Fabrication Of CeO₂/g-C₃N₄ Composite And Improvement Of Its Photocatalytic Performance

Semiconductor photocatalysis technology using solar energy is considered to be a method that can simultaneously solve the problems of environmental pollution and energy shortage.It has a wide range of applications in many fields,such as air purification,water purification and self-cleaning glass,etc.Among many photocatalysts,the construction of CeO₂/g-C₃N₄ heterojunction has attracted attention because of its strong reducibility of g-C₃N₄ and strong oxidation of CeO₂.However,CeO₂/g-C₃N₄heterostructures have some problems in the construction process,such as easy agglomeration of CeO₂ nanoparticles,low visible light utilization efficiency,high recombination rate of photogenerated carriers and limited active sites,which limit their further application.In order to overcome the above shortcomings,it is an effective method to improve the separation and transfer efficiency of light-induced charges through rational design and construction of heterojunction structures.In this paper,CeO₂/g-C₃N₄ heterojunction with high photocatalytic activity was constructed by surface modification,micro morphology control and defect introduction.The contents include the following three aspects:Firstly,the heterojunction photocatalyst 0D/2D CeO₂/C-g-C₃N₄ was synthesized by in-situ hydrothermal method based on the carboxylation g-C₃N₄(C-g-C₃N₄).The interaction of metal Ce ions with the hydroxyl and carboxyl groups on the surface of C-g-C₃N₄ improves the dispersion of CeO₂ nanoparticles.TEM results show that the carboxylation improves the dispersion of CeO₂ compared with CeO₂/C-g-C₃N₄ bulk heterojunction.The highest photocurrent density(7.21?10^-3 m A)was obtained when CeO₂ loading was 3 wt%.In addition,3%CeO₂/C-g-C₃N₄ heterojunction has the best photocatalytic effect,and the Photocatalytic reduction of CO₂ produces 31?mol/g CO and 1.195?mol/g CH₄ within 8 hours.The degradation of ciprofloxacin reached 73%within 120 min,and the photocatalytic mechanism of ciprofloxacin was studied by DFT theory.Secondly,the 2D/2D C-g-C₃N₄/CeO₂-S-H₂ composite heterostructures with abundant oxygen vacancies were prepared by electrostatic self-assembly,calcination and hydrothermal method.The existence of oxygen vacancies was proved by Raman and XPS.Meanwhile,the ratio of Ce³⁺/Ce⁴⁺was increased from 28.2%to 32.08%by hydrogenation treatment,which indicated that the concentration of oxygen vacancies was increased by hydrogenation treatment.Meanwhile,the increase of oxygen vacancies further improved the absorption of visible light and electron capture of heterojunction,and greatly promoted the separation of photo generated carriers in the catalyst.The performance test showed that 60%C-g-C₃N₄/CeO₂-S-H₂ heterojunction photocatalyst showed good CO₂reduction and degradation performance of ciprofloxacin.The degradation capacity of ciprofloxacin reached 78.5%in 120 min.the yield of CO₂to CO and CH₄ was 19.032 umol/g and 11.997 umol/g respectively.The results show that the introduction of oxygen vacancies can effectively enhance the CH₄ production of heterojunction in the process of CO₂ reduction,which can be used as a reference for the selective study of photocatalytic CO₂ reduction products.Finally,different morphologies of CeO₂,including CeO₂ rod(CeO₂-R),CeO₂ cube(CeO₂-C)and CeO₂ octahedron(CeO₂-O)were synthesized by hydrothermal method,and heterojunction photocatalysts were constructed by combining CeO₂ with g-C₃N₄.And a series of characterizations was carried out.The effect of the morphology on the photocatalytic performance of the heterojunction was studied.The results show that CeO₂-O/g-C₃N₄ heterojunction has the best photocatalytic performance for the degradation of dinitrophenol,and the degradation rate of dinitrophenol reaches 63.1%within 120 min,indicating that the morphology of CeO₂ has an important influence on the photocatalytic activity of heterojunction.