Synthesis And Photocatalytic Properties Of Titanium Dioxide-based Nanomaterials With Schottky Junction

The development of human society demands more and more energy.The exploitation and utilization of clean energy can effectively relieve the burden of fossil fuel utilization on the earth's ecological environment.Nuclear energy provides much more energy and without greenhouse gases than traditional fossil fuels,it becomes a promising approach for energy supply.However,a large amount of radioactive wastewater is inevitably produced during the nuclear circulation process.Uranium,with a serious chemical toxicity,is the main radioactive substance in the nuclear wastewater.It is of great practical significance to realize the extraction and recovery of uranium from nuclear wastewater for the sustainable development of nuclear industry and the protection of the earth's ecological environment.At present,the main treatment methods for uranium-containing water are adsorption,extraction and distillation,etc.,the above approaches limited by high cost,equipment requirements,and incomplete treatment.In addition,the organic compounds in the real wastewater are easy to form complexes with uranium,which increases the difficulty of uranium treatment and greatly affects the treatment efficiency of uranium-containing wastewater.Therefore,it is significant and urgent to develop a green,efficient and economic treatment technology for uranium-containing wastewater.Previous studies have shown that the reduction of highly soluble uranium(mainly hexavalent U(VI))from low-soluble uranium(mainly tetraducent U(IV))is an ideal way to treat uranium-containing wastewater.Photocatalytic technology has attracted extensive attention because of its high efficiency and no additional energy input,good environmental compatibility,high efficiency.What's more,the photon-generated electrons and holes can be used in the oxidation of organic matter and the reduction of high-valence uranium,respectively during the photocatalytic process.As a typical photocatalyst,TiO₂ has been widely used due to its advantages of low cost and easy access.However,the photocatalytic activity TiO₂ is limited by its high photogenerating charge recombination rate,poor visible light response ability,high charge transfer resistance,low electron transfer and electron utilization efficiency.It is of great practical significance to design TiO₂ photocatalyst to improve its photocatalytic activity and to apply it to the treatment of uranium-containing wastewater.In this paper,we regulated the energy level structure of TiO₂ and equipped it with Schottky junction,furtherly applied it to the treatment of uranium-containing wastewater.The main research contents and results of this paper are as follows:(1)A core-shell structure CAs@TiO₂ was synthesized via nanowater atomizer assisted strategy.TiO₂ shell obtained a smaller size and good crystallinity by controlling TBOT hydrolysis rate.Ti³⁺was introduced through the further reduce by N₂H₂·H₂O.The CAs@B-TiO₂ photocatalyst with cored shell structure showed excellent photocatalytic performance under visible light excitation,and achieved 98.6%effective degradation of tannic acid.(2)TiOS was obtained by regulating the energy level structure of TiO₂ through S atom injection,which greatly improved the response range of TiO₂to sunlight.TiOS and N-doped hollow carbon spheres were assembled to form hierarchical Schottky junction photocatalytic materials(TiOS/NHCS),which enhanced the transfer of photocarriers and inhibited the recombination of electron hole pairs.The density functional theory calculation further proves that S atom injection can optimize the energy level structure of TiO₂ and enhance the light utilization ability.The experimental results showed that the U(VI)reduction efficiency of more than 90%can be achieve.This work not only provides a feasible photocatalyst for the treatment of uranium-containing wastewater,but also opens a way for the design of energy band structure and the construction of Schottky heterojunction materials.(3)To enhance the recovery ability of photocatalytic materials in practical applications,TiO₂was further assembled on the surface of graphene to form 3D TiO_2-X/rGO aerogel.The energy band structure of TiO₂ was optimized by surface oxygen vacancy defect engineering,which is benifeted the response of sunlight toward TiO₂.The schottky junction formed between TiO₂and rGO promoted photogenerated electron transfer and inhibited electron-hole pair recombination,which significantly improved the photocatalytic reduction efficiency of U(VI).In addition,the prepared 3D TiO_2-X/rGO aerogel photocatalyst also has good anti-heterion interference ability and excellent cycling stability,expecting to achieve large-scale application in the field of U(VI)containing wastewater treatment.To sum up,this paper studied the optimization and regulation of the energy level structure of TiO₂,to boost its light utilization.Through the assembly of schottky junction,the photocatalytic activity toward organic degradation and U(VI)reduction was improved.The synergistic effect of energy level structure and Schottky junction and the mechanism of U(VI)photocatalytic reduction during photocatalysis process were revealed.It is expected to provide theoretical reference for the treatment of real uranium-containing wastewater.