Preparation And Application Of Catalysts For Photoreduction Of Uranyl Ions

Uranium is an important raw material for the development of nuclear energy,as well as a highly toxic and radioactive pollutant.With the rapid development of nuclear industry,more and more nuclear waste water is discharged into the ecological environment.Therefore,it is necessary to treat uranium-containing wastewater to protect the environment from radioactive contamination.Photocatalytic reduction has been proved to be a promising wastewater treatment technology with advantages of environmental protection and high efficiency.However,the current catalysts for U（VI）photoreduction have some problems,such as low light absorption rate,low catalytic activity,poor stability and contamination of sacrificial agent.Based on this,the catalysts for U（VI）photoreduction with high activity,high stability and no sacrificial agents have been successfully developed by constructing plasmonic metal/semiconductor composites.The major results were as follows:（1）A highly active and stable catalyst（CCNCI/Zn O）for photocatalytic reduction of uranium was successfully constructed by depositing Cu₈₀Co₅Ni₅Cd₅In₅nanocrystals on porous Zn O.Due to the surface plasmon resonance effect of Cu,CCNCI/Zn O has obvious light absorption in visible region.The U（VI）enrichment capacity of CCNCI/Zn O reached 2405.3 mg/g.In addition,CCNCI/Zn O exhibits good stability in the photocatalytic process due to the entropy enhancement effect of Cu₈₀Co₅Ni₅Cd₅In₅nanocrystals.Further mechanistic studies indicated that Cu₈₀Co₅Ni₅Cd₅In₅nanocrystals in CCNCI/Zn O generated hot electrons under visible light,followed by the transfer of hot electrons to porous Zn O via the Schottky barrier for photoreduction of uranyl ions.（2）A highly active and stable photocatalyst（Ag/ZIF-8）for photocatalytic reduction of uranium was successfully developed by solvothermal encapsulation of Ag nanoparticles into imidazolate zeolite framework-8,which could achieve high efficiency of U（VI）photoreduction without sacrificing agents.In 200 ppm of U（VI）solution,the removal rate of U（VI）by Ag/ZIF-8 under xenon lamp was up to92.8%.Moreover,under the irradiation of natural sunlight,more than85.8%of U（VI）was enriched via Ag/ZIF-8.Mechanistic studies revealed that hot electrons generated over Ag nanoparticles were transferred to ZIF-8 to efficiently reduce adsorbed U（VI）,while hot holes left by Ag particles are used for oxidizing H₂O.A large number of nitrogen-containing groups in ZIF-8 could be used not only as active sites for efficient adsorption of U（VI）,but also as electron acceptors to promote the photocatalytic reduction of uranium.