A study conducted by researchers at the University of São Paulo (USP) in Brazil and the Università degli Studi di Roma "La Sapienza" in Italy has synthesized fullerenes and hollow spherical graphene particles using only natural graphite, ethanol, water, and sodium hydroxide under ambient conditions. Published in the journal Diamond and Related Materials, the research showed the feasibility of producing structures that previously required extremely high temperatures using an electrochemical route.
"Our work indicates that it's possible to obtain fullerenes, including so-called giant fullerenes, with up to 190 carbon atoms through a simple electrochemical process, without catalysts or high temperatures," says José Mauricio Rosolen , a USP researcher, professor at the Department of Chemistry at the Ribeirão Preto Faculty of Philosophy, Sciences, and Letters (FFCLRP-USP), and coordinator of the study. "This method paves the way for new forms of organic synthesis and technological applications that are still unexplored," the researcher predicts.
Fullerenes are spherical molecules composed entirely of carbon atoms. One famous example is C60, also known as "buckminsterfullerene," because its carbon spheres have the same configuration as the geodesic dome created by American designer, architect, and inventor Buckminster Fuller (1895-1983).
Since their discovery in 1985, these structures have been studied for their unique electronic and structural properties. In 2010, fullerenes were detected for the first time in outer space through observations made with NASA's Spitzer Space Telescope. More precisely, they were found in the planetary nebula Tc 1, which is located about 6,000 light-years from Earth. However, producing fullerenes with more than 100 carbon atoms, known as "giants," under laboratory conditions has remained challenging due to the high temperatures required for carbon atoms to arrange themselves in a spherical configuration, typically in the range of 3,000 °C to 4,000 °C.
In the new study, the researchers demonstrated that anodic polarization of graphite in an electrochemical cell induces the formation of likely oxidized graphene sheets that spontaneously self-assemble into fullerenes and hollow spheres. The final product was characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), mass spectrometry (MALDI-TOF), and visible ultraviolet spectroscopy (UV-Vis).
"We observed clusters of spherical particles of various sizes, ranging from soap bubble-like structures measuring 10 nanometers to large deformable spheres measuring up to 320 nanometers trapped between networks of carbon nanotubes," Rosolen says.
The study also used mass spectrometry to identify characteristic peaks of well-investigated fullerenes (C₆₀ and C₇₀) and larger fullerenes (C₁₄₆, C₁₆₂, C₁₇₆, and C₁₉₀). Successive peaks, separated by approximately 160 units, indicate fragmentation due to the loss of C₁₂ groups. This suggests the presence of hierarchical assembly processes. "The formation of the structures critically depends on the presence of hydroxyl radicals [●OH] and hydroxyl ions [OH⁻], generated by the electrochemical oxidation of water and the effect of ethanol. These radicals attack the edges and defects of graphite, fragmenting the sheets and promoting the exfoliation of the material," Rosolen explains.
The article shows that when the applied electrical voltage exceeds 10 V, the production of fullerenes decreases dramatically, and carbon nanodots (quantum dots) predominate over spherical structures. The results suggest that the self-assembly of oxidized graphene into fullerenes hinges on a delicate balance of several factors: the concentration of ●OH radicals and OH⁻ ions, the type and size of graphite particles used, polarization time, and applied voltage.
The presence of oxygenated functional groups in the structures was also observed. Depending on the desired application, these groups may facilitate future chemical modifications. Since the entire process takes place in a liquid medium, adding other components of interest is easy. "With this work, we've opened up the possibility of producing giant fullerenes via an accessible and environmentally friendly electrochemical route," says Rosolen. "There's still much to understand about the formation mechanisms of these structures, but the results are promising."
The research was supported by FAPESP through two projects ( 24/02535-3 and 20/08322-0 ).
About São Paulo Research Foundation (FAPESP)
The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. You can learn more about FAPESP at www.fapesp.br/en and visit FAPESP news agency at www.agencia.fapesp.br/en to keep updated with the latest scientific breakthroughs FAPESP helps achieve through its many programs, awards and research centers. You may also subscribe to FAPESP news agency at http://agencia.fapesp.br/subscribe.
