Preparation Of Copper-cerium Composite Oxide And Its Application In Electrochemical Degradation Of Phenol Wastewater

Biorefractory and high toxicity of phenol wastewater does harm to the ecological environment and human health,leading to widespread attention to the treatment of refractory wastewater.The electrochemical oxidation technology is considered to be one of the most effective approaches for the field of organic wastewater treatment due to its high efficiency,low cost,and the environment-friendly feature(no serious secondary pollution),making it widely conceured by the researchers attention.Previously studies indicated that the efficiency of electro-catalytic oxidation technology largely depended on the choice of the electrode materials.Recently,the researches of anodic material tend to be mature;and the researches of cathode material is relatively less,mainly carbon material,such as graphite,mesh porous carbon,and activated carbon fiber as the electrocatalyst for ORR.However,most reported carbon materials still exhibited a low yield of H2O2,causing an insuffieient degradation efficiency toward phenol.Therefore,there is an urgent need but it is still a significant challenge to develop an efficient cathode material with an excellent 2-electron oxygen reduction reaction(ORR)and a high yield of H2O2 for the removal of phenol.Rare earth oxides have received widespread attention because of its unique physical and chemical properties.As one of the important rare earth oxides,CeO2 has attracted great attention owing to its high oxygen storage capacity and excellent redox property due to the presence of Ce4+/Ce3+.Furthermore,it has been reported that CeO2 can promote the generation of H2O2 via catalyzing the 2-electron ORR,and then H2O2 can be decomposed into the oxidative ·OH,which is expected as a promising candidate of cathode materials for the removal of phenol.However,the CeO2 cathode still suffered from a low degradation efficiency probably due to its low catalytic activity of 2-electron ORR with a low yield of H2O2.To further improve the catalytic activity,this paper introduces a new type of catalyzed CuO-CeO2 with high stability and catalytic activity as effective electrocatalysts.Due to the strong interaction between CeO2 and CuO,Ce3+/Ce4+ and Cu+/Cu2+ are present in the catalyst.It was reported that during the chemical oxidation of phenol,the CuO-CeO2 composite cathode exhibited a remarkable catalytic activity for promoting the decomposing of the extra added H2O2,and thus resulting in a high degradation efficiency.However,to the best of our knowledge,the CuO-CeO2 composite cathode for the degradation of phenol by the electro-catalytic oxidation technology hasrarely been reported.In this paper,CuO-CeO2 catalyst as an electrocatalytic cathode material is applied to the electrocatalystic treatment of simulate the phenol wastewater.The main research contents are as follows:1.CuO-CeO2 catalyst was prepared by sol-gel method using cerium nitrate,copper nitrate and citric acid as raw materials.The effects of preparation conditions were investigated,and the catalysts were characterized by XRD,SEM,TEM and XPS.The results show that the prepared CuO-CeO2 catalyst has a smooth surface with an average particle size of 20-50nm.Besides,there is a strong interaction between copper oxide and cerium oxide,and the presence of Cu+/Cu2+ and Ce3+/Ce4+ in the catalyst.Therefore,the CuO-CeO2 catalysts are not attained by simply mechanical blends.2.The CuO-CeO2 catalyst was used to degrade the phenol solution by adding hydrogen peroxide,and the effect of the catalyst preparation conditions(the molar ratio of Cu/Ce,citric acid content,calcination temperature and calcination time),reaction temperature and amount of hydrogen peroxide on the degradation of phenol solution were investigated.The results showed that the optimal preparation conditions were as follows:the molar ratio of Cu:Cu=1:3,the amount of citric acid was n(Ce(NO3)3·6H2O)/n(C6H8O7)= 1:2,the calcination temperature was 700℃,and the calcination time was 3h.The removal rate of phenol in the solution was about 78%by high performance liquid chromatography(HPLC)at 50mg of the catalyst in 100 mL concentration of 100 mol/L of phenol solution,adding 30%H2O2 solution of 3mL,70℃ under constant temperature for 180min.3.In this study,the ORR performance of CuO-CeO2 catalyst was evaluated by CV and LSV curves using three-electrode system.The ORR performance of N2 and O2 was compared,and the effect of preparation conditions on ORR was investigated.The results showed that the best conditions are as follows:the calcination temperature was 700 ℃,the calcination time was 3h,the molar ratio of Cu:Ce=1:3,and the amount of citric acid was n(Ce(NO3)3·6H2O)/n(C6H8O7)= 1:2,CuO-CeO2 catalyst exhibits the best oxygen reduction properties.4.Using the foam nickel as the base,the CuO-CeO2 catalyst,carbon black and polytetrafluoroethylene mixed into the catalyst cathode electrode.The content of hydrogen peroxide was determined by potassium oxalate potassium colorimetric method in the three-electrode system(catalyst electrode,graphite sheet and saturated calomel electrode).The influences of the ratio of Cu:Ce and pH on the yield of hydrogen peroxide was investigated.The optimal H2O2 yield is up to 114 mg/L(conditions:molar ratio of Cu:Ce=1:3,pH = 7),which is significantly higher than that of single copper oxide or cerium oxide.The results show that ORR of the CuO-CeO2 catalyst is carried out along a 2-electron pathway to produce hydrogen peroxide.5.The electrochemical treatment of the phenol solution was carried out according to the above three-electrode reaction system.The influence of different reaction conditions was investigated.Then,the stability of the catalyst electrode and the main role of the active substance were studied.The results show that when the anode is graphite,the molar ratio of Cu:Ce = 1:3,the current density is 40 mA/cm2,pH = 7,the electrolyte concentration is 0.1 mol/L,the initial concentration of phenol is 100 mg/L,the aeration rate was 400 mL/min and the reaction time was 180min,the degradation rate of phenol was 91%.Next,in the process of electrochemical degradation of phenol,· OH is the main oxidative reactive species.In addition,after repeated use of nine times for the catalyst electrode,the degradation rate has not decreased significantly and the electrode without damage,which proved that the stability of the catalyst electrode is good and can be reused,indicating that the catalyst has some prospects in the field of electrocatalysis.