Aminated phyllosilicates have been synthesized by a sol±gel process from reactions of nickel ions and three analogous trialkoxysilanes, 3-(trimethoxysilyl)propylamine, N'-[3-(trimethoxysilyl)propyl]ethylenediamine and N'-[3-(trimethoxysilyl)propyl]diethylenetriamine, in aqueous basic medium at 298 and 323 K. The inorganic± organic hybrids SILNix (x~1±3) were denoted following the above sequence of aminated silanes, varying from one to three amino groups on the organosilanes. The amount of nickel in the SILNix matrices showed the presence of cations in two different environments: (i) octahedral sites and (ii) in the gallery space complexed by amino groups. The thermal stability decreased in the order SILNi1wSILNi2#SILNi3. The basal peaks were associated with lamellar distances of 1.64, 2.15 and 2.45 nm for SILNix (x~1±3), respectively. For the phyllosilicates obtained at room temperature, the values were 1.36 and 1.96 nm for SILNi1* and SILNi2*, respectively. The increased values observed from n~1 to 3 can be attributed to the presence of organic chains in these new structures, which was con®rmed by elemental analysis. The samples showed a peak at 2h~60³ (d~0.16 nm) indexed to the 060 re¯ection, characteristic of trioctahedral phyllosilicates. XRD results and IR spectroscopy suggested nickel hydroxide was not obtained. Reactions of the hybrids with 2-pyridinecarbaldehyde were carried out to evaluate the reactivity of the amino groups in the gallery space.
New layered inorganic-organic magnesium organosilicates were prepared by a singlestep template sol-gel synthesis through the reaction of magnesium ions with a synthetic homologous series of urea-alkoxysilanes with the general formula (CH 3 CH 2 O) 3 Si(CH 2 ) 3 -NHC(O)NH( CH 2 ) n CH 3 , for n ) 2, 4, and 6. The nanocomposites were characterized by elemental analysis, solid-state 29 Si and 13 C nuclear magnetic resonance, X-ray diffraction, and thermogravimetry. The results showed that the hybrid materials exhibit lamellar structures similar to those found in the natural inorganic silicate talc. The influence of the length of the organic group of the urea-alkoxysilane employed in the formation of these layered structures is clearly observed by 29 Si NMR spectroscopy. A high degree of condensation for the hybrid synthesized with urea-alkoxysilane containing the longest alkyl chain was obtained. These materials seem to be promising as sorbents for solid-phase extraction of organic pollutant molecules, when dispersed in water, because of their highly hydrophobic character.
As separações por cromatografia líquida de alta eficiência (CLAE) são realizadas, na maioria das vezes, em condições de fase reversa empregando fases estacionárias a base de sílica. Um problema sério com estas fases reversas é a tendência da sílica dissolver em soluções de pH elevado, frequentemente necessárias para separar compostos básicos. A literatura reporta várias maneiras diferentes de tentar solucionar este problema. Este artigo relata os resultados obtidos com fases estacionárias desenvolvidas no nosso laboratório, utilizando suportes de sílica, contendo uma camada de um óxido metálico (zircônia ou titânia) ligada à sua superfície, seguido por imobilização de um polissiloxano ou por organofuncionalização com um trimetóxialquilsilano. Testes de estabilidade, também desenvolvidos no nosso laboratório, indicaram que a camada de óxido metálico aumenta o tempo de vida da coluna cromatográfica, por tornar a fase estacionária menos susceptível à dissolução. High performance liquid chromatographic (HPLC) separations are largely carried out using reversed phase conditions with stationary phases based on silica. A serious problem with these stationary phases is the tendency of silica to dissolve in high pH solutions often needed to separate basic compounds. The literature reports many different ways that have been tried to resolve this problem. This paper reports the results obtained in our laboratory with stationary phases prepared using silica supports having a layer of a metal oxide (zirconia or titania) attached on their surfaces, followed by immobilization of a polysiloxane or by organofunctionalization with a trimethoxyalkylsilane. Stability tests, also developed in our laboratory, indicate that the metal oxide layer increases the HPLC column lifetimes by making the stationary phase less susceptible to dissolution.
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