Holes in valence bands of nanodiamonds discovered
Nanodiamonds are tiny crystals only a few nanometres in size. Mohamed Sennour, MINES ParisTech.
Dr. Tristan Petit (right side) received a C’Nano award under the category of interdisciplinary research for his doctoral dissertation in late 2014. Credit C'Nano © C'Nano
Researchers hope that their properties might be altered to permit nanodiamonds to be used as catalysts for generating hydrogen from sunlight
Nanodiamonds are tiny crystals only a few nanometres 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 dominant role in comparison to their extremely small volumes. Suspended in aqueous solutions, they could function as taxis for active substances in biomedical applications, for example, or be used as catalysts for splitting water. But how are the electronic properties of nanodiamonds deposited on a solid-state substrate different from those displayed by nanodiamonds in aqueous solutions? Dr. Tristan Petit working in the HZB team headed by Prof. Emad F. Aziz has now investigated this with the help of absorption and emission spectroscopy at BESSY II. Their results, just published in Nanoscale, demonstrate that nanodiamonds display valence holes in aqueous solutions, which are not observed when characterized as a thin film.
“The interaction between the nanodiamonds and the neighbouring molecules and ions is especially strong in water”, say Petit. The adsorption of active pharmaceutical ingredients on nanodiamonds can be influenced, for example, by adding salts or changing the pH value. Petit and his colleagues have now discovered that the electronic signature of surface states of nanodiamonds in aqueous dispersions are considerably different from those of nanodiamonds on a solid-state substrate.
With the help of micro-jet technology developed by Emad Aziz at HZB, they examined liquid samples in vacuum using X-ray spectroscopy and developed a detailed picture of the filled and unfilled electron states in valence and conduction bands. Their results show that holes, i.e. missing electrons in the valence band, formed on the surfaces of the nanodiamonds in the aqueous dispersion. “This suggests that electrons at the surface of nanodiamonds are donated to the surrounding water molecules”, Petit suggests. The physicists suspect they might also influence the nanoparticles’ chemical, optical, and catalytic properties through changes to their electronic structure. They would like to determine in future studies whether the catalytic effect of nanodiamonds in aqueous environment can be increased in order to split water molecules into oxygen and hydrogen using light.
Reference: Valence holes observed in nanodiamonds dispersed in water, Tristan Petit, Mika Pflüger, Daniel Tolksdorf, Jie Xiao and Emad Flear Aziz, Nanoscale, 2015, DOI: 10.1039/C4NR06639A
Postscript: Dr. Tristan Petit received a C’Nano award under the category of interdisciplinary research for his doctoral dissertation in late 2014. Several research institutions in France have amalgamated under the umbrella organisation C’Nano to conduct research and development on nanomaterials and nanotechnologies.
For his doctoral work, Tristan Petit conducted research at the Laboratoire Capteurs Diamant (CEA LIST Saclay) on properties of nanodiamonds and their potential suitability for cancer treatment. Dr. Tristan Petit has been pursuing research on a team under Prof. Emad Flear Aziz at HZB through a postdoctoral grant from the Alexander von Humboldt Foundation (since summer 2013).
More information on the C’Nano Doctoral awards:
- Battery research: visualisation of aging processes operandoLithium button cells with electrodes made of nickel-manganese-cobalt oxides (NMC) are very powerful. Unfortunately, their capacity decreases over time. Now, for the first time, a team has used a non-destructive method to observe how the elemental composition of the individual layers in a button cell changes during charging cycles. The study, now published in the journal Small, involved teams from the Physikalisch-Technische Bundesanstalt (PTB), the University of Münster, researchers from the SyncLab research group at HZB and the BLiX laboratory at the Technical University of Berlin. Measurements were carried out in the BLiX laboratory and at the BESSY II synchrotron radiation source.
- New instrument at BESSY II: The OÆSE endstation in EMILA new instrument is now available at BESSY II for investigating catalyst materials, battery electrodes and other energy devices under operating conditions: the Operando Absorption and Emission Spectroscopy on EMIL (OÆSE) endstation in the Energy Materials In-situ Laboratory Berlin (EMIL). A team led by Raul Garcia-Diez and Marcus Bär showcases the instrument’s capabilities via a proof-of-concept study on electrodeposited copper.
- Green hydrogen: A cage structured material transforms into a performant catalystClathrates are characterised by a complex cage structure that provides space for guest ions too. Now, for the first time, a team has investigated the suitability of clathrates as catalysts for electrolytic hydrogen production with impressive results: the clathrate sample was even more efficient and robust than currently used nickel-based catalysts. They also found a reason for this enhanced performance. Measurements at BESSY II showed that the clathrates undergo structural changes during the catalytic reaction: the three-dimensional cage structure decays into ultra-thin nanosheets that allow maximum contact with active catalytic centres. The study has been published in the journal ‘Angewandte Chemie’.