Preparation Of Long Wavelength Fluorescent Carbon Dots And Their Applications In Ion Detection And Photocatalysis

Fluorescent carbon dots were first discovered in 2004 and have attracted much attention due to their excellent optical and physicochemical properties.Carbon dots have photoluminescence properties.Compared with traditional quantum dots,carbon dots are characterized by low toxicity,abundant functional groups on the surface and simple preparation.These characteristics of carbon dots make it have great development prospect in many fields.At present,the carbon dots prepared are mainly short-wavelength carbon dots,and these carbon dots generally need ultraviolet excitation,which will produce blue background fluorescence when applied in the biological field and cause interference to the imaging signal.In addition,the short wavelength carbon dots light absorption range is narrow,which is unfavorable to be used as photosensitizer in the field of photocatalysis.Long wavelength carbon dots are excited in visible light region,with long emission wavelength,strong tissue penetration and wide spectral absorption range,which can solve these problems well.There are also some problems with long wavelength carbon dots,such as fewer methods and types of carbon dots for growing wavelength,complex synthesis,etc.The existence of these problems limits the application of long wavelength carbon dots.Therefore,there is an urgent need to develop more methods to prepare long-wavelength carbon dots to solve the problems existing in the application field of long-wavelength carbon dots.This paper mainly focuses on the preparation of long wavelength carbon dots and their applications in sensing detection and photocatalysis.The main contents are as follows:In the first chapter,several materials of carbon nanometer family are introduced firstly,then the synthesis methods and properties of carbon dots are introduced emphatically,and the luminescence mechanism of carbon dots,including quantum limiting effect,surface state,carbon nucleus state luminescence and molecular state luminescence mechanism,are also introduced.Then,the applications of fluorescent carbon dots in various fields are described,with emphasis on their applications in sensing detection and photocatalysis.At last,the research ideas of this paper are put forward aiming at some problems of carbon dots.In the second chapter,a kind of orange-emission carbon dots with long wavelength was prepared,and its maximum excitation wavelength and emission wavelength were570 nanometers and 585 nanometers respectively.The experimental results show that this kind of carbon dots can be used for selective detection of ferric iron ions,while the fluorescence quenching effect of a dozen other metal ions on orange-emission carbon dots is not obvious.Based on this,we can use orange-emission carbon dots as a probe to detect ferric ions.The correlation coefficient R² was 0.98 and the detection limit was0.169μM when the concentration of ferric iron ranged from 0 to 6μM.We systematically studied the relationship between the fluorescent carbon dots and ferric iron ions,so that the fluorescent carbon dots can be applied to the identification and detection of metal ions.In chapter 3,the preparation of red-emission carbon dots and their applications in photocatalysis are introduced.Red-emission carbon dots（R-CD_S）was used as a stable g-C₃N₄ sensitizer with wide light absorption range.The loading of R-CD_S on the surface of g-C₃N₄ makes up the deficiency of g-C₃N₄ after 460 nm,so as to improve the photocatalytic performance of composite catalysis.The effect of R-CD_S with different content on hydrogen production of g-C₃N₄ was studied by changing the concentration of synthetic carbon dots raw materials.The experimental results showed that the hydrogen production efficiency of the optimal sample CC-50:216 of R-CD_S/g-C₃N₄composite material was 7.74 mol·g^-1·h^-1,which was 2.1 times of that of g-C₃N₄.When the sample was supported by 1%Pt,the hydrogen production efficiency of the composite catalyst 1%Pt CC-50:216 was 1870 mol·g^-1·h^-1,3.2 times that of 1%Pt g-C₃N₄.The hydrogen production mechanism of the composite catalyst was studied by fluorescence spectroscopy and electrochemical measurement.According to the experimental results,two electron transfer paths were proposed in the process of hydrogen production.These results provide a reference for the future research of long wavelength carbon dots in the field of hydrogen production.In chapter 4,two methods of preparing long wavelength fluorescent carbon dots are provided by summarizing the above work,and they are applied to sensing and detection field and photocatalysis field respectively according to their respective characteristics.Although some contributions have been made to the preparation of long-wavelength carbon dots and their applications in sensing detection and photocatalysis,there are still many problems to be solved.Follow-up work needs to continue to study these issues,so as to deepen the understanding of carbon dots,so that it can be better applied in various fields.