Nanodiamond materials have great potential as catalysts. Inexpensive nanoparticles made of carbon provide very large surfaces compared to their volume. However, to catalytically accelerate chemical reactions in an aqueous medium, electrons from the catalyst need to go into solvation and in pure diamond materials this requires high-energy UV light for excitation. On the other hand, the extremely small sizes of the nanoparticles allow new molecular states on the surfaces of nanodiamonds that also absorb visible light.
source https://www.lifetechnology.com/blogs/life-technology-science-news/exploring-nanodiamonds-that-can-be-activated-as-photocatalysts-with-sunlight