TiO₂ Nanoparticles Obtained by Green Synthesis: Characterization and Evaluation of Their Effect on the Self-Cleaning and Antifungal Properties of an Aqueous Paint-Type Coating

This work presents a green chemistry route to obtain titanium dioxide TiO₂ nanoparticles with an average size of about 13.25 nm using lemongrass (Cymbopogon citratus) extract. For these assessments, TiO₂ nanoparticles were added to the coating at concentrations of 1% and 5% w/w on fiber-cement sheets. Self-cleaning evaluation was analyzed by the photodegradation of methylene blue (MB) dye at concentrations of 5, 10, and 20 mg/L applied to the coated sheet, and then exposed to simulated sunlight. The coating containing 5 wt% TiO₂ nanoparticles showed the highest photodegradation, reaching 93.3% after 4 h under simulated sunlight exposure at the lowest MB concentration (5 mg/L). Additionally, average contact angles of 80.4°, 92.03°, and 104.25° were determined for coatings containing 0%, 1%, and 5 wt% TiO₂, respectively. Moreover, the modified 5 wt% TiO₂ exhibited up to 30.9% greater hydrophobicity than the control. Antifungal efficacy against Aspergillus niger and Penicillium was evaluated using the Poisoned Food method with nanoparticles at concentrations of 1 and 3 mg/mL showing a moderate growth inhibition. In conclusion, the versatility demonstrated suggests potential applications such as a nano-additive for aqueous acrylic coatings, improving hydrophobicity, self-cleaning and antifungal properties, which could be attractive to the construction industry.