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P. Gebhardt:
"Nano-structuring of zeolites and cobalt oxide with nanocarbons and block copolymers";
Betreuer/in(nen), Begutachter/in(nen): D. Eder, H. Koller; Institut für Materialchemie E-165, 2016; Rigorosum: 09.02.2016.

"The morphology of heterogeneous catalysts greatly impacts their catalytic efficiency and selectivity.
Recent years have witnessed the rise of the new material class of nanocarbon inorganic hybrids, which
combines the characteristic of functional materials with the exceptional physico-chemical properties
of nanocarbons, which creates additional, synergistic effects that further enhance the material performance
for a wide range of applications.
This work focused on the morphological effects of hybridizations with nanocarbons - in the form
of graphene and carbon nanotubes (CNTs) - and the structuring with block copolymers, exemplified
by (1) the photocatalytic zeolite TS-1 and (2) the versatile catalyst cobalt oxide.
The hybridization of TS-1 with graphene produced a wide range of morphologies depending on the
exact graphene type, such as HG, GO, RGO, or covalently functionalized graphene. Most strikingly,
non-covalently functionalized HG produced a wide range of morphologies - from coffin-shaped crystals
over disks and rectangular plates to nanoparticles smaller than 10 nm - depending on the graphene
concentration. Molecular mechanics simulations helped to develop a mechanism based on the
preferential adsorption of graphene on certain crystal planes that implies a general working principle
and should be applicable for other materials as well. Using graphene with grafted TPA+ (zeolite
structure directing agent) groups produced covalently bound TS-1 crystals on the graphene surface
with a diameter of 4 nm, which is unprecedentedly small and corresponds to only two unit cells.
Further structure engineering tried to introduce ordered mesopores into TS-1 while retaining the
zeolitic crystallinity using block copolymers P123 and ISO. The polymers self-assemble to a mesostructure
during zeolite formation and are thermally removed after synthesis to produce mesopores. Acidcatalyzed
self-assembly (ACSA) with P123 produced hexagonally ordered, cylindrical pores of 5 nm
in an amorphous (i.e. non-zeolitic) material. The ISO polymer yielded a crystalline material by stabilizing
the assembled polymer prior to the hydrothermal crystallization step - either by CASH-assisted
evaporation-induced self-assembly (EISA) or by first producing a hard carbon template that was subsequently
used for a confined TS-1 synthesis.
The hybridization of cobalt oxide with CNTs produced a wide range of morphologies - ranging from
coatings with a controlled thickness, over flake-like structures to octahedral, cubic or round nanoparticles
of controlled size - depending on the non-covalent functionalization agent and the surface
properties of the CNTs. First catalytic results in low-temperature CO oxidation revealed beneficial effects
of the hybridization and a temperature dependence on the phase and particle size of cobalt
oxide, which has to be investigated further in the future.
The results were supported by extensive materials characterization, including electron microscopy
(TEM, SEM), N2 physisorption (BET, t-plot, BJH), X-ray diffraction (XRD), thermal analysis (TG/DTA),
fourier-transformed infrared spectroscopy (FTIR), Raman spectroscopy, and UV-vis spectroscopy."