Study On Preparation And Properties Of Doped Carbon Quantum Dots Based On Lignin And Ammonium Ferric Citrate

Carbon quantum dots?CQDs?are a new type of carbon materials with size below 10 nm.CQDs have many advantages,such as low toxicity,good biocompatibility,excellent photoluminescence performance and easy dispersion.They have broad prospects in applications such as ion detection,bioimaging,drug transportation and so on.Biomass resources have the characteristics of wide source,renewable and non-toxic.Using biomass materials as carbon source to prepare carbon quantum dots can effectively utilize cheap carbon sources,reduce production costs,simplify the synthesis process,and also provide an effective and high-value utilization way for waste biomass resources.In this paper,carbon quantum dots with excellent fluorescence properties were fabricated by acid oxidation method and hydrothermal method respectively,using alkali lignin,sodium lignosulfonate and ammonium ferric citrate as carbon sources.They were used in ion detection and biomolecule detection by fluorescence and colorimetry.Specific content as follows:In the first part of the thesis,lignin-based carbon quantum dots?LCQDs?were prepared by strong acid oxidation using alkali lignin as carbon source.The synthesis conditions were optimized.Under the optimum conditions,the fluorescence quantum yield of LCQDs was 17.3%by using quinoline sulfate as the reference material.The fluorescence analysis of LCQDs showed that Fe³⁺could quench the fluorescence of LCQDs,but the fluorescence intensity gradually recovered after adding ascorbic acid?AA?.Based on this phenomenon,an effective fluorescence-based"turn-off-on"highly sensitive selective chemical sensor was constructed for the detection of Fe³⁺and AA,and the corresponding fluorescence mechanism was explored.In the second part,sulfur-doped carbon quantum dots?S-CQDs?with photoluminescent properties were prepared from sodium lignosulfonate by a green and simple method.The results of transmission electron microscopy and particle size analysis show that the average particle size of S-CQDs is 9 nm and its dispersion is uniform.The fluorescence quantum yield of S-CQDs is 10.29%by using the reference method.The results of fluorescence analysis show that S-CQDs have the characteristics of fluorescence emission depending on the excitation wavelength.S-CQDs has a specific recognition effect on Fe³⁺when the solution p H=2.After analysis,the detection range of S-CQDs for detecting Fe³⁺is 0?1500?M,and the limit of detection?LOD?is 0.7?M.Therefore,S-CQDs can be used to construct fluorescent sensor for trace detection of Fe³⁺.In the third part,nitrogen and iron co-doped carbon quantum dots?N,Fe-CQDs?were synthesized by one-step hydrothermal synthesis using ammonium ferric citrate as carbon source and urea as nitrogen source.The fluorescence properties of N,Fe-CQDs were significantly improved by adding urea,and the fluorescence quantum yield was up to 30.57%.Transmission electron microscopy and laser particle size analysis show that N,Fe-CQDs are spherical and uniformly distributed,and their particle size is about 3 nm.Fluorescence analysis shows that N,Fe-CQDs have a specific recognition effect on Fe³⁺and Fe³⁺can effectively quench the fluorescence of N,Fe-CQDs.According to this phenomenon,a sensor based on fluorescence/colorimetric two-mode method was constructed to detect Fe³⁺concentration.