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 (zeta-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.