Nonionic Poly Ethylene Oxide Surfactant Research Articles

Hierarchical microtubular nanoporous zirconia with an extremely high surface area and pore volume

Hierarchical nanoporous zirconias with an aligned microtubular structure of inner diameter 0.5–1.5 μm and length 5–30 μm and an extremely high surface area and large pore volume (up to 1100 m 2/g and 3.0 cm 3/g, respectively) have been prepared by a simple method from a mixture of zirconium propoxide and chloroform solutions in the presence of nonionic polyethylene oxide surfactant. The tubular walls are composed of wormhole-like nanopores, resulting in very high surface areas and large pore volumes of hierarchical porous materials for multi-applications.

Synthesis of mesoporous silica with tunable pore size from sodium silicate solutions and a polyethylene oxide surfactant

Abstract Mesoporous silica materials with tunable pore sizes were synthesized starting from sodium silicate solutions and a non-ionic polyethylene oxide surfactant (Triton X100). The silicate anions were first transformed into soluble polysilicic acids by adding to an acidic surfactant solution (final pH of the mixture of 2–3) and then polycondensated at a temperature in the range 25–45°C after adjustment of the pH between 3 and 10.5. The regularity and the size of the pores depend, in the first place, on the polycondensation pH and on the sodium cation concentration. If the pH is below 5–6, poorly organized mesostructures with low calcination stability and with a preponderance of micropores are formed. Between pH 5–6 and 8 the pore size increases smoothly from 1.5 to 2.5 nm with the pH and the sodium cation concentration. High concentrations improve the pore volume and the regularity of the pores, especially in the more acidic part of the pH range. A steep increase of the pore diameter until 4–5 nm is observed between pH 8.5 and 10.5. Control of the formation of mesostructured materials by the micelles is probably favored by reducing of the number of water molecules which are hydrogen-bonded to the soluble species (depending on the pH and the sodium cation concentration), which allows more interactions between the surfactant and the polysilicic species. However, the induced changes of the conformation of the surfactant and of its arrangement on the silicic walls produce only a limited increase in the pore size until pH 8. The fast increase of the negative charge density (SiO − ) above pH 8 is responsible for the decrease of the interactions with the surfactant. The latter has less contact with the walls and becomes more stretched. This results in an abrupt increase in the pore size.

Modification of [M]-MSU-X mesoporous silicate pore morphology by post-synthesis treatment

[M]-MSU-X mesoporous silicates prepared from selected low concentration non-ionic polyethylene oxide surfactants have been subjected to post synthesis hydrothermal treatment which significantly modifies the pore morphologies forming stable hexagonal or lamellar structures through an internal dissolution-redirection mechanism.

Mesoporous [M]-MSU-x metallo-silicate catalysts by non-ionic polyethylene oxide surfactant templating

Solutions of low and high pH have been used to form non-ionically templated mesoporous metallo-silicates [M]-MSU-x materials; where [M]=Al, Ti, V and Zr. Two new assembly routes are proposed which exploit the acid and base catalysed hydrolysis and simultaneous condensation of metal oxo-salts and silicon tetraethoxide. Acid catalysed hydrolysis, labeled N0X−I+ or N+X−I+ (N0=nonyl-phenyl polyethylene oxide, X−=Cl− or SO2−4, I+=protonated tetraethyl orthosilicate), produces well-defined materials with uniform pores in the small mesoporous region and moderate pore volumes, but reduced metal incorporation owing to the high solubilities of metal cations in acidic solutions. Base catalysed hydrolysis, labeled N0M+I− (N0=nonyl-phenyl polyethylene oxide, M+=Na+ or NH+4, I−=hydroxylated tetraethyl orthosilicate), also leads to materials with uniform channels in the small mesoporous region. Pore volumes and metal substitution are higher and framework shrinkage during calcination is reduced as a result of thicker pore walls. These new pathways show distinct similarities to those described by Attard et al. [Nature 378 (1995) 366] and Zhao et al. [Science 279 (1998) 548] for the formation of hexagonally symmetric silica from non-ionic surfactants under acidic conditions and also to mesoporous MCM-41 assembly routes via (S+X−I+) anion mediated acid catalysed assembly. The results demonstrate the feasibility of preparing templated mesoporous metallo-silicates from non-ionic polyethylene oxide surfactants and metal oxy-hydroxy cationic precursors, but indicate that further optimisation of the reaction conditions is required to maximise the potential of this synthesis approach.

Assembly of Mesoporous Molecular Sieves Containing Wormhole Motifs by a Nonionic Surfactant Pathway: Control of Pore Size by Synthesis Temperature

Nonionic polyethylene oxide surfactants are versatile structure-directing agents for the assembly of mesoporous molecular sieves, but their greatest benefit may lie in their ability to control the pore size of the mesostructure by the assembly temperature (see dependence of pore diameter R on temperature shown on the right). For mesostructured silicas with wormhole motifs, the average pore diameter can be altered by as much as 2.4 nm by varying the assembly temperature over a relatively narrow range below the cloud point temperature of the surfactant.

Templating of Mesoporous Molecular Sieves by Nonionic Polyethylene Oxide Surfactants

Mesoporous silica molecular sieves have been prepared by the hydrolysis of tetraethylorthosilicate in the presence of low-cost, nontoxic, and biodegradable polyethylene oxide (PEO) surfactants, which act as the structure-directing (templating) agents. This nonionic, surfactant-neutral, inorganic-precursor templating pathway to mesostructures uses hydrogen bonding interactions between the hydrophilic surfaces of flexible rod- or worm-like micelles and Si(OC(2)H(5))(4-x)(OH)(x) hydrolysis products to assemble an inorganic oxide framework. Disordered channel structures with uniform diameters ranging from 2.0 to 5.8 nanometers have been obtained by varying the size and structure of the surfactant molecules. Metal-substituted silica and pure alumina mesostructures have also been prepared by the hydrolysis of the corresponding alkoxides in the presence of PEO surfactants. These results suggest that nonionic templating may provide a general pathway for the preparation of mesoporous oxides.