Effect of Surface Fluorination of TiO2 Particles on Photocatalitytic Activity of a Hybrid Multilayer Coating Obtained by Sol-Gel Method

A multilayer photoactive coating containing surface fluorinated TiO2 nanoparticles and hybrid matrices by sol gel approach based on renewable chitosan was applied on poly(lactic acid) (PLA) film by a step wise spin-coating method. The upper photoactive layer contains nano-sized fimctionalized TiO2 particles dispersed in a siloxane based matrix. For the purpose of improving TiO2 dispersion at the air interface coating surface, TiO2 nanoparticles were modified by silane coupling agent 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FTS) with fluoro-organic side chains. An additional hybrid material consisting of chitosan (CS) cross-linked with 3-glycidyloxypropyl trimethory silane (GOTMS) was applied as interlayer between the PLA substrate and the upper photoactive coating to increase the adhesion and reciprocal affinity. The multilayer TiO2/CS-GOTMS coatings on PLA films showed a thickness of similar to 4-6 mu m and resulted highly transparent. Their structure was exhaustively characterized by SEM, optical microscope, UV vis spectroscopy and contact angle measurements. The photocatalytic activity of the multilayer coatings were investigated using methyl orange (MeO) as a target pollutant; the results showed that PLA films coated with surface fluorinated particles exhibit higher activity than films with neat particles, because of a better dispersion of TiO2 particles. The mechanical properties of PLA and films coated with fluorinated particles, irradiated by UV light were also investigated; the results showed that the degradation of PLA substrate was markedly suppressed because of the UV adsorptive action of the multilayer coating.