Arc-discharge Synthesis Of Fullerenes Influenced By Micro-environment

Fullerenes represent a new form of carbon discovered by Kroto,Curl,and Smally in the experiment of laser-evaporation of graphite in 1985.Fullerenes can be classified into isolated-pentagon rule(IPR)-satisfying fullerenes and IPR-violating fullerenes(i.e.,the non-IPR fullerenes having adjacent pentagons in their carbon skeletons).IPR fullerenes such as C₆₀ and C₇₀ have been widely investigated since they were available in macroscopic quantities in 1990.The synthesis,separation and characterization of non-IPR fullerenes,however,are still of great challenge. Introducing chlorine into plasma system during the formation of non-IPR fullerenes is useful for trapping these new species and in turn of importance for understanding of fullerene formation,as demonstrated by capturing labile C₅₀ as C₅₀Cl₁₀ and C_2v-C₆₀ as C_2v-C₆₀Cl₈.Due to a scarcity of non-IPR fullerene species in soot,only a limited quantity of these interesting fullerenes has so far been purified and isolated.Under this circumstance,a high-yield synthesis of non-IPR fullerenes is definitely needed for further studies of these fullerenes.In this dissertation,the synthesis of non-IPR fullerenes(especially C_2v-C₆₀Cl₈) under an improved graphite arc discharged in the presence of chlorine was systemically explored,and a series of experiments were carried out involving the effective capture of metastable intermediates of fullerenes, the verification of Stone-Wales(SW) transformation and exploratory synthesis of metallofullerenes.The main results are summarized as follows.1.The existed apparatuses for the synthesis of fullerenes are improved for uncomplicated use and maintenance.Synthesis of fullerenes is optimized.Based on the experimental data on fullerene yields,the S-W transformation is tentatively verified and the formation mechanism of fullerenes is suggested.2.A small amount of chlorine,mixed into helium atmosphere,has remarkably enhanced the yields of C₆₀ and C₇₀ in the graphite arc-discharge reaction.By alternating the aperture of carbon anode(rod or tube),an effective method to improve the yield of C_2v-^#1809C₆₀Cl₈ was reported for the first time.This method allows the synthesis of ^#1809C₆₀ with much more yield than D_5h-C₇₀,the second abundant fullerene.Appropriate extraction method for chlorinated fullerenes has been optimized.The stability of the chlorinated fullerenes are also been studied.3.High-yield synthesis of fullerenes and metallofullerenes is explored by adding a small amount of metal such as silver,iron,nickel and copper into the anode.The yields of C₆₀ and C₇₀ in the graphite arc-discharge reaction were remarkably increased and C₇₆,C₇₈,C₈₀,C₈₂,C₈₄ were obviously detected by HPLC coupled with both mass spectrometry(MS) and ultraviolet absorption spectroscopy(UV).The yield was promoted to a factor of 4 folds more than those produced in metal-free conditions (with only chlorine and helium atmosphere).Combining with the experimental results, we can predict that the addition of chlorine and metal facilitates the formation of fullerenes and its intermediates.On the basis of high-yield synthesis of fullerenes,the yield of metallofullerenes can be promoted by stuffing metal oxide into the anode.