Research On Synthesis,Modification And Photocatalytic,Heterogeneous Fenton Catalytic Performance Of Tungstate

Photocatalysis and heterogeneous Fenton catalysis can effectively remove pollutants from water,the catalysts can recycle to reduce the possible secondary pollution and reduce the cost of wastewater treatment.The main research content of this thesis is to utilize the photocatalysis and heterogeneous Fenton catalysis of tungstate(MnWO4 and FeWO4)to removal of pollutants in wastewater.The catalytic performance of single tungstate was enhanced by controlling its morphology.By coupling with Fe3O4,magnetic recovery as well as catalytic performance improvement of FeWO4 was realized.The main contents completed are as follows:1.MnWO4 nanoparticles and nanorods with different sizes were synthesized via hydrothermal method,by adjusting the pH value of the reaction solution,while using sodium tungstate and manganese chloride as the raw materials.The crystal structure,surface components and morphology and sizes of the synthesized samples were examined by multi techniques,including XRD,Raman,FTIR,XPS,TEM,N2-adsorption/desorption.The optical and electrical properties of the products were studied by UV-vis DRS,PL,EIS and transient photocurrent responses.The performance of different morphologies and sizes of MnWO4 products was studied in heterogeneous Fenton catalytic(under dark condition,with H2O2),heterogeneous photo-Fenton catalytic(with H2O2 and visible-light irradiatied)degradation of methylene blue(MB)in water.In addition,the effects of MnWO4 dosage,H2O2 concentration and initial pH on the catalytic degradation of MB were investigated.The experimental results show that when MnWO4 prepared at pH=11 was used as catalyst,under the optimized heterogeneous photo-Fenton conditions(i.e.catalyst dosage 1 g/L,H2O2 concentration 231 mmol/L and pH=7),after visible-light irradiated 120 min,the decoloration rate of 10 mg/L MB solution reached 77%and the removal rate of TOC reached 45.7%.By exploring the catalytic mechanism,it was confirmed that the heterogeneous Fenton catalytic effect of MnWO4 was mainly originated from WO42-,whereas the Fenton-like catalytic effect of Mn2+ was weak.2.Due to the weaker Fenton-like catalytic effect of Mn2+,we replaced Mn2+with Fe2+,which with a stronger Fenton effect,to obtain a more efficient catalyst FeWO4.FeWO4 nanoparticles with different morphology and sizes were synthesized in different pH reaction solutions by hydrothermal method when FeSO4 was used instead of MnCl2.The crystal structure and surface composition of the synthesized samples were characterized by various techniques.The photoelectric properties of the samples were investigated by UV-vis DRS,PL,EIS and transient photocurrent responses.The performance of heterogeneous Fenton catalytic degradation of MB wastewater by FeWO4 with different shapes and sizes was studied.The effects of the dosage of catalyst FeWO4-7(0.1-0.5 g/L),concentration of MB solution(10-30 mg/L),initial pH of MB solution(3-9)and concentration of H2O2(33-99 mmol/L)were investigated.In this chapter,the photocatalytic reduction of hexavalent chromium in water by FeWO4 was also studied.The results showed that FeWO4 was a bifunctional catalyst with photocatalytic and heterogeneous Fenton catalytic activities.3.Although FeWO4 has photocatalytic and heterogeneous Fenton catalytic activity,it still faces the problem of difficult recovery after treating wastewate.In this chapter,magnetic Fe3O4 was combined with FeWO4 to obtain Fe3O4/FeWO4 composites,which has potential to be magnetically recoverable and higher performance than FeWO4.The Fe3O4/FeWO4 composites were prepared by hydrothermal method.The crystal phase,morphology as well as photoelectric and magnetic properties of the synthesized samples were evaluated.The heterogeneous Fenton catalytic performance of Fe3O4/FeWO4 samples with different composite ratios was investigated.The results show that when the mass ratio of Fe3O4 to FeWO4 is 2:10,the prepared photocatalyst has the best photocatalytic and heterogeneous Fenton catalytic activity.According to Mott-Schottky plot and the band gap values,the conduction and valence bands positions of Fe3O4 and FeWO4 were calculated,and the enhanced photocatalytic mechanism was proposed reasonably.The measured saturation magnetization of 20%Fe3O4/FeWO4 was 10.5 emu/g.Under the action of an external magnetic field,it can be rapidly separated from the solution,which is convenient for reuse and easier to realize industrial application.