Julien Parmentier

Template synthesis of a new type of ordered carbon structure from pitch

New ordered nanoporous carbon materials can be synthesized using pitch and mesoporous silica materials as the carbon precursor and template, respectively. In this case, the silica material (type MCM-48 and SBA-15) is impregnated with pitch and further carbonized. After removal of the silica by acid treatment, a graphitizable carbon material with an ordered micro-mesoporosity is recovered. The preparation route as well as the characteristics of the carbon materials are presented in this paper. It appears that the use of pitch as the carbon precursor presents some advantages compared to carbon obtained by other methods. Moreover, study of the thermal stability of the carbon shows that the structural regularity is preserved upon heat treatment at 1675 K.

Solid State NMR and TG/MS Study on the Transformation of Methyl Groups During Pyrolysis of Preceramic Precursors to SiOC Glasses

The sol-gel method was used to prepare two different starting gels containing SiCH3-groups for the preparation of SiOC ceramics. To understand the role of Si—H bonds in the incorporation of carbon into the SiOC network, gels prepared from a 1:2 mixture of triethoxysilane and methyldiethoxysilane (THDH2) and solely methyltriethoxysilane (TMe) were investigated. Thermogravimetric analysis coupled with mass spectroscopy (TG-MS) in inert atmosphere was performed to attain an insight into the decomposition reactions involved during gel-glass transformation. Samples calcined at different temperatures up to 1000°C were characterized by 29Si and 13C magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. The presence of SiH groups in the starting gel allows an efficient conversion of Si—CH3 groups into CSi4 sites at lower temperatures. As a result, despite a much lower amount of carbon in the starting THDH2 gel (C/Si = 0.33) compared to the TMe gel (C/Si = 1), the amount of carbon inserted into the SiOC network of both glasses is equivalent, but the TMe sample contains the 10 fold amount of free carbon.

Direct synthesis of ordered mesoporous polymer and carbon materials by a biosourced precursor

Ordered mesoporous polymer and carbon materials were prepared with a one-pot green chemistry synthesis using tannin as a biosourced carbon precursor. The process is based on the evaporation-induced self-assembly of the tannin with an amphiphilic surfactant. Tannin self-condensation polymerization reactions were used to avoid any carcinogenic cross-linkers such as formaldehyde and to improve the thermal stability of the intermediate ordered mesophase. The calcinations of the mesophase lead to polymer and carbon materials having a hexagonal array of mesopores beside micropores.

Microporous carbon adsorbents with high CO2 capacities for industrial applications

In this study we attempt to investigate the potential use of two zeolite template carbon (ZTC), EMT-ZTC and FAU-ZTC, to capture CO(2) at room temperature. We report their high pressure CO(2) adsorption isotherms (273 K) that show for FAU-ZTC the highest carbon capture capacity among published carbonaceous materials and competitive data with the best organic and inorganic adsorbing frameworks ever-known (zeolites and mesoporous silicas, COFs and MOFs). The importance of these results is discussed in light of mitigation of CO(2) emissions. In addition to these new experimental CO(2) adsorption data, we also present new insight into the adsorption process of the two structures by Monte Carlo simulations: we propose that two separate effects are responsible for the apparent similarity of the adsorption behaviour of the two structures: (i) pore blocking occurring on EMT-ZTC, and (ii) the change of the carbon polarizability due to the extreme curvature of FAU-ZTC.

Influence of the sol-gel synthesis on the formation of spinel MgAl2O4

Spinel precursors have been obtained by sol-gel processing using either magnesium nitrate and chemically modified aluminum alkoxide or a double alkoxide as raw materials. The xerogels have been characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), infrared (IR) spectroscopy, and transmission electron microscopy (TEM). It is proposed that the size of the particles is related to the functionality of the aluminum alkoxide. The use of the double alkoxide allowed pure spinel nanosized materials to be obtained.

First zeolite carbon replica with a well resolved X-ray diffraction pattern

The present study demonstrates that for the nanocasting process with zeolites, a careful choice of the zeolite structure type (EMT) allows the formation of faithful carbon replica exhibiting up to three well resolved XRD peaks.

Influence of the microstructure on the high temperature behaviour of gel-derived SiOC glasses

Abstract Hybrid gels, made from HSi(OEt)3 and CH3SiH(OEt)2, were used to produce SiOC glasses and to study their stability at high temperature. The variation of the hydrolysis ratio allowed the formation of either dense or highly porous xerogels. This difference in microstructure was maintained at 1000°C in the glassy state and influenced the stability of these materials at higher temperature. Indeed, it plays a major role on their carbothermal degradation by promoting or hindering the removal of the gaseous products in the case of porous or dense materials respectively. In the latter case, SiOC glass appears to be a suitable candidate for thermostructural applications.

Kinetics of the hydrothermal treatment of tannin for producing carbonaceous microspheres

Aqueous solutions of condensed tannins were submitted to hydrothermal carbonization (HTC) in a stainless steel autoclave, and the kinetics of hydrothermal carbon formation was investigated by changing several parameters: amount of tannin (0.5; 1.0; 1.5; 2.0 g in 16 mL of water), HTC temperature (130, 160, 180 and 200°C) and reaction times (from 1 to 720 h). The morphology and the structure of the tannin-based hydrothermal carbons were studied by TEM, krypton adsorption at -196°C and helium pycnometry. These materials presented agglomerated spherical particles, having surface areas ranging from 0.6 to 10.0 m(2) g(-1). The chemical composition of the hydrothermal carbons was found to be constant and independent of reaction time. HTC kinetics of tannin were determined and shown to correspond to first-order reaction. Temperature-dependent measurements led to an activation energy of 91 kJ mol(-1) for hydrothermal conversion of tannin into carbonaceous microspheres separable by centrifugation.

Evidence of Eu3+O2− associates by luminescence study of some silicates and aluminosilicates

Abstract Unusual luminescence spectra with a strong 5D0 arr 7F0 line, a high position of the 5D0 level and the occurrence of two lines close to 16550 cm−1, i.e. in a frequency domain at the border between 5D0 → 7F2 and 5D0 → 7F1 transitions, have been evidenced in the case of cordierite, Mg2Al4Si5O18:Eu, mullite, 2Al2O3.SiO2:Eu and lanthanum disilicate, La2Si2 O7:Eu. By comparison with results on apatites and some fluorides, these unusual spectra have been attributed to the presence of a strong and anisotropic crystal field due to an EuO bonding.

Easy and eco-friendly synthesis of ordered mesoporous carbons by self-assembly of tannin with a block copolymer

Ordered mesoporous carbons were prepared by the self-assembly of Mimosa tannin, a natural polyphenolic molecule, and a micellar solution of Pluronic® F127, used as soft template. The synthesis was carried out at 20 °C using water as the only solvent and without crosslinker agent (i.e., formaldehyde). When tannin, at any pH lower than 4.2, and Pluronic solutions were mixed, a phase separation mechanism immediately occurred due to the strong interaction between both polymers. The precipitated resin was recovered, dried and pyrolysed at 400, 700 and 900 °C. Ordered mesoporous carbon materials were obtained, having both high pore volume and surface areas, up to 0.64 cm3 g−1 or 720 m2 g−1, respectively.