Catalytic Ozonation Of Reactive Red195in Aqueous Solution Over A CoO/Al₂O₃-CeO₂Catalyst

Dyeing wastewater has the characteristics of high chroma, high concentrationsof organic matter, with complex composition, toxic, nonbiodegradable and so on,which is difficult to deal by conventional physical and biological methods. Theheterogeneous catalytic ozonation has received increasing attention due to its higheffectiveness in degradation of harmful organic pollutants with low negative effectson the environment. However, the use of ozone and composite carrier catalyst for thecatalytic ozonation of wastewater has seldom been reported. In this work, theCoO/Al2O3-CeO2catalyst was synthesized and the degradation of Reactive Red195(RR195) by catalytic ozonation was studied. The influence of catalyst preparationconditions were investigated, the reaction conditions on catalytic ozonation of RR195were assessed. Finally, the mechanism and kinetics model of RR195degradation wasestablished.The catalysts were prepared by impregnation method combined with ultrasonicvibration, incipient wetness method and immersion precipitation method. The catalystwhich prepared by impregnation method combined with ultrasonic vibration showedthe highest catalytic activity. The optimal preparation conditions are: sonicating for3h, γ-Al2O3doped with20wt%ceria,4%Co loading on the Al2O3-CeO2support. Itcan be found that the expectation catalysts were synthesized successfully from theXRD patterns. It also can be found that the catalytic ozonation by CoO/Al2O3-CeO2exhibited higher COD removal efficiency than that of the single ozonation andCoO/Al2O3catalytic ozonation.The RR195and COD removal efficiency increases gradually with increasingcatalyst dosage,3g/L CoO/Al2O3-CeO2was determined as the optimum dosage forRR195ozonation. It can be found that the CoO/Al2O3-CeO2catalytic ozonation ofRR195might gradually convert to be controlled by a kinetic step when the ozoneflow rate and the stirring speed were more than200mL/min and1400r/min,respectively. It also can be found that the removal efficiencies decrease with increasing RR195initial concentration. Under CoO/Al2O3-CeO2catalytic ozonationprocess, the maximum COD and RR195removal obtained at pH of8. The effect ofNa+、K+、Ca2+、NO3-andSO42-on the catalytic ozonation of RR195were very weak.However, the catalytic ozonation of RR195was significant inhibited by Cl-. Inaddition, the catalytic capacity of CoO/Al2O3-CeO2did not decrease obviously in thefour times of recycling, the leached metal ions in the catalytic ozonation process werevery limited, these results indicated that CoO/Al2O3-CeO2catalyst was effective andstable in the catalytic ozonation of RR195.It can be deduced that the proposed mechanisms of catalytci ozonation mayinvolve two steps. One is the adsorption of ozone over the catalyst with the formationof hydroxyl radical, which will react with the pollutants in liquid phase; the other isthe adsorption of the organic pollutant and reaction with free ozone or hydroxylradical. Finally, kinetic studies indicated that hydroxyl radical play an important rolein the oxidation under initial pH8.