Highly sensitive and selective detection of volatile organic compounds (VOCs) is highly important, and designing a suitable microstructure and constructing heterostructures are two main effective strategies for gas-sensing materials to achieve this goal. In this study, Pt nanoparticle-decorated CoFe₂O₄/Co₃O₄ nanosheets were prepared via a solution method for highly accurate detection of formaldehyde (HCHO), where the CoFe₂O₄/Co₃O₄ nanosheets were derived from a two-dimensional Fe‒Co metal-organic framework (MOF). The response (R_g/R_a, where R_g represents the electrical resistance of the gas sensor when exposed to a specific target gas under defined conditions; R_a denotes the baseline resistance of the gas sensor in clean air) of the ternary Pt₂/CoFe₂O₄/Co₃O₄ composite to 100 ppm HCHO at 280 °C can be calculated as 95.5, and it still exhibits a very high response to low concentrations of HCHO (1.26 to 50 ppb HCHO gas) and an ultralow limit of detection (LOD) of 6 ppb. The ternary composite also presented excellent reproducibility, selectivity, and long-term stability. The first-principles calculations demonstrated that the Pt/CoFe₂O₄/Co₃O₄ model presented the most stable structure and the strongest adsorption capacity for HCHO. The high sensitivity of Pt/CoFe₂O₄/Co₃O₄ to HCHO can be attributed mainly to the formation of multiple heterojunctions and the catalytic effect of the Pt nanoparticles. This work describes the facile preparation of MOF-derived multi-heterojunction materials and highlights the superior gas-sensing performance to that of VOCs.

The reactive air brazing (RAB) process of ceramics was developed in the early 2000s because high-temperature electrochemical devices, such as solid oxide fuel cells (SOFCs), gas separators, reformers, and ion transport membrane systems, are increasingly emerging. Accordingly, the reactive air wetting (RAW) and RAB of oxide ceramics have been investigated. Starting from the introduction of the advantages of the RAB process, the thermal expansion coefficients (TECs) of related materials, and the estimation of the TECs of Ag-based composite fillers, the RAW and RAB of ceramics are reviewed by classifying the employed ceramic materials, which mainly include yttria-stabilized zirconia (YSZ), perovskite oxides, Al₂O₃, and nonoxide ceramics. In particular, the RAW and RAB processes, interfacial microstructures, reaction products, and joint reliability (including joint strength, fracture energy, gas tightness, and high-temperature aging resistance) are highlighted for understanding interfacial behavior and joint performance and developing application-oriented brazing technology. Finally, some helpful conclusions are drawn after summarizing the RAB of oxide ceramics. The prospects for RAB of SiC and high-entropy oxide ceramics are proposed after summarizing the RAB of oxide and nonoxide ceramics, and several aspects are proposed for promoting the development and application of RAB technology.

Two-dimensional nanomaterials (2DNMs) have attracted significant research interest due to their outstanding structural properties, which include unique electrical nanostructures, large surface areas, and high surface reactivity. These adaptable materials have outstanding physicochemical characteristics, making them useful in a variety of applications such as gas-sensing, electronics, energy storage, and catalysis. Extensive research has been conducted in the pursuit of high-performance room-temperature (RT) gas sensors with good selectivity, high sensitivity, long-term stability, and rapid response/recovery kinetics. Metal oxides, transition metal chalcogenides, MXenes, graphene, phosphorene, and boron nitride have all been discovered as 2DNMs with strong potential for gas sensors. This review presents an in-depth analysis of current advances in 2DNM research. It includes synthetic techniques, structural stabilities, gas-sensing mechanisms, critical performance parameters, and factors influencing gas-sensing capabilities of 2DNMs. Furthermore, the present study emphasizes structural engineering and optimization methodologies that improve gas-sensing performance. It also highlights current challenges and outlines future research directions in the domain of tailoring 2DNMs for advanced RT gas sensors. This systematically designed comprehensive review article aims to provide readers with profound insights into gas detection, thereby inspiring the generation of innovative ideas to develop cutting-edge 2DNMs-based gas sensors.