Cocrystallization Enabled Spatial Self-Confinement Approach to Synthesize Crystalline Porous Metal Oxide Nanosheets for Gas Sensing.

Crystalline metal oxide nanosheets show exceptional catalytic performance owing to the large surface-to-volume ratio and quantum confinement effect. However, it is still a challenge to develop a facile and general method to synthesize metal oxide nanosheets. Herein, we report a cocrystallization induced spatial self-confinement approach to synthesize metal oxide nanosheets. Taking the synthesis of SnO2 as an example, the solvent evaporation from KCl and SnCl2 solution induces the cocrystallization of KCl and K2 SnCl6 , and the obtained composite with encapsulated K2 SnCl6 can be in situ converted into SnO2 nanosheets confined in KCl matrix, after water washing to remove KCl, porous SnO2 nanosheets can be obtained. Notably, a series of metal oxide nanosheets can be obtained through this general and efficient green route. In particular, porous CeO2 /SnO2 nanosheets with improved surface O- species and abundant oxygen vacancies exhibit superior gas sensing performance to 3-hydroxy-2-butanone.

The effect of grain boundary on the energy storage properties of (Ba0.4Sr0.6M)TiO3 paraelectric ceramics by varying grain sizes.

(Ba0.4Sr0.6)TiO3 (BST) ceramics with various grain sizes (0.3-3.4 µm) were synthesized by the oxalate coprecipitation method and prepared by plasma activated sintering and conventional solid-state sintering process. The effect of grain boundary on the energy storage properties and the dielectric relaxation characteristics of BST paraelectric ceramics (Curie point ≈ -67°C) with various grain sizes were investigated. The dielectric breakdown strength (simplified as BDS) is obviously improved and then deteriorated with decreasing grain size, accounting for the energy density variation. The enhancement of interfacial polarization at grain boundary layers has a negative effect on the BDS, leading to the decreased values for samples with grain size smaller than 0.7 µm. In addition, the insulation effect of grain boundary barriers was discussed based on the complex impedance spectroscopy analysis, which was found to play a dominant role in controlling the BDS with coarser grain size. Among them, the sharply decreased BDS for BST with grain size of 1.8 µm was believed to be attributed to the combination of lower grain boundary density and higher interfacial polarization, due to the significant increase of oxygen vacancies at higher sintering temperature.