Preparation of nanocrystalline titania films with different porosity by water-based chemical solution deposition

Abstract

This study describes the synthesis of nanocrystalline titania layers on silicon and glass substrates by chemical solution deposition, using a water-based citratoperoxo-Ti(IV) precursor solution. The same aqueous solution-gel precursor is used for deposition of, both, thin dense layers by spin-coating and thicker porous layers by tape-casting. In the latter, the precursor solution is modified by the addition of polyvinyl alcohol (PVA), which acts as a thickener and pore-forming agent. Phase composition, film morphology, and the hydrophilic character of the films are studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-VIS transmission measurements, variable angle spectroscopic ellipsometry (VASE), and by contact angle measurements. The thin 180 nm titania film, deposited from the unmodified precursor solution, shows a density of about 96%. Upon ultraviolet illumination, it acquires a highly hydrophilic surface. One hour of illumination is sufficient to obtain a water contact angle of almost 0 degrees. Furthermore, the hydrophilisation process shows to be reversible. Tape-casting and thermal treatment of the modified precursor solution gives rise to the formation of a 500 nm thick, porous, pure anatase film. The nanocrystalline thick film is composed of 20-40 nm particles, and contains clearly defined pores of 20 nm, homogeneously distributed along the surface.