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Silica-based materials with hierarchical pore systems at three different length scales (small mesopores-large mesopores-macropores) have been prepared through a nanotectonic approach by using mesoporous nanoparticles as building blocks; the resulting materials present a highly accessible foam-like architecture and can be prepared as large monoliths.The design of new materials with frameworks involving hierarchical pore systems and complex macroscale forms is an emerging area owing to potential applications 1 on the basis of the possibility of harmonizing an enhanced accessibility to the functional active groups (across large pores) with the conservation of the high surface area and pore structure. [2][3][4] These very open networks favour diffusion of reagents and products while avoiding undesired pore blocking phenomena. A variety of bimodal materials combining micro-meso, meso-macro or micro-macroporosity has been described to date. 4 However, as far as we know, there is only one report dealing with a solid including a trimodal pore system. 5 The described synthesis approaches are usually based on the use of so many different template agents as pore types. On the other hand, shaping of porous solids in the form of monoliths instead of fine powders (as usually produced) confers on them additional advantages and wide-ranging applications in catalysis. 5-8 Different research groups have been able to prepare zeolite monoliths with additional macroporous voids by using double scale template agents (small molecular templates and bacterial structures, polystyrene latex spheres or polyurethane foams as secondary large templates), and starting from solutions of inorganic precursors or, alternatively, from preformed zeolite nanoparticles as building blocks. 5,9,10 Polymer foams have been extensively used to synthesize ceramic foams of several compositions. 11 These ceramic materials are usually prepared by coating the surface of the polymer with a slurry of ceramic powder; later polymer removal by calcination leads to a ceramic replica of the organic foam. Lee et al. 8 have recently reported on the use for the first time of polyurethane foams as large-scale secondary templates to prepare micro-macroporous silicalite-1 monoliths using softchemistry conditions typical for obtaining zeolites. In this case, the silicalite crystals grow over the polyurethane surface from a solution confined in the macrocellular voids. In contrast, MCM-41 and related mesoporous materials do not present the ability of zeolites to generate large monoliths and multimodal pore systems. Difficulties increase when nanotectonic approaches are intended, taking into account the unavailability of mesoporous nanoparticles on a large scale. Thus, there is no report to date dealing with the preparation of large monoliths using preformed silica mesoporous nanoparticles as building blocks.Here, we present the preparation and characterization of silica-based large monoliths having trimodal pore systems (small meso-, large meso-and macroporous). The monoliths...

Silica-based rigid monoliths exhibiting a trimodal hierarchical pore system have been successfully prepared through coating of a ceramic foam (CF) with sub-micro-/nanometric mesoporous particles (as building blocks). We have selected a bimodal porous silica, denoted as UVM-7 (a nanometric version of the well-known MCM-41 materials), consisting of small aggregates of nanometric surfactant-assisted mesoporous particles. A colloidal suspension of this material in water is used to coat through successive impregnation cycles the CF surface. The small intraparticle mesopore system (with pore diameters around 2-3 nm) is due to the supramolecular templating effect of the surfactant. Textural large-mesopores/ macropores (in the 20-70 nm range) have their origin in the interparticle UVM-7 voids. The large macrocellular macropores are due to the CF support. The resulting monoliths present a good and homogeneous coverage level. Moreover, these composites display better mechanic properties than those of related silica self-supported monoliths.