Stopping carbon dioxide (CO2) before it enters the atmosphere is an important way to reduce greenhouse gas emissions. Carbon capture has been around for many years, but most systems are expensive and inefficient, so it has not been widely adopted. A common industrial approach, aqueous amine scrubbing, requires heating large volumes of liquid to temperatures above 100 °C in order to release the trapped CO2 and reuse the solution. This high energy demand increases operating costs and makes it difficult to use on a large scale.
Solid carbon materials are gaining attention as a more practical option. These materials are relatively inexpensive and have a large surface area that can capture CO2. They can also release gases with less heat, especially if they contain nitrogen-based functional groups. However, there are important limitations. Traditional manufacturing methods place these nitrogen groups randomly throughout the material, making it difficult to pinpoint which particular arrangement will lead to better performance.
To address this challenge, a research team led by Associate Professor Yasuhiro Yamada of the Graduate School of Engineering at Chiba University in Japan and Associate Professor Tomonori Ohba of the Graduate School of Science has developed a new type of carbon material called “bisiazite.” These materials are designed so that the nitrogen groups are arranged next to each other in a controlled manner. Research published in journals carbonco-authored with Kota Kondo, also of Chiba University.
Construction of visiazite by controlled nitrogen pairing
The researchers created three different versions of vishiazite, each with a unique type of adjacent nitrogen arrangement. To generate the vicinal primary amine group (-NH2 group), they first heated a compound called coronene, then treated it with bromine, followed by ammonia gas. This three-step method achieved a selectivity rate of 76%. This means that most of the nitrogen atoms were placed in the intended positions.
Two additional materials were prepared using different starting compounds. One features vicinal pyrrolic nitrogens with 82% selectivity and the other contains vicinal pyridinic nitrogens with 60% selectivity.
Structure validation and performance testing
Each material was applied to activated carbon fibers to create usable samples. The researchers used techniques including nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and computational modeling to confirm the precise placement of the nitrogen groups. These methods confirmed that the nitrogen atoms were arranged side by side rather than randomly distributed.
When tested, the materials showed clear performance differences. Samples containing adjacent -NH2 groups and pyrrolic nitrogen captured more CO2 than untreated carbon fibers. In contrast, little improvement was seen with the pyridinic nitrogen configuration.
CO2 release at low temperatures could reduce energy usage
The most notable discovery concerned how easily the material releases CO2. “Performance evaluation revealed that in carbon materials with adjacent NH2 groups, most of the adsorbed CO2 is desorbed at temperatures below 60 °C. By combining this property with industrial waste heat, we have the potential to achieve an efficient CO2 capture process while significantly reducing operating costs,” emphasizes Dr. Yamada.
Materials containing pyrrolic nitrogen required higher temperatures to release CO2, but their stronger chemical structure may improve long-term stability.
A new path towards cost-effective carbon capture
This study shows that arranging nitrogen groups in specific adjacency patterns can be reliably performed and provides a clear strategy for designing improved carbon-trapping materials. “Our motivation is to contribute to future society and utilize recently developed carbon materials with controlled structures. This study provides a validated route to synthesize engineered nitrogen-doped carbon materials, providing molecular-level control essential for the development of next-generation cost-effective and advanced CO2 capture technologies,” concluded Dr. Yamada.
In addition to capturing CO2, these vithiazite materials can also be used for other applications, such as removing metal ions and acting as catalysts, thanks to their customizable surface properties.
Funding and support
This research was supported by the Mukai Foundation for Science and Technology, the Japan Society for the Promotion of Science (JSPS Grant-in-Aid for Scientific Research JP24K01251), and the Ministry of Education, Culture, Sports, Science and Technology’s Advanced Research Infrastructure Project for Materials and Nanotechnology (ARIM) (grant number JPMXP1225JI0008).
