Hierarchically Mesoporous/Macroporous Metal Oxides Templated from Polyethylene Oxide Surfactant Assemblies

Abstract

Surfactant templating techniques based on electrostatic, hydrogen-bonding, covalent, and van der Waals interactions between organic and inorganic species have been developed for the synthesis of materials with a narrow mesopore size distribution and controlled pore structure. [1,2] The use of block copolymers was recently shown to extend the pore sizes of ordered mesoporous oxides up to ten nanometers. [3,4] In addition, macroporous materials with pore sizes ranging from 100 nm to 1 mm can be obtained using latex spheres as templating agents. [5][6][7][8] The fabrication of hierarchically ordered structures at multiple length scales has attracted much interest from both a fundamental and practical viewpoint. [9,10] The combination of surfactant and colloidal crystal templating methods, together with microfabrication techniques allows the construction of hierarchical micro/meso/ macroporous architectures. [10][11][12][13][14][15] In this report, hierarchical mesoporous metal oxides with a novel macroporous architecture were synthesized in one step by single-surfactant templating without the need for polymeric spheres to act as a template that generates the macroporous structure. Polyethylene oxide (PEO) surfactants were used, which have been shown to efficiently organize mesoporous materials with structures of disordered wormhole-like MSU-type [16][17][18] and ordered SBA-n [19] and CMI-1 [20] materials. The occurrence of pores with a bimodal pore-size distribution in mesoporous materials is important and useful for both catalysis and the engineering of pore systems.[21]Mesoporous metal-oxide molecular sieves with macroporous structures are of interest as potential catalysts and sorbents, partly because the textural mesopores and intrinsic interconnected pore systems of macrostructures should efficiently transport guest species to framework binding sites. Biomimetic vesicular structures can be formed when the ionic strength of the nonionic surfactant solution is raised from that of the pure aqueous solution through the modification of PEOÀH 2 O hydrogen bonding; one kind of bimodal mesoporous silica has been synthesized by adding dilute electrolytes during PEO-templating.[22] Spongelike silica membranes with three-dimensional meso-macrostructures (that is, materials composed of mesopores of 2-50 nm in diameter, and macropores with diameters of between 50 nm and several micrometers) were synthesized from an electrolyte phase of a block copolymer/silica system, though inorganic salt crystals inevitably grew together with the silica membrane.[23] Mesomacroporous niobium oxides have also been prepared by adding NaCl to a ligand-assisted templating mixture of niobium ethoxide and amine surfactants; the salt was emphasized as being necessary for macropore (vesicle) formation. [24] We have used a simple method to prepare mesoporous metal oxides, such as TiO 2 and ZrO 2 , with macroporous hierarchical structure by the cooperative assembly of nonionic alkyl-PEO surfactants and inorganic precursors derived from metal alkoxi...

Hierarchically Mesostructured Titania Materials with an Unusual Interior Macroporous Structure

“…The macrochannels are not interconnected with each other and perpendicular to the dense mesoporous shell as described in our recent paper. [35] This observation supports our formation mechanism proposal that the present meso-macroporous titania materials with mesostructured shell and macroporous core might be formed by combining a reverse micelle templating pathway with a conventional surfactant templating technique of a hybrid composite mesostructured phase. The mesopore size can be adjusted by changing the hydrothermal temperature (Fig.…”

Macroporous TiO2 foam with mesoporous walls

“…For example, highly mesoporous crystalline TiO 2 macrocellular foams can be produced by combining a non-static air-liquid foam strategy and various mesogenic template methods [7]. Also, Blin et al have synthesized the macro/mesoporous zirconia and titania using polyethylene oxide surfactant [8]. Orilall et al reported a combined assembly of soft and hard chemistries to synthesize highly crystalline inverse opal macroporous Nb 2 O 5 and TiO 2 [9].…”

“…Many efforts have been taken to synthesize interconnected macroporous materials with mesoporous walls using simple techniques to enhance the performance of the materials for special applications [7][8][9][10][11][12][13][14][15][16]. For example, highly mesoporous crystalline TiO 2 macrocellular foams can be produced by combining a non-static air-liquid foam strategy and various mesogenic template methods [7].…”

Detailed investigation of nano-emulsions obtained from the Remcopal 4/decane/water system

“…Indeed, one way to design porous materials consists of combining the sol-gel chemistry and the use of surfactant molecule assemblies as templates to create the pore network. Depending on the structure of the initial system, microporous, mesoporous, or macroporous materials are recovered [20][21][22][23][24][25][26]. For example, by this way mesoporous and macroporous materials can be synthesized from micelles [20][21][22] and emulsions [24][25][26], respectively.…”