Study On The Adsorption And Degradation Of Naphthol Blue Black In Ferrites/H₂O System

In rencent years,the water consumption and displacement in printing and dyeing industry are substantially increasing.These toxicity wastewater is one of the main water pollutions.Although a clear standard for wastewater discharge has been established in China,the phenomenon of excessive emissions still occurs.Actually,there are some mineral materials such as iron oxides in the soil,rocks and water,which play an important role in the environmental self-repairing process.Besides,iron oxides,widely found in the natural environment,are easy to adsorb some heavy metal ions and organic pollutants,because of its large surface area and special chemical properties.The research indicates that H2O2,as a active oxygen species,exists widely in natural water and water/solid interfaces.It means that iron oxide/H2O2 system is naturally present in soil and surface water,which may also degrate organics.However,iron oxides exist in nature in various forms including stoichiometric and nonstoichiometric ferrites.Our group has investigated the adsorption and degradation of pollutant performance by various iron oxides.In this paper,stoichiometric and nonstoichiometric ferrites were used as catalysts and naphthol blue and black?NBB?as the simulated pollutants to investigate the degradation of NBB under visible light irradiation.The main research work and results are summarized as follows:?1?Five kinds of ferrites AFe₂O₄?A = Mn,Fe,Co,Ni,Zn?were prepared by co-precipitation method.The as-prepared products were characterized by XRD,TEM,XPS,FT-IR and BET.The maganetic properties of the products were determined.The results indicate that the order of saturated adsorption capacity qm of NBB on five ferrites was found as follows: MnFe₂O₄>ZnFe₂O₄>CoFe₂O₄>NiFe₂O₄>Fe3O4 and the adsorption force b parameter follows the order of MnFe₂O₄>CoFe₂O₄>ZnFe₂O₄>NiFe₂O₄>Fe3O4.The order of degradation rate was found as follows: MnFe₂O₄<CoFe₂O₄<ZnFe₂O₄<Fe3O4.Because the stronger the binding force,the more unfavorable the desorption reaction.NiFe₂O₄ exhibits a largest degradation rate due to its relatively smaller binding force and higher saturated adsorption capacity.?2?NiFe₂O₄ and MnFe₂O₄ were selected as research systems to investigate both the degradation mechanism of NBB and the possibility of catalyst recovery.The results indicate that the degradation rate of NBB in the presence of NiFe₂O₄ was 97 % and the other was 98 %.It could be seen that the degradation paths of NBB on the two catalysts were different.The ferrite materials has good catalytic activity and stability after several cycles.?3?A series of nonstoichiometric manganese ferrite were prepared.The as-prepared products were characterized by XRD,FT-IR and BET.The absorption and degradation of naphthol blue and black by nonstoichiometric manganese ferrite was investigated under visible light irradiation.The results indicate that the adsorption capacity of NBB increases with increasing Mn content,indicating that both Fe and Mn could be used as the active adsorption centers on the surface of the samples.Compared with pure ?-Fe2O3,the introduction of Mn ions increased degradation rate.The degradation rate of NBB increases firstly and then decreases with increasing nMn/nFe.The degradation rate of nMn/nFe0.2 system was close to 98%,as same as nMn/nFe0.3 system and nMn/nFe0.5 system,besides,the degradation rate of nMn/nFe 0.8 system is about 90%.