Modification of Silica Gel by Heteropolyacids

Silica gels containing incorporated heteropolyacids (HPAs) were synthesized in acidic media by co-condensation of tetraethoxysilane (TEOS) with phosphotungstic or phosphomolybdic acids using the sol-gel technique. The effect of the synthesis conditions on their structure and morphology was studied. Yields of modified materials were somewhat lower compared to non-modified silica gels. All materials were mesoporous but contained micropores in their structures. Presence of bands of Keggin’s structures in FT-IR spectra along with absence of XRD patterns of crystalline HPAs confirmed their fine incorporation into silica network. Particle sizes of modified materials were 500-1100 nm except for the W-containing sample obtained with trimethylstearylammonium chloride, which was significantly lower. This unusual effect was attributed to stabilization of primary silica nanoparticles by interactions between the surfactant and HPA. High ratio HPA/TEOS resulted in partial loss of porosity. Obtained results might be used for optimization of synthesis of effective catalysts and adsorbents containing HPAs in mesoporous structure.

Quantitative Evaluation of Polarity of Silica Gel Modified with Transition Metals Chelates for Gas Chromatography

New packings based on Silochrome C80 modified with Cu (II), Co (II) and Ni (II) 8-oxyquinolinates were studied. Their sorption characteristics and chromatographic properties were investigated and the comparative evaluation of sorbents polarity was carried out by applying Rohrschneider-McReynolds coefficients system, thermodynamic data and using the solvation parameter model of Abraham. It was found that the nature of metal and complex structure have a decisive influence on the physico-chemical properties of the packings. Modified silica gels show high selectivity for gas chromatographic separation of oxygen containing and aromatic organic compounds.