Preparation Of Doped Carbon Dots And Detection Of Organic Small Molecules And Ions In Environmental Water

Carbon dot（CDs）has been regarded as a green substitute for traditional quantum dots since its discovery because of its excellent photoluminescence（PL）and high biocompatibility.CDs is one of the emerging carbon nanomaterials with low cost and low toxicity.New carbon dots can be prepared by a simple synthesis route,and the fluorescence properties of CDs can be easily functionalized by heteroatomic doping.Based on the fluorescence advantage of CDs,CDs has been used as nanomaterials in various fields such as sensing and imaging.In the field of environmental detection and analysis,pollution of heavy metal ions and antibiotics is still a major problem faced by human beings.At present,the sensitive detection technologies mainly include high performance liquid chromatography,mass spectrometry and fluorescence sensing.Compared with fluorescence sensing method,other methods have disadvantages such as complex operation,heavy instrument and long time consuming in the detection process,so further research should be done on using CDs as fluorescence sensing method for environmental detection and analysis.In this paper,a variety of co-doped carbon dots were prepared based on heteroatomic doping to regulate the fluorescence performance of CDs,which were successfully used as fluorescence sensors to detect a variety of targets in environmental water.The fluorescence sensing mechanism of carbon dot materials was investigated by the morphology and structure characterization and fluorescence properties analysis.The main contents include:（1）Study of N/S Co-doped Carbon Dots as Fluorescence Sensors for NOR DetectionIn this study,nitrogen and sulfur co-doped carbon dots（N,S-CDs）were synthesized by direct pyrolysis using ammonium citrate（AC）and L-cysteine（L-Csy）as precursors,which were sensitive and convenient to detect Norfloxacin（NOR）as efficient fluorescent probes.The maximum emission wavelength of N,S-CDs is 450nm at the excitation wavelength of 350 nm.Due to the strong hydrogen bond interaction and charge transfer between NOR and N,S-CDs,the fluorescence of N,S-CDs is significantly enhanced in the presence of NOR.N,S-CDs were characterized by transmission electron microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）,Fourier transform infrared spectroscopy（FT-IR）,UV-vis and fluorescence spectroscopy.N,S-CDs responded to NOR in the concentration range of0.5-50μM and showed a linear change with a detection limit of 0.5μM,indicating that N,S-CDs can detect NOR rapidly,stably and sensitively.The recoveries of NOR in lake water and tap water are 92-99.2%and 90.0-104%,respectively.The successful application of actual water samples opens up a new way for the determination of NOR.（2）Nitrogen and Copper（Ⅱ）Co-doped Carbon Dots as Multi-functional Fluorescent Probes for Fe³⁺Ions and TetracyclineThis paper synthesis carbon dots（Cu-NCDs）with nitrogen and copper co-doped,which can be used as a sensor for measurement of heavy metals such as Fe³⁺and tetracycline（TC）.The particle sizes of two kinds of CDs and Cu-NCDs were determined respectively as average 3.9 nm and 4.8 nm,and both exhibited a strong fluorescence emission peak at 450 nm.The presence of carbon,oxygen,and nitrogen atoms and Cu doping is confirmed in the structure of Cu-NCDs.The doping of Cu and N makes the surface of Cu-NCDs positively charged,which enhances the fluorescence intensity.Cu-NCDs can be used as multi-functional fluorescent probes to selectively detect Fe³⁺and TC based on fluorescence quenching.The limit of detection of Fe³⁺and TC separately was found as 1.189μM and 0.416μM.This probe is also suitable for the indirect determination of Fe²⁺because the Fe²⁺is oxidated to Fe³⁺by H₂O₂.The mechanisms of the quenching process were explored that is the complex process of dynamic quenching and static quenching based on internal filtration effect（IFE）,respectively.Actual sample tests were performed with tap and lake water samples showed that Cu-NCDs could be used efficiently for practical applications.（3）Detection of Cr（Ⅵ）by Co/N Co-doped Carbon Dots as Fluorescence SensorsIn this paper,a novel co-doped carbon point（Co-NCDs）has been prepared and successfully applied to the sensing of Cr（Ⅵ）ions on the basis of photoluminescence quenching.The structure of the prepared Co-NCDs was characterized by TEM,FT-IR and XPS.The optical properties of the prepared Co-NCDs were investigated by UV absorption spectrum and fluorescence spectrum.Combined with the comparison of fluorescence lifetime and absorption spectrum,the fluorescence sensing mechanism of Co-NCDs is fully explained.In the presence of Cr（Ⅵ）ion,the fluorescence quenching of Co-NCDs is due to the internal filtration effect（IFE）.In the range of5-380μM（R²=0.999）and 380-1000μM（R²=0.997）,there were two good linear relationships between the concentration of Cr（Ⅵ）and the fluorescence intensity of Co-NCDs,and the detection line（LOD）was 0.121μM.It is important that this method can detect Cr（Ⅵ）ions in tap water and lake water rapidly,and construct a rapid,accurate and stable fluorescence sensing platform.