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 TiO(2) 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 functionalized TiO(2) particles dispersed in a siloxane based matrix. For the purpose of improving TiO(2) dispersion at the air interface coating surface, TiO(2) 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 trimethoxy silane (GOTMS) was applied as interlayer between the PLA substrate and the upper photoactive coating to increase the adhesion and reciprocal affinity. The multilayer TiO(2)/CS-GOTMS coatings on PLA films showed a thickness of ~4-6 μm 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 TiO(2) 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.