A novel approach to make high surface area ZnO thin film semiconductors has been developed, allowing the morphology, porosity and thickness to be controlled by varying the processing and composition. The aim of this study is to evaluate the possibility of using these materials as photocatalysts, and thereafter to systematically correlate surface morphology, porosity and surface area to photocatalytic activity.

Methylene blue (MB) (5-25 mgL^-1) was chosen as the model compound and the reaction was carried out with ultra violet light (UV) supplied by a 254nm low pressure mercury lamp. MB concentration was determined by UV/Vis spectroscopy and reaction intermediates were characterised by high performance liquid chromatography. The thin film morphology and surface area before and after reaction was determined by scanning electron microscopy. Surface hydrophobicity was evaluated with a contact angle goniometer. The photocatalytic activity to MB degradation of the ZnO thin films with different microstructures coated on glass slides were compared with commercially available ZnO powder.

The MB removal for the ZnO thin film slides varied between 0-25% after 4h with the MB degradation rate related to ZnO surface coverage. For example, the MB degradation rate increased from 5 to 15 to 25% when the ZnO surface coverage increased from 10 to 50 to 100%. Photocatalytic activity was lower than commercially available powder however. Furthermore, the thin films showed the same degradation after being reused three times. Therefore these thin films have potential for use as recyclable photocatalysts whose activity can be selected by varying their microstructure.