Construction Of Composite Catalyst Materials Based On G-C3N4 And Its Quantum Dots And Its Performance Research Mechanismosite

Studies have shown that the strategy of constructing heterojunctions is an effective way to enhance the activity of photocatalysts.The recombination of C₃N₄ with semiconductor materials with matching energy band positions can form a high-efficiency heterojunction,which can effectively broaden its absorption of sunlight and reduce the recombination of photogenerated carriers,such as rare metal oxides,TiO₂,etc.The unique electronic structure and physicochemical properties of carbon nitride quantum dots（CNQDs）make it possible to greatly improve the photocatalytic performance of semiconductors after they are combined with semiconductor photocatalysts.The strong interaction between CNQDs and semiconductors can play a good dispersing and stabilizing role.CNQDs have upconversion photoluminescence（UCPL）properties,which can excite semiconductors to generate more holes and electrons and increase the number of effective reactive particles.Therefore,CNQDs are an excellent candidate material to modify TiO₂.As a photocatalyst with excellent performance,TiO₂ is easy to agglomerate by itself.During photocatalytic degradation,it will cover the effective reaction sites and reduce the utilization rate of the light source.Therefore,changing the morphology of TiO₂ is also an important means to improve the photocatalytic efficiency of TiO₂.The research contents are as follows:（1）Large pieces of C₃N₄ are generally made of compounds with high nitrogen content through high-temperature calcination and polymerization.Usually,these large pieces of C₃N₄need to be reprocessed to become g-C₃N₄ with relatively thin sheets.Melamine and cyanuric chloride are used as raw materials.g-C3N₄ nanowires with loose structure and no stacking were synthesized by the low temperature polymerization method.Then,using Ti Cl₄ as the titanium source,the T-CN composites were prepared by loading TiO₂ on the C₃N₄ nanowires by hydrothermal method.A series of characterizations and tests were carried out on the morphology change,crystal structure,intrinsic transition mode,and photogenerated carrier separation ability of the materials before and after loading,and the photocatalytic mechanism of the composites was explored.Finally,the degradation experiments of Rhodamine B（Rh B）were carried out on samples with different loadings under simulated sunlight,and it was concluded that the photocatalytic degradation efficiency of Rh B and 4-CP with the optimal loadings reached 91%and 95%,which is L-1.9 and 2.1 times of L-CN.（2）Combined with the characteristics of traditional single-phase titanium dioxide（TiO₂）in the photocatalytic process,such as high recombination rate of photogenerated carriers,wide energy band,and easy agglomeration in the water phase,carbon nitride quantum dots（CNQDs）were supported on TiO₂ hollow spheres（K-T）to prepare CNQDs/TiO₂ composites.The crystal structure and crystal form of the composites were analyzed by XRD and Raman spectroscopy and used to determine whether CNQDs were loaded;UV-vis DRs were used to characterize the samples themselves.The photocatalytic ability of the sample is inferred from the ultraviolet absorption spectrum and absorption intensity generated by the absorption of ultraviolet and visible light;Intrinsic transitions of the reaction sample according to the PL spectrum and the survival time of photogenerated carriers according to the absorption intensity;SEM and TEM can more intuitively see the morphology change of the material before and after loading;XPS characterization of the peak structure can determine the loading of CNQDs and the effect on the crystal form of TiO₂ hollow spheres.In order to exclude the influence of dye sensitization on the photocatalytic experiment,the photocatalytic degradation experiment of chlorophenol（4-CP）was carried out,and the photocatalytic efficiency reached 93%and85%,about 3.0 and 3.4 times of commercial TiO2,and has Good stability,reusable.（3）CQDs were prepared by hydrothermal method using a"bottom-up"strategy,and then g-C₃N₄ nanowires were prepared by low-temperature thermal polymerization,aiming to utilize the visible light response and UCPL characteristics of CQDs to obtain good optical properties.Catalytic performance of CQDs/g-C₃N₄ composites.The XRD and FR-IR spectra were used to analyze the crystal structure and crystal form of the composite materials and used to determine whether CQDs were loaded;the UV-vis DRs characterization was to use the UV absorption spectrum and absorption intensity generated by the absorption of the sample itself to UV and visible light to determine the sample.The photocatalytic ability of the material can be inferred;the intrinsic transition mode of the PL spectrum reaction sample is judged,and the survival time of photogenerated carriers is based on the absorption intensity;SEM and TEM can more intuitively see the morphology change of the material before and after loading;XPS characterization The peaks of the structure can determine the loading of CQDs and the influence on the crystal form of g-C₃N₄,as well as the element ratio before and after the loading of the substrate material,and determine whether the CQDs are loaded.The best loadings were obtained by degrading Rhodamine B（Rh B）under simulated sunlight with a series of samples prepared.In order to exclude the influence of dye sensitization on the photocatalytic experiments,the photocatalytic degradation experiments of chlorophenol（4-CP）were also carried out.The photocatalytic efficiency of CQD/CN@0.6 reached 95.2%and85.3%,and it has good stability,and the degradation effect still remains after repeated use for5 times.