Study On The Optical Properties Of Carbon Quantum Dots Doped With Non-Metal Elements

In recent years,carbon quantum dots(CQDs)have been favored by researchers because of their easy synthesis and preparation with excellent chemical properties.Compared with toxic heavy metals and semiconductor quantum dots,CQDs offer outstanding advantages,such as good biocompatibility,easy preparation,unique optical and chemical properties,low toxicity and excellent photostability.However,most of CQDs currently have the defects of single color and low quantum yield(QY),which severely limits their wide application and these problems need to be addressed urgently.The results of related experimental studies show that doping with different elements is an effective method to regulate the optical properties of CQDs,and doping with different elements can not only modulate the optical properties of CQDs to change the luminescence wavelength of their fluorescence;it can also adjust the electronic structure of CQDs by producing n-type or p-type carriers.Therefore,the fluorescence intensity and the position of the emission wavelength of the CQDs can be changed by certain specific doping and changing the kind of doped element.In this paper,different non-metal doped CQDs were synthesized using the same carbon source,and the effects of single-atom doping and double-atom co-doping on the fluorescence properties of CQDs were investigated by comparing the electronegativity and atomic radius of non-metallic elements,and the application of doped CQDs in the detection of food additives has been realized.The main research contents are as follows:1.The chemical structure,quantum size and photoluminescence properties of CQDs depend on the chemical structure of the feedstock and the preparation method used.Among the currently reported methods for the synthesis of CQDs,the hydrothermal method is simple,low cost and high efficiency.In this experiment,different non-metal doped CQDs including:N-CQDs,P-CQDs,S-CQDs,Cl-CQDs,F-CQDs were synthesized by hydrothermal method using maltose as carbon source and characterized by ultraviolet and fluorescence,the results of its study showed that: the emission wavelength of single-atom-doped carbon quantum dots is related to the atomic radius,electronegativity and extranuclear electron arrangement of the element.For the same period elements,when the atomic radius are similar,the electronegativity is the main factor affecting the optical properties of CQDs.When the difference of atomic radius is large,the external electron arrangement and electronegativity will affect the optical properties of CQDs,but the atomic radius and off nuclear electron arrangement outside the nucleus become the main factors affecting the optical properties of CQDs.2.Nitrogen is a typical dopant with 5 valence electrons,and its atomic radius is equivalent to the atomic radius of carbon atoms in carbon quantum dots,so doping nitrogen atoms in carbon quantum dots can change their internal electronic environment and the electron density of CQDs,thus effectively improving their fluorescence properties.In this experiment,different nonmetal co-doped carbon quantum dots nitrogen-phosphorus,nitrogen-sulfur,nitrogen-chloride and nitrogen-fluorine doped carbon quantum dots(N-P-CQDs,N-S-CQDs,N-Cl-CQDs and N-F-CQDS)were synthesized using the maltose,ethylenediamine and other inorganic acid as raw materials.Compared with single-atom doped carbon quantum dots,diatomic doped carbon dots not only redshifts the emission wavelength of CQDs,but also improved the quantum yield of CQDs.3.The nitrogen-chlorine co-doped quantum dots(N-Cl-CQDs)synthesized in the previous work were used as fluorescence sensor,In addition,based on the fluorescence internal filtering effect(IFE),N-Cl-CQDs was successfully used as fluorescence sensor for the first time in the detection of tartrazine.The results showed that the fluorescence quenching efficiency of N-Cl-CQDs was related to the concentration of tartrazine in the range of 1.6-60μM,and the detection limit(LOD)was as low as 0.094 μM.The probe has been successfully applied to the detection of tartrazine in orange juice and is expected to be extended to the food industry.