Study On The MIL-53(Fe) As Photocatalysts For Radioactive/Chemical Pollutants Removal In Wastewater

Study on the rapid and low-cost purification technology for radionuclide contaminated wastewater and chemical warfare agents contaminated wastewater is an important issue in the field of military environment.Photocatalysis is a green and simple operation sewage treatment method,however,most photocatalysis systems are visible-light-underutilized resulting in great energy waste.Thus,developing new visible light catalytic systems is an effective method and research hotspot for the sunlight utilization rate improvement.Recently,iron-based metal organic framework（MOF）material is an emerging visible light photocatalyst,which performs good application prospects in heavy metal ions and organic pollutants removal in wastewater.In this paper,iron-based metal organic framework material MIL-53（Fe）was used as a catalyst to construct new photocatalytic systems for the typical radioactive and chemical pollutants photocatalytic removal study,where uranium nitrate and HD were tested as two typical pollutants,the main contents were as follows:（1）Synthesis and characterization of metal-organic framework material MIL-53（Fe）.First,iron-based metal organic framework MIL-53（Fe）was synthesized and accordingly characterized.The crystal structure of this material was characterized by Powder X-ray diffractometry（PXRD）.The organic functional groups and coordination bond Fe-O in the MOF structure were characterized by Fourier transform infrared spectrometer（FT-IR）.The morphology of the micron-rod-structure material was characterized by Scanning electron microscopy（SEM）.Thermogravimetric analysis（TGA）showed that MIL-53（Fe）performed good thermal stability under 300℃.The UV-visible diffuse reflectance spectra（UV-Vis DRS）showed that MIL-53（Fe）could respond to the UV to visible region.Photogenerated electrons of MIL-53（Fe）under illumination was confirmed by xenon lamp source and electrochemical workstation.The above results showed that MIL-53（Fe）performed good structural stability and visible light response activity.（2）MIL-53（Fe）as a photocatalyst for visible-light catalytic reduction of U（VI）in aqueous solutionMIL-53（Fe）and hole trapping agent were used to construct a photocatalytic reduction system,the effects of hole trapping agent kinds,hole trapping agent concentration,initial pH of the reaction solution and catalyst concentration on MIL-53（Fe）photocatalytic reduction of U（VI）were investigated,respectively.The results showed that the photocatalytic reaction rate was greatly accelerated and the catalyst was structurally-stable during the reaction when formic acid was used as hole trapping agent.The optimized reaction rate increased 27 times than the blank sample when formic acid concentration increased from 0 to 10 mmol/L.Apart from this,the reaction rate constant increased from 0.004 to 0.020 min^-1,and then slightly decreased to 0.012 min^-1,when the catalyst concentration was in the range of 0-600 mg/L.XPS tests of reaction products confirmed the presence of U（IV）,indicating that U（VI）was reduced.After 5times of recycling use of the catalyst,the loss rate of MIL-53（Fe）was less than 1%whilst the photocatalytic removal rate of U（VI）was not significantly reduced.The target of MIL-53（Fe）photocatalytic reduction and removal of U（VI）in radioactive wastewater was achieved using formic acid as a hole trapping agent.（3）Photocatalytic degradation of HD and its simulant 2-CEES by MIL-53（Fe）/H₂O₂ system.MIL-53（Fe）/H₂O₂ were used together to construct a photocatalytic system,where the effects of H₂O₂ concentrations,catalyst concentrations and light intensities on MIL-53（Fe）photocatalytic degradation of HD simulant 2-CEES were investigated,respectively.The results showed that the concentration of H₂O₂ was an important factor in the photocatalytic degradation reaction.The reaction rate constant increased 8 times than the controlled sample when the concentration of H₂O₂ increased from 0 to 0.08mol/L.Increasing the lamp current accelerated the reaction as well since the reaction rate constant increased from 0.017 to 0.041 min^-1,showed 2.4 times increase than the controlled sample when the lamp current gradually increased from 0 to 20 A.Apart from this,the catalyst concentration played an important effect on the photocatalytic reaction in which the reaction rate constant increased from 0.010 to 0.021 min^-1（2 times higher than the controlled sample）when the catalyst concentration increased from 0 to400 mg/L.Apparently,it was found that both light and catalyst could accelerate the reaction rate of H₂O₂ catalytic degradation 2-CEES through comparison experiments under different conditions.The 2-CEES degradation reaction rate constant increased from 0.003 to 0.026 min^-1（about 8 times higher than the blank sample）when light,catalyst and H₂O₂ were co-existed in the system.It was found that the main 2-CEES degradation products were hydrolyzate hydroxyethyl ethyl sulfide,oxidation products of hydroxyethyl ethyl sulfoxide and hydroxyethyl ethyl sulfone detected by GC-MS.After that,it was found that the MIL-53（Fe）/H₂O₂ system showed a good degradation removal effect for HD and both sulfoxide and hydrolyzate were the main degradation products.Compared with traditional Fenton reagent,the MIL-53（Fe）/H₂O₂ system showed that the catalysts were reusable and secondary-pollution-free（like iron hydroxide precipitation）,which exhibits a good application prospect in photocatalytic purification of chemical warfare agents contaminated wastewater.In summary,the removal of radioactive or chemical pollutants in wastewater by MOF MIL-53（Fe）as a photocatalyst was systematically studied in this work.The new established green and efficient photocatalysis MIL-53（Fe）/HCOOH system and MIL-53（Fe）/H₂O₂ system were performed photocatalytic removal study of uranium-containing radioactive wastewater and mustard-gas-infected wastewater,which broadened its application of metal organic framework material for the purification of radioactive/chemical wastewater system in the military environment.