The Synthesis Of Fluorescent Carbon Dots By Hydrothermal Oxidation Method And Fluorescence Quenching To Detect Trace Arsenic In The Environmental Samples

With the development of the era and the advance of science, human cognition is becoming more and more wider. At the end of the 20th century, nanotechnology is developing gradually as a new kind of science and technology. With the development of nano science, nano-materials on carbon elements have been discovered constantly, such as, carbon nano-fibers, graphene, carbon nanotubes, nano diamond, etc. Carbon quantum dots have become a new member of the carbon nano-material family as a new type of fluorescent nano-materials.Quantum dot is a zero dimensional semiconductor nanocrystals, it is approximate sphere and its diameter is about 1～12nm. Due to the small size of quantum dots, Quantum dots have surface effect, volume effect, dielectric confined effect, quantum size effect, macroscopic quantum tunneling effect, wide absorption spectrum, narrow emission spectrum, and large stokes shift etc excellent optical performance. There are more and more people beginning to pay close attention to the quantum dots. But the metallic quantum dots are generally toxic, and harmful to living cells, which are limited greatly its application.Compared with other metallic quantum dots, carbon quantum dots fluorescence is stable, no light flashing, regulated emission wavelength and excitation wavelength, small molecular weight and particle size, good biological compatibility and low toxicity etc advantages, so carbon quantum dots gradually replace metal quantum dots in many ways. Carbon quantum dots has wide application prospect, which has attracted a large number of researchers to study carbon quantum dots.At this stage, preparation and application of carbon quantum dots is still in its initial stage, the fluorescence rate of carbon quantum dots is still very low, the solubility difference is big, which far cannot satisfy the market demand. This paper mainly spreads out from the following several aspects, respectively discusses the synthesis, characterization and application of carbon dots.1、The experiment admixes fluorescent carbon dots by the hydrothermal method with activated carbon as carbon source, nitric acid and hydrogen peroxide as mixed oxidants. At the same time,it inspects influence of activated carbon particle size, reaction time and dosage of nitric acid and hydrogen peroxide on the synthesis of carbon dots. Getting the optimal condition parameters by experiment; the activated carbon particle size is 400 mesh, the reaction time is 13 h, the ratio of activated carbon with nitric acid dosage of volume is 1:3; the dosage of hydrogen peroxide is 25mL, and adding hydrogen peroxide in batches. At the same time, the experiment modifies carbon quantum dots of admixing under the optimization condition, the experiment get the optimal conditions of modifying carbon dots by the doping method and surface passivation methods. When modifying carbon quantum dots with ethylenediamine as surface passivation agent, microwave modification time as long as possible, but not too long, and we need strictly control the amount of ethylenediamine. Adding 6mL of ethylenediamine to 30mL preparation carbon quantum dots, microwave heating 60 minutes in medium temperature, which can achieve the best modification effect on carbon quantum dots.2、In this article, we carry on the characterization of carbon quantum dots by using infrared spectrum analysis, XRD analysis, scanning electron microscopy and transmission electron microscopy, which can help to analyze the structure, composition and particle size of carbon dots. The experiment got the carbon dots containing carbonyl, carboxyl and hydroxyl groups, its particle size is about 5nm, its shape is spherical or near spherical. And the experiment investigate the influence of the pH value, and carbon concentration, solvent on the fluorescent properties of carbon dots. When pH value is 6, the carbon dots fluorescence intensity is the biggest, when the pH value less or greater than 6, the fluorescence intensity of carbon dots reduce; with the increase of concentration of carbon dots, its fluorescence intensity increase; But the concentration is greater, the increase slowed markedly, and carbon soluble in water, the increasing trend slow down and carbon dots is soluble in water.3、Using the carbon quantum dots of the optimized conditions synthesis and modification as fluorescent probe, under the certain condition of the acidity and dosage of carbon quantum dots, the carbon quantum dots fluorescent probe can detect trace arsenic in environmental water samples. In arsenic ion concentration is 2ng/mL to 10ng/mL range, arsenic ion concentration and the fluorescence quenching of carbon dots ratio (F0/F) have the linear relationship, the linear regression equation is y=0.2309x+0.9488, the linear coefficient R2=0.9855, the relative standard deviation RSD is 2.4%, the detection limit LOD is 0.32ng/mL. The experiment tested the arsenic content of water of Yan lake and Dong FengQu in campus, the arsenic content are respectively 1.175ng/mL and 1.27ng/mL. But when detecting the arsenic ion of experimental samples, the relative standard deviation is larger and the detection limit is high, so the method and condition need more research and inquirement.