Modifying TiO2 Nanoparticles by Atomic Layer Deposition for Enhanced Photocatalytic Water Purification

Abstract

Photocatalysts, contrary to conventional catalysts, utilize light to drive a reaction. By absorption of photons, electrons are excited and reach higher states to initiate a redox reaction. This principle can be broadly used to produce chemicals such as hydrogen via the reduction of water or transform carbon dioxide into solar fuels, i.e., methane, methanol, and formaldehyde. Besides chemical production, the reductive/oxidative potential of the excited electrons/holes can be utilized to degrade molecules. This is especially useful for self-cleaning materials or for cleaning waste water streams from molecules such as dyes, pesticides, or pharmaceuticals, as water pollution levels increasingly harm human health, especially in developing countries. Despite the great potential and vast research activities over the last decades, the development of cheap and efficient photocatalysts and especially the evaluation of the mechanism of photocatalytic degradation pathways are still lacking, which hampers the translation from lab to application. TiO2 (P25) is a cheap and non-toxic photoactive material, yet too inefficient for water cleaning. This thesis focuses on the surface modification of TiO2 (P25), minimizing various drawbacks of TiO2 (P25) and on the evaluation of the photocatalytic mechanisms. Atomic layer deposition (ALD) allows us to precisely control the deposition of many different materials at the atomic level, an advantage that could improve the photocatalyst design and optimize the activity.