Optimizing the packing density of TiO2 nanorod arrays for enhanced light harvesting by a light trapping effect and its photocatalytic decomposition of gaseous benzene

As photocatalysts, semiconductors can demonstrate a novel performance when the morphology is appropriately manipulated. In this paper, a single-crystalline TiO2 nanorod array with a preferred [002] axial orientation was grown on transparent conductive fluorine-doped tin oxide (FTO) substrates by a hydrothermal process. The packing density of the nanorod array was manipulated by simply changing the hydrochloride acid (HCl)/water volume ratio of the initial growth solution. The growth mechanism of the nanorod arrays was discussed. XRD, SEM and TEM data suggest that more (002) facets were exposed on top of the nanorod with a higher packing density. However, the array with most (002) facets exposed demonstrated a relatively low photocatalytic activity targeting gaseous benzene. Results indicate that the nanorod array is better compiled with a medium packing density (46.6%) to double the photocatalytic performance comparing to both 15.26% and 81.25% packed arrays. The UV-vis absorption measurement and photocurrent test revealed that a medium packing density can provide a greatly enhanced light harvesting efficiency due to a light trapping effect by the array structure. By establishing a simple-but-efficient leverage to manipulate the packing density of the nanorod film, the photocatalytic activity of the array is greatly impacted by variation of the light harvesting efficiency due to a light trapping effect rather than more exposed high energy facets.