The Research On The Carbon Dots Modified Photocatalysts For Enhancement Of Photocatalytic Activity

During 21 st century,the environment pollution and energy crisis have become two major concerns of the international community.Therefore,it is of great importance to find a clean and renewable energy.Photocatalytic water splitting to produce hydrogen by using renewable solar energy is an ideal way to achieve clean energy-hydrogen energy.And the use of photocatalytic technology to deal with environmental pollutants is also a very promising way.However,the current photocatalysts still have a series of problems such as narrow light response range,low separation efficiency of photogenerated carriers and poor stability.Therefore,the focus of the field is to develop effective photocatalysts and improve the efficiency of photocatalytic conversion process.In this thesis,we focused on the carbon dots(CDs),selecting BiOI and CdS as the base photocatalysts.Via an element doping method,sulfur doped carbon dots(S-CDs)/BiOI nanocomposites and different metal doped CDs/CdS nanocomposites were prepared and the photocatalytic degradation of methylene blue and photocatalytic water splitting performance of two photocatalysts were investigated.The relationship between the structure of the catalyst and the reaction performance was studied by various methods.The main contents include the following:(1)BiOI and S-CDs were prepared by hydrothermal method,and a series of S-CDs/BiOI nanocomposites were prepared by chemical adsorption.The photocatalytic activity of the photocatalyst system under visible light(? ? 420 nm)irradiation was investigated by using methylene blue as the target pollutant.The results showed that when the loading amount of S-CDs was 1%,the photocatalytic activity of the composite was the highest,which was 76.2% higher than that of pure BiOI.S-CDs/BiOI also exhibited higher photocatalytic activity than undoped CDs/BiOI.The enhancement of the photocatalytic activity of BiOI after S-CDs modification can be attributed to the improved charge separation and transfer induced by S-CDs.(2)CdS nanowires were fabricated by hydrothermal method.CDs,different metal(Bi,Co,Zn,Ti,Cd)-doped CDs and different Bi doping amounts of Bi-CDs were synthesized by pyrolysis method.Doped CDs/CdS composites were prepared and the performance of photocatalytic water splitting under visible light irradiation was investigated.The results show that CDs/CdS composites have the highest activity when the loading amount of CDs was 1%.Compared with pure CDs/CdS composites,different metal doping can improve the photocatalytic activity of CDs/CdS.The activity of Bi-CDs/CdS is the highest,which is about 5.2 times that of pure CdS and 1.9 times that of pure CDs/CdS.The influence of doping amount of Bi on the photocatalytic performance of the composite was also investigated.It was shown that the doping amount of Bi has the optimal value,when the doping amount of Bi is 20%(the precursor bismuth nitrate is 1 g),Bi-CDs/CdS has the highest hydrogen production activity.Combined with the results of various characterizations,it can be seen that Bi doping increases the charge transfer rate of carbon dots,and the photoelectrons on CdS can be effectively migrated to Bi-CDs,leading to improved separation efficiency of photogenerated charge and photocatalytic activity of the composite.