UV-photolysis of Chlorazol Black in aqueous media: Process intensification using acetone and evidence of methyl radical implication in the degradation process

Abstract

This work explores and elucidates the effect of acetone on the batch photolytic degradation at 253.7 nm of chlorazol black (CB) azo dye in deionized water with relation to various operating parameters, i.e. acetone and CB initial concentrations, liquid temperature and solution pH. A special emphasis has been made, for the first time, on the influence of saturation gases on the acetone effect. It was found that acetone (50 mM) assisted-UV treatment of CB (20 mg/L) resulted in 5.6-fold increase in the initial degradation rate, as compared with UV alone, and near complete removal of CB was achieved after 30 min face to ∼35% with the sole UV irradiation. Radical scavenger tests using sodium nitrite and oxygen saturation have showed that methyl radical was probably the main species responsible for the efficient degradation of CB in UV/acetone system. The degradation rate of the dye increased monotonically with increasing acetone concentration up to 50 mM, above which further increase did not enhance the CB removal rate. Increasing the liquid temperature in the interval 25–65 °C intensified the beneficial effect of acetone whereas the reaction rate was not influenced by varying the solution pH in the range of 3–9. Besides, the degradation rate increased notably with increasing initial CB concentration in the range of 5–50 mg/L. Finally, the degradation of CB upon UV/acetone process was more effective when solutions are saturated with nitrogen, argon and CO2 while oxygen completely suppressed the obtained beneficial effect of acetone toward the degradation rate of the dye.