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 TiO
₂
nanosheets were assembled to form hierarchical 3-D nanoflowers by a low-temperature hydrothermal process and tested for volatile organic compound (VOC) sensing. Structural characterization, such as X-ray diffraction, revealed the anatase crystallinity of the TiO
₂
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 °C, 90 °C, 60 °C, 120 °C, and 60 °C, respectively. The sensor appreciably showed fast response (~6-15 s) and recovery (~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.