Non thermal plasma in liquid media: Effect on inulin depolymerization and functionalization.

We report the complete conversion of inulin in gas/liquid media by a dielectric barrier discharge plasma at atmospheric pressure. Depending on the plasma treatment time (from 1 to 30 min) and the chemical nature of the gases (air, oxygen, nitrogen), it was possible to depolymerize inulin into fructo-oligosaccharides with a degree of polymerization under 5 or to achieve a total conversion of inulin into its two monomeric constituents, fructose and glucose in 20 min, without any degradation products. Combined results from liquid chromatography (HPLC), solid state Nuclear Magnetic Resonance (ssNMR) and mass spectroscopy revealed that the breakage of the ß 1-4-bridged oxygen occurs by an acidic attack, following the oxidation of the polymer. Infrared spectroscopy revealed the oxidation and breakage of the polymer and also adsorption of nitrate species. Non thermal plasma treatment appears as a promising technology for the efficient production of mono and oligosaccharides from various sources for the added value molecules in food and pharmaceutical application domains.

Impact of Nonthermal Atmospheric Plasma on the Structure of Cellulose: Access to Soluble Branched Glucans.

We have investigated the effect of non-thermal atmospheric plasma (NTAP) on the structure of microcrystalline cellulose. In particular, by means of different characterization methods, we demonstrate that NTAP promotes the partial cleavage of the ß-1,4 glycosidic bond of cellulose leading to the release of short-chain cellodextrins that are reassembled in situ, preferentially at the C6 position, to form branched glucans with either a glucosyl or anhydroglucosyl terminal residue. The ramification of cellulosic chain induced by NTAP yields branched glucans that are soluble in DMSO or in water, thus opening a straightforward access to processable glucans from cellulose. Importantly, the absence of solvent and catalyst considerably facilitates downstream processing as compared to (bio)catalytic processes which typically occur in diluted conditions.

How boron nitride forms a regular nanomesh on Rh(111).

Boron nitride forms nearly perfectly regular films with a thickness of precisely one atom on various metal surfaces. Here, we follow the formation of boron nitride layers on Rh(111) with scanning tunneling microscopy (STM) under realistic growth conditions, up to 1200 K. Our STM movies demonstrate in detail how the structure grows and how defects are introduced. Based on these observations we arrive at the optimal recipe for a high-quality overlayer.

Ethene adsorption, dehydrogenation and reaction with Pd(110): Pd as a carbon 'sponge'.

The interaction of ethene with the Pd(110) surface has been investigated, mainly with a view to understanding the dehydrogenation reactions of the molecule and mainly using a molecular beam reactor. Ethene adsorbs with a high probability over the temperature range 130 to 800 K with the low-coverage sticking probability dropping from 0.8 at 130 K to 0.35 at 800 K. The adsorption is of the precursor type, with a weakly held form of ethene being the intermediate between the gas phase and strong chemisorption. Dehydrogenation begins at approximately 300 K and is fast above 350 K. If adsorption is carried out at temperatures up to approximately 380 K, adsorption saturates after about 0.25 monolayer have adsorbed, but above approximately 450 K, adsorption continues at a high rate with continuous hydrogen evolution and C deposition onto the surface. It appears that, in the intermediate temperature range, the carbonaceous species formed is located in the top layer and thus interferes with adsorption, whereas the C goes subsurface above 450 K, the adsorption is almost unaffected, and the C signal is significantly attenuated in XPS. However, the deposited carbon can easily be removed again by reaction with oxygen, thus implying that the carbon remains in the selvedge, that is, in the immediate subsurface region probably consisting of a few atomic layers. No well-ordered structures are identified in either LEED or STM, though some evidence of a c(2 x 2) structure can be seen. The Pd surface, at least above 450 K, appears to act as a "sponge" for carbon atoms, and this effect is also seen for the adsorption of other hydrocarbons such as acetaldehyde and acetic acid.