Research Of G-C₃N₄ Composites Synthesis And Photocatalytic Degradation Of Organic Pollutants

Currently,water pollution is a serious problem,as the widespread use of industrial organic compounds such as dyes and drug molecules can cause severe damage to the water environment,directly affecting the human ecological system.As a non-metallic polymer semiconductor material,graphitic carbon nitride（g-C₃N₄）has unique band structure,high physical and chemical stability,and green and non-toxic properties.However,the low specific surface area,narrow band gap,and easy recombination of photogenerated carriers limit the photocatalytic efficiency of single-component g-C₃N₄.Therefore,using semiconductor/g-C₃N₄heterojunction composite photocatalysts to degrade pollutants such as antibiotics and dyes in water has become a research hotspot.In this paper,g-C₃N₄was used as the main material,and two binary heterojunction composite materials,WO₃/g-C₃N₄and AlN/g-C₃N₄,were constructed by high-temperature solid-state method.The activity and stability of these two materials in degrading organic dyes under visible light and tetracycline under simulated solar light were studied,and their photocatalytic degradation mechanism was preliminarily proposed.Finally,a PVA/chitosan aerogel with high specific surface area,adjustable pore structure,good chemical stability,and excellent adsorption performance was used as a carrier to incorporate AlN/g-C₃N₄photocatalyst to construct an AlN/g-C₃N₄/aerogel composite,which provides some new ideas for the practical application of catalysts.The main research contents are as follows:（1）A Z-scheme heterojunction WO₃/g-C₃N₄porous nanotube（WO₃/CNNT）with one-pot calcination self-assembly method was prepared.Characterization techniques such as field emission scanning electron microscopy（FE-SEM）,X-ray diffraction（XRD）,high-resolution transmission electron microscopy（HR-TEM）,and Fourier transform infrared spectroscopy（FT-IR）were used to study the microstructure and composition of the WO₃/CNNT composite catalyst.The photocatalytic experiment results showed that the 2%WO3/CNNT catalyst with a high specific surface area（SBET=108.8 m²/g）achieved removal rates of 97.4%and87.4%for Rhodamine B（Rh B）and tetracycline（TC）,respectively,under visible light irradiation within a certain time,which were 3.4 times and 83.8 times higher than those of pure CNNT and WO₃for Rh B degradation efficiency,respectively.In addition,the degradation ability of TC was 1.1 times and 14.3 times higher than that of single CNNT and WO₃,respectively.Moreover,after four cycles of experiments,the photocatalytic performance of 2%WO₃/CNNT did not significantly decrease,remaining at 91.8%,proving that the porous WO₃/CNNT heterojunction was stable and reusable.The results of active free radical capture experiments revealed that holes（h⁺）and superoxide radicals（·O₂^-）played a dominant role in the photocatalytic degradation process.Finally,the photocatalytic mechanism of the Z-scheme heterojunction WO₃/CNNT composite catalyst was revealed according to the results of UV-vis diffuse reflectance spectroscopy（UV-vis）and Mott-Schottky experiments.（2）The strategy of combining physical grinding with the calcination of melamine,cyanuric acid,and AlN was successfully used to form a two-dimensional/two-dimensional（2D/2D）structure of AlN/g-C₃N₄composite photocatalyst with a flocculent g-C₃N₄coating on the surface of AlN.A series of characterization techniques,including FE-SEM,energy-dispersive X-ray spectroscopy（EDS）,XRD,FT-IR,and X-ray photoelectron spectroscopy（XPS）,confirmed the uniform coating of g-C₃N₄on the AlN surface to form an AlN/g-C₃N₄heterostructure.N₂adsorption/desorption curve analysis showed that the AlN/g-C₃N₄composite material had a larger specific surface area（SBET=45.64 m²/g）and smaller pore structure（15.29 nm）than the g-C₃N₄with a specific surface area of36.88 m²/g and a pore size of 26.83 nm.It was observed that the catalytic efficiency of AlN was improved after g-C₃N₄coating,as demonstrated by the visible light catalysis of Rh B and TC.The 20%AlN/g-C₃N₄showed good catalytic performance,with 98.4%degradation of Rh B solution in 25 minutes and 83.0%degradation of TC solution in 60 minutes.After four cycles of Rh B degradation experiment,20%AlN/g-C₃N₄maintained a degradation rate of 94.1%towards Rh B.FT-IR detection of the catalyst structure before and after cycling indicated that the 20%AlN/g-C₃N₄composite semiconductor material was structurally stable.Finally,the free radical experiment showed that the·O₂^-free radical played a dominant role in the reaction.UV-vis diffuse reflectance（UV-vis）and Mott-Schottky test results confirmed that the photocatalytic reaction mechanism followed a Z-type charge carrier transport route.Therefore,the AlN/g-C₃N₄heterostructure improved its performance in photocatalytic degradation of pollutants.（3）Using in-situ deposition,freeze-drying,and calcination techniques,an aerogel composite of AlN/g-C₃N₄/PVA/CS was prepared by adding AlN/g-C₃N₄composite powder into an aerogel matrix of polyvinyl alcohol（PVA）and chitosan（CS）with a mass ratio of 1:2.The morphology and structure of the prepared AlN/g-C₃N₄/PVA/CS were characterized by XRD,FTIR,FE-SEM,and other testing techniques,confirming the successful preparation of the AlN/g-C₃N₄/PVA/CS composite aerogel,and the addition of the catalyst enhanced the skeleton structure of the aerogel matrix,forming more and tighter pore channels.The adsorption-catalytic properties of the composite aerogel were also studied,showing that the ratio of PVA to CS and the loading amount of AlN/g-C₃N₄catalyst affected its adsorption and catalytic efficiency.The 20%AlN/g-C₃N₄/PVA/CS composite aerogel could adsorb6.94%of Rh B in 1 hour under shading conditions,followed by 99.05%degradation of Rh B after visible light irradiation for 180 minutes.This work provides ideas for expanding the application field of catalysts.