Mesoporous organic-inorganic hybrid materials, a new class of materials characterized by large specific surface areas and pore sizes between 2 and 15 nm, have been obtained through the coupling of inorganic and organic components by template synthesis. The incorporation of functionalities can be achieved in three ways: by subsequent attachment of organic components onto a pure silica matrix (grafting), by simultaneous reaction of condensable inorganic silica species and silylated organic compounds (co-condensation, one-pot synthesis), and by the use of bissilylated organic precursors that lead to periodic mesoporous organosilicas (PMOs). This Review gives an overview of the preparation, properties, and potential applications of these materials in the areas of catalysis, sorption, chromatography, and the construction of systems for controlled release of active compounds, as well as molecular switches, with the main focus being on PMOs.

Silica-based mesoporous organic-inorganic hybrid materials.

On the Controllable Soft-Templating Approach to Mesoporous Silicates

Since the discovery of MCM-41 more than ten years ago, many investigations have explored the suitability of hexagonal mesoporous silicas for potential practical applications. These range from catalysis and optically active materials to polymerization science, separation technology and drug delivery, with recent successes in the fabrication of hybrid mesoporous organosilicas expected to open up further application possibilities. Because the pore voids of this class of materials exhibit relatively narrow pore size distributions in the range of 2-4 nm in diameter, mesoporous silicas can selectively include organic compounds and release them continuously at a later stage. The functionalization of MCM-41 pore voids with photoactive derivatives provides influence over the material's absorption behaviour, but full control over the release process remains difficult. Here we show that the uptake, storage and release of organic molecules in MCM-41 can be regulated through the photocontrolled and reversible intermolecular dimerization of coumarin derivatives attached to the pore outlets. Successful functionalization requires uncalcined MCM-41 still filled with the template molecules that directed the formation of its pores, to ensure that coumarin derivatives attach preferentially to the pore outlets, rather than their inside walls. We find that this feature and the one-dimensional, isolated nature of the individual pores allow for efficient and reversible photocontrol over guest access to the material's interior.

Photocontrolled reversible release of guest molecules from coumarin-modified mesoporous silica

We report results of nitrogen and argon adsorption experiments performed at 77.4 and 87.3 K on novel micro/mesoporous silica materials with morphologically different networks of mesopores embedded into microporous matrixes: SE3030 silica with worm-like cylindrical channels of mode diameter of approximately 95 angstroms, KLE silica with cage-like spheroidal pores of ca. 140 angstroms, KLE/IL silica with spheroidal pores of approximately 140 angstroms connected by cylindrical channels of approximately 26 angstroms, and, also for a comparison, on Vycor glass with a disordered network of pores of mode diameter of approximately 70 angstroms. We show that the type of hysteresis loop formed by adsorption/desorption isotherms is determined by different mechanisms of condensation and evaporation and depends upon the shape and size of pores. We demonstrate that adsorption experiments performed with different adsorptives allow for detecting and separating the effects of pore blocking/percolation and cavitation in the course of evaporation. The results confirm that cavitation-controlled evaporation occurs in ink-bottle pores with the neck size smaller than a certain critical value. In this case, the pressure of evaporation does not depend upon the neck size. In pores with larger necks, percolation-controlled evaporation occurs, as observed for nitrogen (at 77.4 K) and argon (at 87.3 K) on porous Vycor glass. We elaborate a novel hybrid nonlocal density functional theory (NLDFT) method for calculations of pore size distributions from adsorption isotherms in the entire range of micro- and mesopores. The NLDFT method, applied to the adsorption branch of the isotherm, takes into account the effect of delayed capillary condensation in pores of different geometries. The pore size data obtained by the NLDFT method for SE3030, KLE, and KLE/IL silicas agree with the data of SANS/SAXS techniques.

Adsorption hysteresis of nitrogen and argon in pore networks and characterization of novel micro- and mesoporous silicas

Mesoporous silica nanoparticles (MSNs) provide a non-invasive and biocompatible delivery platform for a broad range of applications in therapeutics, pharmaceuticals and diagnosis. The creation of smart, stimuli-responsive systems that respond to subtle changes in the local cellular environment are likely to yield long term solutions to many of the current drug/gene/DNA/RNA delivery problems. In addition, MSNs have proven to be promising supports for enzyme immobilisation, enabling the enzymes to retain their activity, affording them greater potential for wide applications in biocatalysis and energy. This review provides a comprehensive summary of the advances made in the last decade and a future outlook on possible applications of MSNs as nanocontainers for storage and delivery of biomolecules. We discuss some of the important factors affecting the adsorption and release of biomolecules in MSNs and review of the cytotoxicity aspects of such nanomaterials. The review also highlights some promising work on enzyme immobilisation using mesoporous silica nanoparticles.

Mesoporous silica nanoparticles for bioadsorption, enzyme immobilisation, and delivery carriers

Ordered mesoporous organosilica with large (10 nm) cagelike pores was synthesized using a triblock copolymer template and characterized using 29Si and 13C NMR spectroscopy, nitrogen adsorption, thermogravimetry, TEM, and SAXS

Periodic mesoporous organosilica with large cagelike pores

A practical approach to the determination of the pore entrance size in ordered silicas with cage-like mesoporous structures (OSCMSs) is proposed. A fundamental insight into the OSCMS pore connectivity is gained, including the control of the pore entrance size by post-synthesis surface modification, and by selection of appropriate synthesis temperature. These findings show a new promise for the synthesis of mesoporous solids with molecular size- and shape-selective properties.

Determination and tailoring the pore entrance size in ordered silicas with cage-like mesoporous structures.

Ordered Mesoporous Silica SBA‐15: A New Effective Adjuvant to Induce Antibody Response

Silicas with large (about 10 nm in diameter), uniform, cage-like pores were synthesized from sodium silicate and poly(ethylene oxide)−poly(butylene oxide)−poly(ethylene oxide) B50-6600 triblock copolymer template (EO39BO47EO39) under acidic conditions The synthesis procedure was analogous to that reported by others for FDU-1 silica with highly ordered cubic Im3m structure, but in our study, an expensive tetraethyl orthosilicate (TEOS) was successfully replaced by cost-efficient sodium silicate Adsorption and thermogravimetric properties of the silicas synthesized from sodium silicate were found to closely resemble those of FDU-1 silicas synthesized from TEOS, but the pore volumes and specific surface areas of the former were found to be lower in most cases The uniform cage-like structures assembled from sodium silicate formed at room temperature and 318 K, but no ordered structure was obtained at 333 K, whereas in the case of TEOS, an ordered structure formed also at 333 K The sample synthesized at ro

Synthesis of large-pore silica with cage-like structure using sodium silicate and triblock copolymer template

A new approach is proposed for the synthesis of extra-large-pore (diameter > 7 nm) MCM-41 analogues, potentially useful as hosts for the synthesis of nanowires and as model porous solids for fundam...

Lucildes Pita Mercuri

Papers

Periodic mesoporous organosilica with large cagelike pores

Determination and tailoring the pore entrance size in ordered silicas with cage-like mesoporous structures.

Ordered Mesoporous Silica SBA‐15: A New Effective Adjuvant to Induce Antibody Response

Synthesis of large-pore silica with cage-like structure using sodium silicate and triblock copolymer template

Toward the Synthesis of Extra-Large-Pore MCM-41 Analogues