Self-cleaning and antimicrobial photo-induced properties under indoor lighting irradiation of chitosan films containing Melon/TiO₂ composites

Chitosan films containing visible-light absorbing melon/TiO₂ composites (MTiO₂) (CTS/MTiO₂), prepared by sol-gel method using urea as precursor, were evaluated as self-cleaning and antimicrobial photo-induced surfaces under indoor lighting irradiation. Malachite green and staphylococcus aureus were used as model pollutant and bacteria strain respectively. Characterization revealed that MTiO₂ nanoparticles were successfully incorporated on chitosan films. Presence of nanoparticles on chitosan films did not strongly affect tensile strength of films, however, its solubility was highly reduced. Dye stains on CTS/MTiO₂ films were efficiently removed after 72 h of continuous indoor lighting irradiation. It was found that dye molecule underwent N-demethylation reactions caused probably by the attack of photo-induced ^[rad]OH radicals produced on MTiO₂ surfaces while dye ATR-FT-IR spectrum exhibited the presence of C[dbnd]O groups probably linked to benzophenones generated by the reaction between malachite green molecules and photo-induced singlet oxygen (¹O₂). Furthermore, CTS/MTiO₂ exhibited self-cleaning properties during 15 days of continuous indoor lighting irradiation. S. aureus underwent a culturability dropping of around 3 logs after 3 h of irradiation while chitosan and chitosan/P25 films did not exhibit culturability decreasing. Although self-cleaning properties were not altered by continuous irradiation, it was found that surface morphology and physical-chemical properties of chitosan films underwent changes.