In the research self-cleaning coatings based on photocatalytically active nano titanium dioxide ($TiO_2$) were prepared. When applied directly to cellulose fiber surfaces, $TiO_2$ coatings form weak bonds with fibers. Therefore 3-glycidooxypropyl-trimethoxysilane was used as a coupling agent. It had been applied on the surface of cellulose fibers before the $TiO_2$ coating was performed. In this case, the silane is in the interface region, where it can be most effective as an adhesion promoter. Silane coupling agents have unique chemical and physical properties not only to enhance bond strength, but more importantly to prevent de-bonding at the interface during composite aging and use as well. The coupling agent provides a stable bond between two otherwise poorly bonding surfaces. Surface properties of these coatings have been examined, such as surface morphology and surface microstructure. $TiO_2$ nanoparticles were irreversibly attached to the surface of monodisperse silica ($SiO_2$) spheres and to the surface of Lyocell fibers coated with an epoxy-containing silane coupling agent. Analysis using scanning electron microscopy showed uniform distribution of nanoparticles in the resulting coatings. Fourier transform infrared spectroscopy revealed changes in the surface microstructure occurring after different modifications. In addition, the influence of photocatalytic activity on the mechanical properties of Lyocell fibers was determined. In addition to that, the results indicated that $SiO_2$ and the coupling agent provide a protection against high oxidizing power of $TiO_2$ under exposure to daylight irradiation.