Diamond nanomaterials are believed to be prime candidates for cost-effective photocatalysts. Light is used to activate these materials and improve the rate of reaction for CO2 and water to generate carbon-neutral 'solar fuels'.
Doped Diamond Foam. (Credit: P. Knittel/Fraunhofer IAF)
As part of DIACAT, an EU project, scientists recently doped diamond nanomaterials with boron and demonstrated how this method considerably enhances photocatalysis.
CO2 emissions contribute greatly to climate change, and we are unlikely to be able to lower emissions soon. Thus, improving the efficiency of reactions is vital.
One concept is to return CO2 to the energy cycle: CO2 can be processed with water to convert it into methanol — a fuel that can be transported and stored easily.
The reaction, which is indicative of a partial process of photosynthesis, needs catalysts and energy.
The effective utilization of this solar energy and the development of light-active photocatalysts which are made of cheap and abundantly available materials would make it possible to produce "green" solar fuels in a climate-neutral manner.
Diamond nanomaterials need UV for activation.
Diamond nanomaterials are inexpensive, minute nanocrystals of a few thousand carbon atoms. They are soluble in water and appear more like black slurry, or nanostructured "carbon foams" that have high surface area.
These nanomaterials are a promising candidate for methanol production. However, these materials need UV light to become catalytically active.
This spectral range of sunlight is abundantly rich in energy and allows electrons to be transported from the material into a "free state," following which, solvated electrons are emitted in water and allowed to react with the dissolved CO2 to produce methanol.
Can doping help?
Conversely, the UV component within the solar spectrum is not quite high. Photocatalysts that can also utilize the sunlight’s visible spectrum would be perfect.
This is where the efforts of HZB-researcher Tristan Petit and his cooperation associates in DIACAT come in.
They found that by simulating the energy levels in such types of materials, it is possible to build intermediate stages inside the band gap by doping with foreign atoms.
The trivalent element boron seems to be especially vital.
Petit and his team analyzed samples of nanodiamonds, diamond foams, and polycrystalline diamonds.
The boron atoms present near the surface of these nanodiamonds lead to the desired intermediate stages in the band gap.
These intermediate stages are usually extremely close to the valence bands and hence do not enable the effective usage of visible light.
The measurements, however, demonstrate that this also relies on the nanomaterials’ structure."
Sneha Choudhury, First Author
