Surfactant-Directed Synthesis of Mesoporous Titania with Nanocrystalline Anatase Walls and Remarkable Thermal Stability

Abstract

A synthesis route to mesoporous titania with remarkable thermal stability was developed using an amine or cetyltrimethylammonium-templating procedure. By a treatment of the titania hybrids in aqueous ammonia, a method has been developed to overcome the lack of thermal stability above 350 °C. As for most mesoporous titanias described in the literature, this thermal instability originates from the uncontrolled phase transformation of amorphous template-free titania into massive anatase grains. In situ Raman spectroscopy, X-ray Diffraction, Differential Scanning Calorimetry and Thermogravimetrical Analysis demonstrated that parts of the amorphous titania walls of the NH 3 -treated titania hybrids were transferred into walls built up of rutile nanobuilding blocks before the template was thermally removed. We further found that, after a subsequent increase of temperature to remove the template, the remaining amorphous particles were transformed into anatase in such a way that this crystallographic transformation is accompanied by a retention of the pore structure without massive segregation of anatase nuclei. This leads to ordered high surface area (up to 600 m 2 g -1 ) mesostructured titania having pore volumes up to 0.28 cm 3 g -1 . XRD and N 2 adsorption-desorption data showed an outstanding thermal stability; the mesoscale order of NH 3 -treated titanias was retained after thermal treatment up to 600 °C.

Pore-size expansion of hexagonal-structured nanocrystalline titania/CTAB Nanoskeleton using cosolvent organic molecules

“…[10][11][12][13][14][15][16][17][18][19][20][21][22] This is most likely due to the non-crystallization and -crystal growth of the Hex-ncTiO 2 /CTAB Nanoskeleton and Hex-ncTiO 2 /CTAB/COM Nanoskeleton during thermal treatment. Wide-angle XRD patterns of Hex-ncTiO 2 /CTAB Nanoskeleton and Hex-ncTiO 2 /CTAB/COM Nanoskeleton hardly changed in the temperature range of 150-450 °C (see Figure 12).…”

“…[10][11][12][13][14][15][16][17][18][19][20][21][22]. Therefore, thermal stability of the mesostructured titania materials is one of the important issues to be addressed.…”

“…[30][31][32][33] Compared with the reported methods, [10][11][12][13][14][15][16][17][18][19][20][21] our synthetic system involves benefits, for example, spontaneous formation of hexagonal structure and crystallization of titania (anatase formation) in aqueous solutions…”

“…[10][11][12][13][14][15][16][17][18][19][20][21][22] In addition, preparation of mesostructured crystalline titania typically requires alcohol-based solvents, [10][11][12][13][14][15][16][17][18][19][20][21][22] so the replacement of many conventional alcohols as solvents used in the sol-gel reaction to the environmental benign alternatives is also an important challenge toward achieving the goal of green chemical processing.…”

Formation Mechanism for Hexagonal-Structured Self-Assemblies of Nanocrystalline Titania Templated by Cetyltrimethylammonium Bromide

“…The Hex-ncTiO 2 /CTAB Nanoskeleton was prepared through a hydrolysis reaction of the titania precursor promoted by CTAB spherical micelles in aqueous solutions at 60 for 24 h 20,21) . Compared to the reported methods for mesoporous titania synthesis [22][23][24][25][26][27] , our system involves unique features and advantages, for example, a facile preparation, utilization of water as a solvent, hexagonal-structure autoformation in solutions (without solvent evaluation), crystallization of titania in aqueous solutions in mild conditions (e.g., at 60 for 24 h) 20,21) while crystallization of mesoporous titania normally requires calcinations at high temperature [22][23][24][25][26][27] . To realize the full potential of our approach (and to be able to generalize to other systems) we need better insight on the HexncTiO 2 /CTAB Nanoskeleton formation.…”