Preparation Of Heteroatom-doped Carbon Dots And Their Sensing Research On Metal Ions

As the new star of carbon family,carbon dots(CDs)are a new zero-dimensional carbon nanomaterials with a dimension less than 10 nm.The CDs have exhibited wide application potentical in virous fields such as biological imaging,sensing and drug delivery because of the low toxicity,excellent water solubility and biological compatibility,and outstanding photobleaching resistence.Heavy metal pollution has endowed great threat with environment safe and human health,so the research on heavy metal detection technology is attracting more and more attention.CDs possess advantages of good watersolubility,excellent light stability,facile green synthesis,and easy modification,which make them have large research value in rapid qualitative and quantitative detection of heavy metal ions in aqueous samples.In this paper,different carbon sources and synthetic methods were used to prepare fluorescent CDs with outstanding properties.Two CDs-based fluorescent sensors were constructed to realize the selectively fluorescent detection of specific metal ions.(1)The N-doped CDs,emitting blue fluorescence under 365 nm irradiation of UV lamp,were synthesized by pyrolyzing the carbon source of ethanolamine and modifier of ionic liquid(1-carboxyethyl-3-methylimidazole chloride).The charaterization resluts(TEM,XPS,TGA,etc.)indicated that the synthesized CDs with particle size of 7.8 nm and quantum yield of 17.93%were abundant in surface groups such as amide and hydroxyl.Hence,the CDs displayed good water solubility.Based on the quenching effect of Cr6+ on the fluorescence of CDs,the sensor towards Cr6+ was designed.Two good linear relationships between the concentration of Cr6+ ion and the fluorescence quenching efficiency of CDs were obtained in the ranges from 0.2-2 and 2-40 μM,and the limits of detection(LOD)were calculated as 0.018 and 0.25 μM,respectively.This sensor also could realize the fluorescence detection of Cr6+ in tap water samples with detection ranges of 0.2-2 and 2-60 μM,LOD of 0.048 and 0.40μM,and recoveries of 102.1-106%.(2)The N/S-codoped CDs,emitting blue fluorescence under 365 nm irradiation of UV lamp,were prepared by hydrothermal treating carbons source of glucose acid and dopant of dithiooxamide.The preparation conditions were also simply optimized based on the yield and quantum yield.A lot of characterization means were used to analyze structure and property of the synthesized CDs.The results demonstrated that the CDs with a particle size of about 3.42 nm were capped by abundant amide and hydroxyl groups.Both of the Hg2+ and Pb2+ could quench the fluorescence of CDs.Considering the Pb2+ and P2O74-can form[Pb(P207)2]6_with ultrahigh stability,the seletivc detection of Hg2+ can relized when the P2O74-was used to shelter Pb2+.A good linear relationship between the concentration of Hg2+ and fluorescence quenching efficiency of CDs was obtained in the range from 0-20 μM,the LOD was calculated as 0.338 μM.For detection of Hg2+ in tap water,the detection range and LOD were 0-50 μM and 0.981 μM,respectively.Similarly,the selective detection of Pb2+ was realized when the Hg2 was sheltered by I-.Two good linear relationships between the concentration of Pb2+ ion and the fluorescence quenching efficiency of CDs were obtained in the ranges from 0-1 and 1-25 μM,and the limits of detection(LOD)were calculated as 0.109 and 0.781 μM,respectively.For detection of Pb2+ in tap water,the two detection ranges were 0-1 and 1-30μM,and the corresponding LOD were 0.144 and 0.697 μM,respectively.