Influence Of Lignin Modification/Heteroatom Doping On The Performance Of Carbon Quantum Dots

With the rapid development of economy and the growth of population,the status of environment is gradually deteriorating,especially the persistent and toxic metal pollution,which has received wide attention around the world.Some metal ions,especially heavy metal ions,pose a great threat to the environment and people’s health.Rapid and effective detection methods are urgently needed.Fluorescent carbon material,a kind of fluorescence probe,overcomes some shortcomings of traditional organic fluorescent materials and semiconductor quantum dots.It exhibits many advantages,such as excellent optical properties,small dimensional properties,easy surface functionalization,and good biocompatibility,which make it has good application potential in the fields of environmental detection,biochemical sensing,imaging analysis and drug carriers.Among all the fluorescent carbon materials,carbon quantum dots are research hotspot due to their controllable structure and adjustable luminescence.Although a lot of research has been taken and great progress has been made on fluorescent carbon quantum dots these years,there are still many problems that cannot be effectively solved.For example,how to improve the optical properties of carbon quantum dots by simple methods,there is no accurate explanation of the luminescence mechanism of carbon quantum dots,and how to improve the selectivity of the carbon quantum dots,et al.Therefore,it has both theoretical and practical significance to improve the optical properties of carbon quantum dots by a simple,green method and to explore the large scale preparation methods for the application of fluorescent carbon materials.In this paper,based on the high value utilization of biomass resources and the improvement of the optical properties of carbon quantum dots,we work on the following aspects:（1）Used byproducts of the the pulp and paper industry（lignosulfonate）and graphene quantum dot to prepare the fluorescent composite,the two complementary advantages,which made the fluorescent probe materials with excellent fluorescence luminescence properties and selective recognition of metal ions at same time;（2）Investigated the structure changes of lignin on the optical properties and selective recognition performance of composite;（3）Prepared carbon quantum dots using biomass resources by simple reaction and explored its application.The main work is as follows:1.In this chapter,fluorescent composite material with a core-shell structure was synthesized by hydrothermal reaction between sodium lignosulfonate/calcium lignosulfonate and citric acid.The structure and morphology of the two products were characterized by infrared spectroscopy and transmission electron microscopy.The optical properties of the products were analyzed by UV and fluorescence spectroscopy.The detection performance of the two composites as fluorescent probes for metal ions was analyzed.The results show that the fluorescence intensity of the two composites is much higher than that of pure graphene quantum dots,and they all show high selectivity to Fe³⁺,and have been successfully applied to the detection of Fe³⁺in water sample.The high fluorescence sensitivity of graphene quantum dot and the selective adsorption performance of lignin-based materials for metal ions make composite have better optical properties and ion selective recognition performance.The composite are easy to prepare.Among them,the limit of detection of the composite prepared by sodium lignosulfonate is lower,and the linear equation of which has better linear correlation.2.Aminated sodium lignosulphonate was prepared by Mannich reaction using sodium lignosulfonate,and then ASL/GQDs were obtained by self-assembly of aminated sodium lignosulphonate and graphene quantum dots.The structure of the product was characterized by FT-IR,TEM and other analytical methods.The fluorescence response of the composite to a series of metal ions was investigated by fluorescence spectroscopy.ASL plays two important roles in ASL/GQDs composites:passivating the surface of GQDs which leads to strong fluorescent luminescence,providing functional groups that selectively recognize Ag⁺.The fluorescence intensity of the as-prepared ASL/GQDs composites is more than three times that of the free GQDs.ASL/GQDs based fluorescent probe was applied to sensitively determine Ag⁺with a good linearity in a range from 0.005 to 500μM with a correlation coefficient of0.99.Moreovere,ASL/GQDs was also used successfully to image A549 cells with low toxicity and good biocompatible.3.The HSL/GQDs fluorescent composites were prepared by simple reaction of sodium lignin sulfonate and citric acid.The structure of the product was characterized by FT-IR and TEM.The fluorescence properties of the product were analyzed by UV spectrum and fluorescence spectrum,and the fluorescence response of the composite to a series of metal ions was analyzed.The fluorescence response of HSL/GQDs for different concentrations of Fe³⁺was further studied,and the feasibility of HSL/GQDs to the detection of Fe³⁺was also evaluated.The HSL/GQDs can be used as fluorescent probe to detect Fe³⁺.In the range of10-500μmol/L,the concentration of Fe³⁺has a linear relationship with the fluorescence intensity of HSL/GQDs.The linear equation is:F/F0=0.85112-0.00111*C(Fe³⁺),the linear correlation coefficient is 0.99.The HSL/GQDs acted as fluorescent probe also obtained good results for the detection of Fe³⁺in actual water samples.4.N,S double-doped fluorescent carbon quantum dots were prepared by one-step hydrothermal reaction using sodium lignin sulfonate as carbon source and sulfur source,and cysteine as nitrogen source and sulfur source.The product was characterized by transmission electron microscopy and ultraviolet-visible absorption spectroscopy.The recognition of carbon dots on a series of metal ions was analyzed by fluorescence spectroscopy,and the ability of carbon dots to detect Fe³⁺in water samples was investigated.Results show that carbon quantum dots can be used as fluorescent probe to detect Fe³⁺.In the range of 0.5μM–100μM,the concentration of Fe³⁺has a linear relationship with the fluorescence intensity of carbon dots.The carbon dots was also used successfully to detect Fe³⁺in actual water samples.The raw material cost of carbon dots is low,the preparation is green and simple,and accord withhe principle of green and sustainable development.5.N-doped carbon quantum dots（N-CDs）were prepared by a one-step hydrothermal pyrolysis method using N-containing biomass as carbon and nitrogen precursors.The structure of N-CDs was analyzed by XPS,Raman spectroscopy and FT-IR spectroscopy.The optical properties of N-CDs were analyzed by UV and fluorescence spectroscopy.Results show that the fluorescence intensity of the prepared N-CDs was strong under acidic conditions with high quantum yield（17%）.The prepared N-CDs exhibited good selectivity for Fe³⁺and hydrazine hydrate,and could be used as fluorescent probe to detect Fe³⁺and hydrazine hydrate.In addition,the porous carbon material obtained by activated carbonization of waste,which was obtained in the process of preparing fluorescent carbon dots,can be used as an ORR catalytic material,which is of great significance for exploring a green simple method for preparing a metal-free catalytic material ORR catalytic material.