The Preparation And Application Of Novel Carbon-based Fluorescent Nanomaterials

Fluorescent materials are important in the field of lighting,bio-chemical sensing,biological diagnosis and treatment,catalysis,anti-counterfeiting and others.With the speedy development of technology and the escalation of our living standards,the demand for new fluorescent materials is constantly rising.As a kind of environment-friendly materials,fluorescent carbon nanodots(CNDs)as a member of the family of fluorescent carbon-based nanomaterials have been developing rapidly in recent years.Those materials show unique advantages such as good biocompatibility and easy modification comparing with their inorganic counterparts.While comparing with small molecule organic dyes,they show excellent stability.Till now,numerous routes including hydrothermal methods have been developed for the preparation of CNDs,which is one of the most popular topic of this field.However,although a wide variety of CNDs with diverse properties have been reported,there is still much room for further improvement in the preparation process and the yield of preparation.CNDs with high fluorescence quantum yield or solid fluorescence properties are still limited.Therefore,it is of great significance to develop methods for the rapid and large-scale preparation of CNDs with good performance.Therefore,this thesis focuses on the preparation and application of CNDs with new starting raw materials and synthesis processes.Firstly,a simple method was established to extract large amount of CNDs from a cheap food colorant,and the obtained CNDs were applied as a fluorescent sensor.Then,synthetic ways of CNDs with high quantum yield was explored and the main factors that influenced the quantum yield were discussed.The CNDs were used for multicolor cell imaging and fluorescent sensing.Finally,a solvent-free thermal method was developed for rapid and large-scale preparation of polymer dots with various properties.This thesis contains five chapters.Chapter 1:The concepts and classification of fluorescent carbon-based nanomaterials were introduced briefly.The research progress of carbon nanodots was summarized based on their structure,properties,applications and synthesis.Chapter 2:Blue fluorescent components with high yield(about 60%,w/w)were isolated from commercial caramel by dialysis and used for simultaneous detection of three nitrophenols.Through adequate dialysis of caramel,two kinds of materials with significant difference in optical properties were obtained:the retentate with high molecular weight exhibited brown-black color but it is barely fluorescent;the light brown-yellow dialysate with low molecular weight displayed strong blue fluorescence.Based on a series of characterizations and related literatures,we speculated that the fluorescence of the isolated components originated from moderate crosslinking and random aggregation of oligomers from dehydration of carbohydrate units.The fluorescent components highly match CNDs in terms of morphology,fluorescence behavior and the origin of fluorescence.The components were used as a fluorescent probe for simultaneous detection of TNP,DNP and 4-NP in water and soil samples based on their different responses at different pHs.LODs of 0.09,0.14 and 0.23?M forTNP,DNP and 4-NP were obtained at pH 8.0.Chapter 3:There are two sections in this chapter.In the first section,we used formaldehyde and isophoronediamine(IPDA)as raw materials to prepare highly fluorescent cationic CNDs by the hydrothermal method,and then studied the main factors affecting quantum yield of the prepared CNDs.The pH of the reaction solution,the substituent groups of in the reactant of aldehyde are the key factors affecting fluorescence intensity.With the aid of liquid-liquid extraction,water dissoluble and organic solvent dissoluble portions,W-PNPs and O-PNPs were obtained,which are different in some extent in the optical properties.The absolute quantum yield of O-PNPs and W-PNPs is 61%and 32%,respectively.The possible reasons for the difference of the absolute quantum yield between O-PNPs and W-PNPs were studied through a series of structural characterizations.In addition,the cationic W-PNPs were used as a probe for fluorescence enhancement detection of heparin with an LOD of 18ng/mL.The strong electrostatic attraction between the highly negative-charged heparin and cationic W-PNPs rich of R_xH_4-xN⁺makes the heparin wrapped around the surface of W-PNPs and led to enhanced fluorescence.Based on this,a sensitive and specific method for the detection of heparin in diluted human serum was established.Finally,O-PNPs and W-PNPs were successfully used for multicolor imaging of HeLa cells.In the second section,based on the fact that the fluorescence of W-PNPs can be quenched by nitrite under acidic condition,a rapid detection method for nitrite was established with an LOD of 7 nM.Through capillary electrophoresis with a laser induced fluorescence(LIF)detector,W-PNPs were separated and the interaction between W-PNPs and nitrite was investigated.The results showed that W-PNPs had multiple peaks and nitrite could permanently quench some of components of W-PNPs.Furthermore,this fluorescent probe was applied to the detection of nitrite in sausage and real-time monitoring of nitrogen dioxide in the atmosphere.Chapter 4:CNDs with solid-state fluorescence property were prepared in large scale by solvent-free thermal method using polymeric microsphere formed from formaldehyde and IPDA as raw materials.The CNDs(S-PNPs,yield=90%)were prepared by heating polymer microspheres at 200°C for 30 minutes with a small amount of sulfuric acid.A white LED with good luminescent efficiency was constructed by combining the yellow fluorescence S-PNPs with the blue chip.The polymer wires with bright yellow fluorescence were prepared by melt blending and hot extrusion of S-PNPs powder and cycloolefin copolymer(COC)pellets.The composite fluorescent polymer wires exhibited good acid,alkali and light bleaching resistance.Various fluorescent small models have been 3D-printed using the polymer wires as 3D printing materials.Chapter 5:Functional carbon nanodots(PDs)were rapidly prepared by solvent-free thermal method with polyacrylic acid and thiourea as raw materials in the presence of a small amount of phosphoric acid.The PDs showed blue-purple fluorescence with a relative QY of 33.3%.The PDs displayed two independent fluorescence centers and have different response to Hg²⁺and MeHg⁺.Based on this fact,a ratiometric fluorescent probe was constructed by using synchronous fluorescence scanning for accurate and sensitive detection of these two mercury species.LODs of 6 nM and 390 nM were obtained.