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

Abstract

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.