanol at 350 °C. The enhancement of gas sensing performance gave credit to the special core–shell structure and the more O _V and O _C . Furthermore, the formation mechanism of the core–shell structure was analyzed and we found that the formation of the core–shell structure was closely related to the reaction time. This work not only gave a solution for improving the gas sensing performance of the gas sensors based on NiO, but provided an analysis of the growth mechanism of the core–shell structure.

Gas sensing materials, such as semiconducting metal oxides (SMOx), carbon-based materials, and polymers have been studied in recent years. Among of them, SMOx-based gas sensors have higher operating temperatures; sensors crafted from carbon-based materials have poor selectivity for gases and longer response times; and polymer gas sensors have poor stability and selectivity, so it is necessary to develop high-performance gas sensors. As a porous material constructed from inorganic nodes and multidentate organic bridging linkers, the metal-organic framework (MOF) shows viable applications in gas sensors due to its inherent large specific surface area and high porosity. Thus, compounding sensor materials with MOFs can create a synergistic effect. Many studies have been conducted on composite MOFs with three materials to control the synergistic effects to improve gas sensing performance. Therefore, this review summarizes the application of MOFs in sensor materials and emphasizes the synthesis progress of MOF composites. The challenges and development prospects of MOF-based composites are also discussed.

Since MXene (a two-dimensional material) was discovered in 2011, it has been favored in all aspects due to its rich surface functional groups, large specific surface area, high conductivity, large porosity, rich organic bonds, and high hydrophilicity. In this paper, the preparation of MXene is introduced first. HF etching was the first etching method for MXene; however, HF is corrosive, resulting in the development of the in situ HF method (fluoride + HCl). Due to the harmful effects of fluorine terminal on the performance of MXene, a fluorine-free preparation method was developed. The increase in interlayer spacing brought about by adding an intercalator can affect MXene’s performance. The usual preparation methods render MXene inevitably agglomerate and the resulting yields are insufficient. Many new preparation methods were researched in order to solve the problems of agglomeration and yield. Secondly, the application of MXene-based materials in gas sensors was discussed. MXene is often regarded as a flexible gas sensor, and the detection of ppb-level acetone at room temperature was observed for the first time. After the formation of composite materials, the increasing interlayer spacing and the specific surface area increased the number of active sites of gas adsorption and the gas sensitivity performance improved. Moreover, this paper discusses the gas-sensing mechanism of MXene. The gas-sensing mechanism of metallic MXene is affected by the expansion of the lamellae and will be doped with H₂O and oxygen during the etching process in order to become a p-type semiconductor. A p-n heterojunction and a Schottky barrier forms due to combinations with other semiconductors; thus, the gas sensitivities of composite materials are regulated and controlled by them. Although there are only several reports on the application of MXene materials to gas sensors, MXene and its composite materials are expected to become materials that can effectively detect gases at room temperature, especially for the detection of NH₃ and VOC gas. Finally, the challenges and opportunities of MXene as a gas sensor are discussed.