Photocatalytically Active Amorphous and Crystalline TiO2 Prepared by Atomic Layer Deposition

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.