The Application Of GN-NiO Composites In Dye Wastewater Ozonation Treatment

At present, the annual output of the organic dyes in China has been ranked top in the world, followed by the increasing amount of dye wastewater. Therefore, the wastewater treatment problem has been in focus. Reactive dye is a kind of commonly used dyes, from which the amount of wastewater is very large. The commonly used treatment methods for reactive dye wastewater: physical method, chemical method and biological method. Recently, the ozonation technology has been an important method in the chemical treatment, due to its advantage of low cost, easy operation, good dye removal effect and showing no secondary pollution, which has attracted great attentions of the researchers.In ozonation technology, single ozone system cannot meet the needs of practical applications. However, recently-developed catalytic ozonation technology can effectively improve the utilization of ozone and dye degradation rate. The commonly used catalysts include metal oxides and metal hydroxide. At present, the preparation of the catalysts which show good catalytic properties and easy recycling has been the key research. Considering graphene is a new two-dimensioanl carbon with excellent catalytic properties, in this thesis, grapheme/nickel oxide composites were prepared, and its applications as catalyst in dye wastewater are studied.Different preparation methods of grapheme were selected. A modified Hummers method is finally used by comparing those results. Grapheme/nickel oxide composites were synthesized by the hydrothermal method. The obtained materials were analyzed by XRD, FTIR, SEM and TEM methods. The results showed that nickel oxide and graphene were successfully composited together, and the agglomeration of graphene is suppressed due to the insertion of the nickel oxide.For research of applications of grapheme/nickel oxide composite materials in the ozonation treatment of the dye wastewater, in this paper, anthraquinones reactive brilliant blue and azo reactive black were used to prepare the simulated wastewater. The effect of the amount of ozone flux, the initial pH of the system, the initial concentration of dye and the added amount of composite materials on the decomposition of the organic dyes were studied. The mechanism of ozonation treatment of the composites was discussed. The experimental results show that under acid condition, grapheme/nickel oxide composites can increase the decomposition of organic dyes in the brilliant blue simulated wastewater, which was affected by the ozone flux amount, the initial p H, the initial concentration of the dye. Meanwhile, the accelerated role of grapheme/nickel oxide composites on the reactive black simulated wastewater by ozonation treatment was observed in alkaline conditions. By studying on the influence of grapheme/nickel oxide composites on the generation rate of hydroxyl radicals, the results show that the composites did not promote the generation of hydroxyl radicals. In addition, the chroma removal rate of simulated wastewater has been improved significantly after the addition of the free radicals quenching agent, which also suggests that grapheme/nickel oxide composites had nothing to do with hydroxyl radicals. Therefore, the acceleration of ozone treatment properties of grapheme/nickel oxide composites on the simulated wastewater may be due to the adsorption of grapheme, by which the ozone gas and dye molecules were absorbed on the surface of composites for effective reaction. The holes and the coordination properties of nickel oxide enhanced the above absorption, which effectively improved the decomposition of dyes. The graphene/institute of nickel oxide compounds prepared in this study can promote ozone degradation of reactive dye molecules; in addition, at the end of the degradation reaction, graphene/nickel oxide composites can be recycled easily.