(Invited) Nanostructured Photocatalysts Prepared By Atomic Layer Deposition

Abstract

Semiconductor oxides are widely used photocatalysts to decompose organic contaminations with solar energy. The activity of these photocatalysts can be further improved by doping them with heteroatoms, by making composites of them with other semiconductor oxide materials, noble metal nanoparticles, organic dyes and other organic absorbers, or by increasing their specific surface using highly structured substrates. Since by ALD uniform thin films with thickness control of sub-nanometer precision can be deposited on nanopatterned surfaces, it is a unique tool for preparing, doping and programming nanoscaled photocatalytic material.In the lecture several examples will be shown about how various nanostructured photocatalysts can be obtained by ALD, based on our own experience. By combining electrospinning and ALD, WO3/TiO2, ZnO/TiO2 and TiO2/ZnO core/shell Vis or UV active nanofiber photocatalysts were prepared. By using sol-gel and ALD, SiO2/TiO2 core/shell photocatalytic nanoparticles were obtained. Photocatalysts based on biological substrates can be also manufactured by ALD, e.g. TiO2 coated lotus leaves with both superhydrophobic and photocatalytic activities. C60/TiO2 (Fig. 1), graphene oxide (GO)/TiO2, CNT/TiO2, carbon aerogel/TiO2 and PMMA/TiO2 composites are examples for ALD prepared carbon and polymer nanostructure based photocatalysts.On the previously mentioned substrates, TiO2 thin films were deposited by ALD using TiCl4 or Ti(OPr)4 and H2O as precursors at various temperatures (80, 160, 250, 300 °C), and therefore nanocomposites containing both crystalline and amorphous TiO2 layers were prepared. While TiO2 is considered to have photocatalytic activity only in the crystalline state; unexpectedly, we observed that when TiO2 was deposited in amorphous form on biological or organic substrates, i.e. lotus leaf, C60-OH, GO or PMMA, the amorphous TiO2 layer clearly exhibited photocatalytic property. Figure 1