1. Introduction

Surface technology describes the summary of a large variety of processes that are used when conventional materials no longer meet increasing demands for wear, corrosion or special tribological or optical requirements. The overall function of a component is therefore often divided into subfunctions. In this case, the surface coating takes a specific function and thus enables the selection of a less expensive base material while at the same time fulfilling the range of requirements for the entire component. Today’s application areas of surface technology extend far beyond the function of producing decorative, tribological or corrosion-protective surface coatings. Surface engineering processes are nowadays already an integral part of production and manufacturing, and are often the driving force behind the implementation of product requirements. Furthermore, economic aspects play an important role for the use of coating processes. [1]
All surfaces that we come into contact in our everyday activities have a special role in spreading pathogens. Especially high traffic touched surfaces in public transport or health care can be affected unnoticed. Titanium dioxide is photocatalytically active in its anatase phase and can therefore be used as a self-cleaning, antimicrobial surface coating system. Particularly with regard to the formation and spread of bacteria (e.g. coli bacteria), germs (e.g. MRSA), fungi and algae, anatase can assist in minimizing their formation and spread. In healthcare, follow-up diseases caused by contact with germs, bacteria or viruses are one of the most frequent causes of death worldwide [2]. The so-called multi-resistant germs (MRSA) represent a further problem. In the European economic area, more than 670,000 infections and 33,110 deaths could be attributed to antibiotic-resistant germs during 2015. The total number of infections has increased in the period from 2007 to 2015. Approximately 64 % of all cases in this period occurred due to infections in relation to health care facilities. At least half of the infections are considered to be preventable [3]. All surfaces that patients come into contact with during their stays in a healthcare facility have a major impact on the spread of infections and diseases. A common door handle used by patients and visitors can thus become a critical transmission surface for bacteria and germs. In the analysis of statistical data examining infections for their cause, it was determined that in 21.1 % of the cases the reason was the contact with contaminated medical equipment and in 19.8 % of the cases contamination of the environment was responsible for an infection [4]. The photocatalytic activity of titanium dioxide is based on the release of radicals on the surface which can decompose organic substances in an advanced oxidation process (AOP). The photocatalytically active surface coating offers a physical effect that is able to decompose organic deposits upon irradiation with ultraviolet light. The UV light exposure initiates an advanced oxidation process of the organic substances [5]. A potential formation of a biofilm and a possible risk of infection is thereby reduced and in the best case completely prevented [6]. Further applications of titanium dioxide can be found in the treatment of wastewater with pharmaceutically contaminated residues. [5, 7]