The effect of surface treatment on oxidation of oxalic acid at nanocrystalline diamond films

The surface investigation of undoped and boron doped nanocrystalline diamond (NCD/BDND) films associated to their electrochemical behavior of oxalic acid after four pre-treatments was studied. The films were produced using Hot Filament CVD technique on Si substrate with a gas mixture of CH₄/H₂/Ar. Surface pre-treatments were carried out to analyze the surface chemical changes induced by hydrogen and oxygen plasma and as well as cathodic and anodic treatments performed in 0.1 mol L^? 1 HClO₄. The films wetting analyzed by contact angle presented a strong dependence of their surface before and after each treatment was also confirmed by the electrochemical response from cyclic voltammograms. Independent of the surface pre-treatments, all the electrodes exhibited response for oxalic acid oxidation, but the electrode submitted to hydrogen plasma presented the lowest starting oxidation potential and the highest current density. Nonetheless, the BDND electrode presented higher oxidation current than that for NCD electrodes, after all pre-treatments studied. The use of square wave voltammetry with BDND electrode treated by hydrogen plasma for the analytical determination of oxalic acid is described. The detection limits of 0.75 μmol was obtained from the linear relationship between the peak currents of voltammograms as a function of the oxalic acid concentrations.