Fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed mesh, with fused rings of five to seven atoms. In recent times, a surge in interest in fullerenes has been experienced in the scientific community credit to their unique structures and properties. For instance, they have played a pivotal role as drug-delivery systems, nanosensors, antioxidants, and as solar-cell construction materials; not to mention their other versatile applications based on their electronic properties and chemical reactivity. As such, elucidation of their formation mechanism is an essential issue regarding the selective synthesis of each individual structure, owing to the fact that yields by present methods are only about 10% for C60 and much less for the larger or endohedral fullerenes.
In general, tremendous advances in nanoscience have been made since the discovery of fullerenes. Unfortunately, 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. Therefore, to address this, researchers from the Institute of Chemistry, Chinese Academy of Sciences, Beijing, China: Dr Bo Wu, Dr. Li Jiang and Professor Chunru Wang, in collaboration with Professor Yi Luo at the Royal Institute of Technology in Sweden, proposed to study the variation in the relative yields of fullerenes under different conditions to infer the formation process by controlled experiments. Their work is currently published in the research journal, Angewandte Chemie International Edition.
In their approach, five typical polyaromatic hydrocarbons (PAHs) were mixed with graphite powder in various proportions, and filled into the hollow graphite rods to be used as the sacrificial electrode during the preparation of the fullerenes. From the change yield when adding different PAHs, it was supposed that the formation of C60 was mainly via a fragment-assembling process.
The experiments and theoretical analysis showed that the formation of fullerenes could be affected by the addition of polycyclic aromatic compounds. Consequently, it was proposed that the formation of C60 during arc discharge synthesis was fragment assembling, while the yield of C2m (m = 35, 38, 39) was strongly enhanced by building-block splicing. In addition, several features of the building blocks were put forward to predict the extent of their influence to the formation of larger fullerenes C2n (n ≥ 42).
In summary, the study presented experimental and theoretical approaches for investigating the relative yield variation of fullerenes under different conditions, with the aim being to shed light on fullerene formation. It was shown that generation of debris could effectively improve the yield of C60. Moreover, addition of polyaromatic hydrocarbons was shown to affect the formation of fullerenes thus suggesting a probable building block mechanism for large fullerenes. In a statement to Advances in Engineering, Professor Chunru Wang, the corresponding author highlighted that their study 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.
Bo Wu, Li Jiang, Yi Luo, and Chunru Wang. The Effect of the Polyaromatic Hydrocarbon in the Formation of Fullerenes. Angewandte Chemie International Edition 2020, volume 59, page 3942 –3947.