Homogeneous self-cleaning coatings on cellulose materials derived from TIP/TiO2 P25

The aim of this research was to study TiO₂ nanocoatings formation and to investigate their self-cleaning effects when applied on cellulose materials. Two different approaches for achieving nanocoatings were used. First, coatings were generated in situ through an acid and alkaline catalyzed sol-gel process with or without added water. Another type of coatings was prepared starting from commercial TiO₂ P25 powder. In order to acquire homogeneous coatings from TiO₂ P25 nanoparticles with uniform nanoparticles size distribution, pH of aqueous TiO₂ P25 dispersions was varied. The dispersion preparation conditions were studied by dynamic light scattering (DLS) and zeta potential (ζ-potential) analysis. The resulting TiO₂ nanocoatings were analyzed in terms of their surface morphology using scanning electron microscopy (SEM). Nanocoatings obtained from pure aqueous dispersions of TiO₂ P25 nanoparticles were inhomogeneous with huge agglomerates; however by changing the pH of dispersion and consequently changing the surface charge of TiO₂ P25 nanoparticles as well, more homogeneous nanocoatings with uniform TiO₂ nanoparticles distribution were prepared. Significant differences between solgel derived coatings were observed. Sol-gel process without added water yielded more homogeneous coatings than sol-gel process with addition of water. Completely different surface morphologies were obtained using alkaline or acid catalyst. Acid catalyzed sol-gel process yielded nanocoatings with long, extended, thin structures; contrary, under alkaline conditions particles grow in size with decrease in number. Fourier transform infrared (FTIR) spectroscopy was used to study the coatings’ microstructure. Furthermore the formation of mono-disperse nanoparticles on the fiber surface resulted in enhanced photocatalytic activity. Degradation of colored stain applied on TiO₂-treated samples was investigated by colorimetric measurements. Photocatalytic activity of nanocoatings prepared via acid catalyzed sol-gel process without water addition was comparable to that of nanocoatings derived from aqueous dispersions of commercial TiO₂ P25 nanoparticles.