Laura M. Ilharco

The Sol–Gel Route to Advanced Silica-Based Materials and Recent Applications

Applications Rosaria Ciriminna,† Alexandra Fidalgo,‡ Valerica Pandarus, Franco̧is Beĺand, Laura M. Ilharco,*,‡ and Mario Pagliaro*,† †Istituto per lo Studio dei Materiali Nanostrutturati, CNR, via U. La Malfa 153, 90146 Palermo, Italy ‡Centro de Química-Física Molecular and IN-Institute of Nanoscience and Nanotechnology, Instituto Superior Tećnico, Complexo I, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal SiliCycle Inc., 2500, Parc-Technologique Boulevard, Quebec City, Quebec G1P 4S6, Canada

The evolution of TEOS to silica gel and glass by vibrational spectroscopy

Abstract Fourier-transform infrared and Raman spectroscopies were simultaneously used in order to study the time evolution of the acid-catalyzed hydrolysis and condensation of tetraethoxysilane (TEOS) in ethanol, to form silica xerogel. The transformation to vitreous silica by gradual densification of the gel was also monitored after different heat treatments. The extent of hydrolysis was revealed by the changes in intensity of the IR-active bands of TEOS at 793 cm − (Si O asymmetric stretch), 1102 cm −1 (C O asymmetric stretch), 1168 cm −1 (CH 3 rocking) and 1400 cm −1 (CH 2 wagging) and also the TEOS Raman-active bands corresponding to the strongly polarized Si O symmetric stretch (656 cm −1 ) and the depolarized CH 3 rocking (960 cm −1 ). The intensity of all these bands clearly decreased as the reactions proceeded. Good evidence for the formation of ethanol in the initial steps of hydrolysis and for the subsequent predominance of its evaporation was found in the occurrence of maximum intensities for its infrared and Raman-active bands due to deformation of CH 3 or CH 2 groups (881 cm −1 ) and CH 2 bending (1275 cm −1 ), after a period of time. The intensity of these bands later decreased. The gel to glass conversion was followed through the disappearance of the infrared peaks at 554 cm − ) (Si OH rocking) and 940 cm −1 (Si OH stretching), together with the intensity increase of the peaks at 800 and 1078 cm −1 . The complementary nature of the IR and Raman spectroscopies is of great value for a complete understanding of the TEOS to silica glass transformation.

The Infrared Spectrum of Solid L-Alanine : Influence of pH-Induced Structural Changes

The influence of the pH on the infrared spectrum of L-alanine has been analyzed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The amino acid was precipitated from aqueous solutions and dried at 36.5 degrees C, in order to stabilize cationic L-alanine or alaninium [CH3CH(NH3(+))COOH] at pH 1, the zwitterionic form [CH3CH(NH3(+))COO(-)] at pH 6, and anionic L-alanine or alaninate [CH3CH(NH2)COO(-)] at pH 13. New insight on the specific inter and intramolecular interactions in the different forms of L-alanine was reached by a novel methodological approach: an infrared technique not used before to analyze solid amino acid samples (DRIFTS), in combination with a detailed analysis based on spectral deconvolution. The frequency ranges of interest include the carbonyl/carboxyl stretching and amine deformation modes and the OH/NH stretching modes. It was shown that intermolecular hydrogen bonds between the NH3(+) and COO(-) groups are predominant in the zwitterionic form, whereas in cationic L-alanine, H bonds between the COOH groups are responsible for the formation of dimers. In anionic L-alanine, only strong electrostatic interactions between the COO(-) groups and Na(+) ions are proposed, evidencing the relevant role of the counterion.

Volumetric Properties and Spectroscopic Studies of Pyridine or Nicotine Solutions in Liquid Polyethylene Glycols

Densities and molar excess volumes of the solutions of pyridine or nicotine in liquid polyethylene glycol, PEG200 and PEG400, have been determined at several temperatures. The experimental molar excess volumes are negative, thus indicating strong attractive interactions between the components, as could be expected considering their highly polar nature and good hydrogen bond abilities. For the pyridine systems, this negativity is slightly increased as the temperature rises, while the opposite tendency is observed for the nicotine mixtures. When pyridine and nicotine solutions are compared, the former-particularly those with PEG400-exhibit substantially more negative molar excess volumes than the latter. The effect of the polymer chain length on the results for the nicotine solutions is almost negligible. However, this is not the case when pyridine is one of the components: a longer chain induced considerably higher compression on mixing. The Fourier-transform infrared analysis allowed interpretation of the negative experimental molar excess volumes in terms of specific inter- and intramolecular interactions.

The chemical adsorption of 1-hexene on Ru(0001) studied by reflection-absorption infrared spectroscopy

The chemisorption of 1-hexene on a Ru(0001) surface has been studied using reflection-absorption infrared spectroscopy (RAIRS). At 92 K, a very low dose of 1-hexene produced a RAIR spectrum consistent with the formation of a di-σ type complex. On annealing to 100 K, this species started dehydrogenating on the surface, forming a mixture of rotational conformers of hexylidyne, [C(CH2)4CH3]. A similar result was obtained when adsorbing at 100 K, with predominance of the all-trans conformer of hexylidyne for exposure at a high rate. Hexylidyne proved to be stable up to at least 120 K, although the conformational equilibrium changed, gradually favouring species with gauche rotations. Between 130 and 290 K, the decomposition products did not produce detectable RAIR spectra. Further thermal decomposition into methylidyne was observed at 300 K, in contrast with shorter chain alkylidynes previously studied on Ru(0001), which decompose via ethylidyne.

The structural origins of superior performance in sol–gel catalysts

Why do sol-gel catalysts often show superior performance in terms of selectivity, stability and reactivity? This work is an attempt to provide a rationale which could be used as a predictive tool in the development of novel catalysts for chemical conversions that will be crucial to achieve a more sustainable development.

Microplastics effects in Scrobicularia plana

One of the most common plastics in the marine environment is polystyrene (PS) that can be broken down to micro sized particles. Marine organisms are vulnerable to the exposure to microplastics. This study assesses the effects of PS microplastics in tissues of the clam Scrobicularia plana. Clams were exposed to 1mgL-1 (20μm) for 14days, followed by 7days of depuration. A qualitative analysis by infrared spectroscopy in diffuse reflectance mode period detected the presence of microplastics in clam tissues upon exposure, which were not eliminated after depuration. The effects of microplastics were assessed by a battery of biomarkers and results revealed that microplastics induce effects on antioxidant capacity, DNA damage, neurotoxicity and oxidative damage. S. plana is a significant target to assess the environmental risk of PS microplastics.

Phase behaviour of oleanolic acid, pure and mixed with stearic acid: Interactions and crystallinity.

The phase behaviour of pure oleanolic acid (OLA) and in mixtures with stearic acid (SA) was characterized by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and nuclear magnetic resonance (NMR). The crystalline OLA as received (OLA(ar)) becomes amorphous after being dissolved in chloroform and vacuum-dried at 50 degrees C (OLA(50)). Upon heating, both forms transform to the needle shape crystalline form (OLA(220)). Dimerization through H-bonding between COOH groups was detected both in OLA(ar) and OLA(220). Dimers are stronger in OLA(220), where H-bonding also involves the alcohol groups and plays a role in the crystalline organization. A eutectic type phase diagram was established for mixtures, with the eutectic composition close to pure SA. Mixtures rich in SA are miscible in the liquid and in the amorphous solid states, where the presence of SA-OLA co-dimers, formed through H-bonding between carboxyl groups, was detected. Miscibility and SA crystallinity decrease drastically with the OLA content.

The Structure of Hybrid Gels by Drift and NMR Spectroscopies

Hybrid inorganic-organic gels have been prepared by the sol-gel process using tetraethoxysilane (TEOS) as precursor, mixed with a low concentration of polytetrahydrofuran (PTHF), under acid catalysis. The hybrid xerogels were characterized by DRIFTS and Solid State 1H, 13C and 29Si NMR. The DRIFT spectra indicate that the polymer is responsible for decreasing the number of free silanol groups in comparison to pure silica. Solid-state NMR spectra reveal the types of silicate structures formed and the conditions for establishing chemical bonds between the two phases, which are responsible for the silica network flexibility. We have concluded that it is possible to design a hybrid gel with tailored properties, even at very low polymer concentration, by selecting the appropriate preparation route.

Flexible hybrid aerogels prepared under subcritical conditions

A new flexible insulator was developed, consisting of a silica–latex-fiber nanocomposite aerogel that combines the lightness and insulating properties of silica aerogels with the mechanical properties of silica–latex hybrids and the flexibility of fibers. This was accomplished by coating selected insulating fibers (polyester and glass) with a silica–polymer hybrid aerogel, synthesized in situ by a two-step sol–gel process, consisting of the acidic co-hydrolysis of TEOS and trimethoxysilyl-grafted latex nanoparticles in excess water, followed by basic co-condensation. The hybrid coating has improved mechanical properties that allow its drying under subcritical conditions. The outstanding properties of the insulating blankets produced render them extremely attractive for high-technology applications, and, due to the low energy consumption process, they may even displace the commonly used mineral wool, by presenting a best value-for-money compromise.