F. Rubio

A FT-IR Study of the Hydrolysis of Tetraethylorthosilicate (TEOS).

Abstract The hydrolysis and polymerization of a non-catalyzed silica sol was investigated by Fourier Transform Infrared Spectroscopy (FT-IR) and deconvolution of the infrared spectra. The hydrolysis was followed by the 1168 and 812 cm−1 bands which have been observed that decrease continously with the reaction time, and they dissapear showing the complete hydrolysis. The bands located at 1200 and 1147 cm−1 are assigned to polymerization of Si-OH groups forming Si-O-Si bonds in cyclic or linear structures respectively. Both bands increase with time and are present simultaneously in the spectra showing that both kind of cross-linking of Si-OH groups are taking place in the sol to form the gel. In the gel the presence of Si-OH groups and Si-O− free broken bonds have been detected by means of the bonds located at 960 and 920 cm−1 respectively.

Block-Copolymer assisted synthesis of hierarchical carbon monoliths suitable as supercapacitor electrodes

Three dimensional (3D) hierarchical porous (micro-, meso- and macro-porous) carbon monoliths (HCMs) have recently been proposed as promising supercapacitor electrodes. In this work, we have further explored the use of block-copolymers as templates for the preparation of HCMs via condensation of resorcinol and formaldehyde (RF) and subsequent carbonization. The resulting HCMs exhibited a textured morphology consisting of a bicontinuous macroporous carbon network built of interconnected microporous carbon colloids, as demonstrated by nitrogen adsorption/desorption isotherms, mercury porosimetry and electron microscopy, in both scanning and transmission mode. Such a texture favored the performance of HCMs as supercapacitor electrodes, reaching remarkable values of capacitance of up to 198 F g−1 (normalized by mass) and 34.5 μF cm−2 (normalized by BET surface area). The first electrolyte infiltration into the micropore (prior capacitance measurements) was demonstrated to play a crucial role in the achievement of large capacitance values.

PPO15-PEO22-PPO15block copolymer assisted synthesis of monolithic macro- and microporous carbon aerogels exhibiting high conductivity and remarkable capacitance

Ultralightweight (specific gravity 5 × 10−2) and highly conductive (2.5 S/cm) monolithic carbon aerogels exhibiting a three-dimensionally continuous micro- and macroporous structure have been prepared through a PPO-PEO-PPO block copolymer assisted route. The resulting carbon aerogels were highly suitable as electrodes of electric double layer capacitors, with remarkable values of capacitance of up to 225 F/g (normalized by mass) and 31 µF/cm2 (normalized by BET surface area).

DSC and FT-IR analysis of the drying process of titanium alkoxide derived precipitates

Abstract The drying process of titanium alkoxide-derived precipitates has been studied by means of FT-IR spectroscopy and DSC analysis. From the FT-IR spectrum, it has been possible to observe that unhydrolyzed alkoxide molecules continue the hydrolysis process by using water molecules retained inside the structure of the precipitate or formed by condensation of the Ti–OH groups. However, the quantification of the water content inside the precipitate was carried out by DSC analysis. This technique also allowed to determine two kinds of water molecules: free or interstitial water and coordinatively bound water. These two kinds of water gave two endothermic peaks at ca. 160–180° and 305°C, respectively. The transformation of the amorphous precipitate to a crystalline one is detected by an exothermic peak at ca. 314°C. The elimination of the coordinatively bound water is associated with this crystalline transformation.

Synthesis of inorganic-organic hybrid materials from TEOS, TBT and PDMS

Inorganic-organic hybrid materials have been synthesized by reaction of tetraethoxysilane (TEOS), titanium tetrabutoxide (TBT) and silanol-terminated polydimethylsiloxane (PDMS). The hydrolysis and polymerization reactions of TEOS and PDMS in presence of TBT have been followed by means of FT-IR spectroscopy. Hydrolysis reactions have been characterized by Si—O—C and Ti—O—C bonds and polymerization reactions by Si—O—Si, Si—O—Ti and Ti—O—Ti bonds. The instantaneous hydrolysis of TEOS, the condensation reactions between Si—OH groups forming crosslinked and linear Si—O—Si structures and the copolimerization reactions between Si—OH groups and PDMS molecules have been observed. The reaction between Ti—OH and Si—OH groups or PDMS gives Si—O—Ti bonds. Si—O—Ti bonds are formed during the addition step of TBT and they show a decrease along the reaction time up to gelling. By another hand, the concentration of crosslinked and linear Si—O—Si structures depend on the TBT concentration. High TBT concentration favors the formation of crosslinked chains. TBT influences the hydrolysis and copolymerization reactions between hydrolyzed TEOS and PDMS molecules.

Study of arsenopyrite weathering products in mine wastes from abandoned tungsten and tin exploitations.

Arsenopyrite-rich wastes from abandoned tungsten and tin exploitations were studied to determine the composition and characteristics of the secondary phases formed under natural weathering conditions so as to assess their potential environmental risk. Representative weathered arsenopyrite-bearing rock wastes collected from the mine dumps were analysed using the following techniques: X-ray powder diffraction (XRD) analysis, polarizing microscopy analysis, electron microprobe analysis (EMPA) and microRaman and Mössbauer spectroscopies. Scorodite, pharmacosiderite and amorphous ferric arsenates (AFA) with Fe/As molar ratios in the range 1.2-2.5 were identified as secondary arsenic products. The former showed to be the most abundant and present in the different studied mining areas. Its chemical composition showed to vary in function of the original surrounding rock mineralogy in such a way that phosphoscorodite was found as the mineral variety present in apatite-containing geoenvirons. Other ever-present weathering phases were goethite and hydrous ferric oxides (HFO), displaying, respectively, As retained amounts about 1 and 20% (expressed as As(2)O(5)). The low solubility of scorodite, the relatively low content of AFA and the formation of compounds of variable charge, mostly of amorphous nature, with high capacity to adsorb As attenuate importantly the dispersion of this element into the environment from these arsenopyrite-bearing wastes.

FT-IR Study of the Hydrolysis and Polymerization of Tetraethyl Orthosilicate and Polydimethyl Siloxane in the Presence of Tetrabutyl Orthotitanate

Abstract In this work, we have used FT‐IR spectroscopy to study the hydrolysis and polymerization reactions of tetraethyl orthosilicate (TEOS) and polydimethyl‐siloxane (PDMS) in the presence of tetrabutyl orthotitanate (TBOT). These reactions are used for obtaining SiO2–PDMS–TiO2 organically modified silicates (Ormosils). In order to obtain semi‐quantitative information about such reactions, a deconvolution procedure of the FT‐IR spectra has been done by use of a computer program. Hydrolysis reactions have been characterized by Me–O–C (Me = Si, Ti) bonds, and polymerization reactions by Me–O–Me bonds. Instantaneous hydrolysis of TEOS has been observed, together with condensation reactions between Si–OH groups, which give crosslinked and linear Si–O–Si structures. The TBOT is also hydrolyzed, but the high acid concentration inhibits condensation reactions between Ti–OH groups. The PDMS also condenses mainly with Si–OH groups and probably with Ti–OH, finally forming Me–O–PDMS bonds. The formation of Si–O–Si crosslinked structures and also Me–O–PDMS structures continues until the end of reaction. The gelling time is dependent on TBOT concentration in the reaction medium and, therefore, polycondensation reactions are dependent on TBOT concentration.

Study of the reaction of γ-methacryloxypropyltrimethoxysilane (γ-MPS) with slate surfaces

Thermal Analysis (TA) and Fourier Transform Infrared Spectroscopy (FT–IR); were used in order to study the reaction of γ-methacryloxypropyltrimethoxysilane (γ-MPS) with slate surfaces at different temperature conditions (25, 35 and 50°C), concentrations (0.5–5% weight of silane) and reaction times (1, 3, 5 and 10 min). By these conditions, a typical physical adsorption of the γ-MPS silane on the slate surface has been observed. A monolayer of γ-MPS is firstly adsorbed on the slate surface by hydrogen bonding through the carbonyl group of the silane and after that, silane multilayers are formed where free carbonyl groups are predominant. A concentration of 1% is considered as appropriate for silanization of the slate particles with γ-MPS.

Inverse gas chromatography: a new approach to the estimation of specific interactions

Inverse gas chromatography (IGC) has proved to be a powerful tool for characterisation of solid surfaces, particularly those that cannot be easily studied by other methods, like fibres or powders. One of the magnitudes to be measured by this method is the London component of the surface free energy, which denotes the ability of the surface to interact with external material through Van der Waals forces. This value, is determined by measuring the retention volumes of the series of n-alkanes. The other interesting magnitude is the polar character of the surface energy. Several methods are described in the literature to evaluate this polarity or specific component of the surface energy, not all giving concordant results. In this paper a method is proposed for the evaluation of this specific component of the surface energy, based on the fact, that the shift of Kovats index of polar compounds in a column, taking as reference a non polar column, is directly in relation with the polarity of the column. Some data are given of interactions obtained with some of the polar probes with previously described methods and the new one. The study material is several carbon fibres, cured and uncured epoxy resins, two modified polyethylene samples and a commercial SP100 column.

A DSC study of the drying process of TEOS derived wet silica gels

Abstract The drying process of wet silica gels obtained from TEOS has been studied by means of FT-IR, DSC and specific surface area measurements. FT-IR spectroscopic results have not given any important information about the drying process of silica gels. However, DSC results have shown a dependence of the DSC peak area on drying time. Three different water alkoxide ratio were studied, and the DSC peak area was higher when the water alkoxide ratio increased. A more open xerogel structure was found for the high water alkoxide ratio showing a high specific surface area and therefore lower drying times. For the silica gels obtained with 200 1 and 100 1 water alkoxide molar ratio, a complete drying time was observed for 25 and 28 days, respectively. As the drying time increases the gel structure becomes more closed, being necessary higher temperatures for removing water or alcohol from the gel.