# Cotton Terry Textiles with Photo- and Bio-Activity in a Model Study and Real Conditions
## 1 Introduction  
Photocatalysis is defined as the chemical reactions under the action of ultraviolet, visible or infrared radiation in the presence of photocatalysts, which absorb light and are involved in chemical transformation (International Union of Pure and Applied Chemistry, 2004). The basic mechanism is the formation of ROS (reactive oxygen species) including radical reactive oxygen forms, such as superoxide anion radical (O\({}_{2}\)) and highly reactive hydroxyl radical (OH), and non-radical reactive oxygen forms, such as hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)), singlet oxygen (\({}^{1}\)O\({}_{2}\)) and ozone (O\({}_{3}\)) [1,2]. Photocatalysis is considered as an efficient disinfection technique suitable for medical and pharmaceutical purposes, food protection, wastewater treatment, and the disinfection of water andindoor air [3; 4; 5]. TiO\({}_{2}\) is the most popular photocatalytic material used as a self-cleaning material for surface coating in many applications, for example as an antimicrobial component of construction materials, glass, cement, polymers, ceramics, metals and paint coatings [6; 7]. Textile materials with self-cleaning properties padded/coated with photocatalytic nano-compounds have received intensive scientific interest in recent decades [2; 8]. Self-cleaning finishes have been applied to cotton [9; 10; 11], wool [12], PET [13] and mixed fibers [14]. Disinfection practices still deserve interest for the development of novel photocatalysts with the use of different experimental systems: TiO\({}_{2}\) coating/doping with various metal nanoparticles (NPs), e.g., Zn, Cu, Pt, Ag, Cd, Mo and Co, and type of irradiation, e.g., visible light [15; 16]. The most popular photocatalytic compound for textile applications among other semi-conductor metal oxides is TiO\({}_{2}\), due to its high stability, high photocatalytic activity and non-toxicity [2; 8]. Recently, an increase in the use of ZnO photocatalysts for textile finishing in the literature is observed [17]. Both TiO\({}_{2}\) and ZnO photocatalytic NPs have a similar wide band gap that limits their activity in the UV region of light [18; 19; 20]. Metal/non-metal doping extends their spectral response to visible light [12; 17; 19; 20; 21]. [PERSON] et al. showed that europium doped TiO\({}_{2}\) finished cotton textiles have photocatalytic activity in UV and visible light and were even more effective in visible light [22]. [PERSON] at al. demonstrated, that cotton fabric functionalized with manganese doped TiO\({}_{2}\) showed excellent photocatalytic activity under visible light [23]. TiO\({}_{2}\)/diazonium/graphene oxide composite exhibited photocatalytic degradation of some dyes under visible light [24]. Moreover, the combination of ZnO and TiO\({}_{2}\) metal oxides increases energy absorption, stability and their photocatalytic activities [12]. Photocatalysis proceeds via redox reactions generally by predominating oxidative reaction pathways. Besides the degradation of diverse organic and inorganic compounds, mainly dyes, toxic substances and volatile organic compounds (VOCs), an important aspect is microorganism inactivation by photocatalysis [16; 25]. Recently, studies on photocatalytic activity have been intensively conducted on a wide spectrum of microorganisms, including many species of viruses (e.g., MS2 phage, RNA bacteriophage and phil164), bacteria (e.g., _Escherichia coli_, _Staphylococcus aureus_, _Bacillus subtilis_, total coliforms, _Salmonella_ sp. and _Pseudomonas_ sp. ), fungi (e.g., _Fusarium_ sp., _Candida albicans_ and _Aspergillus niger_), and parasites (e.g., _Giardia intestinalis_ and _Cryptosporidium parvum_) [5; 6; 16; 26]. The main mechanism of photocatalytic antimicrobial reactions under light conditions is based on the complex chemical oxidation of the cell wall and cell membranes, mainly including reactions of ROS with major cell components, such as lipids and proteins [27; 28].