Preparation Of Coal Tar Pitch Based Carbon Quantum Dots And The Application Of Fluorescence Detection

Carbon quantum dots(CQDs),which exhibit many outstanding advantages includingeasy preparation,low-cost,low cytotoxicity,excellent biocompatibility,good dispensability in water and tunable band gap emission.Thus,CQDs have been widely used in many fields including biological imaging,cell sensing,light emitting diodes,organic photovoltaic device,photocatalysis and electrocatalysis and others.However,currently most of CQDs are prepared with complex processes,with severe synthetic conditions,which are expensive and not friendly to the environment.The synthesis of CQDs has focused on the use of various carbon resources,including graphene,fullerene,carbon black,carbon fiber,graphite,graphite oxide,Therefore,use of low-cost raw materials and a facile,green synthesis method to prepare CQDs is highly desirable;Moreover,the structure of the CQDs is uncertain;scientists speculate that quantum dots are defects from the material.Therefore,it is very important to study the crystal structure of the carbon quantum dots and explain the luminescence mechanism.In this paper,we present the preparation of carbon quantum dots by using coal tar pitch as carbon source,and the application of CQDs in fluorescence detection was also studied.The research work is divided into two parts:(1)We propose a green and easily scale method for the preparation of CQDs.Herein,we report on the development of a novel method for preparation of carbon quantum dots(CQDs)using coal tar pitch and an O3 oxidation method,which is simple,environmentally attractive and easy to scale.The overall particle size distribution of the high-quality CQDs was between3-7 nm,and the quantity of the CQDs with a diameter content of 4.9 nm was 42.8%.In addition,the application of CQDs as fluorescent probes for metal ions were investigated,the results showed a highly sensitive and selective detection of the CQDs to Fe3+ ions.A calibration curve displayed a linear response over the range of 0-13 ?M Fe3+,with a detection limit of 0.02 ?M(1.12 ppb).(2)We present the possible crystal structures of CQDs and the detection methods and mechanisms of HCHO in water.We report on the development of a novel method for preparation of CQDs using coal tar pitch and an H2O2 oxidation method,followed by separation and purification by column chromatography,and the structure of the purifiedsubstance is obtained.Finally,the CQDs in aqueous solution were obtained by replacing the solvent method,the overall particle size distribution of the high-quality CQDs was between2~4 nm,and the quantity of the CQDs with a diameter content of 3.2 nm was 46.5%.According to the structure of the elementary molecule,the crystal structure model of the carbon quantum dots is reasonably predicted,In addition,CQDs were used to detect the organic compounds in water,and the detection limit reached 1.3 ppb.Finally,the mechanism of detection is studied by DFT theoretical calculation,and explained the reason for the phenomenon of fluorescence quenching.