Marie Finas

PhD Topic : Bandgap engineering of nanodiamonds for photocatalysis under visible light

Hydrogenated diamond nanoparticles (nanodiamonds) preserve outstanding properties of bulk diamond (negative electron affinity, generation of solvated electrons) [1], with a specific surface area up to 400 m2/g. Few studies underlined CO2 reduction [2] or perfluorocarbides degradation [3] by solvated electrons from hydrogenated nanodiamonds under UV. Recently, the generation of solvated electrons by hydrogenated detonation ND under visible excitation (400 nm) was evidenced by spectroscopic measurements. This effect is linked to the presence of graphitic reconstructions coexisting with C-H terminations at H-ND surface [4]. Moreover, hydrogenated nanodiamonds are dispersable in water with a positive surface charge (zeta potentiel > +60 mV). According to these complementary assets, nanodiamonds are excellent candidates for photocatalysis applications. CEA NIMBE behaves a recognized expertise in the synthesis and in the surface and structural modifications of nanodiamonds using different techniques under gas phase (plasma, annealing at high temperature under H2, NH3, O2, air, vide, etc.).
This PhD aims to perform a bandgap engineering of nanodiamonds to introduce intermediate electronic states improving the photocatalytic properties under visible light. Several strategies will be followed on detonation (5 nm) or milled (5-50 nm) nanodiamonds: tuning of hydrogenation conditions, incorporation of controlled graphitic reconstructions at the surface [5], p-type (boron) or n-type (nitrogen or phosphorus) doping of diamond core, nanostructuration of nanodiamonds surface to enhance their specific surface area.
Surface chemistry and crystalline structure of synthetized nanodiamonds will be characterized at CEA NIMBE by X-ray diffraction (XRD), IR, Raman and XPS spectroscopies and ERDA. The band structure of the different particles will be investigated by XPS and UPS whereas carbon sp2/sp3 hybridization states will be probed by REELS (collaboration with Versailles University).
The different nanodiamonds will be dispersed in water by ultrasonic method. Via a multi-scale study led by SAXS and cryo-TEM (collaboration with Ecole Polytechnique), the spatial organization of nanodiamonds in the aqueous suspension will be determined versus their nature, concentration and surface chemistry. The effect of the atmosphere used for suspension preparation on colloidal properties will be also studied. From SAXS measurements, the area of the nanodiamonds/water interface (m2/L) will be measured for each sample.
Finally, photocatalytic properties for CO2 reduction under visible light will be compared for the most pertinent nanodiamonds. These experiences performed at CEA NIMBE may be completed by in operando XPS on TEMPO beamline at SOLEIL Synchrotron.
Références
[1] Zhu et al, Nature Mater. 12 (2013) 836
[2] Zhang et al, Diam. Relat. Mater. 78 (2017) 24
[3] Maza, Degradation of PFOS by sub-Bandgap Irradiation of Hydrogen Terminated Diamond Nanoparticles, MRS Fall Meeting, 2020
[4] Buchner et al, Early dynamics of the emission of solvated electrons from nanodiamonds in water DOI 10.26434/chemrxiv-2021-f754f (2021)
[5] Ducrozet et al, Nanomaterials 11 (2021) 2671