Use of confinement effects in mesoporous materials to build tailored nanoarchitectures

CONTRERAS, CINTIA BELÉN; GALO J. A. A. SOLER-ILLIA; AZZARONI, OMAR

ELSEVIER SCIENCE B. V.

Comprehensive Nanoscience and Nanotechnology (Second Edition)

Año: 2019

In the last two decades, a remarkable proficiency was achieved in both the synthesis and the physical characterization of mesoporousmaterials (MM), which present high surface areas, and organized arrays of monodisperse pores, with diameters tunablebetween 2 and 50 nm. This length scale is somehow ?magic?, due to the relevant effects of the proximity of a surface, combinedwith the existence of condensed matter (solvent, analytes, reagents) in the mesopore space. Different MM have been thoroughlystudied for the fundamental interest in chemistry and physics under confinement, as well as their possible applications innumerous fields such as heterogeneous catalysis, sensing, optics, drug delivery, cell growth and bioimaging. The synthetic communityhas acquired a large expertise in controlling the size and shape of nanoscopic cavities in inorganic and organic solids, andin their functionalization with a large variety of species, ranging from molecular groups to polymers, biomolecules or nanospecies.The field of MM has experienced an impressive growth since the first demonstration of supramolecular templating in thenineties [1?4]. Three advantages contributed to the success of MM as a dynamic and flourishing fundamental field of study:(a) The precise and independent control over porosity, inorganic framework and surface/pore contents tailorability of thesematerials, (b) the simple, extended reproducible and inexpensive experimental protocols derived from the combination of sol-geltechniques and self-assembly, and (c) the wide possibilities of advanced applications that exploit the high surface area, chemicalfunctionalities and confinement. Furthermore, the possibility of multiscale processing (i.e., control on materials shaping, inclusionin multiscale porous systems, etc.), makes MM suitable building blocks for future technologies.The unique properties of MM derived from their framework composition, pore architectures and tailored pore surfaces representkey features with strong impact on a variety of technological applications. While the first efforts were directed to exploit the highsurface area in straightforward applications towards catalysis, adsorption or sensing processes, there is a bright future in takingadvantage of two less utilized aspects: confinement effects due to the finite pore size and surface effects, and the consequent ability touse these effects to finely tune the positioning of chemical or nanostructured species within the walls, surfaces or pore interior.In this work, we will present and analyze examples from the literature that illustrate the effects of confining matter in thesemesoporous systems, such as solvent structuring, molecular or polymer conformation, or electrostatic effects. Interestingly, theseconfinement ? derived effects can be exploited to build up nanosystems with pre-determined function positioning. In turn, thispossibility opens the path to creating nanosystems with well-defined chemical and nanostructured building blocks arbitrarilyplaced in space. We will show that the very existence of mesopores defines three spaces -the pore wall, the surface and the poreinterior- that determine several properties such as accessibility, reactivity and the distance between functions. These propertiesarise from the combination of architecture (at different length scales) and local chemical functions, which can be in turnadvantageously used to control transport or local reactivity and, consequently, permit a directional mass or energy transfer. Theelaborate nano-architectures resulting from this approach resemble more and more the biological systems, in which local reactivityand transport between locally well-defined environments take place and generate complex physical-chemical behavior.