Preparation Of Heteroatom Doped Carbon Quantum Dots And Application In Detection

Due to the excellent properties of carbon dots（CDs）such as high water solubility,controllable optical properties,easy modification,biocompatibility,and low toxicity,they have become emerging materials in carbon based nanomaterial since 2004.CDs are carbon materials with spherical structures of uniform size,and their particle size is normally smaller than 10 nm.Traditional semiconductor quantum dots also have limitations such as harsh preparation conditions and high costs.Compared with the traditional semiconductor quantum dots and organic dyes,carbon quantum dots are playing an indispensable role in leading human science and technology into the era of nanotechnology.Therefore,in order to further investigate the applications of CDs,it is necessary to explore low-cost and easily controlled synthesis approaches for CDs with high-performance.Herein,hetero atomic doped CDs were systhesised using malic acid with the help of microwave assisted technology to modify the surface functional groups of CDs.Furthermore,the CDs were applied to build an efficient fluorescence sensor that can simultaneously detect different metal ions and organic small molecules.The specific work includes the following:（1）In this work,a series of nitrogen-doped carbon dots（NCDs）were fabricated by a microwave-assistant approach with a combination of malic acid and urea as precursors.The average size of the carbon dots is 4.52 nm,and there are abundant luminescent groups such as amino and hydroxyl groups on the surface.Under the excitation of 280 nm UV light,the blue fluorescence with emission wavelength of450 nm has a fluorescence quantum yield（QY）of 9.8%.On this basis,the fluorescence properties are explained according to the changes of concentration and luminescence center.In addition,to investigate the practical application effect of carbon dots,our research group further used NCDs as fluorescence sensors to detect Fe³⁺ions and ascorbic acid（AA）in solutions.From the metal ion sensing research,Fe³⁺demonstrated significant quenching abilities on NCDs with a detection limit of1.9μmol/L,and the presence of 500μmol/L Fe³⁺has quenched around 75%of the PL intensity.More importantly,the NCDs also showed an excellent quenching response by AA through the static quenching mechanism and inner filter effect with a detection limit of 2.6μmol/L.Meanwhile,the presence of 500μmol/L AA has quenched around 85%of the PL intensity.（2）Nitrogen and fluorine co-doped carbon dots（NFCDs）were designed via a rapid,low-cost,and one-step microwave-assisted technique using DL-malic acid and levofloxacin.The NFCDs emitted intense green fluorescence under UV lighting,and the optical emission peak at 490 nm was observed upon a 280 nm excitation,with a high QY of 21.03%.Interestingly,the spectral measurements illustrated excitation-independent and concentration-independent single-color fluorescence owing to the presence of nitrogen and fluorine elements in the surface functional groups.In addition,to investigate the practical application effect of carbon dots,our research group further used NFCDs as fluorescence sensors to detect Fe³⁺ions and AA in solutions.From the metal ion sensing research,Fe³⁺demonstrated significant quenching abilities on NFCDs with a detection limit of 1.03μmol/L,the presence of300μmol/L Fe³⁺has quenched around 90%of the PL intensity.More importantly,the NFCDs also showed an excellent quenching response by AA through the static quenching mechanism and inner filter effect with a detection limit of 4.22μmol/L,the presence of 500μmol/L AA has quenched around 83.2%of the PL intensity.In conclusion,CDs with high QYs and different dopant elements were successfully prepared in this thesis.It has been found that the dopant of different atoms can change the surface groups of carbon dots.Researches have shown that dopant of different elements has significant impacts on the emission centers of carbon dots,especially with the presence of fluorine atoms,resulting in a red shift in the emission wavelength of carbon dots.In order to study the application of carbon dots using malic acid as raw material,the detection abilities of two carbon dots（NCDs and NFCDs）on metal ions and organic small molecules were investigated.The results showed that malic acid derived carbon dots had high sensitivity and selectivity for Fe³⁺and ascorbic acid,and the doping of fluorine atoms greatly improved the detection effect.