The Preparation And Characterization Of Graphene Quantum Dots-ionic Liquid Composites And Their Application For Detection Of Some Anions

Some anions have harm to the ecological environment and human health.Detection of anions is important in fields of environmental monitoring and food quality control.Development of simple,direct and accurate detection method for anions is important.Rapid,sensitive analysis fluorescent sensor is a hot spot in current research.As new fluorescent carbon materials,zero-dimensional graphene quantum dots(GQDs)are graphene sheets with a thickness of less than 10 nm and size of less than 100 nm.Graphene quantum dots have many excellent properties including simple synthesis,low toxicity and stable luminescence properties.Developing new approach to prepare GQDs-based composite materials and expanding the application for direct detection of anions are of great significance.In this thesis,we selected two ionic liquids as the modifier to prepare graphene quantum dots-ionic liquids composite materials.The preparation and characterization of the composite materials and their application for direct detection of two anions were investigated.The main research results are given as follows:(1)A simple method for the preparation of graphene quantum dots was established and the performance of GQDs was characterized.Briefly,1,3,6-trinitropyrene was used as carbon source.NaOH soultion were applied as supporting solution in hydrothermal treatment to form hydroxyl-rich graphene quantum dots.The synthesized GQDs was characterized by transmission electron microscopy(TEM),x-ray photoelectron spectroscopy analyzer(XPS),atomic force microscopy(AFM),fourier transform infrared spectroscopy(FTIR)and fluorescence spectra(FL spectrum).Results showed that the as-prepared GQDs particle exhibited narrow size distribution.The range of particle size was 2~3 nm.The thickness was 2.8 nm,demonstracting about 3-5 layers' thickness of graphene.GQDs exhibited excitation-independent photoluminescence behaviors and emited green fluorescence under the irradiation of ultraviolet lamp(365 nm).The maximum excitation wavelength was 470 nm and the maximum emission wavelength was 512 nm.Quantum yield of GQDs was 12.1% calculated by using Rhodamine B as standard fluorescent reagents.(2)A simple method for the preparation of graphene quantum dots and ionic liquid(1-Butyl-3-methyl imidazolium tetrafluoroborate,BMIMBF4)compounds was established.The application for Fe(CN)63-detection was investigated.Under the ultrasonic treatment,BMIMBF4 could easily combine with GQDs to form composites due to ?-? or cation-? interactions.Under optimal conditions,the synthesized BMIMBF4-GQDs composites were characterized by TEM,XPS,AFM,FTIR and FL spectrum.The structure characterization indicated the effcient combination between GQDs and BMIMBF4.Results also showed that the fluorescence and size of GQDs did not obviously change after combined with BMIMBF4.The selectivity of the BMIMBF4-GQDs for different anions was investigated.Results showed that Fe(CN)63-can quench the fluorescence of BMIMBF4-GQDs.Based on such phenomenon,fluorescent detection of Fe(CN)63-was developed.Under the optimum condition,the linear range for the detection of Fe(CN)63-was 0.1 ?M-2.5 mM and the detection limit was 0.04 ?M.(3)A simple method for the preparation of graphene quantum dots and ionic liquid(1-butyl-3-methylimidazolium hexafluorophosphate,BMIMF6)composite was established.The morphology,structure and composition of BMIMPF6-GQDs composites were characterized by various characterization methods.The efficient combination between BMIMPF6 and GQDs was established.After combined with BMIMBF6,the size and fluorescence of GQDs did not obviously change.Furthermore,we investigated the selectivity of the composites for different anions.BMIMPF6-GQDs have a good response towards S2-.Thus the method for fluorescent detection of S2-was established.The linear range for the detection of S2-was 0.01 ?M-0.3 mM and the detection limit was 0.008 ?M.