Synthesis of Fullerene by Pyrolysis of Acetylene in Thermal HF-Plasma

94Vol.22 No.1 ZHU Yanjuan et al: Synthesis of Fullere by Prolysis of Acetrlenein..DOI 10.1007/511595-005- 1094-2Synthesis of Fullerene by Pyrolysis ofAcetylenein Thermal HFPlasmaZHU Yanjuan', ZHANG Guofu', ZHANG Wei, LIN Tianjin'XIE Hongbo', LIU Qiuxiang', ZHANG Haiyan2(1.Faculty of Applied Physics, Guangdong University of Technology,Guangzhou 510090,China;2.Faculty of Material and Energy, Guangdong University of Technology,Guangzhou 510643,China)Abstract: Carbon soot containing fullerene was continuously produced in volume by pyrolyzingacetylene in thermal HF-Plasma. The characteristics of the carbon soot and C60 were analyzed bythtransmission electron microscopy, UV/visible, IR and Raman spectroscopy. The results show that the mainfullerene yield in carbon soot is about 2.5 g*hr'. Compared with the graphite arc discharge method, the acetylenethermal plasma method is a preferential one for synthesis of fllreneKey words: acetylene ; thermal plasma method ; fullerene; arc discharge methed1 Introduction2 ExperimentalFullerene has attracted much attention since itsdiscovery, because of its remarkable electronic and 2.1 Preparation ofullerenemechanical properties as an important raw material ofThe preparation of fullerene consists of threesemiconductor, superconductor, photoeletric material, technological processes: carbon soot containingcatalyst, nonlinear optic material and so on. Since fullerene was produced by pyrolyzing acetylene,fullerene of milligram has been first synthesized by the carbon soot was extracted with toluene, and theelectric arc discharge method", extensive research concentrate was obtained.has been done for the synthesis of fullerene, and manyThe high-frequency plasma system consistsmethods have been applied such as the resistance of high- frequency power, plasma-reactor, high-pyrogenation!, flame method'and laser ablation'. temperature chamber, quencher, dust-collector, feedingCurrently, the most widely used technique to produce apparatus, measuring and controlling system, andfullerene is the electric arc discharge. But electric exhaust-gas treatment device. The structure sketcharc discharge cannot fulfill the increasing demand of of the system is shown in Fig. 1. The experiment wasapplication, because of the discontiguous technique carried out at atmosphere pressure, using argon gasand limited output. So, many scientists try to find a (purity 99%)as work gases (cooling gas and burningnew method to produce fullerene. Theodora et al have gas), and high pure acetylene as reactant gas. The workused halogenated hydrocarbons (C2Cl4, C2Cl2F2) to gas was inlet into the plasma area at the tangentialproduce fullerene by thermal plasmals. Wang et al also direction. Acetylene was ripped into the outer plasmareported to produce fullerene by direct evaporation of flame at the diametrical direction, and then decomposedcarbon powder injected into the thermal plasmalo. In into carbon soot and hydrogen. After quenching, carbonthis paper, carbon soot containing fullerene in volume soot and hydrogen were drawn out, and then a powderwas continuously produced by pyrolyzing acetylene collector collected the carbon soot. Exhaust gas wasin thermal high-frequency plasma(HF- Plasma) at vented out from the filter tower.atmosphere pressure.The typical preparation parameters for carbonsoot synthesis were: plasma power 30 kW, frequency 4MHz, cooling gas flow rate 10 m'●h , burning gas flow(Received: April 5,2005; Accepted: Aug.30,2006)rate 1.25 m'.1中国煤化工).25m'h . TheZHU Yanjuan (朱燕娟): Prof; E-mail : zhuyjgz@ 126.comFunded by the National Natural Science Foundation of Chinayield of carbd| YHCNMH Ge flow rate of(No.50372013) and the Guangdong Province Natural Science reactant gas. In our experiment, the yleld was about 0.25Foundation of China(No.004009487, No.04300168).kg*h'..Journal of Wuhan University of Technology-Mater: Sci. Ed. Feb. 200795Aleads to the energy level change of C60.CH,二Shown in Fig.3(a)and (b) are the IR spectra of thecarbon soot and fullerene powder. Four characteristicabsorption peaks of C60 are shown obviously in thespectra, with wavenumber of 1 425, 1 178, 571 and应立可522 cm*. Compared with spectrum (b), the backgroundabsorption of spectrum (a) is stronger, but the fourcharacteristic absorption peaks are weaker. SomeFig.1 The structure sketch of the high-frequency plasma systemsundry peaks are observed, because there are not onlyI . gas distributor 2. plasma generator 3. reacting chambera lot of amorphous carbon and graphite, but also some4. quencher, pulse jet blower 6. bag filthydrocarbon compounds. The sundry peaks are the7. powder collector 8 air pump9. exhaust gas filterThe carbon soot (consisting of amorphous carbon, reflection of the strong absorption of -CH2- and-graphite and fllerene ) was extracted with toluene . C=C=C- radicle. After amorphous carbon, graphiteOnly the C60 can dissolve into toluene , so we can get and hydrocarbon have been removed, so that the fourthe red toluene extraction by decompression filtration. characteristic absorption peaks stand out obviously in .Solid powder was obtained from the toluene extraction spectrum (b).by rotary evaporation. Then the solid powder wasFig.4 shows a TEM image of the carbon soot. Thewashed by ether so as to get pure fullerene powder.carbon soot particles exhibit a spherical nanoparticle,2.2 Determinationwith a diameter of 20-30 nm. The morphology of theThe red toluene extraction was analyzed carbon soot particles in this experiment is similarby ultraviolet(UV)/visible optical absorption to that of those produced by other methods'. Thespectroscopy(UV-2501 PC). The carbon soot and main ingredients of the carbon soot are amorphousthe fullerene powder were examined respectively by carbon, graphite and fullere Shown in Fig.5 is ainfrared(IR) absorption spectroscopy (BRUKER EQUI- TEM image of C60 crystal extracted from carbon sootNOX55), transmission electron microscopy (JEM- by toluene. The crystal shape formed relates to the100SX )and Raman spectroscopy(LABRAM-HR).solution concentration of toluene extraction. A lowerconcentration solution forms acicular crystal (Fig.5(a))3 Results and Discussion, and a higher one forms globular crystal (Fig.5(b)).When the concentration of solution is low, itFig.2(a) shows the UV/Visible absorption needs a longer time to vaporize, and C60 takes morespectrum of the toluene extraction. Because the time to separate from the solution. At this moment, thewavelength limit of UV/Visible absorption spectrum is crystallizing driving force is small, and the effect of the285 nm/] (the solution absorption can not be ignored if energy differences of crystal planes is obvious. By thethe wavelength is lower than that), the test wavelengthcrystal growth lowest energy theoryt, C60 crystalsshould be above 285 nm. The wavelength of the will grow in turn according to the energy of crystalabsorption peak is 337 and 407 nm. Compared with the plane, that means they will grow from the lower to the .spectrum in Fig.2(b)8( 329,404 nm), there is a lttle high energy during their separation process, and finallyred shift. The reason for the red shift may be the strong acicular crystals are formed. Contrastively, when theinfuence of the toluene molecular's p bond , and this solution concentration is high, the solvent is less and\员当(6)200300 400 500 60016001200400中国煤化工100amW avele ngth/amWavelengh/amMHCNMH GFig.2 UV/Vis ible absorption speclraFig.3 IR spectra of the earboasoot (a)Fig. 4. TEM image of the carbon sootof C60's toluene extraction (a) andand fullerene po wder (b)hexy1-alky1 exlraction (b)".96 .Vol.22 No.1 ZHU Yanjuan et al: Synthesis of Fullerene by Pyrolysis of Acetlenein..(a)(b)|300020001000j1.4um .4.6μm200 400 600 8001 0001 2001 4001 60C(a) lower conc entration solution(b) higher conc entration solutionRaman shit/ cm'Fig.6 Ram an spectrum of C60 crystal-Fig.5 TEM image ofC60 crystal--tol uene extract from carbon sootTable 1 Technique and yield of fullerene in Ar atmosphere by the graphite aredischarge method and acetylene thermal plasma methodGraphite arcPlasma pyrolysisStarting materialsGraphite rodsAcetylene gasHeating methodDC are dischargeH.F.thermal plasmaInertatomsnhere2 00-3 000Pressure/atm0.1-0.91.0Yield of carbon soot/g*h:1250Yield of fullerene/gh0.27-0.88CatalyzerFe.Co.Ni particlesNonethe vaporization time is short. So the solution is easy by graphite are discharge method.to become supersaturated, and the crystallizing drivingAccording to our previous work, inert gas is a veryforce is large. At this moment, the effect of the energy important factor that affects the yield of fullerenel"2]differences of crystal planes is puny and can almost and He gas is more effective than Ar gas for fullerenebe neglected. This leads to the same growth speed preparation. So that if He gas instead of Ar gas isof different crystal sides in all directions. At last, the used, the yield of fullerene may be increased largely.globular C60 crystals are formed.In addition, pyrolysis of acetylene in high-frequencyFig.6 shows the Raman spectrum of fullerene thermal plasma can produce fullerene. It can be inferredpowder. C60 with a three dimensional phenyl structure that using other hydrocarbon gas such as ethylene oris aromatics. According to reference "，C60 molecule methane can also produce fullerene. So this methodhas ten Raman-active patterns,1 562,1 458,1 430，can be popularized to produce fullerene in a large scale1 315,1 140,776,708,496,433 and 274 cm' .496 cmi' using different hydrocarbon gas as carbon source.corresponds to C atom vibration model at the radialdirection, 433 cm' at the tangent direction . Ourresult 4 Concusionsbasically accords with it.In our experiment, by extracting from the carbonThe carbon soot containing fullerene produced bysoots toluene solution, the yield of fullerene is 2.5 pyrolysis of acetylene in the thermal plasma, consistedg*h' measured by weight. Compared with graphite of amorphous carbon, graphite and fullerene. The yieldarc discharge method, the advantage of the acetylene of fullerene was about 2.5 g*hi'. The advantage ofthermal plasma method is that it can be performed at this method is that it can be controlled easily, and theatmosphere pressure, and acetylene gas is cheap, soit cost is low, so it is easy to be magnified in technicalis easy to be magnified in technical application.application. By improving the technical condition, thisIn Table 1, we compared the technique and the method can be applied to produce fullerene in volume,yield of fullerene produced by acetylene thermal providing a foundation for the wide application ofplasma method with that by graphite arc discharge fullerene.method. The typical preparation parameters for carbonsoot synthesis by graphite arc discharge method are:Referencesdiameter of graphite electrode of 6 mm，electriccurrent of 60 A, and voltage of20 V. 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