Evaluation of the oxidative degradation of aromatic dyes by synthesized nano ferrate(VI) as a simple and effective treatment method

Abstract

In this study, ferrate nanoparticles are prepared by solution plasma process and are employed for degradation of different dyes including Bromothymol blue, Cresol Red, Methylene blue, Methyl orange, Methyl Red, Methyl violet and Blue 203. TEM image indicates that particle size of synthesized nano-ferrate is lower than 50 nm. The effects of nanoparticle dosage, pH and temperature on dye degradation are examined. The degradation efficiency indicates that ferrate is capable for oxidation of dyes with high efficiency in very low reaction time. Moreover, removal efficiency of dyes increases more than 96 % by enhancing ferrate dosage especially with multiple addition of ferrate in very low dosage. The optimum temperature for oxidation is 25° and effective pH range is 6–8. The reaction kinetic of dye oxidation with ferrate is second order reaction and the calculated overall reaction rate constants indicate higher values for methyl orange and blue 203. The oxidation efficiency indicates no considerable variation in the presence of anions SO42−, Cl−, and HCO3− and monovalent cations K+ and Na+, while divalent and trivalent cations (Mg2+, Ca2+, Cu2+ and Fe3+) and humic acid inhibit dyes oxidation. In addition, real water systems including tap and river water without pH control are applied and the results show that removal efficiencies for most of dyes change very low. Mineralization efficiency of dyes measured by total organic carbon are about 50 % indicates that dyes are not degraded to CO2 completely. In addition, liquid chromatography equipped with mass spectrometry analysis after oxidation proves the TOC removal data.