For the development of high-performance gas sensors, ultrafast response and high selectivity are critical requirements for many practical applications. An alternative strategy is to employ hierarchical nanostructured materials in gas sensors. In this work, we report newly synthesized TiO2 hexagonal nanosheets with a hierarchical porous structure, which demonstrate an ultrafast gas response and high selectivity toward acetone vapor for the first time. A simple one-step annealing process to prepare hierarchical TiO2 nanosheets derived from layered TiSe2 nanosheet templates is reported. The hierarchical structure interlaced with anatase TiO2 nanosheets showed an open porous characteristic. The average pore size was about 20 nm examined using a high-resolution TEM. The gas sensing properties toward acetone vapor of the novel hierarchical structured TiO2 nanosheets were characterized in detail including optimal operation temperature, sensitivity, selectivity, response/recovery time, and long-term stability. The gas sensing response and recovery times were 0.75 s and 0.5 s, respectively. We attribute these superior response properties to its unique hierarchical pore structure with a high specific surface area. The results show great potential for acetone vapor detection, particularly in dynamic ultrafast monitoring by using the synthesized hierarchical structured TiO2 nanosheets.

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Solution method is a mild, controllable and commonly used synthetic method. However, the reported solution methods for the preparation of TiSe 2 nanosheets usually use trioctylphosphine (TOP) as solvent. TOP is poisonous and potentially harmful to the human body as well as the environment. In this paper, hexagonal TiSe 2 nanosheets were synthesized by simple solution method without TOP. The shape evolution of TiSe 2 nanosheets was investigated by adjusting the reaction time. The crystal phase, morphology, elements, and the optical property of TiSe 2 nanosheets were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and UV-Vis spectroscopy, respectively. The spiral growth steps can be clearly observed in SEM images. A spiral layer by layer growth mechanism was proposed based on the morphology evolution of TiSe 2 nanosheets. The photocatalytic activity of TiSe 2 nanosheets was evaluated by the degradation of RhB under sun light irradiation. Compared with the commercial P25, the as-prepared TiSe 2 nanosheets exhibit a superior photocatalytic activity, which indicates that TiSe 2 nanosheets are promising candidate as photocatalytic material for environmental protection.

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