Preparation Of Silicon-nitrogen Doped CQDs And Their Detection Of Cr(?) In Water

In recent decades,hexavalent chromium(Cr(?))pollution has intensified along with the rapid development of modern industry.Carbon quantum dots(CQDs)have attracted attention as a new type of fluorescent probes,but it is difficult to obtain high quantum yield and wide response range.Therefore,it is of great significance to develop heteroatom-doped and surface-modified CQDs as fluorescent probes for the detection of Cr(?).In this paper,Cr(?)was used as the target detection object,and silicon and nitrogen were doped in CQDs as heteroatoms,which greatly improved the quantum yield of CQDs.The detection of Cr(?)in water was realized by specific fluorescence quenching of Silicon and nitrogen co-doped CQDs(Si,N-CQDs)and Cr(?).Surface modification of Si,N-CQDs increases the sensitivity of Si,N-CQDs to Cr(?)detection.Firstly,Si,N-CQDs were prepared by one-step hydrothermal method.The optical stability,structure and properties of the prepared Si,N-CQDs fluorescent probe were investigated,and the quenching mechanism was analyzed.The results show that the best excitation wavelength of Si,N-CQDs is 355nm,the best emission wavelength is 464nm,and the Si,N-CQDs emit blue fluorescence under ultraviolet light.Si,N-CQDs have high quantum yield(QY=75%)and good photostability and dispersion of aqueous solution.The response of Si,N-CQDs to Cr(?)detection ranged from 0 to 75?M(R~2=0.9931),and the detection limit was 0.995?M.When Cr(?)concentration was 500?M,the quenching rate was more than 80%.The mechanism of Cr(?)detection was also discussed,and the quenching mechanism was verified as F(?)rster resonance energy transfer.In order to further increase the sensitivity of Cr(?)detection,broaden the response range of Cr(?)detection and reduce the detection limit of Cr(?)detection,Si,N-CQDs fluorescence probes were optimized.PEG400 passivated Si,N-CQDs(P-CQDs)were prepared by surface modification of Si,N-CQDs using PEG400passivated Si,N-CQDs,and more sensitive detection ability and lower detection limit were obtained.The best excitation wavelength and emission wavelength of the prepared P-CQDs are 335nm and 420nm respectively,and they emit bright blue fluorescence under ultraviolet light.P-CQDs has higher quantum yield(QY=77%)and better optical stability.The response range of P-CQDs to Cr(?)is 0-200?M(R~2=0.9962),and the detection limit is 0.089?M.When Cr(?)concentration is 200?M,the quenching rate is over 80%.The mechanism of P-CQDs broadening the detection range of Cr(?)is discussed.In conclusion,the effects of silicon,nitrogen element doping and PEG400 surface modification on improving the quantum yield of CQDs,broadening the response range and reducing the detection limit were investigated,and provides a theoretical basis for the feasibility of rapid on-site detection of Cr(?)in water.