Impregnation Of Mesoporous Silica Research Articles

Impregnation of mesoporous silica with poor aqueous soluble molecule using pressurized carbon dioxide: Is the solubility in the supercritical and subcritical phase a critical parameter?

Recently, mesoporous silica (MS) has been used as a material able to maintain amorphous state of active compounds and therefore, enhance the oral bioavailability of BCSII drugs. Among impregnation methods of MS, techniques using supercritical carbon dioxide (Sc-CO2) are promising tools. Solubility of compounds in Sc-CO2 is reported as one of the most critical parameters, which usually limits its use in drug formulation. Indeed, most of compounds have poor solubility in Sc-CO2. The aim of this work is to compare different MS and to study alternative processes using pressurized CO2 for insoluble molecule in Sc-CO2. By using high pressure reactor, DSC, HPLC and in vitro dissolution tests, the crystallinity and dissolution profiles of MS with different pore size (6.6 nm, 25.0 nm and 2.5 nm) impregnated with fenofibrate (FF) under Sc-CO2 were compared to select the most appropriate carrier. Then, the selected MS has been impregnated under supercritical, subcritical and atmospheric conditions. We have shown that the MS pore size of 6.6 nm provides the higher amorphous drug loading capacity as well as the faster and higher drug dissolution. In addition, FF-MS formulations produced with pressurized CO2 as fusion medium, both in subcritical and supercritical conditions; give similar crystallinity and dissolution results compared to those produced with supercritical fluids as solvent. Through this study, we show new possibilities of using CO2 for insoluble compounds in this fluid.

PEG-templated mesoporous silicas using silicate precursor and their applications in desiccant dehumidification cooling systems

Polyethylene glycol (PEG) was employed as a templating agent for the preparation of mesoporous silica materials starting from sodium silicate solutions using a sol–gel method. We show that PEG can serve as a structure-directing agent resulting in silica structures with pores spanning a range of 3.3–3.9 nm depending on the PEG concentration and the PEG removal method. The use of a PEG template increased significantly the surface area from 252 m2 g−1 without PEG to >340 m2 g−1 and >634 m2 g−1 when the PEG was removed by, respectively, calcination and solvothermal extraction. It appears that calcination at high temperature caused a densification of the pore structure resulting in a smaller surface area and pore diameter. The impregnation of mesoporous silica with CaCl2 significantly increased the adsorption capacity of water. At high humidity, the composite adsorbents containing approximately 42 wt.% CaCl2 yield a maximum adsorption capacity of 1.6 times their own weight and 4.4 times that of bare silica. The adsorption is physical in nature as viewed from the adsorption energy calculated by the Dubinin–Radushkevich (D–R) equation.

Al<sub>2</sub>O<sub>3</sub>/SiO<sub>2</sub> Materials with Bimodal Pore Size Distribution as Support for Heterogeneous Catalysts

The Al2O3/SiO2 materials prepared by impregnation of mesoporous silica with water solution of Al(NO3)3·9H2O were suggested to be used as supports for catalyst of high-temperature catalytic reactions. It was shown that the distribution of Al2O3 component inside wide pores of silica (10-50 nm) occurs with the formation of Al2O3 layer in case of low loading and porous layer or particles, if Al2O3 loading increases. Thus, materials with bimodal pore size distribution were obtained. The Cr-containing catalysts were prepared on the basis of these supports and tested in the process of isobutane dehydrogenation at 540 °C. It was observed that the activity of the obtained Cr/Al2O3/SiO2 materials was comparable with the one for Cr/Al2O3 catalyst. Thus, the suggested Al2O3/SiO2 materials with unique porous structure are promising to be used as supports for catalysts for high-temperature reactions.

Tuning of γ-Fe2O3 particle sizes by impregnation of mesoporous silica

A wet impregnation procedure of preformed silica matrices with different porosity and surface area resulted in the successful tailoring of the maghemite particle size. The magnetic features of the maghemite nanoparticles were checked by Mössbauer spectroscopy. Transmission electron microscopy and nitrogen physisorption measurements allowed the determination of a relationship between maghemite particle size and the porous features of the support matrix.

ZnO/SiO 2 nanocomposites obtained by impregnation of mesoporous silica

The synthesis of ZnO–SiO 2 nanocomposites through impregnation of a commercial mesoporous silica with zinc nitrate aqueous or ethanolic solutions is reported. During thermal treatment the samples evolve toward the formation of nanocrystalline ZnO particles (zincite phase) dispersed onto amorphous silica stable up to the temperature of 700 °C. The nanoparticle size distribution is affected by the process parameters used in the impregnation. A narrower and more homogeneous distribution is obtained using ethanolic instead of aqueous solutions. At higher temperatures the samples evolve towards the formation of a zinc silicate phase.

Optical properties of ZnO loaded in mesoporous silica

The optical absorption and photoluminescence (PL) of ZnO loaded inmesoporous silica have been investigated. These ZnO/SiO2composites are synthesized by impregnation of mesoporous silica with anaqueous solution of zinc acetate, followed by firing at 550 °C. Asignificant blue shift of the absorption edge compared to that of bulk ZnOin the absorption spectra is observed, and the band gap luminescence of ZnOis predominant in the emission spectrum, while the defect induced greenluminescence, typical of ZnO, does not appear. However, the above sample,after additional annealing at 350 °C in air for three hours,exhibits an absorption edge (365 nm) near to that of the bulk ZnO; thecolour of the sample also turns to yellowish from colourless, and greenluminescence also appears. Combining the analysis of x-ray photoelectronspectroscopy (XPS), we propose that Zn-O-Si cross linking bonds formed inthe interface between ZnO and the pore walls of silica have a greatinfluence on the optical properties of ZnO/SiO2 before theadditional annealing at 350 °C and the corresponding opticalproperties reflect both those of SiO2 and ZnO. After annealing,the Zn-O-Si cross linking bonds mentioned above are destroyed, and theoptical properties of ZnO are exhibited alone.