Effects of Precursors and Plasma Parameters on Fullerene Synthesis in RF Thermal Plasma Reactor

Synthesis of fullerenes from graphite powders of different grade was studied in a radiofrequency (RF) plasma reactor. Dependence of fullerene yield on the properties and feed rate of precursors and on the helium content of plasma gas was studied in details. The fullerene yield was influenced by the mean size and the thermal conductivity of graphite particles on the one hand, and the helium content of the gas phase on the other. Soot containing fullerene mixture of 5.9% was produced in best conditions found in this work. The main component of the fullerene mixture was C₆₀. In addition, it contained about 30% of C₇₀ (corresponding to a C₆₀/C₇₀ mass ratio of 2.64). Higher fullerenes such as C₈₄ were also detected by mass spectroscopy (MS) and high performance liquid chromatography (HPLC).     

Yield of fullerenes generated by contact arc method under He and Ar: dependence on gas pressure

The yields of toluene-soluble material from carbon soot depend on the buffer gas as well as the pressure. Helium was more effective for yielding fullerenes than argon, and the optimum pressure was 20 Torr, under which a maximum yield of about 13 wt% was obtained. C₆₀ showed a maximum abundance at 20 Torr, while C₇₀ and higher fullerenes (C₇₆, C₇₈ and C₈₄) at a slightly higher pressure between 20 and 50 Torr. Raw soot was also studied by electron microscopy. The pressure dependence of the fullerene yield is discussed in terms of the cooling rate and diffusion of carbon vapor around the evaporation source.     

Single-stage plasma-arc synthesis of metallo-endofullerences

Single-stage plasma-arc synthesis of metallo-endofullerences of the types C₆₀Pd, C₆₀Ni, and C₆₀Cr, whose content in a mixture of extracted fullerenes was 0.05 to 0.15 wt %, was performed. The effect of introduction of these metals into the reaction plasma on the total yield of fullerenes and on the fraction composition of the fullerene mixture was studied. The fullerene mixtures were analyzed by mass spectrometry and liquid chromatography.     

Mechanism of selection of perfect fullerenes in arc synthesis

Joint consideration of the gas flow dynamics in an arc chamber for fullerene production and fullerene assembly kinetics shows that the efficient fullerene annealing and the giant prevalence of magic fullerenes C₆₀ and C₇₀ are associated with the gas flow structure generated by the arc in the discharge chamber. Most nascent fullerenes are not immediately removed from the chamber; rather, they are entrained by closed gas flows. Analysis of fullerene annealing makes it possible to optimize fullerene production not only for arc parameters but also for chamber geometry.     

The Effect of the Polyaromatic Hydrocarbon in the Formation of Fullerenes

Tremendous advances in nanoscience have been made since the discovery of fullerenes. However, the short timescale of the growth process and high‐energy conditions of synthesis result in severe constraints to investigation of the mechanism of fullerene formation. In this work, we attempted to reveal the formation process by analyzing the variation in the yield of fullerenes under different conditions. Experiments and theoretical analysis show that the formation of fullerenes could be affected by the addition of polycyclic aromatic compounds. It is proposed that the formation of C₆₀ during arc‐discharge synthesis is fragment assembling, while the yield of C_2m (m=35, 38, 39) is strongly enhanced by building‐block splicing. In addition, several features of the building blocks are put forward to predict the extent of their influence to the formation of larger fullerenes C_2n (n≥42). This work not only provides essential insight into the formation process of fullerenes, but more importantly also paves the way to improving the yield of larger fullerenes selectively.     

The Effect of Doping Different Heteroatoms on the Interaction and Adsorption Abilities of Fullerene

Density functional method has been employed to compare the interaction and adsorption abilities of simple and doped fullerenes with various heteroatoms (Al, B, Si, N, P, and S). Three sulfur‐containing molecules (H₂S, SO₂, and thiophene) were selected to study of their interactions with fullerenes. These interactions will be important in the design of new sensor, adsorption, and elimination of pollutants and chemical reactions. The calculated adsorption energies (E_ad) in the gas phase and solvents (water, using the polarized continuum model) showed that all adsorbates have exothermic interaction with all fullerenes. The maximum E_ad values were calculated for aluminum‐doped fullerene (AF) and nitrogen‐doped fullerene (NF), and the adsorption energies in solvent are not so different with those in the gas phase. Natural Bond Orbitals (NBO) calculations showed the complexes of AF and then boron‐doped fullerene (BF) have the highest E2 interaction energies, whereas simple fullerene (F) and phosphorus‐doped fullerene (PF) have the least E2 energies. Population analyses showed that doping by heteroatoms bearing extra electrons reduces the energy gap and this decrease is more than the decrease observed from doping by heteroatoms with electron defect. Moreover, the change in the energy gaps of the complexes, obtained from the density of states (DOSs) plots, showed that these structures could be used in sensor devices. All calculated data confirmed the better adsorption of SO₂ by fullerenes versus H₂S and thiophene and among all fullerenes, AF and then BF and NF are the best adsorbent for these structures.     

Gas dynamics in an arc discharge chamber as a factor governing the isolation of C60 and other “magic” fullerenes

A joint analysis of fullerene assembly kinetics and gas flow dynamics in an arc chamber for the production of fullerenes showed that the effective annealing of fullerenes and the evident dominance of “magic” fullerenes C₆₀ and C₇₀ were mainly explained by the difference between the thermal dissociation rates of these and less stable C₆₂ and C₆₈ fullerenes. The percent of “nonmagic” fullerenes was also shown to depend on the structure of the gas flows formed in the arc discharge chamber. The majority of newly formed fullerenes were not immediately removed from the chamber, bur were trapped by closed gas flows. Back in the hot region of the chamber, fullerenes were simultaneously annealed and dissociated under the action of high temperature and, partially, UV radiation. The “nonmagic” fullerenes were most actively suppressed in a non-pumpable discharge chamber.     

提高大分子Fullerene含量的有效方法

通过用掺有异相物质的石墨电极进行电弧反应，所得的混合物中大分子Ｆｕｌｌｅｒｅｎｅ的含量在１０％以上，为进一步分离，提纯以及深入研究大分子Ｆｕｌｌｅｒｅｎｅ打下了基础。研究发现，阳极材料中完整石墨结构的存在是生成Ｆｕｌｌｅｒｅｎｅ的必要条件，异相物质的存在为Ｆｕｌｌｅｒｅｎｅ的生长提供了热的载体，从而使产物中大分子Ｆｕｌｌｅｒｅｎｅ的含量增加。     

Direct Measurement of the Gas Entrainment Into a Turbulent Thermal Plasma Jet

An experimental study is conducted to investigate the entrainment characteristics of a turbulent thermal plasma jet issuing from a DC arc plasma torch operating at atmospheric pressure. The mass flow rate of the ambient gas entrained into the turbulent plasma jet is directly measured by use of the so-called “porous-wall chamber” technique. It is shown that a large amount of ambient gas is entrained into the turbulent plasma jet. With the increase of the gas mass flow rate at the plasma jet inlet or the plasma torch exit, the mass flow rate of entrained ambient gas almost linearly increases but its ratio to the jet-inlet mass flow rate decreases. The mass flow rate of the entrained gas increases with the increase of the arc current or jet length. It is also found that using different ways to inject the plasma-forming gas into the plasma torch affects the entrainment rate of the turbulent plasma jet. The entrainment rate expression established previously by Ricou and Spalding (J. Fluid Mech. 11: 21, 1961) for the turbulent isothermal jets has been used to correlate the experimental data of the entrainment rates of the turbulent thermal plasma jet, and the entrainment coefficient in the entrainment rate expression is found to be in range from 0.40 to 0.47 for the turbulent thermal plasma jet under study.     

Synthesis of Ozone at Atmospheric Pressure by a Quenched Induction-Coupled Plasma Torch

The technical feasibility of using an induction-coupled plasma (ICP) torch to synthesize ozone at atmospheric pressure is explored. Ozone concentrations up to ~250 ppm were achieved using a thermal plasma reactor system based on an ICP torch operating at 2.5 MHz and ~11 kVA with an argon/oxygen mixture as the plasma-forming gas. The corresponding production rate and yield were ~20 g ozone/hr and ~2g ozone/kWh, respectively. A gaseous oxygen quench formed ozone by rapid mixing of molecular oxygen with atomic oxygen produced by the torch. The ozone concentration in the reaction chamber was measured by Fourier Transform infrared (FTIR) spectroscopy over a wide range of experimental conditions and configurations. The geometry of the quench gas flow, the quench flow velocity, and the quench flow rate played important roles in determining the ozone concentration. The ozone concentration was sensitive to the torch RF power, but was insensitive to the torch gas flow rates. These observations are interpreted within the framework of a simple model of ozone synthesis.     

Design-Oriented Modelling of Different Quenching Solutions in Induction Plasma Synthesis of Copper Nanoparticles

The aim of this paper is to compare the effects of different mechanisms underlying the synthesis of copper nanoparticles using an atmospheric pressure radio-frequency induction thermal plasma. A design oriented modelling approach was used to parametrically investigate trends and impact of different parameters on the synthesis process through a thermo-fluid dynamic model coupled with electromagnetic field equations for describing the plasma behaviour and a moment method for describing nanoparticles nucleation, growth and transport. The effect of radiative losses from Cu vapour on the precursor evaporation efficiency is highlighted, with occurrence of loading effect even with low precursor feed rate due to the decrease in plasma temperature. A method to model nanoparticle deposition on a porous wall is proposed, in which a sticking coefficient is employed to model particle sticking on the porous wall used to carry a quench gas flow into the chamber. Two different reaction chamber designs combined with different quench gas injection strategies (injection through a porous wall for “active” quenching; injection of a shroud gas for “passive” quenching) are analysed in terms of process yield and size distribution of the synthetized nanoparticles. Conclusion can be drawn on the characteristics of each quenching strategy in terms of throughput and mean diameter of the synthesized nanoparticles.     

甲烷氧等离子体直接合成过氧化氢

本文利用介质阻挡放电(DBD)方法, 在室温和常压下将甲烷和氧气的混合气体进行等离子体活化, 通过甲烷和氧等离子体直接气相反应高收率合成H2O2. 该方法能有效克服氢氧直接法合成H2O2受到原料气配比严格限制的缺点.     

Quantum transition theory and dynamics of ionic molecule formation in cluster collisions

We apply the quantum transition theory of chemical reactions to ionic molecule formation in collisions between alkali-metal clusters and two types of reactive species: halogens and fullerenes. We show that the probability of a sticking collision is strongly dependent upon the nuclear dynamics. It turns out that although both halogens and fullerenes have a high electron affinity and appear promising for a harpooning reaction, this process is inhibited in the fullerene case by unfavorable Franck-Condon factors. This conclusion is in agreement with experimental observations. We predict that a strong reactive channel should reappear if the bare fullerene is replaced by a fullerene-rare gas complex. The product translational and vibrational energy distribution for such a collision is evaluated.     

Towards the selective formation of specific isomers of fullerenes: T - and p-dependence in the yield of various isomers of fullerenes C60–C84

Systematic fractional change in the yield of various isomers of fullerenes was revealed to strongly depend on temperature of a buffer gas. A new kinetic consideration is proposed for understanding the observed temperature- and pressure-dependence of yield of fullerenes. The model consists of three competitive reactions in consideration of plausible behaviors of a precursor, (1) decomposition into smaller fragments, (2) isomerization leading to formation of a stable fullerene cage, and (3) growth into a larger carbon cluster. Arrhenius activation energy of formation of stable fullerenes was determined to be 0.8 eV for both C₆₀ and C₇₀, while a higher energy of 2.0?3.3 eV for seven different isomers of higher fullerenes ranging from C₇₆ to C₈₄. Correlation in the activation energy is noted for a series of higher fullerenes with different sizes, suggesting the existence of a specific precursor in their formation processes.     

An efficient route to the synthesis of symmetric and asymmetric diastereomerically pure fullerene triads

A new synthetic route based on the stepwise functionalisation of fullerene cages allows the facile formation of linear, diastereomerically pure triads incorporating two different fullerene cages linked by an organic spacer group. The critical coupling step of two fullerene cages via activation by N,N′-dicyclohexylcarbodiimide was systematically investigated to reveal that the yield of the coupling is maximised in o-dichlorobenzene at high concentrations of the reactant fullerene nucleophile, while in more polar solvents or at lower concentrations of reactants the formation of unwanted side-products (such as guanidine-, N-acylurea- and anhydride-functionalised fullerenes) is favoured. The resultant triads possess an atypically good solubility for this class of compound, which enabled full detailed characterisation by ¹H and ¹³C NMR, IR and UV–vis spectroscopies and by MALDI-TOF mass spectrometry.     

Regioselective synthesis of 1,4-di(organo)[60]fullerenes through DMF-assisted monoaddition of silylmethyl Grignard reagents and subsequent alkylation reaction

Monoaddition of Grignard reagents, in particular tri(organo)silylmethylmagnesium chlorides, to [60]fullerene took place smoothly in the presence of dimethylformamide to produce (organo)(hydro)[60]fullerenes, C60R(1)H, in good yield (up to 93% isolated yield). The hydrofullerene was then deprotonated to generate the corresponding anion, C60R(-), which was then alkylated to obtain 58pi-electron di(organo)[60]fullerenes, C60R(1)R(2), in good to high yield (up to 93% overall yield). The two-step methodology provides a wide variety of 1,4-di(organo)[60] fullerenes bearing the same or different organic addends on the [60] fullerene core. By changing the addends, one can control the chemical and physical properties of the compounds at the molecular and bulk levels.     

Preparation of highly photosensitizing liposomes with fullerene-doped lipid bilayer using dispersion-controllable molecular exchange reactions

Fullerene-containing liposomes with high photosensitization ability were prepared. Disaggregated fullerenes were efficiently injected into the bilayer of liposomes by a phototriggered molecular exchange reaction. These liposomes showed far higher photoreactivity than liposomes thermally produced by heating and microwave irradiation. This result indicates that control of self-aggregation of fullerene leads to a high quantum yield for the photoreaction because of the suppression of self-quenching of photoexcited fullerenes.     

Influence of the Shroud Gas Injection Configuration on the Characteristics of a DC Non-transferred Arc Plasma Torch

The characteristics of the plasma jet emanating from a dc non-transferred plasma torch is affected by many factors including arc current, type of gas, gas flow rate, gas injection configuration and torch geometry. The present work focuses on experimental investigation of the influence of shroud gas injection configuration on the I–V characteristics and electro-thermal efficiency of a dc non-transferred plasma torch operated in nitrogen at atmospheric pressure. The plasma gas is injected into the torch axially and shroud gas is injected through three different nozzles such as normal, sheath and twisted nozzles. The effects of flow rates of plasma/axial gas and arc current on I–V characteristics and electro-thermal efficiency of the torch holding different nozzles are investigated. The I–V characteristics and electro-thermal efficiency of the torch are found to be strongly influenced by the shroud gas injection configuration. The effect of arc current on arc voltage decreases with increasing the axial gas flow rate. At higher axial gas flow rate (>?45 lpm), the I–V characteristics of the plasma torch are similar irrespective of the nozzle used. The variation of electro-thermal efficiency with arc current is almost similar to that of arc voltage with arc current. As expected, the electro-thermal efficiency is increased when the axial gas flow rate is increased and at higher axial gas flow rate, it is not influenced by the arc current and shroud gas configuration. The plasma torch with normal nozzle may be better in the range of operating conditions used in this study.     

Evolution spectrum of C60 isomers in buffer gas

The energy spectrum of C60 nonclassic fullerenes with single heptagon defects calculated by Brenner empirical potential is found to submerge into the spectrum of classic fullerenes. Geometry analysis indicates that these nonclassic fullerene isomers can be more attainable than classic fullerenes at higher Stone-Wales (SW) stacks. Molecular dynamic simulations of the C60 isomer evolution in He buffer gas at 2500 K demonstrate that nonclassic fullerenes, especially those with heptagon defects, play an important role in the dynamics of C60 annealing, and that the Stone-Wales stack-by-stack transition mainly occurs at lower SW stacks. A non-SW multistep rearrangement is first observed in the simulation with its transition sequence and intermediate state presented in detail.     

Using cyanide to put noble gases inside C60

After fullerenes are heated in the presence of a noble gas or an unreactive molecule at 650 degrees C and 3000 atm pressure, a small fraction of the fullerene molecules contain the atom or molecule. The incorporation fraction is greatly enhanced by adding potassium cyanide to the reaction mixture. The details of the preparation are described here.