| The problem is to treat PFOA wastewater with refractory degradation.Sm?NO3?3,Fe?NO3?3,FeSO4 and EuCl3,FeCl3,FeCl2 are used as raw materials.Rare earth Sm-doped ferrite and Eu-doped ferrite are prepared by coprecipitation method.The crystal structure,elemental composition and magnetic properties of rare earth ferrite were analyzed by means of XRD,FTIR,SEM and VSM.The results of XRD and FTIR show that the rare earth elements have been successfully doped into the spinel structure of ferrite.The spinel structure has its own tetrahedral and octahedral positions with vibration peaks.XPS and EDS results show that the chemical formula of Sm-doped ferrite is Sm0.08Fe2.8O4,and the chemical formula of Eu-doped ferrite is Eu0.08Fe2.66O4.The results of UV-Vis DRS show that Sm-doped ferrite and Eu-doped ferrite are absorbed in both ultraviolet and visible light regions.The forbidden band width is2.86eV and 2.32eV respectively.The VSM results show that the doping of rare earth elements has successfully modified the magnetic properties of spinel ferrite.The coercivity of Sm-doped ferrite is Hc=207.87Oe,the coercivity of Eu-doped ferrite is Hc=99.07Oe,which are typical soft magnetic materials.The photocatalytic performance of PFOA was studied under the optimal conditions of Sm-doped ferrite,Eu-doped ferrite and traditional photocatalytic material TiO2.The results show that 0.02g/L Sm-doped ferrite can directly photocatalyze the degradation of 0.5mmol/L pH=4PFOA 27.45%,and the photocatalytic performance was the best.The oxidation abilities of three different oxidants of H2O2,KMnO4 and K2S2O8 were studied,the results showed that the degradation rate of PFOA was increased to 48.61%by adding 8%of 30%H2O2 as oxidant.In order to further improve the degradation rate of PFOA,microwave-ultrasonic-UV was used to synergistically degrade PFOA.The results showed that it was operated under microwave works at 400W 10?/min for 10min,ultrasonic operation at 80W 100kHz for 50min,and 20W 185nm UV lamp for 1.5h,the degradation rate can be increased to 59.63%,and the defluorination rate is 11.57%.Experiment by investing in a capture agent?tert-butanol,potassium iodide?,the results show that photogenerated holes?h+?and hydroxyl radicals?·OH?are the main active substances involved in the degradation,and the contribution rates are 34.15%and 22.06%,respectively.The ultraviolet light intensity Ii=4.79×1016quanta/s under the photocatalytic system was calculated by the potassium oxalate photometer.The light energy utilization rate?=13.5%,the quantum yield of direct photodegradation of PFOA was?i=0.07,the quantum yield?i=0.53after the addition of Sm-doped ferrite and H2O2,indicating that both the photocatalytic material and the oxidant can increase the photon yield and increase the photocatalytic activity.Finally,the energy consumption index EE/O under each degradation process was evaluated.The EE/O=1.729kWh/L was directly degraded by 2.5h,and the EE/O=4.146kWh/L with microwave-ultrasonic synergistic degradation for 1.5h was introduced.Taking 0.02mmol of PFOA?100mL 0.5mmol/L?as the index,the direct photodegradation required 2.06h,the energy consumption was 0.041kJ,and the unit energy consumption degradation per unit time was Nt=0.238mmol/kJ·h;microwave-ultrasonic synergy was introduced,the degradation requires1.01h,the energy consumption is 0.087kJ,and the unit energy consumption degradation per unit time was Nt=0.228mmol/kJ·h.With the total power consumption of 0.2kJ as the index,the degradation rate of direct light degradation for 10h was 93.02%,unit depletion energy consumption per unit time was was Qt=0.043kJ/mmol·h;the degradation rate of microwave-ultrasonic synergistic degradation of 3.3h was 67.07%,unit depletion energy consumption per unit time was Qt=0.181kJ/mmol·h.The rare earth Sm-doped ferrite and Eu-doped ferrite prepared by the experiment all show excellent photocatalytic activity.By studying the photocatalytic reaction system,it can be applied to the treatment of organic pollutants in water environment. |
PDF Full Text Request