Preparation And Application Of Mesophase Pitch-based Carbon Quantum Dots

Quantum dots?QD?,whose three-dimensional sizes are all less than the double Bohr radius of exciton,is a novel nano material.The characteristic optical property of QD have attracted the researchers.Compared with common QD,such as cadmium sulfide and cadmium selenide,carbon quantum dots?CQDs?have low toxicity,good biocompatibility and chemical inertia,and excellent fluorescence properties,which have triggered a research boom at home and abroad.CQDs have shown great potential in the fields of chemical sensing,biosensor,drug delivery,photocatalysis and electrocatalysis.Although various carbon-containing chmicals are used to produce CQDs,the preparation process of CQDs are complex and expensive,and the fluorescence quantum yield?QY?of the product is low.The development of a novel and low-cost preparation methods for CQD are very important for its large-scale application.In addition,the mechanism of the fluorescence properties of nitrogen-doped carbon quantum dots?NCQDs?and the properties of the fluorescence curve of CQDs moving with the excitation wavelength is unclear.Therefore,the study of the luminescent properties of CQDs can further promote people's understanding of CQDs.In this paper,the"top-down"method is used to prepare CQDs with controllable particle size.Firstly,mesophase asphalt,a unique material,was prepared in this work.CQDs were prepared by one-step method,taking advantage of the uniform size and orderly structure of mesophase asphalt crystallizing units.Compared with the traditional preparation method,this process has no subsequent complex purification process.1)The preparation and application of CQDs from mesophase pitch.In this work,CQDs were prepared directly from vacuum cut 2 petroleum products by dispersing and carbonizing the carbonaceous microcrystals in mesophase pitch.It was found that mesophase asphalt grew continuously and showed different morphologies with the increase of heating time and temperature.In addition,the prepared mesophase has the highest solubility in xylene.A series of CQDs?2-4.5 nm?with narrow particle size distribution were prepared by carbonization of mesophase at different growth stages.These CQDs have strong blue fluorescence properties,and the quantum yield is as high as 87%.The position of the fluorescence peaks did not change with the excitation wavelength.In the study of ion quenching,the CQDs are highly specific and sensitive to Fe³⁺ions.2)The preparation and fluorescence characterization of NCQDs.In order to study the effect of nitrogen doping on the fluorescence properties of CQDs.One is to etch CQDs with nitrogen plasma,the other is to mix melamine into raw oil to prepare doped mesophase,and then to prepare NCQDs.The nitrogen bonding modes of NCQDs prepared by plasma?NCQDs-P?are pyridine nitrogen and graphite nitrogen,while the nitrogen bonding modes of NCQDs prepared by melamine?NCQDs-C?are pyrrolic nitrogen and graphite nitrogen.The fluorescence curves of NCQDs-C and CQD are similar,as the position of fluorescence peaks do not change with the excitation wavelength,while the peaks of NCQDs-P change with the position of excitation wavelength,and the longer the plsama etching time,the more obvious peak movement of NCQD s-P.Excluding the influence of particle size change,we confirm that introduction of pyridine nitrogen causes the fluorescence peak wavelength to shift with the excitation peak wavelength.In a word,we used mesophase pitch as raw material to prepare high quantum yield CQDs with different particle sizes by direct carbonization of carbonaceous microcrystals.The CQDs exhibited blue light under ultraviolet irradiation,and well be applied to metal ion detection.Two nitrogen-doping methods were used to prepare NCQDs.The binding mode of N affected the fluorescence peak position.