Preparation Of Polyynes By Arc Discharge Between Metal Electrodes In Organic Liquids And Its Spectroscopic Characterization

Carbyne,a true one-dimensional carbon allotrope,is defined as an infinitely long linear carbon chain composed of sp hybridized carbon atoms.Theoretical calculations show that Carbyne is the hardest material in the world and has twice the tensile strength of carbon nanotubes and graphene.However,as the number of continuous sp carbon atoms increases,linear carbon chains?LCCs?become more and more unstable,so synthesizing ultralong LCCs in the laboratory remains a great challenge.Polyynes can be as a precursor molecule to be filled into DWCNTs,and further form ultralong LCCs by heating.In addition,Polyynes is not only an interesting model for Carbyne,but also widely used as a precursor to functional materials,molecular conductors for charge transport,and specific nonlinear optical materials.Recently,Polyyne-based materials hold great promise in live-cell and sorting as well as in high-throughput diagnostics and screening.Here,the preparation system of Polyynes with organic molecules as the precursor was established by using submerged electric arc between two metal electrodes instead of graphite electrodes in organic liquids for the first time.In order to explore the internal connection between the formation of Polyynes and precursor molecules,we tried to use a series of alkanes with different molecular weights or different molecular structures as precursors for the synthesis of Polyynes.Based on the analysis of the formation rate and chain length distribution of Polyynes in different alkanes,the formation mechanism of Polyynes has been discussed,the details are as follows:The first chapter mainly introduces the structure,properties and characterization of one-dimensional linear carbon chains?LCCs?,and the current progress in experimental synthesis and application.In the second chapter,the experimental process of synthesizing Polyynes by arc discharge between metal electrodes is introduced in detail.The Polyynes are synthesized by arc discharge between copper,silver and tungsten electrodes in n-hexane and ethanol precursor molecules.The solution sample and the precipitated sample were respectively tested by Ultraviolet-Visible?UV-Vis?absorption spectra and Raman spectrum.Studies have found that metal electrodes have an important influence on the growth of Polyynes.By comparing the purity and yield of Polyyne samples obtained by arc discharge between different metal electrodes,it is shown that copper electrode is a good choice for preparing high-purity Polyyne samples.In the third chapter,the experimental process of synthesizing Polyynes by arc discharge between copper electrodes is introduced,and seven kinds of alkane precursors for synthesizing Polyynes are tried.The formation rate of Polyynes in the seven alkane precursor molecules was estimated by UV absorption spectra.It has been found that the formation rate of Polyynes increases as the carbon-hydrogen ratio of alkanes increases.In the fourth chapter,the chain length distribution of Polyynes synthesized in different precursor molecules was analyzed by high-performance liquid chromatography?HPLC?,and the single isolated samples were subjected to surface-enhanced Raman spectra?SERS?.The results show that the longest Polyynes with cyclopentane as the precursor can have a chain length of up to 14 carbon atoms.However,when n-pentane is used as the precursor,the longest Polyynes have a chain length of only 12 carbon atoms.This indicates that the precursor molecules have an effect on the chain length distribution of Polyynes.The fifth chapter mainly analyzes the physical and chemical processes of the Polyyne formation,it is concluded that the formation rate of Polyynes depends on the energy consumed to produce the same amount of C₂ radicals.In addition,the volume density of C₂ radicals in the plasma has certain regulatory effect on the length of Polyyne chains.In the sixth chapter,the research work of this paper is summarized and further research directions are proposed.Finally,the application of Polyynes is prospected.