Study On The Performance And Mechanism Of Photocatalytic Reduction Of U（Ⅵ） By Quantum Dots Modified G-C₃N₄

Since the 21st century,with the rapidly development of atomic energy industry,a large amount of uranium containing wastewater was produced in the in the process of natural uranium mining and smelting,nuclear fuel processing and treatment&disposal for spent fuel inevitably.Which bring the risk of radioactive pollution was one of the most challenging problems for the world,especially the nuclear industry containing countries.Photocatalysis technology can degrade pollutants by using the most common solar energy in nature.It was playing an important role for solving the problems of energy shortage and environmental pollution increasingly.Graphite phase carbon nitride（g-C₃N₄）,two-dimensional semiconductor material,which was typical materials in photocatalyst.It had many advantages,such as narrow band gap,wide spectral response capability and switchable energy band structure,etc.,Whereas,cause of structural defects,it had high recombination rate of electron-hole pairs,poor absorption capacity for visible light and low efficiency of electron transmission,The current research on photocatalytic reduction of heavy metals was limited,it was significance to develop novel photocatalytic materials.In this paper,g-C₃N₄ energy band structure was optimized by modifying quantum dots,and improve its photoelectric performance.Keeping the high separation effective of electron-hole pairs.Improving the photocatalytic performance of U（Ⅵ）reduction degradation.The specific research contents of paper were as follows:Pt quantum dots with the size of 10 nm were synthesized by Na BH₄ reduction method on the surface of g-C₃N₄,Pt quantum dots doped carbon nitride（Pt-C₃N₄）was obtained.It was used for the photocatalytic reduction of U（Ⅵ）.The results show that Pt₃-C₃N₄ reduction efficiency on U（Ⅵ）was 2.4 times higher than that of g-C₃N₄,when the Pt quantum dots doping amount rate was 3%.And the reduction rates of U（Ⅵ）were all above 90%in five photocatalytic cycle experiments,showing prefect reusability.The introduction of Pt quantum dots enhanced the absorption of visible light,Due to the surface plasmon resonance effect of Pt quantum dots.And the recombination rate of photogenerated electron-hole pairs was reduced.The band gap structure was optimized,which reduced by 0.4 e V compared g-C₃N₄.And the conduction band potential was exchanged form-1.03 V to-1.14 V.The reduction of the lowest unoccupied molecular orbital enhanced the photocatalytic reduction ability.Dissolved oxygen would interfere the reduction of U（Ⅵ）.Which confirmed by Active particle capture experiments.Modification of g-C₃N₄ by Pt quantum dots was an effective strategy.Carbon quantum dots were prepared by top-down method and calcined with melamine to obtain carbon quantum dot modified carbon nitride（CD-C₃N₄）composite photocatalytic material.The introduction of carbon quantum dots widening the light response range.The band gap structure was optimized,when the carbon quantum dots doping amount rate of 5%,the energy gap was only 2.2 e V,the conduction band potential reduced from-1.03 V to-1.07 V.Comparing the unmodified g-C₃N₄,the photocatalytic reduction efficiency of U（Ⅵ）improve2.8 times,and showing prefect reusability in five photocatalytic cycle experiments.Carbon quantum dots can participate the formation of melon units,lead to the destruction of interlayer hydrogen bonds in g-C₃N₄.Which was conductive to electron conduction.Active particle capture experiments confirmed that photogenerated electron was the main active particles for reducing U（Ⅵ）,however,UO₂ was reoxidation by hydroxyl radicals probably.Photocatalytic reduction performance of carbon quantum dots modified g-C₃N₄ on U（Ⅵ）had been significantly improved.Mo O₃ quantum dots were prepared by one-step oxidation method with Mo S₂ as the precursor,and fixed on the surface of g-C₃N₄ to obtain Mo O₃ quantum dots modified carbon nitride（MQD-C₃N₄）composite photocatalytic material.The morphological characteristics and functional group structure of g-C₃N₄ were maintained during this process.The large number of crystalline gaps inα-Mo O₃ provided convenient channel for electrons conduction at the interface of catalyst.Photoelectrochemical tests confirmed that the introduction of Mo O₃quantum dots can reduce the resistance electrons transmission in g-C₃N₄.Maintaining high efficiency of separation for photogenerated electron-hole pairs.When the doping amount of Mo O₃ quantum dots rate was 3%,the photocatalytic reduction efficiency of MQD₃-C₃N₄ to U（Ⅵ）was increased by 1.8 times compared with g-C₃N₄.The energy gap was reduced by 0.05e V,the conduction band position was reduced from-1.03 V to-1.11 V.Modification of g-C₃N₄with Mo O₃ quantum dots had great significance for improve the performance of photocatalytic reduction to U（Ⅵ）.