Preparation Of PON And Its Photocatalytic Reduction Of Wastewater Containing Uranium

As a new type of clean and high-density energy,nuclear energy is a realistic and rational choice to solve the energy crisis.The mining of uranium and the operation of nuclear power plants produce large amounts of wastewater containing uranium,which is highly radioactive and chemically toxic and can cause irreversible harm to the ecological environment and human health,and is an important factor limiting the development of nuclear energy.Therefore,there is an urgent need to develop a clean and efficient technology to treatment uranium-containing wastewater.Based on the characteristics of high efficiency and no secondary pollution,photocatalytic technology has become a promising technology for treating wastewater containing uranium.However,the existing photocatalytic materials have the disadvantages of low solar energy utilization and photocatalytic activity,which limit their further application.Therefore,the development of a photocatalytic material with high visible light activity has become the focus of current research.To address the above problems,phosphorus oxynitride（PON）was selected as the research object based on the summary of the current status of photocatalytic materials at home and abroad,and obtained a photocatalytic material with high visible light activity by modulating its crystalline shape and microstructure from the relationship between structure and performance.PON was applied to photocatalytic reduction of wastewater containing uranium,which expanded its new application field.The growth mechanism of PON and the mechanism of photocatalytic reduction of U（VI）were discussed by XRD,SEM,Uv-vis,EIS,XPS and PL.The specific conclusions are as follows:（1）A new process for the preparation of PON was developed by solvothermal method using ethylenediamine and red phosphorus pretreated by oxidation as raw materials.The results show that oxidation pretreatment is the key step in the preparation of PON,and P-O and P=O can be introduced into the surface of red phosphorus to improve the reaction activity.The oxidation pretreated red phosphorus"chelates"with NH₂^-produced by the ionization of ethylenediamine to form P-N and P=N bonds,thus forming high crystallinity PON crystals.PON responds in the ultraviolet-visible light region and has a lower conduction band potential（-0.19 V）,electron-hole recombination rate and higher electron migration rate,so it has a strong photocatalytic reduction ability.（2）The effects of different process conditions on the crystal form,microstructure and U（VI）removal rate of PON were studied.Through optimizing the process,a new process for efficient removal of uranium containing wastewater was obtained.The results show that the crystal form and preferential growth of（101）plane are the key factor affecting the photocatalytic performance of PON.The optimal process conditions of PON were as follows:the oxidation pretreatment temperature was 180℃,the oxidation pretreatment time was 12 h,the solvothermal temperature was 160℃,the solvothermal time was 24 h,the amount of red phosphorus was 0.6 g,the initial p H value of uranium containing wastewater was 6,the amount of photocatalyst was 15 mg,and the photocatalytic time was90 min.The removal rate of uranium containing wastewater was 91.3%,and the removal capacity was 2130.3 mg/g.Combined with UV-vis,XPS and other characterization techniques,the possible photocatalytic reduction mechanism of PON was proposed:the conduction band potential of PON was lower than that of U（VI）（0.27 V）,which met the thermodynamic requirement of reducing U（VI）to U（IV）,and PON can reduce U（VI）by self generated photogenerated electrons.