Extrusion polymerization: catalyzed synthesis of crystalline linear polyethylene nanofibers within a mesoporous silica

Synthesis of cyclic sulfites from epoxides and sulfur dioxide with silica-immobilized homogeneous catalysts

Quaternary ammonium- and amino-functionalized silica catalysts have been prepared for the selective synthesis of cyclic sulfites from epoxides and sulfur dioxide, demonstrating the effects of immobilizing the homogeneous catalysts on silica. The cycloaddition of sulfur dioxide to various epoxides was conducted under solvent-free conditions at 100 °C. The quaternary ammonium- and amino-functionalized silica catalysts produced cyclic sulfites in high yields (79-96 %) that are comparable to those produced by the homogeneous catalysts. The functionalized silica catalysts could be separated from the product solution by filtration, thereby avoiding the catalytic decomposition of the cyclic sulfite products upon distillation of the product solution. Heterogenization of a homogeneous catalyst by immobilization can, therefore, improve the efficiency of the purification of crude reaction products. Despite a decrease in catalytic activity after each recycling step, the heterogeneous pyridine-functionalized silica catalyst provided high yields after as many as five recycling processes.

TEM 3D Tomography of Noble Metal Nanowires Growth Inside SiO2 Mesoporous Aggregates

The use of bright-field transmission electron microscopy 3-D tomographic reconstruction allowed us to localize the synthesized nanostructures within the pores of mesoporous nanotemplates. Using this technique, we found that noble metal impregnation resulted in the inclusion of metal nanostructures within the SBA-15 mesoporous silica hexagonal pores (from nanoclusters to nanowires). The method allowed corroborating if the nanostructures were synthesized inside the pores or if they were alternatively on the nanotemplate aggregates exterior surface.

Self-assembled template-directed synthesis of one-dimensional silica and titania nanostructures

Mineralized biological materials such as shells, skeleton, and teeth experience biomineralization. Biomimetic materials exploit the biomineralization process to form functional organic-inorganic hybrid nanostructures. In this work, we mimicked the biomineralization process by the de novo design of an amyloid-like peptide that self-assembles into nanofibers. Chemically active groups enhancing the affinity for metal ions were used to accumulate silicon and titanium precursors on the organic template. The self-assembly process and template effect were characterized by CD, FT-IR, UV-vis, fluorescence, rheology, TGA, SEM, and TEM. The self-assembled organic nanostructures were exploited as a template to form high-aspect-ratio 1-D silica and titania nanostructures by the addition of appropriate precursors. Herein, a new bottom-up approach was demonstrated to form silica and titania nanostructures that can yield wide opportunities to produce high-aspect-ratio inorganic nanostructures with high surface areas. The materials developed in this work have vast potential in the fields of catalysis and electronic materials.

Smart nanocontainers and nanoreactors

We highlight recent advances in the synthesis of nanocarriers and nanoreactors from synthetic and biological building blocks with emphasis on the stimulus-responsive regulation of their function.

Robust hairy microspheres and derived hairy surfaces by an "inside-out" wet approach

Robust hairy microspheres were conveniently synthesized through an "inside-out" protrusion approach consisting of a sol-gel reaction and a radical polymerization, from conventional organosilanes and vinyl monomers. Their hierarchical structures of hard cores and plastic hairs can be adjusted in terms of their sizes and compositions to impart various chemical and physical properties on their surfaces. These hairy microspheres can also be built into hairy surfaces with many useful functions, such as superhydrophobicity. This work opens up a new route for the synthesis of hierarchical particles and enriches the tool library of material and surface engineering.

Novel functionalized mesopore of SBA-15 as prospective sorbent for praseodymium and lutetium

In the present work, results of γ-irradiation on normal and functionalized SBA-15 by aurintricarboxylic acid have been reported. Characterization of normal and functionalized SBA-15 particles before and after γ-irradiation was carried out using Fourier-transform infrared technique. Aurintricarboxylic acid ligand connected to SBA-15 was also analyzed using UV/Vis spectrophotometer. The modified sorbent was then used as a new sorbent for separation of trace amounts of praseodymium and lutetium ions from nuclear waste waters in batch techniques. Based on the results of distribution coefficients determination, and investigation of sorption process in various conditions, the parameters were optimized for separation lanthanides. It can be concluded that the functionalized SBA-15 is a promising sorbent for praseodymium and lutetium cations.

Statistical mechanical modeling of catalytic polymerization within surface-functionalized mesoporous materials

A discrete lattice model is developed to describe diffusion-mediated polymerization occurring within mesopores, where reaction is enhanced at catalytic sites distributed within the interior of the pores. Diffusive transport of monomers and polymers is one-dimensional, diffusion coefficients for the latter decreasing with polymer length. Kinetic Monte Carlo simulation is utilized to analyze model behavior focusing on a "clogging" regime, where the amount of polymer within the pores grows. We characterize the evolution of the overall and mean length of polymers, the mean number of polymers, as well as the polymer spatial and length distributions.

Ethylene Extrusion Polymerization by Heterogeneous bi-Supported Ziegler-Natta Catalysts

The MCM-41 (Mobil Composition of Matter) and SBA-16 (Santa Barbara Amorphous) supported TiCl4 and TiCl4/MgCl2 catalysts with different molar ratios of Mg/Ti were synthesized and used for ethylene polymerization under atmospheric pressure. The nanochannels of these supports serve as a nanoscale polymerization reactor and the polyethylene nanofibers were extruded during the reaction. The effect of MgCl2 on catalytic activity and morphology of resulting polyethylene has been investigated too. MgCl2 has enhanced the catalytic activities and made the SBA-16/MgCl2/TiCl4 catalytic system has fibrous morphology.