Elimination de polluants organiques par voies physico-chimique et photochimique

Abstract

This study is a contribution to the elimination of organic pollutants by photochemical and physico-chemical methods in aqueous medium and on solid supports. Two benzothiazole derivatives, 2-mercaptobenzothiazol (MBT) and methabenzthiazuron (MBTU) has been studied. In a first step the photochemical behaviour of pollutants on clay surface has been studied. Two commercial clays (Montmorillonite and Kaolinite) and three natural clays (A, B and C) of El-golea (Ghardaia-Algeria) region were selected for this study. Along the study of pollutants photodegradation in suspension (heterogenic phase) no evident photoinductive effect has been observed, but mainly adsorption phenomena. Montmorillonite showed a stronger capacity of adsorption in the case of MBTU (adsorbed amount » 9mg.g-1) over other clays with 1mg.g-1. Moreover, the adsorbed amount of MBT was less then 1mg.g-1 with all clays. The photodegradation products were produced in lower concentration but revealed to be similar to those observed by direct photolysis thus confirming the involvement of screen effect. The results on dried phase showed that clay have a great efficiency in the elimination of pollutants. The disappearance rate of MBT up to 95% after 100 h of irradiation on Kaolinite and clay A while the complete elimination is reached after the same irradiation time on clay B. Montmorillonite with MBTU presented a higher efficiency compared to other clays (72% of disappearance). In the second step the photochemical degradation of benzothiazole derivatives, 2- mercaptobenzothiazol (MBT, 0,1mM) and methabezthiazuron (MBTU, 0,1mM) has been studied in aqueous solution in the presence of decatungstate anion DTA (W10O32 -4 , 0,5g/l) used as photocatalyst under irradiation at 365nm. The total mineralization of MBT and MBTU has been obtained in the presence of DTA after 100 and 170 h of irradiation respectively. This result attests the possibility of the potential application of DTA in the elimination of different organic pollutants, particularly benzothiazole derivatives.