Diamonds are a molecule’s best friend

Scientists have turned tiny specks of diamond into “molecular anvils” with the power to trigger chemical reactions, paving the way to a greener method of chemistry.

The study, published in the journal Nature and led by scientists at the US Department of Energy’s SLAC National Accelerator Laboratory and Stanford University, describes how minuscule pieces of diamond and other super-hard materials can squeeze and twist molecules, causing chemical bonds to snap and atoms to exchange electrons.

This is the first time that chemical reactions have been triggered solely by mechanical pressure.

Lead author Hao Yan, from the Stanford Institute for Materials and Energy Sciences (SIMES), explains: “Unlike other mechanical techniques, which basically pull molecules until they break apart, we show that pressure from molecular anvils can both break chemical bonds and trigger another type of reaction where electrons move from one atom to another.”

The experiments in the study used an anvil cell the size of an espresso cup to squeeze samples between two flattened diamonds, each of which weighed about a quarter of a carat. By tightening screws to bring the diamonds closer, enormous pressures were reached — up to one and a half times the pressure at the Earth’s core.

The samples did not deform uniformly; rather, the harder and softer areas compressed by different amounts, twisting the chemical bonds. The team subsequently exploited this behaviour to break specific bonds within individual molecules.

Several experiments used “diamondoids” — specks of diamond weighing less than a billionth of a billionth of a carat — to show that minute changes in the sizes and positions of the anvils could trigger changes at specific points in a molecule, while leaving other areas untouched.

This mechanically-driven method is not only precise, but also efficient and environmentally friendly, since heat or solvents are unnecessary to drive the reactions.

According to co-author Wendy Mao from SLAC and SIMES, the team is now “interested in looking at how pressure can affect a wide range of technologically interesting materials, from superconductors that transmit electricity with no loss to halide perovskites, which have a lot of potential for next-generation solar cells”.

This technique could also trigger reactions that are tricky to do in conventional ways.

“If we want to dream big, could compression help us turn carbon dioxide from the air into fuel, or nitrogen from the air into fertiliser?” Yan says. “These are some of the questions that molecular anvils will allow people to explore.”