Rare Earth Modification Of C₃N₄ And Its Photocatalytic Performance

Photocatalysis technology can use green sunlight to degrade pollutants in the environment and decompose water to produce hydrogen.Therefore,it shows great development potential in dealing with the challenges of energy shortage and environmental pollution.Graphite-like carbon nitride has many advantages,such as no metal,environmental protection and energy saving,non-toxic and harmless,high chemical and thermal stability,low price,low band gap energy,and can effectively absorb visible light,etc.,and has received extensive attention.However,the unmodified graphitic carbon nitride has problems such as easy recombination of photogenerated electrons and holes,small specific surface area,and narrow spectral response range,resulting in low photocatalytic efficiency.In view of the above problems,this paper modified graphitic carbon nitride by doping method to prepare materials with near-infrared photocatalytic activity,and used various characterization methods to explore the reasons for the improvement of photocatalytic efficiency and the relationship between doped rare earth ions and matrix energy transfer process.The main research contents of the paper are as follows:（1）The melamine precursor in the liquid phase was used for doping,and then the graphite-like carbon nitride co-doped with ytterbium and thulium was synthesized by thermal shrinkage polymerization under the protection of nitrogen flow.After the photocatalytic test,it was found that the visible photocatalytic efficiency before and after doping increased from 39% to 97% after the same time of illumination.The samples were tested by XRD,SEM,FT-IT,UV-vis,PL,FL and other tests,and it was found that the graphite-like carbon nitride material modified by rare earth ion codoping had a narrower forbidden band width and a higher density.The low band gap energy and longer fluorescence lifetime improve the utilization efficiency of the solar spectrum,and at the same time reduce the recombination rate of photogenerated electrons and holes,thereby effectively improving the photocatalytic performance of graphitic carbon nitride.（2）The graphite-like carbon nitride was modified by microwave method.First,pure g-C₃N₄ was prepared by calcining melamine under nitrogen flow,and then appropriate proportion of Yb³⁺ solution and Er³⁺ solution were added,mixed and stirred evenly under ultrasonic conditions,moved to a crucible,placed in a microwaveMoven,reacted at 700 W for 5min,centrifuged,Take the precipitate and dry it in an oven at 80°C to obtain g-C₃N₄:Yb³⁺,Er³⁺ photocatalysts.PL,UV-vis and other tests were carried out on the graphite-like carbon nitride photocatalyst co-doped with ytterbium and erbium ions.When the width is narrowed,the bandgap energy of g-C₃N₄ decreases,so that the light absorption range can be enlarged.After the photocatalytic test,the visible light catalytic efficiency of pure g-C₃N₄ to rhodamine B was 39% after 52 min of illumination.At the same time,the visible light catalytic efficiency of the doped g-C₃N₄:Yb³⁺,Er³⁺ photocatalyst increased to 93.4%.Using a 980 nm laser as the light source,the doped samples were tested for near-infrared photocatalysis.The experimental results showed that the g-C₃N₄:Yb³⁺,Er³⁺ photocatalysts degraded 29.7% of Rhodamine B within 8 hours,which proved that the co-doping of ytterbium erbium ions The heterographite-like carbon nitride photocatalyst exhibits near-infrared photocatalytic performance.