Design of Fluorescent Probes Based on Carbon Dots and Their Applications in the Detection of Typical Pollutants

Author:Liu Yong Li

Supervisor:zhou qing xiang


Degree Year:2018





The problem of environmental pollution can not be ignored,and the pollutants in water do great harm to human health.Heavy metal ions pose serious impairment to the reproductive system,immune system and central nervous system.Nitroaromatic compounds have mutagenicity and carcinogenicity.Phenolic compounds are common environmental endocrine disruptors and have carcinogenicity,teratogenicity,mutagenicity.Therefore,it is urgent to develop some simple,rapid and high efficient methods for the detection of pollutants.Fluorescence analysis has attracted tremendous attention due to its simple equipment,easy operation,high selectivity and rapid detection.Most of the fluorescent materials are obtained from complex preparation processes and which will easily pollute the environment.Carbon dots(CDs)have gained wide applications in the determination of various pollutants owing to their advantages of easy preparation,low toxicity,excellent aqueous solubility and superior fluorescence stability.The aim of this thesis is to synthesize a series of CDs from different carbon sources and investigate their applications in the determination of typical pollutants,in which novel fluorescent probes were constructed with CDs and other materials.The research work of this thesis was as follows:Chapter 1:A review on CDs was presented.The basic properties of CDs were introduced.The preparation methods and the research progress of their applications in the fields of fluorescent probes,photocatalysis,light-emitting diodes,fluorescent inks,bioimaging and drug delivery were simple summarized.Chapter 2:CDs were synthesized from chocolate and the fluorescence intensity of the CDs under acidic condition showed a good linear relationship with pH in the range of pH 1.0-3.0 and 9.0-12.5,suggesting the CDs could be applied for the pH sensor.The fluorescence intensity of the obtained CDs under alkaline condition was effectively quenched by Pb2+.Based on this,the fluorescence probe with highly selective detection performance of Pb2+was constructed.The method had a linear range of 0.033-1.67μmol/L and the limit of detection was 12.7 nmol/L under the optimized conditions.This method was applied for Pb2+detection in real water samples and the spiked recoveries were in the range of 96.6-102.0%.Chapter 3:CDs were obtained using sodium citrate and polyacrylamide as the carbon source.The CDs were used as a fluorescence probe for the sensitive detection of Pb2+and pyrophosphate(PPi)based on the“off-on”mechanism.The fluorescence intensity of the CDs was quenched by Pb2+,and then the stronger binding force between PPi and Pb2+led to the release of Pb2+from the surface of the CDs and then the fluorescence intensity was recovered.On the basis,a novel method was established for the determination of Pb2+and PPi.Under the optimized detection conditions,the fluorescence probe had the detection ranges of Pb2+and PPi were 0.0167-1.0μmol/L and 0.67-26.7μmol/L,respectively,and the detection limits were 4.6 nmol/L and 54 nmol/L,respectively.This method had been successfully applied to the detection of Pb2+in the real water samples and PPi in the human urine.This method had the merits of simplicity,rapidity,high sensitivity,good selectivity and strong stability,which revealed that it had the great application potential for monitoring environmental and biologic samples.Chapter 4:Based on the competitive adsorption between the CDs and 2,4,6-trinitrotoluene(TNT),a novel fluorescent probe composed of the CDs and amino-functionalized magnetic nanoscale zero-valent iron was designed for the sensitive detection of TNT.It was found that the the solvent,the concentration of CDs,the magnetic material dosage,the reaction time,and pH value had great influence on the detection results.Under the optimal conditions,the probe had a good linear relationship with TNT in the concentration range of 10-2000μg/L and the detection limit of the method was as low as 2.15μg/L.In addition,the synthesized magnetic nanoscale zero-valent iron material had good reproducibility.The method had been successfully used for the detection of TNT in real water,dust and soil samples.Chapter 5:A novel fluorescent probe for sensitive detection of BPA was prepared by using the molecularly imprinted polymers capped CDs with specificity to the template molecule of BPA.In the detection process,the detection results were much affected by the probe concentration,pH value and the reaction time.Under the optimal conditions,the linear range and the detection limit of this method were 10-2000 nmol/L and 1.5nmol/L,respectively.Finally,this method had been applied for the determination of BPA in real samples with the spiked recoveries in the range of 97.2%-103.4%.Chapter 6:Another novel fluorescence probe consisted of CDs and silver nanoparticles was designed for the highly selective and sensitive determination of Hg2+.The fluorescence intensity of CDs was quenched by the inner filter effect between CDs and silver nanoparticles.The inner filter effect was weakened by the effect between Hg2+and silver nanoparticles and then the fluorescence intensity of CDs was restored.A novel method was established for detecting Hg2+based on this principle.It was found that the concentration of CDs,the concentration of silver nanoparticles,the pH value of solution and the reaction time all played important roles in the detection process.Under the optimized detection conditions,this probe exhibited good linearity for the concentration of Hg2+in the range of 0.01-2.5μmol/L,and the detection limit of this method was 3.6nmol/L.The probe had been successfully applied for sensing Hg2+in real water samples with satisfactory results.