CONTRIBUTION A L’ETUDE DE L’ELIMINATION DE QUELQUES POLLUANTS MINERAUX ET ORGANIQUES PAR ADSORPTION ET PHOTOCATALYSE

Abstract

In this work, a co-doped Bi-Zn-TiO2 photocatalist is synthesized by an original synthesis route of layered double hydroxide followed by heat treatment at 670°C. After characterization the photocatalyst efficiency is estimated by the photocatalytic test on two different pollutants, an organic pollutant (anionic dye (indigo carmine)) and an inorganic pollutant (hexavalent chromium) under visible light and compare to TiO2-P25 as reference material. In this new photocatalyst, anatase and ZnO wurtzite are the only identified crystalline phase, rutile and Bi2O3 being undetected. Moreover, the binding energy of Bi determined (XPS analysis) is different from the one of Bi in Bi2O3 .Compared to TiO2-P25, the absorption is red shifted (UV-Vis DRS) and the Bi-Zn-TiO2 photo-catalyst showed sorption capacity towards two pollutants higher than that TiO2-P25. The kinetics of the photo-discoloration and photo-reduction is faster with Bi-Zn-TiO2 than with TiO2-P25. Indeed, a complete discoloration is obtained after 70 min and 120 min in the presence of Bi-Zn-TiO2 and TiO2-P25 respectively, and the reduction of Cr (VI) in the presence of an organic acid (oxalic acid) was obtained after 120 min and 240 min in the presence of Bi -Zn- TiO2 and TiO2-P25. The identification of the responsible species on photo-discoloration of indigo carmine was carried out in the presence of different scavengers. The study showed that the first responsible is h+ specie with a moderate contribution of superoxide anion radical and a minor contribution of the hydroxyl radical. The material showed high stability after five uses with the same rate of photo-discoloration.