Study On Synthesis And Application Of Nano Nickel Oxide For Water Pollution Control

Environmental pollution has attracted more and more attention with the rapid development of industry.For the high concentration organic matter in wastewater,it is hard to meet the discharge requirements by using traditional biochemical treatment.Catalytic oxidation technology can degrade organics into biodegradable small molecules by producing radicals with high oxidation,which makes toxic industrial wastewater harmless.Among them,heterogeneous catalytic oxidation technology at low temperature and atmospheric pressure is widely used because of its relatively mild reaction conditions and effectiveness for high concentration of refractory organic pollutants.It is of great significance for heterogeneous catalytic oxidation technology to improve the degradation of pollutants by designing the composition and morphology of catalyst reasonably.This thesis consists of two parts.In the first part,the solvent effect on the solvothermal synthesis of mesoporous nickel oxide catalysts for activation of peroxymonosulfate（PMS）to degrade acid orange 7（AO7）were studied.In the second part,the application of graphene-nickel oxide composite catalyst in the photocatalytic degradation of methylene blue with sodium hypochlorite was studied.In the first part,we successfully synthesized three kinds of porous nano nickel oxide catalysts with different morphology by solvothermal method,which were applied to PMS degradation of AO7.It is found that the pore size,pore shape and micro morphology of the catalyst can be effectively controlled by changing the solvent.Nickel oxide,which was synthesized by ethanol as solvent,was the flower ball assembled by flakes,while nickel oxide,which was synthesized by hydrothermal method,was sponge like hexagonal porous plate.The nickel oxide synthesized with ethylene glycol as the solvent is in the shape of flake,and the main plane is（111）plane with high activity.The open slit pore is conducive to the adsorption and desorption of reactant molecules in the catalytic reaction,which effectively improves the degradation efficiency of the catalytic reaction.Under the neutral condition,the degradation rate of AO7 can reach 95%within 30 minutes.The structure characterization and performance test show that the nickel oxide synthesized by ethylene glycol has high charge transfer rate,abundant oxygen vacancies and surface active sites,wide pH range and high stability.After four times of recycling,94%degradation rate can be still achieved.Free radical quenching experiments showed that there were three main active species in Ni O/PMS system:sulfate radical,superoxide radical and hydroxyl radical.In the second part,we also prepared different proportion of graphene-nickel oxide composite catalyst by solvothermal method,characterized and evaluated its microstructure and photocatalytic degradation of methylene blue with sodium hypochlorite.After compounding with graphene,the specific surface area of nickel oxide catalyst increased from 86.34 m²/g to 226.16 m²/g.Meanwhile,graphene can improve the surface defects,charge transfer capacity and light absorption capacity of nickel oxide catalyst,making an increase on the photocatalytic performance of the catalyst.Within 30 minutes,the photocatalytic degradation of methylene blue by graphene nickel oxide composite catalyst can achieve 98%of decolorization rate and93%of chemical oxygen demand removal rate.The prepared graphene nickel oxide composite catalyst has high catalytic activity in a wide pH range（5-9）.The study on the quenching of free radicals showed that three kinds of active radicals,superoxide radical,photohole radical and hydroxyl radical,were produced in this system,among which superoxide radical was the main active species.Furthermore,due to the formation of Ni²⁺/Ni³⁺redox pairs and the synergistic effect of graphene,the composite catalyst shows excellent stability,which makes it high application potential in the photocatalytic degradation of organic pollutants with sodium hypochlorite.