Review—Recent Progress in Low Temperature Synthesis of Crystalline TiO 2 Photocatalytic Films by Highly Controllable Electrodeposition

Eco-friendly photocatalysis has already been known for decades. In the photocatalytic process, photoinduced oxidation and reduction reactions at the photocatalysts surface enable the degradation of organic compounds into harmless substances like carbon dioxide or water. Titanium dioxide has demonstrated to be one of the most prominent photocatalysts, which can be ascribed to its outstanding physico-chemical properties, low cost and environmental friendliness. Thin films of TiO 2 are of special interest due to cost saving reasons and for applications where recycling technologies cannot be implemented. However, efficient photocatalysts are based on crystalline TiO 2 , which is typically obtained after heat treatment. This is energetically unfavourable and prohibits the usage of temperature-fragile substrates. Consequently, there is a need to find low-temperature synthesis routes, which allow the direct crystallization of TiO 2 or subsequent crystallization at mild temperatures. Electrodeposition allows superior control over morphology, homogeneity and thickness due to precise parameter control. This review summarizes recent developments in low-temperature electrodeposition of crystalline TiO 2 with emphasis on final crystallinity and photocatalytic activity. Furthermore, the different approaches will be classified with regard to practicableness as well as industrial implementability. As a final conclusion, the current technical challenges as well as future perspectives will be discussed.