Photocatalytic and Protective Thin Films for Enhanced Self-cleaning Activity and Durability of Painted Steel Roofings

Fouling of painted steel roofings over time due to biological organisms and other pollutants is a well-known aesthetic, functional and environmental problem that highlights the importance of developing greener self-cleaning technologies for roofing applications. Accordingly, a series of novel photocatalytic coating systems have been developed in this study by introducing a copolymer of tetratethyl orthosilane and methyltrimethoxysilane as the photochemically stable binder and intermediate protective layer. Visible light active carbon doped titanium dioxide and surface modified nano titanium dioxide with anatase-rutile hetero junctions were used as the semiconductor photocataysts. The concentration of titanium dioxide was set as 10 %, 25 % and 40 % by weight of the dried photocatalytic film. Methylene blue photoderadation reaction kinetics and antimicrobial assays were used as the key measures of assessing the self-cleaning performance. The morphological and chemical composition changes were analyzed as a function of time using scanning electron microscopic and spectroscopic techniques as a measure of service life of these putative photocatalytic coating systems. According, a high degree of self-cleaning activity was observed in these novel photocatalytic coating systems having 10 % (w/w) to 40 % (w/w) titanium dioxide loading compared to the painted steel roofing control sample. A complete eradication and 2-3 orders of log reduction were achieved respectively against E.coli bacteria and A.niger and Cladosporium fungies. The introduction of the intermediate polysiloxane protective layer has significantly enhanced both the self-cleaning activity and service life, minimizing the diffusion of photogenerated reactive oxygen species into subsequent underneath paint layers. The photocatalytic self-cleaning activity and the rate of photodegradation have been increased with titanium dioxide concentration. The coating system with 10 % (w/w) surface modified nano titanium dioxide loading having the intermediate protective layer was found to be the optimum coating formulation to obtain a high degree of self-cleaning activity at a minimum rate of photodegradation in this study.