Optimization of azo printing dye removal with oak leaves-nZVI/H2O2 system using statistically designed experiment

The paper investigates the potential use of nano zero-valent iron (nZVI) particles as a cheap, natural and effective catalyst in the Fenton-like system for the removal of water-based Magenta flexographic dye from aqueous solution. The functional nZVI was successfully synthesized within an environmentally friendly method, by using the natural product extract, oak leaves (OAK-nZVI). The process of Magenta removal was optimized using statistically designed experiment. The influence of four quantitative parameters on decolorization efficiency was investigated: initial dye concentration (20–180 mgL-1), OAK- nZVI dosage (0.75–60 mgL-1), H2O2 concentration (1–11 mM) and pH value (2–10). The results of statistical analysis show that OAK-nZVI dosage and pH significantly contribute to the decolorization efficiency, while the concentration of H2O2 has a significant influence on their impact. The optimization yielded highest removal efficiency of 91.95% under following conditions: initial dye concentration of 180 mgL−1, OAK-nZVI dosage of 60 mgL−1, H2O2 concentration of 11 mM and pH value 2. Optimization results were experimentally verified. Treatment of real effluent under optimized experimental conditions resulted within 84.06% Magenta removal after a reaction time of 60 min. The absorption spectra of Magenta dye clearly indicate the changes in the molecular structure in the form of the destruction of azo bond in the chromophore, leading to the decolorization of dye solution. Based on the GC–MS analysis, the mechanism for Fenton-like oxidation of Magenta was proposed.