Catalytic Efficiency Of Black Carbon On Permanganate Oxidation Of Anilines

Black carbon is a kind of black powder produced by the pyrolysis of carbon containing material under the condition of relative hypoxia or complete isolation of oxygen. It has really special microstructure, particle morphology and surface properties. Compared with other common carbon materials, the surface of black carbon has many advantages such as strong stability, reducibility, and the surface functional groups are rich in variety and quantity. What’s more, the preparation cost of black carbon is much lower. To further investigate the application of permanganate in drinking water treatment processes and environmental remediation, the aniline organic pollutants such as aniline, bromo-amine and SMZ oxidation by permanganate were studied. The effects of black carbon and manganese dioxide on the oxidation reaction were also studied. Permanganate oxidation and ozone oxidation were applied to modify black carbon to search for the most possible explaination for its catalytic mechanism.Anilines oxidation by permanganate was influenced by reaction p H and permanganate/phenol molar ratios. While in the absence of catalyst, SMZ could not be oxidized by permanganate.On the reaction kinetics between permanganate and anilines such as aniline and bromo-amine, the promoting effect of manganese dioxide formed in situ at slightly acidic p H(e.g., p H 5~6) was obvious but negligible effect at neutral/alkaline p H. While the oxidation of SMZ by permanganate could not be catalyzed by manganese dioxide at all p H conditions. The catalytic mechanism of manganese dioxide was due to the formation of surface complex and the participation of permanganate in the electron transfer of the surface complex.Anilines oxidation by permanganate was enhanced by the presence of black carbon at p H 6~9. The effects of black carbon on anilines oxidation by permanganate were dependent on carbon black concentration and permanganate/phenol molar ratios. It was worthwhile to note that the reaction rate decreased with the reaction going on and finally closed to balance at p H=7~9. While when the concentration of black carbon increased, the final removal rate of target compound increased too. It indicated that the catalytic active sites on the surface of black carbon surface were continually consumed during the catalytic reaction. When the concentration of catalytic active sites was relatively insufficient to the target compound, the reaction rate decreased and finally closed to balance.In order to further explore the catalytic mechanism, permanganate oxidation and ozone oxidation were applied to modify black carbon. The catalytic performance of black carbon was decreased after pre oxidation treatmeant at p H=7~8. With the increase of oxidant concentration and time of pre oxidation, the catalytic performance of black carbon was further reduced. It indicated that the oxidation degree of black carbon surface increased after pre oxidation, and the concentration of surface reduction sites decreased. During the catalytic reaction, the reduction of surface reduction sites induced a decrease in the concentration of the manganese dioxide formed in situ, therefore the catalysis ability of black carbon was weakened. However, the catalytic mechanism of black carbon was not just indirect catalytic pathway. The oxidation of SMZ by permanganate could not be catalyze by manganese dioxide at all p H conditions, while it was enhanced by the presence of black carbon. So there may also be other catalytic mechanism of black carbon under this condition. The results of experiments shows that SMZ could be derectly oxidized by black carbon after pre oxidation treatmeant. There may be two direct catalytic pathways of black carbon as follows:(1) Black carbon and target compounds may form complex compounds by adsorption of target compounds, and the complex compounds with higher density of electron cloud are more likely to be attacked by potassium permanganate.(2) Persistent carbon radicals may generate during the oxidiation of black carbon surface by potassium permanganate, which has a stronger ability for degradation of target compounds.The catalysis ability of black carbon and carbon nanotubes(CNTs) during the oxidation of SMZ by permanganate was compared in two kinds of actual water. Compared to artificial water, the catalysis ability of black carbon in actual water decreased significantly at slightly acidic p H conditions, while there was no significant decrease at neutral and alkaline p H conditions. Compared to artificial water, the catalysis ability of CNTs had decreased significantly in actual water at both acidic and alkaline p H conditions. The catalytic efficiency of black carbon were higher than that of CNTs both in artificial and actual water. With the increase of p H, the deference between the catalysis ability of black carbon and CNTs was gradually decreasing. The BET surface area measurement showed that the specific surface area was higher than that of black carbon, but the pore structure of black carbon was much more developed. From the XPS analysis, we can know that the oxygen content on the surface of black carbon was lower than that of CNTs and the reducibility surface of black carbon was higher than that of CNTs, which is advantageous to the adsorption and catalytic ability of black carbon.