A new method for the synthesis of giant fullerenes

Professor Zaifa Shi's team at Xiamen University developed an ultra-high temperature flash vacuum pyrolysis (UT-FVP) device to form giant fullerenes from single-carbon molecules within a short time (15 s) at extremely high temperatures (∽3000 ℃). Due to the strong intermolecular forces between giant fullerene molecules and soot, traditional ultrasonic or Soxhlet extraction methods cannot separate most giant fullerenes from soot in toluene. To overcome these strong intermolecular forces, two separation techniques—mechanical grinding and sublimation—were optimized to separate the giant fullerenes from the pyrolysis products, and laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS) was used for comprehensive and thorough detection. These methods extended the mass distribution of synthesized giant fullerenes to 2760 Da (greater than C₂₃₀). Notably, the separation technology can also recover giant fullerenes that have long been neglected due to incomplete separation in flame and arc discharge methods. This separation strategy has broad applicability in the synthesis of giant fullerenes, providing a new perspective for the synthesis and utilization of these carbon materials. The article was published as an open access research article in CCS Chemistry, the flagship journal of the Chinese Chemical Society.

Background information:

Since the first discovery of fullerenes in 1985 through laser evaporation of graphite, fullerenes have rapidly become a research hotspot due to their unique structure and properties. Fullerenes are cage-like all-carbon molecules composed of isolated five-membered rings and any number of six-membered rings; theoretically, their carbon number can extend from C₂₀ to infinity. "Giant fullerenes" generally refer to fullerenes containing more than 100 carbon atoms, starting from C₁₀₀. They are mainly found in the raw soot obtained by arc discharge, plasma discharge, or laser irradiation of graphite. Although fullerenes were isolated and purified as early as 1990, reports on giant fullerenes remain scarce. Compared to C₆₀ and C₇₀, giant fullerenes have extremely low yields, and their isolation and characterization are extremely difficult, severely hindering the research progress of these carbon materials. To date, there are no mature characterization methods, resulting in very few studies on offline or in-situ observation of giant fullerenes. In 1998, researchers detected fullerene cations up to C₆₅₀₊ in acetylene-oxygen flames, but offline analysis showed that larger fullerenes extracted from flame ash only reached C₉₆. Due to the extremely low abundance of giant fullerenes in toluene extracts, further characterization of in-situ discovered giant fullerenes is difficult. This is likely due to the strong π-π intermolecular forces between giant fullerene molecules and other substances in the ash (such as polycyclic aromatic hydrocarbons, amorphous graphite, and onion-like carbon). Therefore, developing new methods for the efficient synthesis and separation of giant fullerenes is crucial for advancing research in this field. In this study, we used the previously reported ultra-high temperature flash vacuum pyrolysis (UT-FVP) apparatus to prepare sufficient quantities of giant fullerenes, and then efficiently separated them from the substrate ash using mechanical grinding and sublimation. Thanks to this separation technique, the enriched giant fullerenes exhibited high-quality signals in laser desorption/sorption spectroscopy, achieving comprehensive and thorough characterization.

Highlights of this article:

This study optimized two separation strategies—mechanical grinding and sublimation— to address the strong π-π interactions between giant fullerenes and fly ash , achieving efficient separation of giant fullerenes from fly ash. Furthermore, laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS) was used to successfully characterize and analyze giant fullerenes with a C value greater than 100 without a matrix.

This study also revealed the influencing factors on the formation of giant fullerenes. It confirmed that higher temperatures promote the formation of giant fullerenes and indicated a possible competitive reaction between the formation of smaller fullerenes (such as C₆₀ and C₇₀) and giant fullerenes. Furthermore, the chlorine content of the reactants is also a key factor in the formation of giant fullerenes during the UT-FVP process; as the chlorine content increased from 50% to 100%, the mass peak of the giant fullerene shifted to the right. In summary, temperature and chlorine content synergistically regulate the yield and size distribution of giant fullerenes, providing clear experimental evidence and an optimized pathway for their controllable synthesis.

Summary and Outlook:

In summary, the authors efficiently synthesized abundant giant fullerenes from chlorinated single-carbon molecules using the UT-FVP method, with the largest reaching C₂₃₀. Experimental results show that in the UT-FVP method, higher chlorine content in the single-carbon molecule and higher synthesis temperature are more favorable for the formation of giant fullerenes. Giant fullerenes can be effectively extracted from fly ash through mechanical grinding and sublimation treatment, and characterized by LDI-TOFMS. This work realizes the entire process from the pyrolysis synthesis of giant fullerenes from single-carbon molecules to the separation and characterization of giant fullerenes. This opens the door to the synthesis and large-scale utilization of giant fullerenes and demonstrates the general applicability of these strategies in other fullerene synthesis processes.

Lijun Huo (Xiamen University) and Haotian Ying (Xiamen University) and co-first authors on the paper.  Cunhaio Cui (Xiamen University) and Zaifa Shi (Xiamen University) are the corresponding authors.

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About the journal: CCS Chemistry is the Chinese Chemical Society’s flagship publication, established to serve as the preeminent international chemistry journal published in China. It is an English language journal that covers all areas of chemistry and the chemical sciences, including groundbreaking concepts, mechanisms, methods, materials, reactions, and applications. All articles are diamond open access, with no fees for authors or readers. More information can be found at https://www.chinesechemsoc.org/journal/ccschem.

About the Chinese Chemical Society: The Chinese Chemical Society (CCS) is an academic organization formed by Chinese chemists of their own accord with the purpose of uniting Chinese chemists at home and abroad to promote the development of chemistry in China. The CCS was founded during a meeting of preeminent chemists in Nanjing on August 4, 1932. It currently has more than 120,000 individual members and 184 organizational members. There are 7 Divisions covering the major areas of chemistry: physical, inorganic, organic, polymer, analytical, applied and chemical education, as well as 31 Commissions, including catalysis, computational chemistry, photochemistry, electrochemistry, organic solid chemistry, environmental chemistry, and many other sub-fields of the chemical sciences. The CCS also has 10 committees, including the Woman’s Chemists Committee and Young Chemists Committee. More information can be found at https://www.chinesechemsoc.org/.