New porous diamond structure created from carbon

The 2025 Nobel Prize in Chemistry was awarded for the development of new porous materials built from carbon-based molecules and metal ions, known as metal–organic frameworks (MOFs). Karl Börjesson’s research group at the University of Gothenburg has long been interested in creating porous materials without metal ions, in which carbon-based molecules instead bind to non-metals to form so-called covalent organic frameworks (COFs). The new diamondiyne structure can be regarded as an entirely carbon-based version of a COF.

“One of the most intriguing features of COFs is their highly programmable nanopore systems. Using organic chemistry tools, these pores can be deliberately designed to selectively accommodate target species, enabling applications in CO₂ capture, water purification, and battery technologies, says Yizhou Yang, Assistant Professor at Chalmers University of Technology.

He was previously a postdoctoral researcher in the research group at the University of Gothenburg and carried out a large part of the experimental work behind the new study.

A major challenge to create the theoretical structure

The idea for diamondiyne came after a colleague told Karl Börjesson about a website where theoretical chemists had listed carbon allotropes that calculations suggested should be possible to form. The list was almost infinite.

Allotropes are different structural forms of the same chemical element. Diamond and graphite are examples of carbon allotropes. Diamondiyne, whose tetrahedral structure was first described theoretically 35 years ago, is another.

Successfully linking the carbon atoms into the predicted structure has taken a long time.

“The first two years involved more failed attempts than I can remember. I explored many different reaction conditions. The chemistry itself was relatively straightforward. The main challenge was obtaining a crystalline product,” says Yizhou Yang.

Diamondiyne can be produced using relatively simple and inexpensive equipment. The material forms as a thin film at the interface between two liquids. There, the carbon atoms arrange themselves into tetrahedra that connect corner to corner in all three dimensions.

“The structure creates voids between the tetrahedra. The carbon allotrope can therefore be compared to a porous diamond. But unlike diamonds, diamondiyne does not require high pressure to make the carbon atoms bond to one another,” says Karl Börjesson.

"A beautifully ordered crystal lattice"

Yizhou Yang clearly remembers the first time he saw signs of the crystal structure using the transmission electron microscope at Chalmers Materials Analysis Laboratory.

“When bright, star-like spots appeared in the FFT (fast Fourier transform) pattern – a typical sign of crystallinity – my heart leaped into my throat. Holding my breath, I carefully fine-tuned the microscope’s focus until a beautifully ordered crystal lattice appeared on the screen. At that moment, my excitement was beyond words – I knew we had made it.”

The crystal structure was subsequently confirmed using electron microscopy at Stockholm University, although it could only be observed in patches on the surface of the film. Many things can go wrong and prevent the carbon atoms from forming diamondiyne.

“We have at least managed to produce repeating patterns of diamondiyne in a volume measuring 10 nanometres on each side, and the images of the patterns correspond well with the theoretical models,” says Karl Börjesson.

Further studies of properties and applications

For a long time, the known carbon allotropes were limited to diamond and graphite. These were later joined by the synthetically produced carbon structures fullerene, carbon nanotubes and graphene. In recent years, further carbon allotropes have been produced, but according to the researchers, diamondiyne stands out because of its three-dimensional structure.

The discoveries of both fullerenes and graphene have been recognised with Nobel Prizes. In both cases, the discoveries opened up entirely new ways of structuring carbon and paved the way for materials with new properties.

“We will now investigate the properties of diamondiyne and how it might be used. One exciting aspect of the porous structure is that several diamondiyne structures could potentially be interwoven through each other’s voids,” says Karl Börjesson.

Yizhou Yang ‘s research team at Chalmers specifically focuses on the utilisation of framework materials.

“In the next stage, we will explore diamondiyne as a functional component in electronic devices and investigate how different particle species move through its porous networks,” he says.