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

Abstract

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.