Inorganic oxides, such as TiO2 and ZnO, show photocatalytic oxidation manifested as degradation of organic pollutants and antimicrobial activity dependent on the intensity and spectrum of incident light. The mechanism for photocatalytic oxidation is explained by 1) absorption of visible light or UV radiation by the catalyst leading to an excited state, such as creation of electron-hole pair 2) participation of this excited state on redox reactions with adsorbed molecules, such as reduction of O2 to ∙O2- radical by an electron or oxidation of water molecule producing ∙OH radical and finally 3) participation of those reactive particles in oxidation of the substrate [1]. In case of TiO2, in the presence of moisture, formation of hydroxyl radicals following absorption of UV photons was identified as the source of antibacterial activity [2] and this mechanism has been successfully exploited for sunlight driven disinfection of water [3] or degradation of pollutants in wastewaters [4].
Since inorganic oxides are used in form of glasses, cements and ceramics, addition of oxides with photocatalytic activity yields such materials for everyday objects exhibiting self-cleaning and antimicrobial properties [5]. Regarding antimicrobial activity of these materials, photocatalysis proved efficient for deactivation of viruses, shoving activity against both enveloped (influenza) and unenveloped (feline calicivirus) viruses. Regarding antibacterial properties activity has been demonstrated against methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis, and penicillin-resistant Streptococcus pneumoniae, which implies potential for use of such materials for mitigation of healthcare acquired infections [3, 5]. Similar functionalization of polymers has been achieved in the form of surface treatments [7].
Textile materials consist of filaments having only micrometers in diameter and thus have a significant specific surface, which is an important factor determining the rate of heterogenous reactions, such as oxidation of a pollutant with oxygen in the air. Additionally, textiles are applied in numerous applications ranging from clothing and household items to filter materials and architectural components. Adding photocatalytic effect to, for example air filters, represents an attractive way of improvement of functionality of such items. Photocatalytic degradation of air pollutants absorbed on textiles modified by TiO2/Ag nanoparticles incorporated onto fiber surface was already investigated for their potential to increase indoor air quality by use in upholstery [8] or by use of similar modification for nonwoven filtration textile used in air filters [9] Photocatalytic activity demonstrated as degradation of methylene blue as probing substance has been reported for Polypropylene/ZnO nanocomposites produced by melt compounding [10]. Due to the mentioned benefits of photocatalytic materials and surface treatments, manufacturers of additives and pigments for coatings and polymers market different pigments based on inorganic oxides with claims of their self-cleaning and antimicrobial properties due their photocatalytic activity. Here we present a demonstration of production of polypropylene yarns dope dyed with 1% by weight photocatalytic TiO2 and ZnO. Orange II dye and sodium salicylate were used as probes, or model pollutants, due to convenient determination of change of present quantity of the probe by spectroscopic methods. Polypropylene yarn without any additive and polypropylene yarn containing 1% Fe2O3 by weight were produced by the same means and used as control samples with no expected activity.