Carbon nanotubes (CNTs) are among the most promising nanomaterials for future technologies because of their exceptional mechanical strength, electrical conductivity, and thermal performance. However, translating these remarkable properties into practical products depends on the ability to efficiently grow long, high-quality CNTs. One of the major challenges is that the catalyst nanoparticles responsible for CNT formation gradually lose activity during synthesis, limiting growth duration and restricting the attainable length and quality of CNT forests.
Addressing this challenge, a research team was led by Associate Professor Hisashi Sugime, along with Lecturer Hiroyuki Asakura from the Department of Applied Chemistry, Faculty of Science and Engineering, Kindai University, Japan, and Dr. Shin-ichi Naya from the Environmental Research Laboratory, Kindai University, Japan. The researchers investigated whether rare-earth cocatalysts could improve the stability of iron (Fe)-based catalysts during CNT growth. They compared three rare-earth elements—erbium (Er), gadolinium (Gd), and scandium (Sc)—to determine their effectiveness in extending catalyst lifetime and promoting the growth of centimeter-long CNT forests. Their findings were made available online on May 05, 2026, and published in Volume 256 of the journal Carbon on June 01, 2026.
The team prepared catalyst systems consisting of Fe deposited on an aluminum oxide support together with one of the three rare-earth cocatalysts. Using chemical vapor deposition, they monitored CNT growth under different temperature conditions and analyzed the resulting materials with scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, atomic force microscopy, and X-ray absorption spectroscopy. These techniques allowed the researchers to evaluate catalyst behavior, CNT structure, and the chemical state of Fe during growth.
At a growth temperature of 800 °C, all three rare-earth cocatalysts successfully prolonged catalyst lifetime compared to Fe alone, enabling the growth of centimeter-scale CNT forests. Growth rates and CNT structures were broadly similar among the three systems. However, the differences became striking when the researchers increased the temperature to 900 °C, a more demanding growth condition that accelerates catalyst degradation. Under these conditions, the Fe–Sc catalyst remained active for about 18 minutes, whereas catalysts containing Er or Gd lost activity after only 7–8 minutes.
Detailed analyses revealed the reason behind Sc’s superior performance. The Fe nanoparticles experienced much less coarsening and aggregation when Sc was present. X-ray measurements further showed that Sc helped maintain Fe in a more oxidized state, which is associated with greater resistance to structural changes and deactivation. This stabilization effect allowed the catalyst to continue producing CNTs for a substantially longer period even under elevated temperatures.
“This study demonstrates that Sc can significantly improve the durability of Fe catalysts during CNT growth,” explains Dr. Sugime. “ Maintaining catalyst stability is essential for producing longer and higher-quality CNTs efficiently.”
The researchers emphasize that this is the first report of a binary catalyst system composed of Fe and Sc for high-temperature reactions. The discovery provides new insights into how catalyst chemistry can be engineered to control nanoparticle stability and extend catalyst lifetime.
According to the team, the work could support the development of novel electrode materials for higher-power, longer-lasting batteries as well as advanced electrochemical biosensors. “Our motivation has been to find practical ways to harness the outstanding properties of CNTs, ” says Dr. Sugime. “Previous studies suggested that suppressing structural changes in catalyst nanoparticles could prolong CNT growth, and this inspired us to explore new cocatalyst combinations.”
Overall, the findings establish Fe–Sc as a promising catalyst system for growing long, high-quality CNT forests under demanding conditions. By providing a new strategy for stabilizing catalysts at high temperatures, the study could contribute to future innovations in advanced materials, energy-storage devices, sensing technologies, and high-strength structural applications over the coming decade.
Reference
DOI: https://doi.org/10.1016/j.carbon.2026.121661
About Kindai University
Kindai University was established in 1949 after the merger of Osaka Technical College (founded in 1925) and Osaka Science and Engineering University (founded in 1943). Over the past several decades, the university has transformed into a comprehensive educational organization with an ever-growing reputation. Kindai University has over 2,200 full-time faculty members, 6 campuses, and 18 research centers. As an academic institution offering a broad range of programs from across disciplines, Kindai University strives to impart practical education while nurturing intellectual and emotional capabilities. The university’s academic programs are fully accredited by Japan’s Ministry of Education, Culture, Sports, Science and Technology as well as by the National Institution for Academic Degrees and University Evaluation.
Website: https://www.kindai.ac.jp/english/
About Associate Professor Hisashi Sugime from Kindai University
Dr. Hisashi Sugime is an Associate Professor in the Department of Applied Chemistry, Faculty of Science and Engineering, Kindai University, Japan. His research focuses on carbon nanotubes, MXenes, electrochemical biosensors, chemical engineering, physical chemistry, and nanotechnology. He has authored 109 publications that have received 2,596 citations, reflecting his contributions to advanced materials and sensing technologies. From April 2016 to March 2021, he served as an Assistant Professor at Waseda University, Japan. He earned his Ph.D. in Engineering, specializing in Chemical System Engineering, from The University of Tokyo, Japan, and continues to advance interdisciplinary research in emerging nanomaterials.
Funding information
This work was financially supported by the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (KAKENHI, grant number: 24K08209). This work was performed under the approval of the Photon Factory Program Advisory Committee (proposal number: 2023G109).
Carbon
Experimental study
Not applicable
Effect of rare-earth cocatalysts on the growth of centimeter-long carbon nanotube forests
1-Jun-2026
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.