On-line spectrophotometric method for the determination of optimum operation parameters on the decolorization of Acid Red 66 and Direct Blue 71 from aqueous solution by Fenton process

The decolorization of two azo dyes including Acid Red 66 (AR66) and Direct Blue 71 (DB71) from aqueous solution has been investigated using Fenton process by on-line spectrophotometric method. The effects of different operational parameters such as H2O2, Fe2+ and dye concentrations, pH and temperature of solution and various salts on the decolorization process have been studied to determine the optimum conditions for Fenton process. The results have showed that the amounts of 2.94 × 10−5 M AR66 and DB71 decolorization are 99.6% and 99.8%, respectively, under the optimum conditions ([H2O2]/[Fe2+] = 30:1 for AR66 and 200:1 for DB71, pH = 3.5 and T = 45 °C) at the end of 180 min. The presence of NaCl exhibits a negative effect on the decolorization of azo dyes, on the contrary of Na2SO4. An increase in the reaction temperature gives rise to an increase in the decolorization rate of AR66 and DB71. The results of spectral analyses indicate that the destruction of azo linkages in the AR66 and DB71 during the Fenton process occurs quickly compared with the destruction of benzene and naphthalene rings in the dye molecules. The decolorization kinetics of azo dyes has also been investigated in the different reaction conditions. It has been found that experimental kinetic data are represented well by Behnajady–Modirshahla–Ghanbery model.

► In situ monitoring of spectral changes is available by spectrophotometric method.
► The decolorization of Acid Red 66 (AR66) and Direct Blue 71 (DB71) can be achieved.
► The azo linkages in dye moleculess are more destroyed than the aromatic rings.
► NaCl displays a negative influence on the decolorization of azo dyes.
► Decolorization kinetics of dyes follows the Behnajady–Modirshahla–Ghanbery model.