Purification Of Simulated Benzene Polluted Air And Dye Wastewater By Modified Lithium Cobalt Oxide

At present,the problem of air and water pollution is still severe.Volatile organic compounds（VOCs）and dye are two kinds of extremely harmful pollutants,which will cause serious damage to the ecological environment and organisms if not disposaled properly.In addition,the number of waste lithium-ion batteries is becoming larger and larger and needs special attention.On one hand,these waste lithium-ion batteries usually contain a variety of toxic and harmful substances,which may cause pollution if not handled properly.On the other hand,the electrode materials of the lithium-ion batteries are generally composed of metal oxide composites,which may have good catalytic activities.Therefore,the purification experiments of simulated benzene polluted air and rhodamine B wastewater were carried out with Ag HPWLi Co,H₂O-LCO and LiCoOH as catalysts,which were prepared by modifying the lithium-ion battery cathode material-lithium cobalt oxide（LiCoO₂）.Combined with the results of activity test and characterization analysis,the reaction mechanism was studied deeply.The main results of this thesis are as follows:（1）The LiCoO₂ was modified by AgNO₃ and phosphotungstic acid（HPW）via a one-pot method to obtain the Ag HPWLiCocatalyst.The Ag HPWLiCocatalyst exhibited a high activity for benzene oxidation:under the reaction conditions of 120 L·g^-1·h^-1of space velocity,450–480ppm of benzene and 300°C,～95%of benzene conversion was achieved,whereas only～62%,～45%and～11%of benzene could be removed respectively over the HPWLi Co,Ag LiCoand LiCoO₂ catalysts.The different catalysts were studied by XRD,ATR,H₂ pulse chemisorption,SEM,TEM,C₆H₆-TPD,XPS,EPR,H₂-TPR and O₂-TPD.From the results of C₆H₆-TPD,we found that Ag and HPW played an imperative role in increasing the benzene adsorption capacity,and strengthened the interaction of benzene with catalyst surface,which is beneficial to the activation of benzene.Meanwhile,XPS results showed that both Ag and HPW also increased the content of oxygen defects on the catalyst surface and make the active surface oxygen more easily formed（H₂-TPR and O₂-TPD）.Moreover,adding HPW could inhibite the build-up of oxidation products on the catalyst surface during benzene oxidation（ATR）.Besides,the effects of water vapor and SO₂ on catalyst activity were investigated,and it was found that the presence of water vapor was beneficial to the catalytic oxidation of benzene on the modified materials,while SO₂ inhibited the activity of the modified catalysts.（2）The H₂O-LCO catalyst was prepared by water treatment of the pristine LiCoO₂,which could fulfill 100%of conversion under the reaction conditions of 120 L·g^-1·h^-1of space velocity,431 ppm of benzene and 300°C,whereas only～20%of benzene could be removed over the pristine sample at 400°C.It is found that water treatment played two roles in updating the LiCoO₂ surface properties.One was to remove the excessive Li₂CO₃（ATR）;another was to remove the surface oxygen species（O₂-TPD and H₂-TPR）and thus making the bulk lattice oxygen more easily contact the gaseous benzene.According to the results of the C₆H₆-TPD experiment,surface oxygen and Li₂CO₃ only acted as benzene adsorption sites inert towards benzene oxidation whereas bulk lattice oxygen was reactive for oxidation reaction at high temperatures,which was different from the oxidation behavior of benzene on Ag HPWLiCocatalyst.（3）In this study the pristine LiCoO₂ powder was further treated in Na OH solution in order to simulate a real battery recycling process,and the purification experiment of simulated Rh B wastewater was carried out.We found that Na OH-treatment could improve the performance of the catalyst for the degradation of Rh B,and 60%of Rh B could be removed after 20 minutes under the conditions of 0.2 g of catalyst,50 m L of 5 mg·L^-1Rh B solution and 30 ^oC,whereas only～20%of Rh B was degraded over the pristine sample after 2 hours.The most important finding in this experiment is that the activity of the reused LiCoO₂ became better and better with cycling runs,and when the sample was reused for the third time,the removal rate of Rh B increased to 86%.According to the research reports and XPS results,it is known that the in situ nitrogenization of the LiCoO₂ via Rh B degradation occurred over the catalyst,offerring the reused material a much better activity than the fresh one due to the formation of more defect oxygen species,which were the main active species for Rh B removal in this experiment,so the reused catalyst had a better activity than the fresh one.Besides,the effects of Rh B concentration,reaction temperature,solution p H,air blowing and concomitant ions were systematically investigated.This research provides a new concept of reusing electronic wastes for aqueous pollutant removal,and the conclusions are helpful to the development of sustainable catalytic systems.