Synthesis of bimodal nanostructured silicas with independently controlled small and large mesopore sizes

We report on the synthesis of bimodal, structured silicas by a fully chemical, templating-scaffolding route that enables independent control over small and large mesopore sizes. Mesoporous MCM-41 nanoparticles, synthesized in a first step, are cross-linked in a second step, leading to a bimodal porous material. Triblock copolymer surfactants added during the second synthesis step form assemblies, around which the nanoparticles aggregate and cross-link considerably influencing both the average and the width of the secondary pore size distribution, without affecting the primary pore size. By changing the conditions of the second step, one can easily synthesize a broad variety of silicas with a controlled bimodal nanopore size distribution. Textural and structural properties were characterized by X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, Si-29 solid-state NMR spectroscopy, N-2 adsorption and desorption, and thermogravimetric analysis.