Thermogravimetric analysis was applied to the characterization of the porosity of silica gels. Results from thermogravimetric
method are compared with those obtained from the nitrogen method. The consistency of the parameters characterizing the porous
structure of silica gels derived from the data of various methods is satisfactory.
Authors:Y. Minai, T. Fukushima, M. Ichikawa, and T. Tominaga
Silica supported Rh–Fe catalysts were characterized by means of in situ57Fe Mössbauer spectroscopy. The Mössbauer spectra indicated that iron on the silica support existed either as Fe/O/ in the Rh–Fe alloy or as Fe3+ in Rh–Fe metal cluster compounds. The (Fe3+/Fe/O/) ratio and Mössbauer parameters were found to depend on the (Fe/Rh) atomic ratio in the catalysts. Such dependence corresponded to the change of catalytic properties of the supported Rh–Fe catalyst with the varying (Fe/Rh) ratio.
Silica-containing -zirconium phosphate (-ZrSiP) was prepared by the precipitation method. X-ray diffractometry was used to characterize -ZrSiP and to compare it with other -zirconium phosphates (ZrP). A monoclinic cell with parameters of a=0.9038 nm, b=0.529 nm, c=1.4183 nm and =91.76° was identified for -ZrSiP, i.e. silica modifies the original -ZrP structure. The specific surface area of -ZrSiP was found to be two orders of magnitude higher then that of -ZrP.
Authors:D. Sternik, P. Staszczuk, J. Pękalska, G. Grodzicka, B. Gawdzik, J. Osypiuk-Tomasik, and P. Witer
The adsorption of a polar (water)
and a non-polar (n-octane) liquid on silica
gels, modified by adsorption of proteins, has been studied by thermal analysis.
Silica gels with physically adsorbed BSA and ovalbumin layers were used. Thermodesorption
energies were determined from Q-TG and Q-DTG curves recorded under quasi-equilibrium
conditions. Significant differences in liquid desorption were observed from
the surfaces due to heterogeneous changes (energetic and geometrical) as a
result of modification. These results are compared with those obtained for
the samples heated at 160C for 1 h.
Authors:V. Yanishpolskii, A. Pavlenko, V. Tertykh, V. Il'in, R. Leboda, and J. Skubiszewska-Zieba
Mesoporous titanium-containing silicas with TiO2 contents from 1 up to 70 mol% were prepared. The obtained samples have been characterized by the powder X-ray diffraction
data, the diffuse reflectance infrared Fourier transform method, and nitrogen adsorption at 77 K. Specific surface area, total
pore volume, distribution pore volume on pore sizes were determined from nitrogen adsorption isotherm for synthesized titanosilicas.
Sorption behavior of europium, Eu3+, on SiO2 . xH2O (silica gel) has been investigated as a function of time, the amount of silica gel, Eu3+ concentration, the ionic strength, and pH (in absence and in presence of carbonate). The sorption data were fitted to Freundlich,
Langmuir and Dubinin-Radushkevich (D-R) isotherms. The sorption capacity of silica gel was determined to be in the range of
(2.62-8.00) . 10-7 mol/g at pH 5.30±0.05 and 0.20M NaClO4. The mean energy of sorption was calculated to be 13.50±0.05 kJ/mol from the D-R isotherm, suggesting the involvement of
ion-exchange reactions in the sorption process. Sorption of Eu3+ decreased with increased ionic strength. A gradual decrease in pH with increased ionic strength supports the involvement
of an ion-exchange mechanism in the sorption process. The diffusion coefficient of Eu3+ ion on silica gel was calculated as (3.98±0.12) . 10-13 m2 . s-1 under the particle diffusion-controlled conditions.
Various silica gel materials were chemically modified with imidazole, diaza-18-crown-6 (DA18C6) and dibenzod-18-crown-6 (DB18C6). The degree of functionalization of the covalently attached molecule was calculated from C, H, N analysis and ranged between 0.270 and 0.552 mmol/g (for sorbents with imidazole) and between 0.043 and 0.062 mmol/g (for sorbents with DA18C6 and DB18C6). The degree of functionalization depends on the reflux time and silica gel matrix used. Experimental sorption capacity ranged between 0.038 and 0.228 mmol/g (for sorbents with imidazole) and between 0.019 and 0.050 mmol/g (for sorbents with DA18C6 and DB18C6). Synthesized hexagonal mesoporous silica matrix MCM-41 with uniform pore diameter <40 Å was used too. Change of pore diameters of silica gel support to larger pores should have a positive influence on access of cobalt ion to sorption centers to increase of sorption capacity of sorbents. The sorption kinetics of cobalt and the influence of cobalt concentration, pH of various kinds of silica gel matrix with immobilized imidazole group in static conditions on sorption were measured. The sorption of cobalt in various conditions (pH, contact time of phases) with constant liquid-solid ratio (V/m = 50 ml/g) was studied. The distribution coefficients ranged between 200 and 50 000 ml/g (for imidazole), 85 and 120 ml/g (for DB18C6) and between 230 and 500 ml/g (for DA18C6) according to silica gel matrix used and according to the method of sorbent preparation. pH plays important role in the sorption of cobalt on prepared sorbents with immobilized crown ethers due to protonization of crown ethers. Protons significantly competes to sorption of cobalt in acidic solutions. The influence of presence of other heavy or toxic metals (Hg(II), Cd(II), Mn(II), Zn(II), Cu(II), Fe(III), Cr(III), Al(III) and the influence of sodium and potassium on sorption Co(II) from aqueous solutions was investigated. Sorption of cobalt decreases in order Hg > Cu > Cd > Zn, Fe > Mn > Al, Cr. The presence of sodium and potassium ions at concentration 0.05 mol/l significantly influences on the sorption of cobalt with sorbent with immobilized DB18C6 functional group.
Authors:Grażyna Janowska, Teresa Mikołajczyk, Dorota Wołowska-Czapnik, and M. Boguń
The paper discusses the thermal properties of alginate fibres made from alginic acid or sodium alginate and from alginates
substituted with divalent metal ions during the fibre-forming stage. Alginate fibres with an addition of silica nanoparticles
have also been examined. The selection of fibre-forming parameters was intended to obtain the best either sorption or strength
properties depending on the specific fibre application. Thermal curves of the fibres under investigations obtained by under
air atmosphere and differential scanning calorimetry (DSC) under neutral gas atmosphere have been interpreted from the view
of physical and chemical changes in the fibre-forming material. Based on thermogravimetric curves, the fibre thermal stability
indices have been determined. It has been found that the addition of silica nanoparticles exerts a positive influence on the
thermal properties of the examined fibres.
This study was undertaken to investigate the sorption behavior of chromium hydroxide sol on silica type adsorbent in aqueous solution. Radioisotopic tracer method was used to assess data. This technique allowed sensitive kinetic and equilibrium measurements in both direction: sorption and desorption, which are strongly dependent on solution conditions, such as pH, ionic strength or the presence of complexing species. Total removal of sol particles could not be achieved, even under the most favorable experimental conditions (acidification).
The temperature influence on the adsorption mechanism of anionic polyacrylic acid (PAA) macromolecules on the silica surface
was studied. For this purpose, the following techniques were applied: spectrophotometry, thermogravimetry, potentiometric
titration and microelectrophoresis. This method allowed to determine the adsorbed amounts of polymer, changes in thermal characteristic
of silica surface with adsorbed PAA, surface charge density of the solid as well as zeta potential of SiO2 particles in the presence and absence of polyacrylic acid. All measurements were carried out in the temperature range 15-35 °C.
The free energies of adsorption were calculated from the adsorption data fitted by the Langmuir model. The obtained results
of increase of PAA adsorption and its adsorption free energies with the rising temperature suggest that adsorbed polymer conformation
changes from the coiled structure to more stretched one. Moreover, the polymer adsorption on the silica surface at 25 °C leads
to changes in the course of thermogravimetric curves as a result of surface properties modification of the solid by bonded