Noble-metal-decorated metal oxide sensors have shown promising gas-sensing properties. However, the optimal dispersion of metal particles on a semiconductor is still challenging for most sensing materials. In this study, Co3O4 nanocubes (NCs) and Pt-supported Co3O4 NCs were prepared as sensing materials for acetone gas detection. Transmission electron microscopy and X-ray diffraction were used to examine the structure and exposed facets of Co3O4 NCs. As a result, the Co3O4 NCs were identified as the single-crystalline phase of spinel Co3O4, and each surface exposed the {100} plane. To examine the cocatalytic effect of Pt combined with Co3O4 NCs on the sensing performance, Pt nanoparticles were photodeposited on Co3O4 (Pt–Co3O4 NCs). The Pt–Co3O4 NC-based sensor provided a higher p-type response than the Co3O4 NC sensor in the detection of 500 ppb acetone at 200 °C, with the highest response of 3.1 (R g/R a). The enhanced performance of the Pt–Co3O4 NCs is caused by the exposed {100} planes of Co3O4, in addition to the loaded Pt nanoparticles. The sensor with Co3O4 NCs has a larger neck diameter and hole accumulation layer at the interface than that with Co3O4 nanospheres and thus provides a wide channel for charge carriers, resulting in better gas-sensing responses and high selectivity toward acetone over other volatile compounds. Moreover, the Pt nanoparticles stimulate O2 dissociation on the Co3O4 surface, thus increasing the concentration of chemisorbed oxygen species by the spillover effect. Thus, the incorporation of Pt with Co3O4 NCs promotes the sensitivity of the material in the detection of acetone gas and also enhances the selectivity. This study highlights the possibility of the rapid deposition of metal nanoparticles for the improvement of gas sensors.

A BiVO4/Bi2S3 composite comprising Bi2S3 nanowires on top of a BiVO4 film was prepared via hydrothermal reaction. Because additional Bi3+ ions were not delivered during the reaction, BiVO4 served as the Bi3+ ion source for the development of Bi2S3. A detailed growth mechanism of the nanowire was elucidated by an analysis of the concentration gradient of Bi3+ and S2– ions during the reaction. The in situ growth was followed by the etching of BiVO4 to Bi3+ and VO4 3– ions and regrowth to Bi2S3, which resulted in the rapid evolution of nanowires on the BiVO4 substrate. The fabricated BiVO4/Bi2S3NW composite exhibited an improved photoelectrochemical activity compared to other Bi2S3 samples. The improved efficiency was mainly attributed to both improved charge separation and effective adhesion obtained by the in situ growth.

In this study, the structure–activity relationship of the WO3 photocatalyst and the role of cocatalysts deposited on the WO3 surface were analyzed. Investigation of the phase transformation of WO3 microplates revealed that amorphous WO3 was progressively crystallized into monoclinic WO3 during consecutive thermal treatments. The obtained WO3 microplates were used for the photocatalytic decomposition of organic dyes under simulated solar light irradiation to understand the effect of the crystal structure on the photocatalytic activity. The crystal phase of the WO3 microplates with a monoclinic structure was optimal for the photocatalytic reaction. However, the effects of the crystal phase and the surface area of the WO3 sample were very small, and a deposited metal cocatalyst was essential for achieving photocatalytic activity. The detailed mechanisms and influence of cocatalysts on the WO3 surface were discussed.