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The high-pressure structures of alkaline earth metal hydride-fluorides (AHFs) (A = Ca, Sr, Ba) were investigated up to 8 GPa. While AHF adopts the fluorite-type structure (Fm3¯m) at ambient pressure without anion ordering, the PbCl2-type (cotunnite-type) structure (Pnma) is formed by pressurization, with a declining trend of critical pressure as the ionic radius of the A2+ cation increases. In contrast to PbCl2-type LaHO and LaOF whose anions are fully ordered, the H−/F− anions in the high-pressure polymorph of SrHF and BaHF are partially ordered, with a preferential occupation of H− at the square-pyramidal site (vs. tetrahedral site). First-principles calculations partially support the preferential anion occupation and suggest occupation switching at higher pressure. These results provide a strategy for controlling the anion ordering and local structure in mixed-anion compounds. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO)-based materials are deemed as promising candidates for fabrication of room-temperature gas sensors, while a tougher challenge is to develop an effective strategy for improving gas responses. Here, a noble metal decoration strategy is developed to enhance NO2 responses of α-Fe2O3/SnO2–rGO hybrids. Noble metal decorated α-Fe2O3/SnO2–rGO hybrids were prepared by depositing noble metals onto α-Fe2O3/SnO2–rGO hybrids through reduction of noble metal ions by NaBH4. Most importantly, Pt modified α-Fe2O3/SnO2–rGO hybrids (designated as Pt-FSR) exhibit the highest response value of 21.3 toward 5 ppm NO2, which is much higher than that of α-Fe2O3/SnO2–rGO (8.8). Combined characterization studies indicate that the enhanced NO2 response of Pt-FSR is attributed to the narrow band gap of Pt-FSR, small particle size and excellent catalytic activity of Pt. The NO2 sensing mechanism is also investigated by FT-IR spectroscopy. The findings proposed in this work not only broaden the study of room-temperature gas sensors, but also provide suggestions for discovering the gas sensing mechanism. [ABSTRACT FROM AUTHOR]

Toluene is widely used as a solvent and reactant in a wide range of industrial fields; however, gaseous toluene is toxic to humans, causing severe acute respiratory effects. In this case, Co3O4-based chemiresistive gas sensors are promising candidates for monitoring toluene. However, it is challenging to prepare Co3O4-based sensing materials with good toluene sensing performances on a large-scale. In this study, oxygen vacancy-rich Co3O4 materials were successfully synthesized via the reduction of commercial Co3O4 using NaBH4 as the reducing agent (designated as Co3O4-R), and the oxygen vacancy concentrations in Co3O4-R materials were effectively modulated by regulating the NaBH4 concentration. With an increase in oxygen vacancies, the optimal Co3O4-R-5 samples displayed better sensing performances toward 100 ppm toluene at 190 °C than that of the pristine commercial Co3O4, including an enhanced response value of 3.18 (vs. 1.22 for commercial Co3O4) and fast response time of 48 s and recovery time of 38 s. The combination of band structure analysis and chemisorption analysis indicated that the enhanced toluene sensing performances of Co3O4-R is attributed to the synergistic effect of reducing the band gap and activating the surface oxygen species. This work demonstrates the first utilization of commercial Co3O4 for toluene sensing applications, providing a universal and high-throughput preparation method to prepare gas sensing materials using commercial metal oxides. [ABSTRACT FROM AUTHOR]