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The marriage of traditional gas-sensing semiconductors with low dimensional nanostructures is expected to exhibit interesting properties in the detection of hazardous gases. Herein, novel hollow-spherical heterojunctions are assembled for thin film gas sensors by using p-type black phosphorus (BP) and n-type tin oxide (SnO 2). Green synthesis strategies are employed to prepare BP nanodots and SnO 2 quantum dots. The aerosol-assisted chemical vapor deposition is used to prepare thin films with hollow-spherical heterojunctions. The BP incorporation significantly improves the gas-sensing properties of SnO 2 -based thin films, which demonstrate excellent response and repeatability to H 2 S at room temperature. The BP-SnO 2 heterojunction demonstrates more than twice the response and sensitivity of pristine SnO 2 thin film. Moreover, the recovery ability is significantly improved and LOD is decreased to 50 ppb. The hollow-spherical heterojunction has a joint gas-sensing mechanism contributed by both of SnO 2 and BP. The SnO 2 provides fundamental receptor function for gas detection while incorporated BP facilitates the adsorption of target H 2 S and provides additional electrons through the p-n junction tunnel. In addition, a slight negative dependence on humidity is observed for the gas sensor. It is ascribed to the competitive adsorption of water molecules on the BP-SnO 2 heterojunction surface against H 2 S molecules and chemisorbed oxygen. This work not only proposes novel heterojunction nanostructures for room-temperature gas detection, but also contributes to the functional integration of traditional gas-sensitive materials and emerging 2D materials in sensor technology. [ABSTRACT FROM AUTHOR]

In recent years, lanthanide doped materials have been extensively studied in the field of fluorescence temperature sensing due to their abundant emission levels and sensitive thermal response. Temperature sensing based on fluorescence intensity ratio (FIR) of upconversion nanoparticles has the advantages of fast temperature response, non-aggressiveness, and high spatial resolution. However, the most reported FIR sensing has limited sensitivity, probably due to the use of thermal coupling levels. Herein, we report a novel FIR temperature measurement based on non-thermal coupling levels of NaGdF 4 :Yb3+/Er3+@NaGdF 4 @NaGdF 4 :Yb3+/Tm3+ core-shell-shell nanostructure, which has high sensitivity and robustness simultaneously. The relative sensitivity based on I 801 / I 654 and I 801 / I 841 of Tm3+ to Er3+ can reach up to 4.56 (303 K) and 3.82% K−1 (313 K), respectively. Between them, FIR of I 801 / I 841 is independent of excitation power and time. These results show the great potential of FIR based on non-thermal coupling levels in high-sensitive and robust temperature sensors. [ABSTRACT FROM AUTHOR]

The mullite phase in porcelain is important to the porcelain strength; however, its formation from clay minerals usually requires high temperature. Here we found that the activation of kaolin by citric acid would lower the formation temperature of mullite phase to 935.1 °C, which is 67.5 °C lower than that for the raw kaolin. Needle-like mullite crystal, a desired crystal shape in kaolin, could be observed in activated kaolin at 1050 °C. The reduction of mullite formation temperature is due mainly to the surface change in kaolin. Upon citric acid activation, the pseudohexagonal platelets of kaolinite crystal are disintegrated to non-uniform flakes, and the specific surface area increases from 8.18 m 2 /g to 31.21 m 2 /g, both leading to improved activity of kaolin and increased sintering driving force. The results are of interest in producing high-strength porcelain at reduced sintering temperatures and consequent energy saving for sintering process. [ABSTRACT FROM AUTHOR]

Aerogels are usually synthesized from supercritical drying of wet-gels. High quality aerogels are usually characterized with high specific surface area (measured by BET method here) and high degree of polymerization of silicate (characterized by 29 Si NMR here). The quality of the aerogels depends highly on the quality of the corresponding wet-gels because the skeletal structure in the wet-gels changes only slightly in the supercritical drying process. Here we present a simple method to predict the quality of the desired silica aerogels before the supercritical drying. We found that the relative optical transmittance of the silica wet-gels at 500 nm had good linear correlation with the specific surface area and the degree of silicate polymerization in the corresponding aerogels. We can assess the quality and screen out the low-quality wet-gels from supercritical drying operation, and greatly reduce the cost for aerogel production. [ABSTRACT FROM AUTHOR]

Abstract Polycrystalline Bi 4 (Ti 3- x Fe x /2 Co x /2)O 12 (0 ≤ x ≤ 0.4) ceramics are prepared by solid state reaction method. The low temperature ferromagnetism is successfully induced by Fe/Co co-doping. Particularly, the x = 0.3 ceramics possess the largest remnant magnetization (2 M r) of about 0.272 emu/g at 100 K. Furthermore, all the doped ceramics undergo a ferromagnetic to paramagnetic transition, and show typical spin glass behavior, which is confirmed by the isothermal remnant magnetization and Memory Effect. The magnetic mechanisms probably originate from the coexistence and competition between ferromagnetic double exchange interactions and antiferromagnetic superexchange interactions, which lead to the appearance of the spin glass behavior in the doped ceramics and the strongest ferromagnetism in the x = 0.3 ceramics. The present work provides basic data and theoretical reference for the exploitation of the new multifunctional materials. [ABSTRACT FROM AUTHOR]