Nanodiamonds as photocatalysts

October 19, 2018, Helmholtz-Zentrum Berlin für Materialien und Energie
Doped diamond foam. Credit: P. Knittel/Fraunhofer IAF

Climate change is in full swing and will continue unabated as long as CO2 emissions continue. One possible solution is to return CO2 to the energy cycle: CO2 could be processed with water into methanol, a fuel that can be easily transported and stored. However, the reaction, which is reminiscent of a partial process of photosynthesis, requires energy and catalysts. Developing light-active photocatalysts from abundant, easily obtained materials would enable green, climate-neutral solar fuels.

A candidate for such photocatalysts are so-called diamond nanomaterials—these include nanostructured carbon foams with a , and tiny nanocrystals of a few thousand that are soluble in water and look like a black slurry. In order for these materials to become catalytically active, however, they require UV light excitation. Only this spectral range of sunlight is rich enough in energy to transport electrons from the material into a free state. Only then can solvated electrons be emitted in water and react with the dissolved CO2 to form methanol.

However, the UV component in the solar spectrum is not very high. Photocatalysts that could also use the visible spectrum of sunlight would be ideal. This is where the work of HZB-scientist Tristan Petit and his cooperation partners in DIACAT comes in: Modelling the energy levels in such materials shows that intermediate stages can be built into the band gap by doping with foreign atoms. Boron, a trivalent element, appears to be particularly important.

Petit and his team therefore investigated samples of polycrystalline diamonds, diamond foams and nanodiamonds. These samples had previously been synthesized in the groups of Anke Krüger in Würzburg and Christoph Nebel in Freiburg. At BESSY II. The researchers used X-ray absorption spectroscopy to measure the unoccupied energy states where electrons could possibly be excited by visible light. "The present near the surface of these nanodiamonds actually lead to the desired intermediate stages in the ," explains Ph.D student Sneha Choudhury, first author of the study. These intermediate stages are typically very close to the valence bands, and thus do not allow the effective use of . However, the measurements show that this also depends on the structure of the nanomaterials.

"We can introduce and possibly control such additional steps in the diamond bandgap by specifically modifying the morphology and doping," says Tristan Petit. Doping with phosphorus or nitrogen could also offer new opportunities.

Explore further: Nanostructuring increases efficiency of metal-free photocatalysts by factor 11

More information: Sneha Choudhury et al, Combining nanostructuration with boron doping to alter sub band gap acceptor states in diamond materials, Journal of Materials Chemistry A (2018). DOI: 10.1039/c8ta05594g

Related Stories

Chemists test a new nanocatalyst for obtaining hydrogen

October 17, 2018

A chemist from RUDN was the first to use catalysts with ruthenium nanoparticles to obtain hydrogen under the influence of visible light and UV radiation. In the future, such catalysts may be used for large-scale production ...

Holes in valence bands of nanodiamonds discovered

January 28, 2015

Nanodiamonds are tiny crystals only a few nanometers in size. While they possess the crystalline structure of diamonds, their properties diverge considerably from those of their big brothers, because their surfaces play a ...

Reducing CO2 with common elements and sunlight

June 26, 2018

An international collaborative research group including Tokyo Institute of Technology, Universite PARIS DIDEROT and CNRS has discovered that CO2 is selectively reduced to CO when a photocatalyst composed of an organic semiconductor ...

Recommended for you

Materials chemists tap body heat to power 'smart garments'

January 22, 2019

Many wearable biosensors, data transmitters and similar tech advances for personalized health monitoring have now been "creatively miniaturized," says materials chemist Trisha Andrew at the University of Massachusetts Amherst, ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

szore88
1 / 5 (3) Oct 19, 2018
What a load of nonsense. Hey, lefties, your plot to destroy the American industrial base is pathetic. The Earth is cooling anyway.
mrburns
1 / 5 (2) Oct 19, 2018
Man-made climate change remains theory most of whose predictions have proven false. All the evidence points to the theory being false. So one must rate this article as total crap

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.