Frédéric Goettmann

The plasmon band in noble metal nanoparticles: an introduction to theory and applications

Noble metal nanoparticles chemistry is a domain in rapid expansion, as those objects lead to interesting applications in the fields of catalysis, biosensing, electronics and optics. Because of their structure, intermediate between that of molecules and of bulk material, they enable to bridge the gap between molecular chemistry and surface science. In particular, their optical properties, known since antiquity, have already shown a part of their potential and further major discoveries can reasonably be expected. Their most insightful optical properties rely on a strong absorption in the visible spectrum, called the plasmon band, that colloidal solutions of gold, silver or copper feature. Herein we wish to present a comprehensible overview of the fundamentals of the theories explaining the phenomenon dedicated to chemists seeking an introduction to those features. We will also give a brief review of the recently published body of relevant literature with reference to the aforementioned theory.

Selective partial hydrogenation of hydroxy aromatic derivatives with palladium nanoparticles supported on hydrophilic carbon

Selective hydrogenation of phenol to cyclohexanol in the aqueous phase was achieved using a new catalytic system based on palladium particles supported on hydrophilic carbon prepared by one-pot hydrothermal carbonisation.

How does confinement affect the catalytic activity of mesoporous materials

So-called confinement effects in porous materials are known to strongly affect diffusion, phase transformations, catalytic properties, etc. In the field of catalysis, it is generally admitted that antagonistic effects at the mesoscale result in the existence of an optimal catalytic efficiency depending on pore size. Herein we highlight some recent examples of pore size effects and their proposed mechanisms. Confinement studies on periodically organised mesoporous materials must be developed because they should provide a certain clearness of arguments and understanding.

High-surface-area TiO2 and TiN as catalysts for the C-C coupling of alcohols and ketones

To design more sustainable processes for the alkylation of ketones, the use of both atom-ineffective leaving groups such as halides and boron as well as noble-metal-based catalysts should be avoided. For that purpose, high-surface-area titanium nitride was prepared from high-surface-area titanium dioxide using cyanamide as a transcription agent. The resulting nitride as well as the initial oxide proved to be effective and versatile catalysts for the alkylation of ketones with alcohols. Interestingly, the TiN catalyst yields unsaturated compounds, while the oxide-based catalyst mainly yields saturated coupling products. As a result of its metallic properties, TiN shows a strong tendency to catalyse the dehydrogenation of alcohols, which then undergo aldol condensation with ketones. In contrast, TiO(2) promotes the direct nucleophilic attack of ketones on alcohols.

Mesoporous materials in the field of nuclear industry: applications and perspectives

In the context of increasing global energy demand associated with high prices for classical fossil fuels and rising concerns about CO2 emissions, nuclear power is attracting renewed interest. Despite the recent accident in the Fukushima power plant, numerous countries maintain very ambitious nuclear programmes. The Generation IV International Forum [A Technology Roadmap for Generation IV Nuclear Energy Systems, Generation IV International Forum, 2002] (an initiative launched by the US Department of Energy in 2000 to coordinate and promote efforts to design the next generation of nuclear power plants) supports works to develop new power plant designs and innovative concepts in the nuclear fuel cycle. These new concepts aim at achieving higher levels of security and resource efficiency as well as a higher resistance towards nuclear proliferation. Because of this blossoming of new ideas, mesoporous materials, which are already widely found in applications such as catalysis, sensing and optics, are expected to make their way in the field of nuclear power production. Up to now, some (hybrid) mesoporous solids have already been investigated as solid ligands to remove actinides and fission product contaminants from liquid effluents, but also as model materials to investigate radiation defects, as possible nuclear waste disposal form and as functional materials to be placed in or close to new forms of nuclear waste matrices. This contribution aims at reviewing the applications of mesoporous materials already described in the field of nuclear industry, and to underline some promising research directions in this area.

Study of metal nanoparticles stabilised by mixed ligand shell : a striking blue shift of the surface-plasmon band evidencing the formation of janus nanoparticles

Mixed ligand shells stabilising gold nanoparticles have been synthesised using diphenylphosphinine 1 (phosphinine is the phosphorus equivalent of pyridine) and a family of thiol ligands: mercaptoundecanoic acid (2), dodecanethiol (3) and thiophenol (4). Phosphinine 1 and thiols 2 and 3 feature little affinity to one another, so we expected them to self-segregate in pure domains. We studied the resulting particles with UV-vis, FT-IR and TEM (transmission electron microscopy). The plasmonic band of those particles features an unprecedented blue shift compared to the pure ligand-shell nanoparticles, strongly suggesting a polarisation of the particle caused by ligand segregation. FT-IR evidences the formation of nano domains of ligands in pure phase, and some self-aggregation behaviour of the nanoparticles themselves was observed by TEM.

Stability of mesoporous silica under acidic conditions

The stability of various structured mesoporous materials (SBA-1, SBA-3, SBA-15, MCM-41, MCM-48) was tested under acidic stress in order to understand the mechanism of their alteration. The native materials and the materials resulting from acidic attack under various conditions were analysed by small angle X-ray scattering coupled with nitrogen adsorption and solid 29Si NMR. Among three acid media (HCl, H2SO4, H3PO4) at similar ionic strength, we focused particularly on phosphoric acid, which proved to have the strongest impact on the starting materials. The results are discussed by correlating the wall thickness and pore diameter values with regard to stability. In particular, the alteration kinetics were interpreted for the case of SBA-15 in the following scenario: the micropores were first damaged by the acidic stress, and then the mesopores were partially collapsed or partially blocked. We show that a materials resistance against acidic media is linked to a critical wall thickness–pore diameter threshold.

Synthesis of Early-Transition-Metal Carbide and Nitride Nanoparticles through the Urea Route and Their Use as Alkylation Catalysts

The use of urea as either a carbon or a nitrogen source enabled the synthesis of various early-transition-metal nitride and carbide nanoparticles (TiN, NbN, Mo(2)N, W(2)N, NbC(x)N(1-x), Mo(2)C and WC). The ability of these particles to promote alkylation reactions with alcohols was tested on benzyl alcohol and acetophenone at 150 degrees C for 20 h in xylene. Group IV and V ceramics proved to be able to catalyse the formation of 1,3-diphenyl propenone, whereas group VI ceramics showed a tendency to promote the Friedel-Crafts-type reaction of benzyl alcohol on xylene (the solvent). TiN featured the highest activity for the alkylation of ketones and was further tested for more difficult alkylations. Group VI ceramics were further investigated as catalysts for the Friedel-Crafts-type alkylation of aromatics with activated alcohols. Interestingly, even hexanol could be effectively used for these reactions.

Highly regioselective terminal alkynes hydroformylation and Pauson–Khand reaction catalysed by mesoporous organised zirconium oxide based powders

Zirconia-silica mesoporous powders act as very efficient heterogeneous catalysts for both alkyne hydroformylation and Pauson-Khand reaction and yield regioselectivities opposite to those usually observed.

Chlorine borrowing: an efficient method for an easier use of alcohols as alkylation agents

Chlorine functionalised tin dioxide nanoparticles proved able to partially convert alcohols into the corresponding chlorides, which act as alkylation agents with an increased electrophilicity, as evidenced on ether formation and Friedel–Crafts reactions.