Carbonate anion photolyzed by solar radiation or combined with peracetic acid to form reactive species for dye degradation

Abstract

The carbonate anion radical (CO3•−) has a high oxidative capacity and is therefore used for the degradation of persistent environmental contaminants. In this sense, this work aimed to evaluate combinations to obtain this radical, such as Na2CO3 with solar radiation or peracetic acid (PAA), using the efficiency of the degradation of methylene blue as a parameter to evaluate the performance of the process. The combination of PAA + Na2CO3 showed the ability to degrade the dye without the presence of solar radiation, but with a low reaction speed. The dye degradation process involving PAA + Na2CO3 follows a first-order kinetic model. This behavior can be explained by the formation of singlet oxygen from the reaction between CH3COOO− and OH−. In photolyzed processes with solar radiation, the presence of CO32− was the main factor for the degradation of the dye; consequently, the reactants PAA and acetic acid, which have greater protonation capacity of the CO32− to HCO32− anion, reduced the degradation efficiency. The formation of CO3•− is spontaneous when the carbonate anion CO32− is in contact with the radicals •OH, CH3C(O)O• and CH3C(O)OO•. Another important behavior was the degradation of the dye in the Na2CO3 + solar radiation process due to the excitation of colored dissolved organic matter (CDOM) (dye) to CDOM* in the triplet state and subsequent formation of singlet oxygen.