Improving Catalytic Activity by Synergic Effect between Base and Acid Pairs in Hierarchically Porous Chitosan@Titania Nanoreactors

The beneficial effect of the bifunctional character of the chitosan@titania hybrid in heterogeneous catalysis was elucidated: considering a prototypical Henry condensation, Michael addition, and Jasminaldehyde synthesis, the cohabitation of a basic site (NH2) and an acidic site (Ti) in the same reactor provided clear activity and selectivity enhancements, with respect to the monofunctional acidic titania and basic chitosan counterparts

Single-Step Dispersion of Functionalities on a Silica Surface

A new process for coating a mesoporous silica gel with a mixture of the grafting reagents para-aminophenyltrimethoxysilane and phenyltrimethoxysilane is thoroughly analyzed. The dilution of para-aminophenylsilane with phenylsilane at different ratios allows the density of the functional amino groups present on the silica surface to be controlled, while keeping constant the overall number of grafts. Furthermore, the choice of a rigid linker prevents undesirable interactions between the active function and the inorganic support that could alter the function reactivity. This simple and new method, which results in the improvement of the dispersion of a functionality in a one-pot synthesis, could be particularly interesting in the field of supported catalysis and molecular recognition. The dispersion of the functional groups of the synthesized hybrid solids is investigated using a pyrene derivative covalently linked to the free amino groups of the para-aminophenylsilanes by analyzing the excimer and monomer fluorescence properties of the probe

Design of Stable Nanoporous Hybrid Chitosan/Titania as Cooperative Bifunctional Catalysts

A new method describing the synthesis of hybrid porous materials based on chitosan/titania featuring high surface area and shaped as microspheres is reported. The particular self-assembly properties of chitosan in addition to the mutual chemical interaction between the glucosamine units and the titania precursors control the titania condensation inside the beads of chitosan. The intimate mixing of organic and inorganic frameworks entails a notable improvement on the hydrolytic stability of resulting material when compared to the individual component ones. Moreover, highly active and selective catalytic properties for monoglyceride synthesis stems from the coexistence of the basic sites (NH2 from biopolymer) and acid sites (titanium center) through their cooperative effect

Different Routes for Preparing Mesoporous Organosilicas Containing the Tröger’s Base and Their Textural and Catalytic Implications

Organosilica materials with different contents of Tröger’s base (TB) as builder moieties have been synthesized from previously synthesized bis-trialkoxysilylated Tröger’s base. Three well-nanostructured hybrid mesoporous materials were prepared through different approachs: (a) anchoring the TB on a preformed silica SBA-15 material by postsynthesis grafting, (b) incorporating the TB fragments into the rigid and ordered periodic mesoporous organosilica (PMO) with hexagonal structure (HMS) by self-assembling process, and (c) using anion fluoride as catalyst for a sol−gel synthesis process in the absence of structural directing agents (SDAs), at neutral pH and low synthesis temperature, to introduce the TB units into the walls of high surface orderless mesoporous materials with flexible structure. The degree of long-range ordering of the materials was determined from X-ray diffraction and transmission electron microscopy and the texture of the various samples were analyzed by nitrogen sorption volumetry. The composition of the materials was determined by elemental analyses and thermogravimetry, and the integrity, topology and structuration level of the Tröger̀s base units were characterized by 13C NMR and 29Si MAS NMR spectroscopy. The materials were used as basic organocatalysts in Knoevenagel reaction. The disordered mesoporous hybrid materials show the highest catalytic activity due to the appropriate combination of high accessibility and structural flexibility. These mesoporous organosilica materials are stable upon recycling

Porous Chitosan-Silica Hybrid Microspheres as a Potential Catalyst

Chitosan/silica hybrids were synthesized and shaped as microspheres, which may or may not present a core/shell structure, depending on the experimental conditions. The core is constituted by a homogeneous hybrid, while the shell is pure silica. The amino groups of the biopolymer are still accessible as active sites for heterogeneous catalysis

Hybrid Materials and Periodic Mesoporous Organosilicas Containing Covalently Bonded Organic Anion and Cation Featuring MCM-41 and SBA-15 Structure

We report the synthesis of a new trialkoxysilylated ionic liquid based on disilylated guanidinium and monosilylated sulfonimide species. This compound allowed the successful preparation of new periodic mesoporous organosilicas containing covalently anchored ion-pair through both organo-cationic and organo-anionic moieties which have never been reported up to now. Two classes of hybrid materials containing guanidinium−sulfonimide ion-pairs (IPs) have been synthesized. The first type of material was prepared by grafting the silylated IP onto both MCM-41-type and SBA-15-type silicas according to a surface sol−gel polymerization. The second class was synthesized following a one-pot sol−gel procedure using silylated IP and tetraethoxysilane as framework precursors. These latter materials correspond to so-called periodic mesoporous organosilicas (PMOs) and gave “organo-ionically” modified MCM-41 and SBA-15 related solids. The materials were characterized by a series of techniques including XRD, nitrogen sorption, solid-state NMR, FTIR, transmission electronic microscopy, and elemental analysis. The highest structural regularity in terms of pore size distribution and channel size homogeneity was observed for IP-PMOs possessing SBA-15-type architecture due to an enhanced trialkoxysilylated IP precursor/surfactant interaction. Solvatochromic experiments with Reichardt’s dye showed good accessibility of the silica-supported ion-pair and suggested the formation of monophasic materials