A three-step electrochemical method designed for the production of nickel- and platinum-doped TiO 2 multi-nanoporous thin-film electrodes: An application in the degradation of acid red G

Abstract

This study reports on the production of the platinum- and nickel-doped anatase multi-nanoporous thin-film electrodes. These doped electrodes were fabricated from titanium plates by a three-step electrochemical method, which comprises (i) anodization of titanium plates in oxalic acid electrolyte, (ii) electrodeposition of transition metals on the oxide produced, and finally, (iii) re-anodization of the whole assembly in sulfuric acid electrolyte, which leads to the production of stable transition metal-doped TiO 2 thin-film electrodes. Some investigations concerning the degradation of a non-biodegradable azo dye (acid red G) in the presence of these electrodes irradiated by artificial UV-light were performed. The degradation of about 92% was obtained at pH 2.1 after 5.0 h illumination of acid red G 23 ppm using TiO 2 electrode while only about 50% degradation was observed at pH 12.2. The photocatalytic degradation of the dye was strongly favored in acidic solutions. A simplified kinetic study of the degradation of the dye by UV/TiO 2 electrodes system was carried out and the adsorption equilibrium constant ( K ads), the pseudo-first order rate constant ( k), and the degradation rate ( r) were evaluated for different electrodes. The ratios of the degradation rates of acid red G 23 ppm in respect with the undoped TiO 2 were 2.63, 1.00, and 0.58 using Pt–TiO 2, TiO 2, and Ni–TiO 2, respectively. The photocatalytic efficiency was remarkably enhanced in samples doped with Pt 4+ while the incorporation of Ni 2+ was detrimental to this process. The efficiency of the metal-doped TiO 2 electrodes was explained on the basis of the electroaffinity and the electron work function. The COD removal of about 86.3% was obtained at pH 2.1 after 3.0 h illumination of acid red G 7.5 ppm using Pt–TiO 2 electrode. The experimental results showed that the reduction of COD removal decreased with increasing pH and the augmentation of the initial concentration of the azo dye.