Preparation and Characterization of a Dual-Layer Coating with Synergistic Ionic Selectivity and Photocathodic Protection Property

Inspired by the mechanism of ion exchange resins, this study is a first-report in constructing a dual-layer photocathodic protective coating with ionic selectivity to enhance corrosion resistance property. The microstructure, composition, and ion selectivity of the coating are characterized by scanning electron microscopy, Raman spectroscopy, infrared spectroscopy, and membrane potential. It shows that the outer g-C3N4/TiO2 cation-selective layer plays a role in preventing corrosive Cl− ions passing through the coating; the inner g-C3N4-TiO2-CTAB anion-selective layer could prevent Fe2+ ions from diffusing through the coating. Furthermore, the coated carbon steel sample demonstrates a minimum OCP (open circuit potential) value of −770 mV (vs. SCE) under illumination in 3.5% NaCl media. Interestingly, the OCP remains around −720 mV (vs. SCE) even after light deprivation. The synergistic effect between ion selectivity and photocathodic protection is described, in detail, in the following.