Project „NanoKat“

Project „NanoKat“

Development of composite catalyst layers made of titanium dioxide and carbon quantum dots to improve visible light photocatalysis

Photocatalysis using sunlight or artificial light is an almost ideal technology for breaking down pollutants into non-toxic or significantly less harmful substances or for reducing bacterial contamination under ambient conditions. One of the best-studied photocatalysts is the semiconductor titanium dioxide (TiO2). The basic mechanism for the photocatalytic degradation of pollutants is the absorption of UV-A radiation and the generation of charge separation. The generated charge carriers can subsequently trigger redox reactions and enable the formation of reactive oxygen species (ROS), which ultimately lead to the destruction of the contaminants.


However, TiO2 has a very limited ability to utilize solar energy and artificial visible light due to its large band gap. Carbon nanoparticles, so-called carbon quantum dots (“C-Dots”), are able to sensitize photocatalysts such as TiO2 to visible light by transferring electrons from photoexcited C-Dots into the conduction band of TiO2. C-Dots are a comparatively new class of materials that were discovered in 2004. They consist of carbon clusters and have a particle size of up to 10 nm. C-Dots can be produced easily and cost-effectively from natural products or renewable raw materials and are a focus of current materials research. If synthesized appropriately, they also have an electron storage function, so that undesirably rapid recombination of charge carriers in TiO2/C-Dots composites is prevented. Another advantage with regard to photocatalysis with visible light is that C-Dots often occur in different sizes at the same time during their synthesis. Since the particle size essentially determines the absorption behavior, C-Dots can absorb a wide spectral range from the visible to the NIR range. They also enable the active surface area of the photocatalyst to be improved and increased.


When using TiO2/C-Dots composites, powders have usually been dispersed directly in (waste) water to carry out photocatalysis. Although this process allows complete contact of the catalyst particles with the pollutants and high degradation efficiencies, the recovery of the catalyst powder represents an additional problem. It is very difficult to completely recover it from the treated water, especially since it involves nanoparticles. In fact, incomplete recovery of the catalyst particles would lead to secondary pollution. Air and surfaces cannot be treated sensibly with this approach.


In order to overcome the disadvantages mentioned, the “NanoKat” project aims to immobilize TiO2/C-Dots composites on suitable transparent supports such as glass and polymers. Strategies should be developed that lead to environmentally friendly, inexpensive, effective and reusable photocatalysts that are immobilized in the form of thin layers. This enables applications in which the catalyst can be easily recovered and completely new concepts, e.g. an internally coated reactor that is irradiated from the outside, can be implemented. Likewise, window panes, railings or other outdoor surfaces can be photocatalytically activated with sunlight, which, in addition to the formation of radicals, leads to the development of superhydrophilicity and a reduction in the water contact angle. When it comes into contact with water (e.g. rain or condensation), a thin film of water forms on the surface and impurities are easily removed (easy-to-clean effect). If there is sufficient illumination, such photocatalytic applications are also interesting indoors, for example to reduce germ contamination on surfaces or to eliminate odors.

Duration of the project: October 1st, 2022 to March 31st, 2025
The project is funded by