Nanodiamond materials have great potential as catalysts. Inexpensive carbon nanoparticles provide very large surface areas relative to their volume. However, for catalytic acceleration of chemical reactions in aqueous media, electrons from the catalyst must go into solvation, and this requires high-energy ultraviolet light for excitation in pure diamond materials. On the other hand, the extremely small size of nanoparticles allows the creation of new molecular states on the surfaces of nanodiamonds that also absorb visible light.
As part of the DIACAT project, the team from HZB has now investigated different variants of nanodiamond materials during light excitation and analyzed the processes with extremely high temporal resolution. Nanodiamond samples with different surface chemistries were produced by the group of Dr. Jean-Charles Arnaud, CEA, France, and Prof. Anke Kruger, now at the University of Stuttgart. Nanoparticles differed in their surface, which contained different amounts of hydrogen or oxygen atoms.
Hydrogen helps – and so does fullerene-like carbon
“Hydrogen on surfaces makes it much easier to emit electrons,” explains Dr. Tristan Petty, nanodiamond expert at HZB. “Among the many options, we found that a certain combination of hydrogen as well as fullerene-like carbon on the surface of the nanoparticles was ideal,” he says.
Ultrafast laser excitations
At the HZB Laser Laboratory, they studied aqueous dispersions of nanodiamonds with different end surfaces, such as hydrogen, -OH or -COOH, after exciting them with ultrafast laser pulses. “We were able to experimentally measure exactly how the absorption profile behaves with different excitation wavelengths in the UV range at 225 nm and with blue light in the visible range at 400 nm,” explains Dr Christoph Mershian, HZB.
Picoseconds after excitation
“We wanted to find out what happens in the first crucial picoseconds after being excited by light, because that’s when the electron leaves the surface and goes into the water,” Mershian says. A theoretical group led by Dr. Anika Bende contributed modeling using density functional theory to interpret the spectra. The data showed, as expected, that UV light drove electrons into solution in all samples, but for those samples that had a fullerene-like carbon on their surface, this was also achieved with visible light.
Blue light can work
“In this work, we show for the first time, as far as we know, that the emission of solvated electrons from nanodiamonds in water is possible in visible light!”, Petty summarizes the results. This is a decisive step towards the discovery of nanodiamond materials as photocatalysts. These low-cost, metal-free materials could be the key to further CO recycling2 into valuable hydrocarbons with sunlight in the future, or even for N conversion2 in ammonia.
Note: DIACAT has received funding from the European Union’s Horizon 2020 research and innovation program under Grant Agreement no 665085.
Materials is provided Helmholtz-Zentrum Berlin für Materialien und Energie. Note: Content can be edited for style and length.