Self-cleaning anatase nanorods : photocatalytic removal of structure directing agents and subsequent surface modification

Anatase nanorods were synthesised via the non-hydrolytic condensation of TiCl4 and Ti(OPr)4 in the presence of trioctylphosphine oxide and dodecylamine as structure directing agents, to produce rod-like particles approximately 5 nm in diameter and 15 nm in length. The crystal structure was confirmed as pure anatase by Raman spectroscopy and X-ray diffraction. The as-prepared nanorods can be dispersed in organic solvents as a result of hydrophobic surface functionalities imparted during the synthesis. Subjecting nanorod suspensions in CHCl3-water mixtures to UV irradiation leads to complete photocatalytic removal of surfactants from the TiO2 surface, enabling, in turn, transfer of the nanorods into the aqueous phase. Quaternary ammonium hydroxides were used to stabilise optically clear aqueous suspensions, through a combination of electrostatic and steric repulsion between particles; dispersions of individual nanorods are a prerequisite for many technological applications. Once 'stripped' of their organic ligands, the nanorods can be further functionalised using, for example, aminopropyltriethoxysilane to modify the isoelectric point, dispersibility, or photocatalytic activity; these effects are demonstrated by electrophoretic and dye degradation experiments.