Photocatalytic enamel/TiO2 coatings developed by electrophoretic deposition for methyl orange decomposition

Abstract

The aim of this study was to obtain photocatalytic coatings, capable to decompose organic pollutants, through Electrophoretic Deposition (EPD) of enamels containing respectively 0%, 5%, 10%, 15% (in wt%) of TiO2 onto carbon steel substrates. High quality and homogeneous coatings were obtained by applying 12.5 V during 10 s, as the best EPD conditions. The layers were subsequently heat treated at 740 °C for 10 min, in order to obtain dense glazes.Rietveld refinement of XRD patterns and Raman results show that, after the heat treatment at 740 °C, TiO2 mostly exists as anatase, responsible of the photocatalytic effect. Semi-quantitative chemical analysis indicate segregation of TiO2 on the coatings surface, reaching saturation in the sample with 10 wt% TiO2. FEG-SEM observations reveal rod-like and spherical Ti-rich phases along the cross section of the coatings; some Ti was also dissolved into the enamel. 3D topographical mapping shows that, by adding TiO2, surface roughness increases significantly.Photocatalytic tests were carried out using a 2 × 10−5 M aqueous solution of Methyl Orange (MO) as an organic pollutant. By comparing the decomposition rate of MO achieved with the pure enamel (0% of TiO2) and with the sample with 10% of TiO2, it was shown that the addition of 10% of TiO2 results in 90% photocatalytic efficiency.Moreover, the permeation of organic compounds and their UV degradation were studied by measuring the water contact angle onto the enamel surface directly after dipping into oleic acid and after various UV irradiation times. The longer the UV irradiation time, the lower the contact angle, down to a minimum of 14.54° after 8 h of UV irradiation. This means, the compound was initially adsorbed on the enamel/TiO2 coating surface (10 wt% TiO2) but was efficiently decomposed upon UV irradiation.