# Cotton Terry Textiles with Photo- and Bio-Activity in a Model Study and Real Conditions
## 4 Discussion
Other parameters which can affect photocatalytic activity under real conditions include air pollution with dust, especially with organic compounds, air flow, types of building materials, structures and equipment in the rooms, and hygienic conditions of the room. Studies carried out within this project reveal the significant impact of air humidity on photocatalytic processes. RH = 30-75% is considered to be optimum for effective photocatalysis, and a humidity increase in the presented range contributes to a rise in the photocatalytic inactivation of microorganisms [3; 32]. Some papers describe high activity at RH = 45% [7], while others demonstrate that effectiveness is greatly reduced over RH = 75-85% [3; 32]. In the present studies, high air humidity (RH = 65.6-66.8%) was observed in the bathroom with artificial lighting, where a reduction in the number of microorganisms was discovered. A slightly higher reduction in the number of microorganisms was observed in the air in the bathroom with natural lighting, where RH = 36-44.5%. The temperature in the tested bathrooms was 21-23 \({}^{\circ}\)C, which according to the literature, is not significant for photocatalysis [3]. In the present studies, the real conditions in the tested bathrooms, where the photocatalytic processes were conducted, were demonstrated as sufficient for reducing the number of microorganisms in the air by 1 log on average. The reduction in air microbiological contamination from 10\({}^{3}\) to 10\({}^{2}\) CFU/m\({}^{3}\) for bacteria and from 10\({}^{2}\) to 10\({}^{1}\) CFU/m\({}^{3}\) for fungi is a satisfactory result for the environment. Air was considered as non-contaminated under household conditions, which was the desired effect. Many microorganisms proliferate in air, including pathogenic bacteria, and toxinogenic and allergenic mold [60]. Removing bacteria and mold from the air in model photocatalytic systems in visible light has been the subject of a number of papers, which have demonstrated high antimicrobial effectiveness [53]. The present study covered textile fabrics modified with TiO\({}_{2}\) and ZnO, used in bathrooms. The results suggest that the modification can support air cleaning. One should note that in the tested bathrooms with a volume of 12.86-40.5 m\({}^{3}\) only two towels (size: \(70\times 150\) cm\({}^{2}\)) were used, which can affect photocatalytic effectiveness. A reduction in gas concentration (NO2, CO2, CO) in the air in bathrooms where modified towels were used is testimony to the occurrence of photocatalytic processes. The number of VOCs and their concentration were also observed to decrease significantly above the modified towels compared to the control towels. The main VOCs were of cosmetic origin; however, some compounds of textile and microbiological origin were also observed. The literature provides evidence for the oxidation of such inorganic and organic compounds as dyes (methylene blue, rhodamine B, methyl orange, sunset yellow, Reactive Black 5 and Acid Orange 7), toxic compounds (cyanide, bisphenol A, 2,4 dichlorophenol, phenol, toluene, benzene and humic acid) and inorganic compounds (nitrate, bicarbonate, sulphate and NOx) under model conditions [16]. The oxidation of organic compounds was confirmed under real conditions when photocatalysis was used for the treatment of wastewater or river water and air [16]. This study is the first to be carried out under real conditions where a reduction in the concentration of inorganic and organic compounds in the air was demonstrated as a result of the activity of photocatalytically modified textile fabrics. Visible light was confirmed to be able to induce photocatalysis, which effectively removes some VOCs and undesired gases from the air. Moreover, observations of the modified towels during seven days of use revealed lack of odors, compared to the control towels. Due to the type and application of the tested terror towels, they should be relatively often washed at high temperatures. Hence, the modification should be resistant to washing.