Self-cleaning, titanium dioxide based, multilayer coating fabricated on polymer and glass surfaces

A photocatalytic self-cleaning titanium dioxide (TiO₂) coating was prepared as a multilayer coating structure by the spin-coating method. Three substrate materials (two thermoplastics and one ceramic) were used: (1) high-density polyethylene (HDPE), (2) poly(vinyl chloride), and (3) borosilicate glass (BK7). The multilayer structure consisted of a polyurethane protective layer on the substrate, two layers of photocatalytic TiO₂ on the protective layer, and finally immobilized TiO₂ particles bound in a diluted polyurethane dispersion. Photocatalytically active surfaces were achieved by reactive oxygen-plasma surface etching of the fabricated coatings. The structure and properties of the coating surfaces were characterized with scanning electron microscopy and contact-angle measurements. The coatings on HDPE and BK7 were rendered superhydrophilic by an oxygen-plasma treatment. The photocatalytic activity and self-cleaning properties of the prepared surfaces were studied with palmitic acid (model soil), the degradation of which was confirmed by contact-angle measurements and gas chromatography analysis.