Growth stages of nano-structured mixed-phase titania thin films and effect on photocatalytic activity

Abstract

The development of nano-structured mixed-phase titania thin films and the relationship to photocatalytic activity (PCA) is of interest for pollution reduction and antimicrobial applications. A set of lms grown by pulsed pressure metallorganic chemical vapour deposition using titanium tetraisopropoxide precursor was studied. The growth method is single-stage, scalable and produces high-quality, adherent lms. Film thicknesses were 101nm to 4:0 μm. Three growth stages were identi ed. All lms were a mixture of anatase and rutile. Early stage lms had rounded morphologies, low surface roughness and low PCA. Transition stage lms developed columnar [110] orientated anatase dendrites, contained amorphous carbon and had reduced UV transmittance. Late stage lms had strong anatase (220) and rutile (200) textures, contained amorphous carbon and exhibited highly branched anatase dendrites with nanoscale secondary plates. PCA was determined from degradation of stearic acid and correlated with increasing surface roughness. The most active lm had formal quantum e ciency of (6:62 0:64) 10ð€€€4 molecules=photon, 59 times higher than a commercially available control. The performance is attributed to the combination of phases yielding polymorphic phase boundaries and amorphous carbon enhancing the adsorption of organic molecules, the unusual (220) anatase texture yielding nanostructured anatase dendrites in combination with nanocrystalline rutile and hierarchical porosity.