Si/BDD/TiO_2 anodes: morphology and efficiency for the (photo) oxidation of oxalic anions

摘要

The use of TiO_2 as a photocatalyst for the destruction of organic chemical pollutants in aqueous systems has been extensively studied [1], [2]. There is a great deal of interest in using TiO_2 for waste treatment due to the low cost of the TiO_2 catalyst as well as the potential for using sunlight as the energy source. Illuminated slurries of TiO_2 has been shown to oxidize a wide range of organic pollutants, but the quantum yields for the photodegradation of organics are low and a costly catalyst recovery is needed from the large volumes of treated water. TiO_2 layers deposited onto titanium foils [3] recently used in solar decontamination of water [3], [4] have been shown to be more efficient than the TiO_2 slurries because the applied bias enhances a better separation of photogenerated charge carriers. The present work is devoted to the study of morphological properties and (photo)electrochemical behaviour of Tio_2 layers deposited onto electrically conducting boron doped diamond (BDD) films. During the last years, BDD films deposited on silicon wafers have been found to achieve electrochemical oxidation of many pollutants [5], [6] with a current efficiency close to 100% except in a very few cases, such as that of oxalic acid for which only 70% has been reached. With TiO_2 deposits on the Si/BDD surface, the electro-oxidation process could be enhanced but, due to the high cost of diamond films, these haven't been yet used as substrates for TiO_2 layers. However, in the recent years, large area, up to 0.3 m~2, of conducting diamond films, have been currently deposited on various substrates such as metallic foils, ceramics or silicon wafer [5] and this opens up new perspectives for using new composite materials such as Si/BDD/TiO_2. In order to reach more fundamental information about the morphological and photo-electrochemical properties of TiO_2 layers deposited onto conductive boron doped diamond (BDD) films one micron thick, we have systematically studied several thin layers of TiO_2 having thickness between 100 nm and 10 microns.