Evaluation of titanium dioxide and cerium oxide as anodes for the electrooxidation of toluene

The influence of fluoride on the physicochemical properties of anodic oxide films formed on titanium surfaces

The influence of fluoride (and its concentration) on the electrochemical and semiconducting properties of anodic oxide films formed on titanium surfaces was investigated by performing electrochemical measurements (potentiodynamic/pontiostatic polarization, open circuit potential (OCP), and capacitance measurements) for a titanium/oxide film/solution interface system in fluoride-containing 1.0 M HClO(4) solution. On the basis of the Mott-Schottky analysis, and with taking into account both the surface reactions (or, say, the specifically chemical adsorption) of fluoride ions at the oxide film surface and the migration/intercalation of fluoride ions into the oxide film, the changes in the electrochemical behavior of titanium measured in this work (e.g., the blocked anodic oxygen evolution, the increased anodic steady-state current density, the positively shifted flat band potential, and the positively shifted film breakdown potential) were interpreted by the changes in the surface and the bulk physicochemical properties (e.g., the surface charges, surface state density, doping concentration, and the interfacial potential drops) of the anodic films grown on titanium. The fluoride concentrations tested in this work can be divided into three groups according to their effect on the electrochemical behavior of the oxide films: < or =0.001 M, 0.001-0.01 M, and >0.01 M. By tracing the changes of the OCP of the passivated titanium in fluoride-containing solutions, the deleterious/depassive effect of fluoride ions on the titanium oxide films was examined and evaluated with the parameter of the film breakdown time. It was also shown that the films anodically formed on titanium at higher potentials (>2.5 V) exhibited significantly higher stability against the fluoride attack than that either formed at lower potentials (<2.5 V) or formed natively in the air.

Electrochemical degradation of Acid Blue and Basic Brown dyes on Pb/PbO2 electrode in the presence of different conductive electrolyte and effect of various operating factors

Electrocatalytic degradation of Acid Blue and Basic Brown dyes from simulated wastewater on lead dioxide anode was investigated in different conductive electrolytes. It was shown that complete degradation of these dyes is dependent primarily on type and concentration of the conductive electrolyte. The highest electrocatalytic activity was achieved in the presence of NaCl (2g/l) and could be attributed to indirect oxidation of the investigated dyes by the electrogenerated hypochlorite ions formed from the chloride oxidation. In addition, contribution from direct oxidation could also be possible via reaction of these organic compounds with the electrogenerated hydroxyl radicals adsorbed on the lead dioxide surface. In the presence of NaOH, the electrocatalytic activity of the employed anode was not comparable to that in NaCl due primarily to the absence of chloride. This indicates that dyes degradation in NaOH occurs exclusively via direct electrochemical process. However, in H2SO4, the electrode performance was poor due partially to the absence of chloride from the conductive solution. The possibility of electrode poisoning as a result of growth of adherent film on the anode surface or production of stable intermediates not easily further oxidized by direct electrolysis in H2SO4 might also be accountable for the poor performance observed in this conductive electrolyte. Optimizing the conditions that ensure effective electrochemical degradation of Acid Blue and Basic Brown dyes on lead dioxide electrode necessitates the control of all the operating factors.