Preparation And Applications Of Carbon Dots From Biomass Materials

Carbon dots(CDs),as a new type of photoluminescent carbon nanomaterials,have the advantages of good biocompatibility,high stability,high specific surface area and so on.Biomass is a green and renewable carbon resource for preparing CDs because it is rich in C,N,S,P elements.Most of CDs from biomass are synthesized by hydrothermal method which had the limitation of lower quantum efficiency and optical stability.In this paper,Heteroatom doped CDs were simply and efficiently prepared through the self-exothermic reaction using biomass as carbon source,and the obtained CDs were applied to the analytical applications for food and environmental samples.The main contents of this paper are as follows:(1)Nitrogen doped CDs(N-CDs)were successfully prepared by one-step hydrothermal method using bread fermented beverage as carbon source and ethanediamine as dopant.The fluorescence emission peak of N-CDs was in the blue region(Em 440 nm)with a fluorescence quantum yield of 26.3%.It was found that tartrazine(TAR)had obvious fluorescence quenching effect on N-CDs.The characteristic absorption of TAR at 430 nm overlaps with the fluorescence emission peak of N-CDs,and the fluorescence lifetime of N-CDs does not change significantly before and after mixing TAR,which indicates that the fluorescence quenching mechanism of TAR on N-CDs is Inner filter effect(IFE).Based on IFE mechanism,a new analytical method for TAR with high sensitivity and high selectivity was established.Under the optimized experimental conditions,the detection limit(3σ)of the method is 90 n M,the relative standard deviation(RSD)is 3.9%(C =10 μM,n=7),and the linear range is 0.5-30 μM.The method has been successfully applied to the determination of trace TAR in food samples.(2)Nitrogen doped CDs(N-CDs)were prepared quickly and efficiently through self-exothermic reaction between nitric acid and diethylenetriamine(DTA)using locust powder as carbon source.The N-CDs were purified by an activated carbon adsorption procedure,and the average particle size of purified N-CDs was 2.8 nm,the optimal excitation wavelength was 390 nm,and the emission peak was 470 nm.The characteristic absorption of p-NP at 400 nm overlaps well with the fluorescence excitation spectra of N-CDs,so that p-NP has obvious IFE on N-CDs,and the absorption peaks of other nitrobenzene compounds almost do not overlap with the fluorescence excitation spectra(or emission spectra)of N-CDs,so that no IFE is generated.Based on IFE mechanism,a new analytical method for the determination of p-NP with high sensitivity and high selectivity was established.Under optimized experimental conditions,the detection limit(3σ)of the method is 0.13 μM,the relative standard deviation(RSD)is 4.09%(C =10 μM,n=9),and the linear range is0.5-80 μM.The developed method has been successfully applied to the analysis of trace p-NP in environmental water samples.(3)Nitrogen and sulfur co-doped CDs(N,S-CDs)were prepared quickly and efficiently through self-exothermic reaction between nitric acid and ethanediamine using maltose as carbon source.The average particle size of the prepared N,S-CDs was 7.3 nm,the optimal excitation wavelength was 400 nm,and the emission peak was 470 nm after a purification procedure with activated carbon.Because the characteristic absorption of Methylorange(MO)at 460 nm overlapped greatly with the fluorescence emission spectra of N,S-CDs,MO had obvious fluorescence quenching effect on N,S-CDs by dynamic quenching.It was found that when BAC was added to the N,S-CDs-MO system,the ion association complex between BAC and MO was formed,which destroyed the interaction between N,S-CDs and MO,and thus the fluorescence of N,S-CDs was restored.Based on fluorescence quenching-recovery mechanism,a new method for the determination of BAC with high sensitivity and selectivity was developed.Under optimized experimental conditions,the detection limit(3σ)of the method is 2 n M,the relative standard deviation(RSD)is 5.97%(C =10 μM,n=13),and the linear range is 0.5-50 μM.The developed method was successfully applied to the analysis of BAC in personal care samples.