Structure Control And Photocatalytic Performance Of G-C₃N₄/TiO₂ Based Composite Powder

Both pure TiO₂or g-C₃N₄have problems such as severe photogenerated carrier recombination,and insufficient photocatalytic activity.The g-C₃N₄/TiO₂composite nanomaterials can enhance the separation efficiency between photogenerated carriers by forming heterojunctions.However,nanopowders are difficult to be separated and recovered in contaminated water,and the hierarchical porous structure formed by the assembly of composite matrix elements can reduce the difficulty of nanopowder recovery while providing efficient reactive sites.Therefore,exploring the preparation method and structural modification mechanism of facile and efficient hierarchical porous g-C₃N₄/TiO₂（g-CT）composites has far-reaching influence and significance in theoretical research and practical application.In this dissertation,hierarchical porous g-CT composites with different morphologies were prepared by solvothermal method using urea as the nitrogen source and butyl titanate（TBOT）as the titanium source to investigate the effect of potassium doping on their photocatalytic activity.Combined with characterization methods such as FESEM,TEM,BET,XRD,EDS,PL and UV-Vis,the effects of primary process parameters on the g-CT composite structure,phase composition and photocatalytic performance were analyzed,and the nanosheets in the solvothermal process were determined,the evolution mechanism of orderly assembled hierarchical porous structure and the influence mechanism of potassium doping on the photocatalytic activity of composite materials was studied.The primary results were as follows:（1）Solvothermal preparation conditions of orderly assembled g-C₃N₄/TiO₂ composites:urea to TBOT molar ratio 10:1,H₂O to ethanol volume ratio 1:7,solvent treatment at 130℃for 24 h and calcination at 500℃for 2 h resulted in nanosheets assembled g-CT composites made of TiO₂and g-C₃N₄particles overlapped with multi-level pore structure,including 0.5-2nm micropores,3-20 nm mesopores and 100-250 nm macropores,with specific surface area of 98.4 m²/g.The degradation rates of tetracycline hydrochloride and Rh B reached 89.8% and 99.9%,respectively,after 60 min of irradiation with 500 W Xe lamp.（2）The molar ratio of urea to TBOT is crucial for the evolution and regulation of the g-CT composites structure during the solvothermal process.When the molar ratio of urea to TBOT increases from 0:1 to 12:1,the g-CT composites gradually evolve from nanoparticle agglomerated structure to nanosheet 3D assembly and sea urchin-like hierarchical structure,and the band gap decreases from 3.25 e V to 3.02 e V.（3）Optimal modification conditions:TBOT to potassium molar ratio of 7.5:1,H₂O to urea to TBOT molar ratio of 45:4.5:1,solvent heat treatment at 130℃for 24 h,followed by calcination at 500℃for 2 h.The potassium-doped g-CT nanosheet assembly composites with a specific surface area of 183.2 m²/g was produced.The degradation rate of Rh B could reach 99.9%after 40 min of 500 W Xe lamp radiation.The band gap was further reduced to2.96 e V,and the light absorption range was extended to 423 nm,which increased the degradation rate by 148%.