Photolysis of bromophenol blue in aqueous solution under uv-irradiation: optimization of the parameters influencing the kinetics of degradation

Abstract

Although water purification technologies have advanced considerably, they still come up against certain recalcitrant molecules that are difficult to degrade, such as pesticides, dyes and other indus-trial or agricultural residues. The degradation by photolysis of bromophenol blue (BPB), a textile dye, is studied under UV irradiation in the absence of the catalyst. Various parameters which influ-ence the kinetics of degradation have been studied, of which we can cite the pH, photonic intensity, BPB concentration and irradiation time. This study shows that the change in the chemical oxygen demand (COD) as a function of irradiation time and the mineralization of the solution occurs slowly. 4h of irradiation are necessary to observe 20% of COD which is determined by K2Cr2O7 oxidation in the presence of Ag+ as a catalyst, 96% of the organic compounds are oxidized under these con-ditions. The results show that the apparent rate constants of the BPB degradation augment linearly with the light flux. The discoloration rate of BPB solution augments with increasing pH until an optimum pH of 12, the degradation kinetics shows that the Langmuir–Hinshelwood model gives a better correlation. A total disappearance of BPB was observed after 150min of irradiation, indicating the effectiveness of direct photolysis in eliminating the dye. The apparent rate constants are deter-mined for the different parameters to confirm the validity of the model. The measurement of COD is a determination of organic matter which characterizes the amount of chemically oxidized sub-stances present in water. The results show that the apparent rate constants of the BPB degradation increase linearly with the photonic flux applied in the field of study