Hydrothermal Synthesis Of Carbon Quantum Dots For Picric Acid Recognition And Free Radical Scavenging

Carbon quantum dots(CQDs),as a kind of nano-materials,have attracted a lot of attention in recent years.There were many reports about the synthesis and applications of CQDs.In this paper,CQDs were prepared by hydrothermal method and used for the detection of picric acid and free radicals scavenging.The main contents were summarized as follows:(1)N-CQDs were prepared by hydrothermal method using ascorbic acid and valine as materials.The morphology and surface functional groups of N-CQDs were analyzed by TEM,FTIR and XPS.The results showed that the average diameter of N-CQDs was 4 nm,and there were various functional groups on the surface of N-CQDs,such as-COOH?-OH?C=O and-CONH-.The existence of O-rich groups improved the solubility and dispersion of N-CQDs in aqueous solution.In addition,N-CQDs had an absorption peak at 272 nm,and a strong emission peak at 430 nm was observed when we excited the as-synthesised N-CQDs solution at 352 nm.We also found that the fluorescence of the N-CQDs was intensively quenched by the addition of picric acid(PA)based on the fluorescence resonance energy transfer between PA and N-CQDs.The decrease of the fluorescence intensity made it possible to determine PA in the linear range of 0.06-7.81 ?g/ml and the detection limit was as low as 11.46 ng/ml.The proposed approach was further successfully applied for the determination of PA in water sample collected from Fenhe river for public safety and security,suggesting its great potential towards water routine analysis.(2)CQDs were synthesized by hydrothermal method using oat,green tea,spinach,broccoli,grape seed,tomato,walnut and strawberry as materials.The morphologies and surface functional groups of all the CQDs were analyzed by TEM and FTIR,respectively.It was found that the average diameter of most CQDs were between 2-3 nm,and the average diameter of a few CQDs were between 3-6 nm.In addition,all CQDs had functional groups such as-COOH,C=O and-OH.The UV-vis absorption spectra showed that each CQDs had an absorption peak between 270 nm and 285 nm.There was no CQDs had absorption after 500 nm,which also eliminated the background absorption of CQDs at 515 nm for DPPH free radical scavenging experiments.The scavenging effects of each kind of CQDs and ascorbic acid onDPPH free radical were investigated.It was found that the scavenging ability of each kind of CQDs to DPPH free radical was different,and the scavenging ability of CQDs prepared by green tea was comparable to that of ascorbic acid.(3)Hydroxyl free radicals were produced by Fenton reaction,than the scavenging effects of each kind of CQDs and ascorbic acid on hydroxyl free radicals were investigated.By comparing the EC50 of each kind of CQDs and ascorbic acid,we found that the scavenging ability of CQDs prepared by grape seed was comparable to that of ascorbic acid.Besides,the scavenging abilities of CQDs synthesized by oat,green tea,spinach,broccoli,grape seed,tomato,walnut and strawberry were better than that reported in the literature.