Highly Selective Low-Temperature Acetone Sensor Based on Hierarchical 3-D TiO2 Nanoflowers

The dimensionality of the nanostructures plays a pivotal role in determining the sensing performance of metal oxide semiconductors. In this paper, 2-D TiO2 nanosheets were assembled to form hierarchical 3-D nanoflowers by a lowtemperature hydrothermal process and tested for volatile organic compound (VOC) sensing. Structural characterization, such as X-ray diffraction, revealed the anatase crystallinity of the TiO2 nanoflowers. The chemical composition of the nanoflowers was confirmed through energy dispersive spectroscopy and X-ray mapping techniques. Field emission scanning electron microscopy results demonstrated the 3-D nanoflower like structure, consisting of 2-D nanosheets of length 120 nm and a thickness of 12-23 nm. A suitable growth mechanism for hierarchical nanoflowers has been proposed. The nanoflowers were found to offer promising sensing performance toward VOCs, such as acetone, methanol, 2-butanone, toluene, and 2-propanol at relatively low optimum operating temperature of 60 degrees C, 90 degrees C, 60 degrees C, 120 degrees C, and 60 degrees C, respectively. The sensor appreciably showed fast response (similar to 6-15 s) and recovery (similar to 15-39 s) characteristics. Furthermore, the sensor offered high selectivity toward acetone. The sensing performance of the nanoflowers has been correlated with a space charge model at the grain boundary.