Tristan Petit

Surface properties of hydrogenated nanodiamonds: a chemical investigation

Hydrogen terminations (C-H) confer to diamond layers specific surface properties such as a negative electron affinity and a superficial conductive layer, opening the way to specific functionalization routes. For example, efficient covalent bonding of diazonium salts or of alkene moieties can be performed on hydrogenated diamond thin films, owing to electronic exchanges at the interface. Here, we report on the chemical reactivity of fully hydrogenated High Pressure High Temperature (HPHT) nanodiamonds (H-NDs) towards such grafting, with respect to the reactivity of as-received NDs. Chemical characterizations such as FTIR, XPS analysis and Zeta potential measurements reveal a clear selectivity of such couplings on H-NDs, suggesting that C-H related surface properties remain dominant even on particles at the nanoscale. These results on hydrogenated NDs open up the route to a broad range of new functionalizations for innovative NDs applications development.

Engineering oxygen-containing and amino groups into two-dimensional atomically-thin porous polymeric carbon nitrogen for enhanced photocatalytic hydrogen production

Polymeric carbon nitride (PCN) is a promising earth-abundant photocatalyst for solar energy conversion. However, the photocatalytic activities of PCN-based materials remain moderate because of their poor dispersion in water and their fast electron–hole recombination. Here, a facile two-step continuous thermal treatment strategy is presented to endow the bulk PCN nanosheets with an atomically-thin structure, strong hydrophilicity and Lewis basicity to dramatically enhance the photocatalytic hydrogen (H2) generation performance. The formation of the oxygen-containing and amino groups in the atomically-thin PCN sheets improves the charge separation and provides rich active sites for the surface reaction. Such synergistic effects lead to a superior visible-light-driven photocatalytic activity and its H2 evolution rate (1233.5 μmol h−1 g−1) is more than 11 times higher than the bulk PCN using Ni as a cocatalyst. Additionally, the H2 evolution rate can reach 20948.6 μmol h−1 g−1 using Pt as a cocatalyst under AM1.5G solar irradiation.

Interactions with solvent

Abstract Interaction between nanodiamonds and solvent molecules are discussed in this chapter, with a special emphasis on water as a solvent. The impact of solvent adsorption on NDs surface properties and solvent structure modifications induced by nanodiamonds are presented. First, solvent interaction with nanodiamonds in vacuum is discussed. Experiments performed under gaseous atmosphere and in liquid phase are then successively presented. Most of the results are based on vibrational or electronic spectroscopy measurements, but other methods are also mentioned. Soft X-ray spectroscopy methods to investigate nanodiamonds in liquid are particularly highlighted.

Combining nanostructuration with boron doping to alter sub band gap acceptor states in diamond materials

Diamond is a promising metal-free photocatalyst for nitrogen and carbon dioxide reduction in aqueous environment owing to the possibility of emitting highly reducing solvated electrons. However, the wide band gap of diamond necessitates the use of deep UV to trigger a photochemical reaction. Boron doping introduces acceptor levels within the band gap of diamonds, which may facilitate visible-light absorption through defect-based transitions. In this work, unoccupied electronic states from different boron-doped diamond materials, including single crystal, polycrystalline film, diamond foam, and nanodiamonds were probed by soft X-ray absorption spectroscopy at the carbon K edge. Supported by density functional theory calculations, we demonstrate that boron close to the surfaces of diamond crystallites induce acceptor levels in the band gap, which are dependent on the diamond morphology. Combining boron-doping with morphology engineering, this work thus demonstrates that electron acceptor states within the diamond band gap can be controlled.

Multiscale Photo-Based In-Situ and Operando Spectroscopies in Time and Energy Landscapes

Following catalytic reactions, in-situ and operando are now the focus of a number of dedicated experiments at light sources which have been developed to track the electronic and molecular structural dynamics of catalysts. The challenges for this goal are two-fold: first, the development of spectroscopic tools in the energy domain and time domain is required. The photocatalytic processes have early dynamics of tens of femtoseconds, while further reaction takes seconds, minutes, and even hours. Second, a combination of tools to probe processes not only in solids, but also in solutions and at interfaces, is now needed. In this special issue, we present recent developments at the synchrotron facility BESSY II using photon energy from the infrared and extreme ultraviolet up to the soft X-ray regime for in-situ and operando applications addressing these two major challenges. As this work is a result of contributions from several groups, each section will present the groups activities and related team members involved.