Effect of Ce conversion underlayer coating on the photo-catalytic activity of TiO2 sol–gel film deposited on hot-dip GI

In the present work, a photocatalytic titanium dioxide (TiO2) thin film was prepared by dip coating using an alkoxide sol–gel solution that included crystalline nano-sized TiO2 particles (P-25) on hot-dip galvanized steel (GI). A cerium (Ce) conversion coating was used as an interface layer between the steel substrate and TiO2 film to improve the photocatalytic activity and anti-corrosion performance of the film. The Ce conversion coatings were deposited on the GI via the sol–gel dip coating process using a Ce nitrate/hydrogen peroxide solution. The properties of the coating layers were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), UV–vis light absorption spectroscopy, and electrochemical impedance spectroscopy (EIS). The thickness of the TiO2 sol–gel film and Ce conversion coating were approximately 150 nm and 30 nm, respectively. It was clearly demonstrated that the addition of nano-sized TiO2 particles in the sol–gel film significantly enhanced the filmʹs photocatalytic activity. The higher quantity of nano-sized TiO2 particles induced a higher absorption of UV light and improved photocatalytic activity. In particular, the photocatalytic activity was improved further by applying the Ce conversion coating because in most cases, the crystalline CeO2 interlayer reduced the band gap energy of the coating layer from 3.2 eV to 2.8 eV. In addition, the EIS measurements indicated that the Ce conversion coatings improved the anti-corrosion property of the coating layer on the hot-dip galvanized steel.