New antibacterial TiO2 coating works in visible light

We are one step closer to germ-proof surfaces for environments such as hospitals after an unexpected discovery of a black variant of TiO2 coatings that does not require UV activation and works more effectively than existing standard TiO2 solutions.

A research team at the University of Canterbury in New Zealand has succeeded in developing an antibacterial coating that, once commercially available, can be applied to frequently used surfaces, such as door handles, which will help to reduce the risk of infection spreading in hospitals.

The famously bright white or transparent coating turned black during the research. The material was tested for the self-cleaning performance, and it turned out to be photocatalytically active without requiring any UV radiation. Research showed that the TiO2 structure had changed shape.

TiO2 has antibacterial properties when exposed to UV radiation. This action creates energy, causing oxygen ions to form, which are fatal for bacteria. Therefore, the material is ideal for surfaces such as door handles and other (metal) surfaces in environments where sterility is a priority, such as hospitals.

Solution for existing challenges

The new coating offers a solution to the challenges faced by the research team when developing antibacterial coatings: how to apply a TiO2 coating to an object such as a door handle and how to activate it indoors, where there is no natural UV radiation present. The nanostructure and the black colour showed that the new development was effectively a new type of material. Instead of the typical smooth pyramid crystals of the white TiO2, the crystals turned out to have a nanostructure that could only be obtained by hydrothermal growth of individual nanoparticles. Furthermore, the material was found to have an antibacterial activity in visible light.

This study showed that bacteria were destroyed after brief exposure to visible light. The TiO2 was applied to a stainless steel surface as a solid layer of more than 10 µm. The effectiveness of the coated surface was estimated to be a hundred times higher than standard TiO2 coatings and powders. The coatings more than tripled the reduction in E-coli after four hours of exposure to visible light.

Since no radiation is needed to activate this new form of TiO2 and a modified nanostructure is present that allows the composition to be incorporated in coatings, the conditions are met to develop commercial applications. The black coating was already successfully applied on a door handle and a partnership with several companies was set up to make the development suitable for design and scaling up for advanced production.

Read more about this research here.

In the e-book on functional surfaces, we dedicate a section to antibacterial coatings. More info? Download the e-book here.

To align the European R&D efforts on this type of coating, several European networks have been created. Sirris is an active member of the European COST Action Network AMiCI, of which the main objective is to evaluate the impact of (introducing) AntiMicrobial Coatings in healthcare on the spread of infections and on the efficacy in fighting HealthCare Associated Infections and bacterial resistance to current antibiotics.

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