Version 2 2023-11-27, 14:38Version 2 2023-11-27, 14:38
Version 1 2023-11-20, 17:21Version 1 2023-11-20, 17:21
journal contribution
posted on 2023-11-27, 14:38authored byLysander
Q. Wagner, Eric Prates da Costa, Chantal Glatthaar, Frederik Breckwoldt, Marco Zecca, Paolo Centomo, Xiaohui Huang, Christian Kübel, Helmut Schlaad, Manfred Kriechbaum, Heinz Amenitsch, Matthias Thommes, Bernd M. Smarsly
Mesoporous materials with defined pore geometry act as
important
models for porous substances being applied in various fields of materials
research due to their large surface areafrom catalysis to
coatings and from solar cells to batteries and capacitors. Thus, understanding
structure-property relationships requires the capability of deliberately
and precisely tuning the mesoporosity, i.e., pore diameter, connectivity,
and wall thickness. However, especially for the interesting pore size
range between 35 and 70 nm, only a few convenient block copolymer
templates are available using micellar self-assembly. In this study,
we synthesized poly(ethylene oxide)-block-poly(hexyl
acrylate) copolymers (PEO-b-PHA) by a supplemental
activator reducing agent atom transfer radical polymerization (SARA
ATRP) and employed them as soft templates for the preparation of ordered
mesoporous metal oxide powders with spherical mesopores of ca. 40
nm in diameter, as shown by scanning electron microscopy (SEM), scanning
transmission electron microscopy (STEM), and small-angle X-ray scattering
(SAXS). With the aid of argon physisorption, STEM-based tomography,
and time-of-flight secondary ion mass spectrometry (ToF-SIMS), we
performed in-depth elucidation of pore shape and their mutual connection.
In the case of mesoporous silica, 40 nm spherical mesopores are connected
to 3–4 adjacent pores by 15 nm pore windows as well as 1–2
nm-sized micropores. These micropores seem to originate from single
PEO chains penetrating the 17 nm thick pore wall. Compared to such
mesoporous silica, mesoporous, crystalline zirconia possesses significantly
higher pore accessibility. Furthermore, we prepared a set of PEO-b-PHA block copolymers with different block lengths, showing
that mainly the PHA block length governs the mesopore size and thus
enables mesopore size tuning. These results highlight that PEO-b-PHA is a promising template for the preparation of mesoporous
metal oxides (in particular, crystalline ones) with tailored mesopore
sizes, which enables systematic studies on property-porosity relationships.