Photocatalytically Active Amorphous and Crystalline TiO2 Prepared by Atomic Layer Deposition

Abstract

In this work, the photocatalytic properties of amorphous and crystalline TiO₂ deposited on oxide and polymer nanoparticles by atomic layer deposition (ALD) were studied. Beside TiO₂, as reference, both ALD grown amorphous Al₂O₃ and crystalline ZnO layers were also examined. When choosing the carrier, the priority was that it had no effect on the photocatalytic activity of TiO₂; therefore the oxide layers were deposited on SiO₂ and poly(methyl-methacrylate) (PMMA) nanoparticles. The amorphous SiO₂ particles were synthetized by the Stöber method, while the PMMA particles were prepared by emulsion polymerization. Both the bare and core/shell composite nanoparticles were investigated by SEM-EDX, TEM, FT-IR, and XRD. Finally, the photocatalytic activity of PMMA, SiO₂ and the core/shell nanoparticles was measured by the decomposition of methylene orange, monitored by UV-Vis spectroscopy. Based on the results, the SiO₂ was uniformly coated with the deposited oxide films, while in the case of the PMMA a contiguous web-like polymer/TiO₂ matrix was formed. During the photocatalytic reactions, the amorphous Al2O3 was not active, while the crystalline ZnO and TiO₂ showed good photocatalytic activity. The amorphous TiO2 deposited by ALD on the SiO2 and PMMA nanoparticles had smaller, but a clearly detectable photocatalytic effect on the photodegradation of methylene orange.