PHOTOLYSIS AND PHOTOCATALYSIS OF AQUEOUS METHYLENE
BLUE UNDER UVC RADIATION
VEYET Jonathan, THIVEL Pierre-Xavier, DELPEH Françoise
LEPMI, 1130 rue de la piscine, Domaine universitaire, BP75,
38402 SAINT- MARTIN-D’HERES
pierre-xavier.thivel@ujf-grenoble.fr, francoise.delpech@ujf-grenoble.fr
Abstract
k (min-1)
Methylene blue (MB) is a standard model of dye used in order to study various treatment
processes for textile wastewater. It is an organic compound, which could be directly
decomposed by photolysis under UV and visible light. Among the colored wastewater
treatment processes (adsorption, biodegradation, oxydative method as ozonation),
photocatalysis using titanium dioxide (TiO2) is an emerging and interesting way leading to the
mineralisation of organics compounds. Photolysis is a chemical reaction involving direct
photons (h) absorption by the organic compounds :
Organic compound + h  subproducts
Photocatalysis is a very interesting process for organic compound removal in aqueous or
gaseous effluents. In this case, photons are absorbed by a semi-conductor (TiO2) leading to
the production of hydroxyl radicals and then leading to the radical oxidation of the organic
compound.
TiO2 + h  e- + h+
VOC + OH (ou h+)  subproducts + CO2 + H2O
In this study, we use a 254 nm light source, classified as UVC radiation and used for
bacteriological decontamination of water. Photolysis and the photolysis/photocatalysis with
TiO2 of methylene blue were performed. The influences of pH, TiO2 concentration and
temperature are evaluated. The figure below shows a comparison of apparent constants k of
photolysis and of photolysis/photocatalysis.
0,12
0,1
0,08
photolysis
photolysis/photocatalysis
0,06
0,04
0,02
0
15°C
30°C
42°C
The presence of TiO2 enhances the methylene blue degradation but the increase of
temperature limits this phenomemon. At high temperature (40-45°C), the association of
photolysis and photocatalysis becomes not interesting enough.
The originality of this work lies in the use of the UVC radiation instead of UVB for
photolysis and photocatalysis in aqueous phase and in the good results obtained.