Study On Treatment Of Dye Wastewater By Combination Of Ultrasound And Exfoliated Graphite

Increasing attention has been focused on the application of ultrasound for the destruction of organic contaminants in water. Ultrasonic technology has been proven to be effective for the degradation of the most refractory organic pollutants. Compared with conventional treatment methods, the ultrasonic treatment increases the degradation efficiency and reduces the time required for removing the organic contaminants. The principle and the major influencing factors on degradation efficiency and methods (including ultrasound irradiation individually and ultrasonic waves in conjunction with other techniques such as bio-catalyst, chemical oxidation, and adsorption) of ultrasonic degradation are described. Progress in treatment of organic pollutants in water by using ultrasound technology is reviewed in this paper.Exfoliated graphite is an excellent inorganic carbon material with a porous structure, which has many characteristics including low density, no pollution of the environment and easy disposal. The expandable graphite has been prepared from natural flake graphite by using perchloric acid-acetic anhydride-potassium permanganate system or perchloric acid-glacial acetic acid-potassium permanganate system. Results showed that sulfur-free and exfoliated graphite of 300 mL/g (prepared by perchloric acid-acetic anhydride-potassium permanganate system) and 280 mL/g (prepared in perchloric acid-glacial acetic acid-potassium permanganate system) could be produced under the optimum conditions. The graphite intercalation compounds, expandable graphite and exfoliated graphite were determined by the methods of XRD, UV-Vis, IR, and SEM.Removal of dyes from aqueous solution by combination of ultrasound and expandable graphite or combination of ultrasound and expandable graphite/H2O2 was studied. The kinetics and possible mechanism of sonochemical decolorization of dyes were investigated through UV-Vis, IR and SEM.A combination of ultrasound and expandable graphite has been used to treat disperse blue 2BLN aqueous solution and direct scarlet 4BS aqueous solution, respectively. The results showed that the ultrasound/exfoliated graphite process is effective in removing direct scarlet 4BS and disperse blue 2BLN. It can achieve better results than either exfoliated graphite or ultrasound alone. The various affecting factors, such as reaction time, reaction temperature, pH value of the solution, irradiation frequency and the volume of exfoliated graphite were studied. Low pH value and large exfoliation volume of exfoliated graphite favored the ultrasonic removal of the dyes. The decolorization of acid black 210 by ultrasonic irradiation in the presence of exfoliated graphite was also investigated. The combination method of ultrasonic waves and exfoliated graphite achieved better results than either exfoliated graphite or ultrasound alone. The decolorization efficiency was obviously higher in ultrasound/exfoliated graphite process than in ultrasound/activated carbon process. In view of kinetic, the sonochemical decolorization of acid black 210 showed a pseudo-first-order behavior. From the IR spectra of before and after treating acid black 210 using exfoliated graphite in the presence and absence of ultrasound, it could be speculated that ultrasound/exfoliated graphite process differs from exfoliated graphite adsorption in reaction mechanism.At its natural pH (6.95), the decolorization of reactive red 24 in ultrasound, ultrasound/H2O2, exfoliated graphite, exfoliated graphite/H2O2, ultrasound/exfoliated graphite and ultrasound/exfoliated graphite/H2O2 systems were compared. An enhancement was observed for the decolorization in ultrasound/exfoliated graphite/H2O2 system. The decolorization of reactive red 24 fitted pseudo-first-order kinetics in ultrasound/exfoliated graphite/H2O2 system. IR spectra of exfoliated graphite before and after treating reactive red 24 using ultrasound/exfoliated graphite/H2O2 indicated that the reactive red 24 has been oxidized.Wastewater from dye manufacturing process containing a high concentration dyes and NaCl was treated by the combination of ultrasound/exfoliated graphite and/or the combination of ultrasound/exfoliated graphite/H2O2, respectively. The data demonstrate the ultrasound/ exfoliated graphite and the ultrasound/exfoliated graphite/H2O2 process both are effective in decolorizing of dyes. The new methods could be used in general as an initial step for industrial wastewater treatment.