The effects of plasma nitriding pretreatment in steel substrates on the photocatalytic activity of TiO2 films

This paper presents a comparative study of TiO2 films deposited on plasma nitrided and non-nitrided carbon steel substrates. It is well known that plasma nitriding contributes to increase film adhesion and corrosion resistance of the substrate. However, most studies about photocatalytic properties of TiO2 on steel substrates do not address the use of nitrided carbon steel. The main goal of this paper is to investigate the deposition of photocatalytic TiO2 film on nitrided carbon steel, obtained through a duplex treatment of plasma nitriding and reactive plasma sputtering deposition. TiO2 films were deposited on nitrided and non-nitrided AISI 1015 steel samples. The samples were characterized by X-ray diffraction (XRD), profilometry, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The photocatalytic activity was evaluated by monitoring the effect of photoinduced hydrophilicity and through the degradation of methylene blue dye (MB). The pretreatment by plasma nitriding increases the substrate surface roughness and improves the growth of rutile phase. The roughness of the substrate surface affects wettability only when the TiO2 film is not photoactivated. All samples become super-hydrophilic upon UV irradiation and remaining in this state for at least 24 h. A slightly higher performance in photocatalysis of MB is obtained by TiO2 film deposited on non-nitrided substrate.