Controllable Synthesis Of Modified Carbon Dots/Metal Oxide Semiconductor Composites And The Application In Photocatalysis

In recent years,with the continuous advancement of industrial modernization,water pollution caused by organic substances such as dyes and antibiotics has become a common challenge for mankind.Photocatalytic technology,which has the advantages of high efficiency,recyclability,and environmental friendliness,has shown great application prospects in the field of water treatment.Among many catalysts,metal oxide semiconductors have the advantages of many crystal types,low toxicity,stable chemical properties,and low preparation costs,and have become one of the research hotspots in the field of photocatalysis.Although researchers have done a lot of research work on metal oxide semiconductors in recent years,such materials still have problems such as high photorecombination rate,slow charge migration speed,and low utilization rate of sunlight,which limit their practical applications.Therefore,further reducing the recombination rate of photo-generated carriers of metal oxide semiconductor materials,expanding the light absorption range,and developing a metal oxide semiconductor composite photocatalyst with high-efficiency and broad-spectrum response have become the most critical issues that need to be resolved.Due to their unique physical and chemical properties,carbon dots(CDs)can help enhance the light absorption of the catalyst,effectively promote the separation and transfer of photogenerated carriers,and increase the number of reactive sites in the photocatalytic process.Therefore,the composite of the carbon crossing point and the transition metal oxide will be able to effectively solve the current problems faced by the transition metal oxide.This thesis mainly focuses on carbon dot/transition metal oxide(Sn O₂,WO₃and Ti O₂)composite materials.On the one hand,the photocatalytic performance of metal oxide semiconductors is enhanced by adjusting the morphology and structure of the metal oxide semiconductor and the influence of microstructure on properties is also revealed;on the other hand,the optical and electron transport properties of carbon dots are controlled by element doping modification,and they are combined with the above-mentioned metal oxide semiconductors,and their photocatalytic properties are systematically studied to clarify the regulation mechanism.The main research contents of the thesis are as follows:(1)The N and Cu co-doped carbon dots(N,Cu-CDs)were synthesized by hydrothermal method,and they were combined with Sn O₂of different morphological structures(hollow sphere,solid sphere,flower-like and box-like nanostructures),a series of N,Cu-CDs/Sn O₂composite catalysts were obtained.The results show that the introduction of N,Cu-CDs can effectively enhance the visible light absorption capacity of Sn O₂and inhibit the recombination of photo-generated holes and electrons.The combination of Sn O₂and N,Cu-CDs significantly improved the catalytic activity,and the square-box nanostructured N,Cu-CDs/Sn O₂catalyst showed the highest photocatalytic degradation performance for rhodamine B under visible light irradiation.(2)In order to further improve the photocatalytic performance of CDs/WO₃composites,a block copolymer PEOx-b-PSy was used as a template to synthesize a WO₃catalyst with an ordered mesoporous structure and composite with N,Cu-CDs.The mesoporous N,Cu-CDs/WO₃composite catalyst was prepared.The results show that the highly ordered and uniform pores effectively increase the specific surface area of the catalyst,and the material has good degradation performance for organic pollutants such as rhodamine B under ultraviolet,visible and infrared light conditions.The excellent photocatalytic activity of the mesoporous N,Cu-CDs/WO₃composite catalyst is mainly attributed to the ordered and uniform pore structure,narrow band gap and efficient photo-generated carrier separation efficiency.(3)In order to investigate the universal applicability of N,Cu-CDs in the water treatment process,this study used the widely-used semiconductor material titanium dioxide in the market for further verification.A series of N,Cu-CDs/Ti O₂composite catalyst with ordered mesoporous structures were prepared using different template Pluronic F127.The results show that the specific surface area of mesoporous Ti O₂obtained when Pluronic F127 is used as the template is as high as 118.18 m~2/g,and the pores are uniformly distributed and highly ordered.The introduction of N,Cu-CDs makes the mesoporous N,Cu-CDs/Ti O₂composite catalyst exhibit good light absorption properties in the near-infrared region.Catalytic activity experiments confirmed that this type of mesoporous N,Cu-CDs/Ti O₂composite material system exhibits excellent degradation performance on organic pollutants,and the improvement of catalytic performance is mainly due to the ordering of mesopores and doping modification CDs'optical capture and electron transfer/storage capabilities.(4)Finally,in order to explore the transition metal oxide composite photocatalyst with high efficiency and broad-spectrum response,the N and Fe co-doped carbon dots(N,Fe-CDs)were synthesized and combined with WO₃with different morphologies and structures.The N,Fe-CDs/WO₃composite catalyst was obtained.The results show that the composite material exhibits a wider visible and near-infrared light absorption range.Among them,the three-dimensional tooth-shaped composite material has the best performance in light absorption,and shows excellent photocatalytic performance for a variety of organic pollutants(rhodamine B,methylene blue,tetracycline hydrochloride,ciprofloxacin and oxytetracycline).,ciprofloxacin and oxytetracycline).The enhancement of the photocatalytic performance of N,Fe-CDs/WO₃composites is attributed to the good electron transfer/storage performance of N,Fe-CDs,as well as the better light-harvesting ability of the three-dimensional tooth-shaped structure,abundant oxygen vacancies,and larger specific surface area.