Preparation Of Composite Catalysts Modified By Carbon Quantum Dots And Their Photocatalytic Performance

Carbon quantum dots（CQDs）are a new type of carbon nano-materials composed of quasi-spherical discrete nanoparticles with a size of less than 10 nm.Due to its unique up-conversion luminescence performance,environmental friendliness,superior water solubility,low cost,and high chemical stability,CQDs are widely used in the fields of biological imaging,optoelectronic devices,catalysis and functional materials.For the application of photocatalysis,the up-conversion effect of CQDs can significantly expand the solar absorption of semiconductor materials to the visible light band and even the near-infrared region,thus greatly broadening the utilization efficiency of solar light.In addition,CQDs can be used as electron acceptors and donors,which means that the photocatalysts modified by CQDs can absorb photogenerated electrons and act as electronic depositories,thus achieving effective separation of photogenerated electrons and holes.Therefore,CQDs can be used in the design of high-performance photocatalysts and play an important role in various application fields of photocatalysis.This paper focuses on the design and photocatalytic degradation activity of three kinds of composite photocatalyst materials based on CQDs,namely,CQDs/g-C₃N₄/MoS₂,CQDs/g-C₃N₄/MoO₃and CQDs/Bi₄O₅Br₂.With the help of up-conversion and electron absorption functions of CQDs,the photocatalytic performance of g-C₃N₄/MoS₂（MoO₃）and the simple material Bi₄O₅Br₂ can be further improved,and its application in the field of environmental protection and"double carbon"can be broadened.The main contents and conclusions of the study are as follows:1.CQDs were dotted on the surface of g-C₃N₄ using a calcination process,and the composite photocatalyst was formed with MoS₂ by ultrasonic stirring and the photocatalytic performance of the system was evaluated by degrading two common model dye molecules,methyl orange（MO）and methylene blue（MB）.Under visible light,the degradation performance of CQDs/g-C₃N₄/MoS₂ was significantly better than that of the monolithic and binary composite CQDs/g-C₃N₄/MoS₂,with the CQDs-modified catalyst with a 10:1 mass ratio of g-C₃N₄ to MoS₂ possessing the best photocatalytic performance and a 6.28-fold improvement in the degradation performance of MO,as well as good cycling stability for repeated use.2.The heterostructure CQDs/g-C₃N₄/MoO₃ is constructed by replacing MoS₂ with MoO₃,a molybdenum-based semiconductor（by which synthesis method）,which has a wider band gap than MoS₂（1.88 e V for MoS₂ and 3.02 e V for MoO₃）,which facilitates the formation of a Z-type heterostructure with a more suitable redox potential and higher charge-hole separation efficiency.This facilitates the formation of Z-type heterostructures with more suitable redox potentials and higher charge-hole separation efficiencies.The photocatalytic performance was determined by the degradation of four pollutants,Rhodamine（Rh B）,MO,MB and Tetracycline（TC）.The results showed that for the degradation of the above pollutants,the best performing ternary CCNM25 improved by3.6,2.5,3.7 and 2.2 times respectively compared to CNM25 without CQDs.The composites have the advantages of degradation diversity and fast degradation rate.3.In order to verify the facilitative role of CQDs more effectively in photocatalytic degradation,CQDs were directly compounded with energy band-matched Bi₄O₅Br₂monomeric materials to form CQDs/Bi₄O₅Br₂ photocatalysts by a one-step hydrothermal method.The mechanism of catalytic degradation of bisphenol A（BPA）was analyzed in depth by numerous characterization tools such as free radical trapping,electron paramagnetic resonance（ESR）and total organic carbon content（TOC）measurements.The results show that the photocatalytic performance of CQDs/Bi₄O₅Br₂ under visible light is greatly enhanced compared to Bi₄O₅Br₂ alone,especially under xenon irradiation at wavelengths>400 nm,where the degradation performance of CQDs/Bi₄O₅Br₂（4 mg）is enhanced by 69 times compared to Bi₄O₅Br₂ alone.The above work demonstrates that it is feasible to improve the photocatalytic performance by composing CQDs with other materials in a multifaceted composite structure,mainly due to the up-conversion luminescence and electron absorption properties of CQDs,and therefore the unique energy band structure and up-conversion properties of CQDs can be fully utilized to achieve efficient degradation of many organic pollutants.Figure 42 Table 7 Reference 160...