Investigation of silica - PVA xerogel microstructure evolution during thermal treatment by SANS experiment

The purpose of the study was to investigate the appearance of certain microstructures developing in the SiO2/PVA nanocomposite xerogels at different temperatures by small-angle neutron scattering (SANS). The samples were prepared by the alcoxide route of the sol-gel method. The SANS measurements were performed over a q (scattering vector) range from 0.05 to 3.7 nm-1, providing structural information at length scales (2π/q) between approximately 1 and 100 nm. The measured small-angle scattering intensities of silica and silica/PVA samples aged at 60°C and heat-treated at different temperatures, are presented in log-log plots. It is shown that both the molecular mass of organic and the temperature of thermal treatment have strong influence on transition tendency from mass fractal toward surface fractal structures

Mesoporous silica matrices derived from sol-gel process assisted by low power ultrasonic activation

The present work contributes to elucidating the differences between silica gels obtained by low doses ultrason- ic activation, and those obtained by the conventional method, termed as classical sol gel. Silica matrices were produced by sol-gel synthesis process, assisted and non-assisted by an ultrasonic field, and subsequently char- acterized by various methods. Nitrogen adsorption and small-angle neutron scattering (SANS) measurements provided texture and microstructure of the dried gels. The adsorption results show that the sample sonicated for 2 hours presents the most ordered microstructure, characterized by pore shape close to spherical and the narrowest size distribution – about 90 % of the pores for this sample fall into the mesopore range (2–50 nm). SANS data reveal the formation of primary structural units of sizes around 1.5–2 nm which are small linear or branched polymeric species of roughly spherical shape and with rough surface. They are generated in the very early stage of sol gel process, as a result of hydrolysis and condensation reactions. The aggregated primary units form the secondary porous structure which can be described as a rough surface with fractal dimension above 2. The best porosity characteristics were obtained for the sample activated for 2 hours, indicating the optimal doses of sonication in the present conditions. Our results demonstrate the possibility of tailoring the pore size distribution using a low power ultrasonic bath

Synthesis and luminescence properties of some Ce3+ doped silica sols

Ce -doped silica sols samples were prepared by acid, or two steps catalyzed sol-gel process, at different concentration of Ce3+ dopant. As silica precursors, tetraetoxysilane, or tetrametoxysilane, or a precursors mixture consisting of tetraetoxysilane and isobuthyltrietoxysilane, were used. By UV excitation, all synthesized samples presented strong luminescence emission with maxima situated at ~ 386 nm. Regarding the emission efficiency, better results were achieved at lower Ce3+ concentrations. Depending on precursors nature, a favorable influence had the use of precursors mixture

Silica aerogels synthesized with butyl-4-methylpyridinium tetrafluoroborate

The supercritical drying effects were investigated, on a series of samples synthesized with: tetramethoxysilane and methyltrimethoxysilane, used as precursors, and butyl-4- methylpyridinium tetrafluoroborate (BMPyBF4) ionic liquid (IL), as gelation catalyst. These results show that the IL addition has a significant impact on the structure of the aerogel as a function of used nIL/nSi molar ratio

Urea formaldehyde coated with Silica (Nano) capsules synthesis in ultrasonic field

Silica nanomaterials with meso- and macroporosity are of great interest due to their variety of potential applications. These hybrid nanomaterials, including hollow silica nano and micro-particles have attracted more and more attention with potential applications in medicine, environmental protection and analytical chemistry. In this work we present a fast and simple method for of urea-formaldehyde (UF) nanoparticles obtained in basic medium encapsulation by a thin shell coating of silica, thus yielding organic-inorganic hybrid materials. It was employed (U:F): SiC^: mole ratios of (1:1 ):5; (1:1): 10; respectively. The influence of reaction parameters variation as temperature, pH, and time were studied. The morphology and structure of the products were characterized by FTIR spectroscopy, and Scanning Electron Microscopy; SEM. It was put in evidence some of resulted samples characteristics that are correlated to synthesis conditions

Ultrasonic preparation of mesoporous silica using pyridinium ionic liquid

Mesoporous silica matrices have been prepared via classic acid catalyzed and sono-catalyzed sol-gel routes. Tetramethoxysilan (TMOS) and methyl-trimethoxysilane (MTMS) were used as silica precursors, and N-butyl-3-methylpyridinium tetrafluoroborate ([bmPy][BF4]) was employed as co-solvent and pore template. The ionic liquid (IL) to silica mole ratio was varied between 0.007 and 0.07. Nitrogen adsorption-desorption and small-angle neutron scattering measurements were used to characterize the obtained materials. The ionic liquid played the role of catalyst that affected the formation of the primary xerogel particles, and changed the porosity of the materials. Ultrasound treatment resulted in microstructure change on the level of the colloid particle aggregates. In comparison with IL containing xerogels, the IL containing sonogels show increased pore diameter, bigger pore volumes and diminished surface areas

Standardization process by NAA method for phytopharmaceutical industry

The ancient therapeutic remedies for modern needs are represented by medicinal crop plants, the raw material for phytopharmaceutical forms. Medicinal plants are generally viewed only in terms of beneficial effects without considering the potentially toxic side [1]. In this context in the present study elemental composition for seven representative medicinal crop plants as: coriander, dill, Echinacea, lavender, chamomile, mint and plantain, cultivated in unpolluted areas in Romania, were analyzed. Among many analytical methods used for determination of plant elemental content, that generally imply the vegetal matrix disintegration, the Neutronic Activation Analysis (NAA) is classified as primary ratio method [2]. By validating the NAA procedure by statistical evaluation of the nominal error En≤1 (ISO 13528-2015) [3], NAA proved to be an accurate, specific and multielement analysis technique for medicinal plants with the advantage of eliminating the preliminary step of digestion, in this way certain errors being avoided. This method is differentiated as one with high potential to obtain internal plant standards in the phytopharmaceutical industry. These standards can be vegetable matrix, or plant specific, once achieved can be used a long period of time to verify and validate more routinely accessible analytical techniques, which in turn require a digestion stage. A critical assessment provided by the results include the essential nutrients (K, Ca, Mg, Na, Fe, K, Mn, Zn), micro- and trace elements (Co, Cr, Cu, Ni, Se, V), as well as the undesirable, potentially toxic elements (Al, As, Ba, Co, Cr, Ni, Sb) together with rare earth elements. The values are comparable with literature. These plants may provide a useful contribution to food intake with essential macronutrients (K, Ca, Mg) and the concerns regarding the toxicity of metals for a person, are removed. Seemingly the Al (4997 ppm) and Fe (3315 ppm) [4] content in lavender is of some worry. In fact, many studies [5] revealed that some plants species, and lavender among them, exhibit metal bioaccumulation properties and are used for phytoremediation of contaminated soils. This dual implication, beneficial for soil depollution, but critical in transmitting the accumulated metals to humans, is to be considered. Choosing an unpolluted area, in order to cultivate medicinal plants, seems to be an efficient strategy from this point of view. Still, another conclusion is that a rigorous analytical control of the raw materials is advisable for some of the elements (among them aluminium) to avoid risks

Bioorganically doped sol-gel materials containing amyloglucosidase activity

Amyloglucosidase (AMG) from Aspergillus niger was encapsulated in various matrices derived from tetraethoxysilane, methyltriethoxysilane, phenyltriethoxysilane and vinyltriacetoxysilane by different methods of immobilization. The immobilized enzyme was prepared by entrapment in two steps, in one-step and entrapment/deposition, respectively. The activities of the immobilized AMG were assayed and compared with that of the native enzyme. The effects of the organosilaneprecursors and their molar ratios, the immobilization method, the inorganic support (white ceramic, red ceramic, purolite, alumina, TiO2, celite, zeolite) and enzyme loading upon the immobilized enzyme activity were tested. The efficiency of the sol-gel biocomposites can be improved through combination of the fundamental immobilization techniques and selection of the precursors

Elemental Characterization of Romanian Crop Medicinal Plants by Neutron Activation Analysis

The metallic elements concentrations of medicinal plants (coriander, dill, Echinacea, lavender, chamomile, mint, and plantain, used for phytopharmaceutical products), cultivated in unpolluted region, were analyzed by neutron activation analysis. The essential nutrients, macro-, micro-, and trace elements (K, Ca, Mg, Na, Fe, Mn, Rb, Sr, and Zn), potentially toxic elements (Al, As, Ba, Co, Sb, Cr, and V), and rare earth elements were monitored and were compared with those presented in the literature. An estimation of their contributions to intake and toxicity for a person was made, which revealed that (a) teas prepared from the examined plants represent useful contribution to the food provided intake of three essential macronutrients (K, Ca, and Mg); (b) the Cu, Mn, Rb, Sr, Zn, and rare earths levels are normal or low; (c) the quantities of As, Ba, Co, Sb, Cr, and V do not represent toxicological concerns; (d) the examination of the estimated Al and Fe quantities recovered in infusions in the conditions of usual daily tea consumption is below the Tolerable Daily Intake values. The strategy of cultivation of medicinal plants in unpolluted areas is efficient and beneficial. However, individual plants ability to concentrate preferentially certain elements suggests controlling the contamination level of raw materials

Mesoporous silica matrices derived from sol-gel process assisted by low power ultrasonic activation

The present work contributes to elucidating the differences between silica gels obtained by low doses ultrasonic activation, and those obtained by the conventional method, termed as classical sol gel. Silica matrices were produced by sol-gel synthesis process, assisted and non-assisted by an ultrasonic field, and subsequently characterized by various methods. Nitrogen adsorption and small-angle neutron scattering (SANS) measurements provided texture and microstructure of the dried gels. The adsorption results show that the sample sonicated for 2 hours presents the most ordered microstructure, characterized by pore shape close to spherical and the narrowest size distribution – about 90 % of the pores for this sample fall into the mesopore range (2–50 nm). SANS data reveal the formation of primary structural units of sizes around 1.5–2 nm which are small linear or branched polymeric species of roughly spherical shape and with rough surface. They are generated in the very early stage of sol gel process, as a result of hydrolysis and condensation reactions. The aggregated primary units form the secondary porous structure which can be described as a rough surface with fractal dimension above 2. The best porosity characteristics were obtained for the sample activated for 2 hours, indicating the optimal doses of sonication in the present conditions. Our results demonstrate the possibility of tailoring the pore size distribution using a low power ultrasonic bath