Preparation of lamellar and hexagonal forms of mesoporous silica and zirconia by the neutral amine route: lamellar–hexagonal transformation in the solid state

Spherical Particles of Zirconia–Titania of Hexagonal Structure from a Neutral Amine Route

“…1, exhibited an intense and relatively sharp peak at 4.5°, with d 100 ϭ 1.96 nm, that is in agreement with the hexagonal nature of the obtained matrix (1,2). A great advantage of this method is the occurrence of the reaction in an open system without any special experimental conditions.…”

Effect of Addition of Divalent Transition Metal Chlorides on the Structure and Thermal Stability of Lamellar Silica Synthesized by the Neutral Amine Route

“…For the lamellar silica in Fig. 2a three di!raction peaks are observed at 2 values of 3.83, 7.33, and 11.53 attributed to the 001, 002, and 003 di!raction planes (16,17), which correspond to d spacings of 2.3, 1.2, and 0.70 nm, respectively. However, an important feature to be considered is related to the disposition of the n-alkyldiamine molecule in the gallery space.…”

“…6 and 7, respectively. Some hybrids presented a "rst step of mass loss due to the release of physisor- The consecutive release of diamine molecules leads to transitions in the solid-state phase such as lamellarPhexa-gonalPamorphous (16,17,22). For the original lamellar silica sample, the "rst and third mass loss steps are associated with structural transitions corresponding to the sequence lamellarPhexagonal and hexagonalPamorphous.…”

“…In this connection, the sol}gel method can be successfully employed to prepare lamellar inorganic}organic hybrid compounds from alkyltrimethylammonium bromide salts (12}15) or neutral n-alkyldiamines (16,17) as template molecules, by including some silicon or transition metal alkoxides. However, in the synthetic route for neutral n-alkyldiamines, template chain length and solvent composition, mainly water content, play a crucial role in formation of the "nal product, which could be derived to lamellar or hexagonal silicas (16).…”

Síntese e reatividade de sílica lamelar

“…Na preparação de sílica lamelar utilizando-se o processo solgel, o número de átomos de carbono na cadeia da dialquilamina neutra ou do surfactante e o número de moles de água presentes no sistema reacional são fatores determinantes para que o produto final obtido seja amorfo, hexagonal ou lamelar. Em princípio, cadeias carbônicas maiores e maior quantidade de água, determinam a formação de um produto lamelar, enquanto a reduçao da cadeia carbônica da molécula "template" conduz à formação de material hexagonal 125 . Observa-se que a distância interplanar do produto lamelar obtido, aumenta linearmente com o aumento da cadeia carbônica do surfactante ou da diamina neutra utilizada 128,144 .…”