Hierarchically Structured MCM‐41 Silica Beads via Nanocasting in Combination with “Pore‐protected” Pseudomorphic Transformation

Abstract

The following study discusses the synthesis of macroporous glass beads, featuring variable pore sizes, and their application as starting material for a double templating route according to the nanocasting principle. In the first step, the initial porous glass was filled with the carbon precursor, a mesophase pitch, which after the subsequent carbonization and dissolution of the glass matrix results in an inverse macroporous carbon replica. Afterwards, the carbon beads were filled with amorphous silica by a typical sol‐gel‐process. The next step can be divided into two phases. The silica gel phase was first “structured” inside the macropores of the inverse carbon replica by converting it into an ordered mesoporous phase via pseudomorphic transformation. This process demanded alkaline conditions and a surfactant, that finally converts the silica into hierarchically structured beads with the dimension and the pores of the initial glass and MCM‐41 pores inside the walls. The final step comprised the template removal via calcination. The obtained materials were characterized by mercury intrusion, nitrogen adsorption, scanning electron microscopy, x‐ray powder diffraction and particle size analysis. In comparison to the previously reported approaches, the new method allows a higher flexibility in the texture properties of the resulting hierarchically structured materials including a variable ratio between ordered mesopores and additional macropores by parallel control of the total porosity and wall thickness in the starting porous glass.

Towards Macroporous α-Al2O3—Routes, Possibilities and Limitations

“…A different approach towards porous α-Al 2 O 3 is found in the attempt to prevent pore collapse upon high temperature calcination by infiltrating porous γ-Al 2 O 3 with a carbonaceous precursor solution. Carbon filling of porous materials is usually employed in syntheses of porous carbon materials and can easily be realized with different carbonaceous precursors [42][43][44]. Utilizing this method not to template a porous carbon but to protect the pores of a ceramic material such as Al 2 O 3 has been patented by Shell in 1971 [45] and seconded by Exxon in 1978 [46].…”

“…AAO-0 (A) pristine 32-49 AAO-1100 (B) 1100 °C 29-47 AAO-Mn-900 (C) 900 °C, Mn-impregnated [42][43][44][45][46] This pore diameter of 44 nm (with an extremely small deviation of approximately ±2 nm) is the smallest one published for pure α-Al2O3 published hitherto. We hence included this finding in our calculations of the theoretically attainable porosities and corresponding ABET of porous α-Al2O3 materials in Section 4.1.…”

Quantized Self-Assembly of Discotic Rings in a Liquid Crystal Confined in Nanopores

“…Finally, we envision that the spontaneous, temperature-tunable nanoscale ring formation demonstrated here along with the one-dimensional charge carrier pathways and mechanical stability of the membranes may provide a versatile playground for the study of electronic and magnetic confinement effects [76] or even of the fluid-wall-interaction-induced deformations of nanopores [77]. It may also serve as nanotemplating mechanism for organic semiconductor-based devices [9,12,17,76] given the nowadays readily available nanoporous solids [27,28,[78][79][80][81] and the simple preparation by capillarity-driven, spontaneous melt imbibition [30].…”

Pseudomorphic Transformation of Porous Glasses into Micelle‐Templated Silica

“…Materials with a hierarchical meso‐/macropore structure cannot be obtained in any case. Therefore, Kuester et al proposed the concept of the pore‐protected pseudomorphic transformation (Fig. ).…”

“…Synthesis scheme of the pore‐protected transformation (reproduced with permission from , © 2014 Wiley‐VCH Verlag GmbH & Co. KGaA).…”