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Due to the small size of commercial BN crystal and the unique interlayer interaction of BN, the traditional exfoliate method makes it difficult to fabricate BN nanosheets (BNNSs) with high aspect ratio (> 5000). High aspect ratio BNNSs were obtained by sintering ammonium borane and centrifugal separation of the sintering products. The synthesis mechanism and structure of BN nanosheets were characterized by FTIR, TG, TEM and XRD. The results show that the cross-linking and dehydrogenation of ammonium borane begin when the temperature is over 80 ℃. Hydrogen releasing results in the formation of foam structure during the cross link process of ammonium borune, and finally the inorganic process was completed at 1000 ℃ to obtain the BN foam containing BNNSs. The as-prepared BNNSs are hexagonal crystal structure, with a thickness of about 1.5 nm and an average width of 30 μm. The width-thickness ratio reaches 20000. The high aspect ratio BNNSs were introduced to polyvinyl alcohol (PVA) to prepare the BNNS/PVA composite film. The composite film shows significant improvement in thermal conductivity and mechanical properties, fully explains the application advantages of high aspect ratio BNNSs in the field of BN based composites.

Continuous SiC fibers reinforced SiC ceramic matrix composites have wide applications in the aerospace and nuclear fields owing to their excellent high-temperature resistance, good oxidation resistance and mechanical properties. The precursor-derived method has been the most important method for preparing continuous SiC fibers. The introduction of specific hetero elements could effectively improve properties of SiC fibers. Based on the research work on precursor-derived SiC fibers of high performance carried out by our group in the past forty years, this review firstly summarizes the addition methods of hetero elements, mainly including physical blending or chemical modification methods; The role and mechanism of hetero elements have been elucidated from several aspects: increasing the ceramic yield of the precursor, facilitating densification during sintering of the precursor-derived SiC fibers, improving high-temperature resistance of the final SiC fibers, and generating functions of SiC fibers; The composition, microstructure, properties, and developmental status of SiC fibers containing hetero elements, such as Ti, Al, Zr, Fe, B, as well as refractory metals (Hf, Ta, Nb), have been introduced. Furthermore, future research in the development of precursor systems, quantitative study of the relationship between the types and contents of hetero elements and properties of derived fibers, as well as engineering applications of the precursor-derived SiC fibers, has been prospected.

Continuous SiC fibers with excellent mechanical properties and high‐temperature resistance possess immense potential as reinforcements for aeroengines. In this work, we prepared functionalized boron nitride nanosheet (F‐BNNS) composite SiC (F‐BNNS/SiC) fibers by polymer‐derived method. Due to the existence of F‐BNNS, the F‐BNNS/SiC fibers demonstrate an improved tensile strength up to 2300 MPa, representing a 25% increase compared to the original SiC fibers. Furthermore, owing to the chemical bonds established between the F‐BNNS and the SiCxOy network, the decomposition of the SiCxOy amorphous phase and the crystallization of SiC at high temperatures is effectively suppressed. The F‐BNNS/SiC fibers exhibit improved high‐temperature resistance, maintaining a tensile strength of 720 MPa up to 1500°C, while the SiC fibers completely degraded under the same conditions. The successful preparation of BNNS/SiC fibers may offer new insights into the performance enhancement of advanced ceramic fibers. [ABSTRACT FROM AUTHOR]

The strong potential of platinum single atom (PtSA) in gas sensor technology is primarily attributed to its high atomic economy. Nevertheless, it is imperative to conduct further exploration to understand the impact of PtSA on the active sites. In this study, the evolution of PtSA on (100)CeO2 and (111)CeO2 is examined, revealing notable disparities in the position and activity of surface PtSA on different crystal planes. The PtSA in (100)CeO2 surface can enhance the stability of Ce3+ and construct a frustrated Lewis pair (FLP) to form a double active site by combining the steric hindrance effect of oxygen vacancies, which increases the response value from 1.8 to 27 and reduce the response‐recovery time from 140–192 s to 25–26 s toward five ppm NO2 at room temperature. Conversely, PtSA tends to bind to terminal oxygen on the surface of (111)CeO2 and become an independent reaction site. The response value of PtSA‐(111)CeO2 surface only increased from 1.6 to 3.8. This research underscores the correlation between single atoms and crystal plane effects, laying the groundwork for designing and synthesizing ultra‐stable and efficient gas sensors. [ABSTRACT FROM AUTHOR]

The near stoichiometric SiC fiber has been reported to play significant roles in the application of aeroengine field. An in‐depth understanding on the degradation mechanism of the fiber during its corrosion in air and under a simulated aeroengine environment (PH2O:PO2:PAr = 14:8:78 kPa) will shine a light on the performance evaluations of the near stoichiometric SiC fiber‐based materials as well as the development of their potential applications. In this study, X‐ray diffraction, scanning electron microscope, and FIB‐TEM were utilized to analyze the mechanical properties and microstructure of the fiber. After oxidation in dry air and Ar–H2O–O2 for 1 h, respectively, the fiber strength retention rate has been found to decrease with the increased oxidation temperature. The raise in oxidation temperature also led to the increase of the thickness and the crystallization rate of the oxide scale. The most different oxidation behaviors of SiC being treated under the simulated environment than in air are the lower oxidation activation energy and the higher crystallization activation energy for cristobalite. Water vapor can promote the oxidation reaction and inhibit the crystallization of cristobalite in the oxide scale. Few significant differences have been observed otherwise in the oxidation process and oxidation chromatography crystallization mechanism of fibers being treated under different conditions. The increase of oxide layer thickness and the formation of cristobalite impair the structural integrity and compactness of the oxide scale and thus lead to the deterioration of the mechanical properties of SiC fibers. Therefore, it is proposed that oxidation resistance of SiC fiber can be improved by insulating the reaction between the oxidizing agents and the SiC fiber or by increasing the crystallization temperature of cristobalite in the oxidation process and reducing the crystallization rate. [ABSTRACT FROM AUTHOR]

The tripartite combination of a high density and stability of surface reaction sites, complemented by the longevity and efficient transfer of interface carriers, along with the effective adsorption and activation of target gas molecules, jointly determines the efficiency of chemiresistors. In this work, the strong metal–support interaction (SMSI) of Pt─Ce3+ is formed by the NaBH4 reduction method and thus prepares metal‐dynamically stable PtNR─CeO2 with Pt─Ce3+ and Pt─Pt reaction sites. The formation of SMSI induces the recombination of the chemical structure of the CeO2 surface causing the localization of electron‐rich Ce3+, which greatly increases the charge concentration at the interface. The experimental findings of the strong interaction of Pt─Ce3+ bonding and the catalytic effect of Pt optimized the adsorption mode of PtNR─CeO2 on target gas, which maintains stable catalytic activity at 20–500 °C and achieving a notable detection response value of 1.43 for 20 ppb NO2. This work offers fresh insights into designing stable oxide chemiresistors with efficiency and stability by customizing reaction sites at the atomic level. [ABSTRACT FROM AUTHOR]

The strong potential of platinum single atom (Pt SA ) in gas sensor technology is primarily attributed to its high atomic economy. Nevertheless, it is imperative to conduct further exploration to understand the impact of Pt SA  on the active sites. In this study, the evolution of Pt SA  on (100)CeO 2  and (111)CeO 2 is examined, revealing notable disparities in the position and activity of surface Pt SA  on different crystal planes. The Pt SA  in (100)CeO 2  surface can enhance the stability of Ce 3+  and construct a frustrated Lewis pair (FLP) to form a double active site by combining the steric hindrance effect of oxygen vacancies, which increases the response value from 1.8 to 27 and reduce the response-recovery time from 140-192 s to 25-26 s toward five ppm NO 2  at room temperature. Conversely, Pt SA  tends to bind to terminal oxygen on the surface of (111)CeO 2  and become an independent reaction site. The response value of Pt SA -(111)CeO 2  surface only increased from 1.6 to 3.8. This research underscores the correlation between single atoms and crystal plane effects, laying the groundwork for designing and synthesizing ultra-stable and efficient gas sensors., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Prolonging energetic hot electrons lifetimes and surface activity in the reactive site can overcome the slow kinetics and unfavorable thermodynamics of photo-activated gas sensors. However, bulk and surface recombination limit the simultaneous optimization of both kinetics and thermodynamics. Here tandem electric fields are deployed at (111)/(100)Au-CeO 2 to ensure a sufficient driving force for carrier transfer and elucidate the mechanism of the relationship between charge transport and gas-sensing performance. The asymmetric structure of the (111)/(100)CeO 2 facet junction provides interior electric fields, which facilitates electron transfer from the (100)face to the (111)face. This separation of reduction and oxidation reaction sites across different crystal faces helps inhibit surface recombination. The increased electron concentration at the (111)face intensifies the interface electric field, which promotes electron transfer to the Au site. The local electric field generated by the surface plasmon resonance effect promotes the generation of high-energy energy hot-electrons, which maintains charge concentration in the interface field by injecting into (111)/(100)CeO 2 , thereby provide thermodynamic contributions and inhibit bulk recombination. The tandem electric fields enable the (111)/(100)Au-CeO 2 to rapidly detect 5 ppm of NO 2 at room temperature with stability maintained within 20 s., (© 2024 Wiley‐VCH GmbH.)