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Falco C.,Max Planck Institute for Colloids | Baccile N.,CNRS Laboratory of Condensed Matter Chemistry, Paris | Titirici M.-M.,Max Planck Institute for Colloids
Green Chemistry | Year: 2011

Hydrothermal carbonization (HTC) has demonstrated that it is an effective technique for the production of functionalized carbon materials from simple carbohydrates, such as monosaccharides and disaccharides. The chemical structure of the HTC carbon has been identified in detail by means of solid-state MAS 13C NMR investigations. However, it has not yet been clearly shown what the effects are of the processing temperature and time on the chemical structure and morphology of the generated HTC carbon. This study shows, with the help of SEM, elemental and yield analysis and solid-state MAS 13C NMR, the effects of these two key variables on the final nature of the produced material, allowing the development of a mechanistic model. According to the chosen set of processing parameters, the chemical structure of the HTC carbon can be tuned from polyfuran rich in oxygen containing functional groups to a carbon network of extensive aromatic domains. The same kind of investigation using lignocellulosic biomass as a carbon precursor shows a striking difference between the HTC mechanism of glucose and cellulose. The biopolymer, when it is treated under mild hydrothermal conditions (180-280 °C), tends to react according to a reaction scheme which leads to its direct transformation into an aromatic carbon network and which has strong similarities with classical pyrolysis. This journal is © The Royal Society of Chemistry. Source

Falco C.,Max Planck Institute for Colloids | Perez Caballero F.,Max Planck Institute for Colloids | Babonneau F.,University Pierre and Marie Curie | Babonneau F.,CNRS Laboratory of Condensed Matter Chemistry, Paris | And 7 more authors.
Langmuir | Year: 2011

The objective of this paper is to better describe the structure of the hydrothermal carbon (HTC) process and put it in relationship with the more classical pyrolytic carbons. Indeed, despite the low energetic impact and the number of applications described so far for HTC, very little is known about the structure, reaction mechanism, and the way these materials relate to coals. Are HTC and calcination processes equivalent? Are the structures of the processed materials related to each other in any way? Which is the extent of polyaromatic hydrocarbons (PAH) inside HTC? In this work, the effect of hydrothermal treatment and pyrolysis are compared on glucose, a good model carbohydrate; a detailed single-quantum double-quantum (SQ-DQ) solid state 13C NMR study of the HTC and calcined HTC is used to interpret the spectral region corresponding to the signal of furanic and arene groups. These data are compared to the spectroscopic signatures of calcined glucose, starch, and xylose. A semiquantitative analysis of the 13C NMR spectra provides an estimation of the furanic-to-arene ratio which varies from 1:1 to 4:1 according to the processing conditions and carbohydrate employed. In addition, we formulate some hypothesis, validated by DFT (density functional theory) modeling associated with 13C NMR chemical shifts calculations, about the possible furan-rich structural intermediates that occur in the coalification process leading to condensed polyaromatic structures. In combination with a broad parallel study on the HTC processing conditions effect on glucose, cellulose, and raw biomass (Falco, C.; Baccile, N.; Titirici, M.-M. Green Chem., 2011, DOI: 10.1039/C1GC15742F), we propose a broad reaction scheme and in which we show that, through HTC, it is possible to tune the furan-to-arene ratio composing the aromatic core of the produced HTC carbons, which is not possible if calcination is used alone, in the temperature range below 350 °C. © 2011 American Chemical Society. Source

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