Silica gel

About: Silica gel is a research topic. Over the lifetime, 22313 publications have been published within this topic receiving 325516 citations. The topic is also known as: Amorphous silica & Precipitated amorphous silica.

Influence of water in the reaction of γ-aminopropyltriethoxysilane with silica gel. A Fourier-transform infrared and cross-polarisation magic-angle-spinning nuclear magnetic resonance study

Abstract: Silica gel has been modified with γ-aminopropyltriethoxysilane under varying conditions, controlling the influence of water in the different modification stages. Diffuse reflectance infrared Fourier-transform (DRIFT) spectra revealed the influence of surface water in the reaction stage and of air humidity in the curing stage. These results were confirmed and refined by 29Si and 13C cross-polarisation magic-angle-spinning nuclear magnetic resonance (CPMASNMR) spectroscopy. Combining the results of both techniques, four modification structures present on the silica surface are proposed, depending on the conditions used.

THE ION EXCHANGE PROPERTIES OF SILICA GEL. I. THE SORPTION OF Na$sup +$, Ca$sup 2+$, Ba$sup 2+$, UO$sub 2$$sup 2+$, Gd$sup 3+$, Zr(IV) + Nb, U(IV) AND Pu(IV)

Abstract: The metal ion sorption on silica gel was investigated. The silica gel acts in this respect as an ion exchanger of the weakly acid type and in the case of a monovalent cation the exchange reaction can be written as Si - OH + Me/sup +/ (?) Si - OMe + H/sup +/. For this equilibrium the law of mass action seems to be valid. Moreover an amount of hydrogen ions equivalent to the amount of metal ions sorbed is set free at the sorption on silica gel that is saturated with hydrogen ions. The amount of metal ion sorbed depends strongly on the pH of the solution. At the sorption of strongly hydrolyzed (presumably high molecular) ions the equilibrium is reached slowly, whereas the sorption of nonhydrolyzed (low molecular) ions is quite rapid, the equilibrium usually being reached within five minutes. (auth)

Synthesis of silica gel immobilized thiourea and its application to the on-line preconcentration and separation of silver, gold and palladium

Abstract: A new silica gel based chelating sorbent with thiourea as a functional group was used for the flow injection (FI) on-line preconcentration and separation of trace levels of silver, gold and palladium. Its sorption characteristics were evaluated by FI-FAAS. The selected metal ions were adsorbed on a column packed with thiourea modified silica gel (TuSG) with a sampling flow rate of 5.0 ml min1, eluted with 5% thiourea with a flow rate of 2.5 ml min1 and determined by FAAS. Common co-existing ions did not interfere with the preconcentration and determination. The detection limits, defined as three times of the standard deviation of the blank (3σ), of Ag, Au and Pd are 1.3, 14 and 21 ng ml1, respectively, with a 1 min sample loading time. The RSD is not more than 3.0% for 0.040 µg ml1 of Ag, 0.20 µg ml1 of Au and 0.30 µg ml1 of Pd. With 40 min of the sample loading time, 1.0 ng ml1 of Ag, 5.0 ng ml1 of Au and 7.5 ng ml1 of Pd were successfully preconcentrated. The total dynamic capacity of TuSG was 24.5, 50.9 and 30.3 mg g1 for Ag, Au and Pd, respectively. The sorbent exhibited excellent stability. Its sorption properties did not change after 1000 cycles of use. The selected metals in a secondary nickel alloy, an anode slime, an electrolytic solution and three national certified ore samples were determined satisfactorily using the proposed method.

Methane hydrate equilibria in silica gels with broad pore-size distributions

Abstract: Equilibrium pressures for the dissociation of methane hydrates confined in silica gel pores of nominal radii 7.5, 5.0 and 3.0 nm were measured over a wide temperature range, and were observed to be higher than those for bulk methane hydrate. A model is presented that allows the pore radius involved in each equilibrium to be determined from these data, so that the model exactly reproduces the experimental equilibrium pressure. Based on this model, pore volume distributions were reconstructed and found to be in good agreement with those obtained from nitrogen desorption isotherms, indicating that hydrate formed nearly uniformly in the available pores.