57 research outputs found
Porous nanostructured metal oxides synthesized through atomic layer deposition on a carbonaceous template followed by calcination
Porous metal oxides with nano-sized features attracted intensive interest in
recent decades due to their high surface area which is essential for many
applications, e.g. Li ion batteries, photocatalysts, fuel cells and
dye-sensitized solar cells. Various approaches were so far investigated to
synthesize porous nanostructured metal oxides, including self-assembly and
template-assisted synthesis. For the latter approach, forests of carbon
nanotubes are considered as particularly promising templates, with respect to
their one dimensional nature and the resulting high surface area. In this work,
we systematically investigate the formation of porous metal oxides (Al2O3,
TiO2, V2O5 and ZnO) with different morphologies using atomic layer deposition
on multi-walled carbon nanotubes followed by post deposition calcination. X-ray
diffraction, scanning electron microscopy accompanied with X-ray energy
dispersive spectroscopy and transmission electron microscopy were used for the
investigation of morphological and structural transitions at the micro- and
nano-scale during the calcination process. The crystallization temperature and
the surface coverage of the metal oxides and the oxidation temperature of the
carbon nanotubes were found to produce significant influence on the final
morphology
Atomic layer deposition-based tuning of the pore size in mesoporous thin films studied by in situ grazing incidence small angle x-ray scattering
Atomic layer deposition (ALD) enables the conformal coating of porous
materials, making the technique suitable for pore size tuning at the atomic
level, e.g., for applications in catalysis, gas separation and sensing. It is,
however, not straightforward to obtain information about the conformality of
ALD coatings deposited in pores with diameters in the low mesoporous regime (<
10 nm). In this work, it is demonstrated that in situ synchrotron based grazing
incidence small angle x-ray scattering (GISAXS) can provide valuable
information on the change in density and internal surface area during ALD of
TiO2 in a porous titania film with small mesopores (3-8 nm). The results are
shown to be in good agreement with in situ x-ray fluorescence data representing
the evolution of the amount of Ti atoms deposited in the porous film. Analysis
of both data sets indicates that the minimum pore diameter that can be achieved
by ALD is determined by the size of the Ti-precursor molecule
Synthesis of a 3D network of Pt nanowires by atomic layer deposition on carbonaceous template
The formation of a 3D network composed of free standing and interconnected Pt
nanowires is achieved by a two-step method, consisting of conformal deposition
of Pt by atomic layer deposition (ALD) on a forest of carbon nanotubes and
subsequent removal of the carbonaceous template. Detailed characterization of
this novel 3D nanostructure was carried out by transmission electron microscopy
(TEM) and electrochemical impedance spectroscopy (EIS). These characterizations
showed that this pure 3D nanostructure of platinum is self-supported and offers
an enhancement of the electrochemically active surface area by a factor of 50
Photocatalytic acetaldehyde oxidation in air using spacious TiO2 films prepared by atomic layer deposition on supported carbonaceous sacrificial templates
Supported carbon nanosheets and carbon nanotubes served as sacrificial
templates for preparing spacious TiO2 photocatalytic thin films. Amorphous TiO2
was deposited conformally on the carbonaceous template material by atomic layer
deposition (ALD). Upon calcination at 550{\deg}C, the carbon template was
oxidatively removed and the as-deposited continuous amorphous TiO2 layers
transformed into interlinked anatase nanoparticles with an overall morphology
commensurate to the original template structure. The effect of type of
template, number of ALD cycles and gas residence time of pollutant on the
photocatalytic activity, as well as the stability of the photocatalytic
performance of these thin films was investigated. The TiO2 films exhibited
excellent photocatalytic activity towards photocatalytic degradation of
acetaldehyde in air as a model reaction for photocatalytic indoor air pollution
abatement. Optimized films outperformed a reference film of commercial PC500
Synthesis and Characterization of Photoreactive TiO2/Carbon Nanosheet Composites
We report the atomic layer deposition of titanium dioxide on carbon nanosheet
templates and investigate the effects of post-deposition annealing in a helium
environment using different characterization techniques. The crystallization of
the titanium dioxide coating upon annealing is observed using in-situ X-ray
diffraction. The (micro)-structural characterization of the films is carried
out by scanning electron microscopy and advanced transmission electron
microscopy techniques. Our study shows that the annealing of the atomic layer
deposition processed and carbon nanosheets templated titanium dioxide layers in
helium environment results in the formation of a porous, nanocrystalline and
photocatalytically active titanium dioxide-carbon nanosheet composite film.
Such composites are suitable for photocatalysis and dye-sensitized solar cells
applications
Independent tuning of size and coverage of supported Pt nanoparticles using atomic layer deposition
Synthetic methods that allow for the controlled design of well-defined Pt nanoparticles are highly desirable for fundamental catalysis research. In this work, we propose a strategy that allows precise and independent control of the Pt particle size and coverage. Our approach exploits the versatility of the atomic layer deposition (ALD) technique by combining two ALD processes for Pt using different reactants. The particle areal density is controlled by tailoring the number of ALD cycles using trimethyl(methylcyclopentadienyl) platinum and oxygen, while subsequent growth using the same Pt precursor in combination with nitrogen plasma allows for tuning of the particle size at the atomic level. The excellent control over the particle morphology is clearly demonstrated by means of in situ and ex situ X-ray fluorescence and grazing incidence small angle X-ray scattering experiments, providing information about the Pt loading, average particle dimensions, and mean center-to-center particle distance
Carbon based materials and hybrid nanostructures investigated by advanced transmission electron microscopy
Highly efficient hyperbranched CNT surfactants : influence of molar mass and functionalization
End-group-functionalized hyperbranched polymers were synthesized to act as a
carbon nanotube (CNT) surfactant in aqueous solutions. Variation of the
percentage of triphenylmethyl (trityl) functionalization and of the molar mass
of the hyperbranched polyglycerol (PG) core resulted in the highest measured
surfactant efficiency for a 5000 g/mol PG with 5.6% of the available hydroxyl
end-groups replaced by trityl functions, as shown by UV-vis measurements.
Semiempirical model calculations suggest an even higher efficiency for PG5000
with 2.5% functionalization and maximal molecule specific efficiency in general
at low degrees of functionalization. Addition of trityl groups increases the
surfactant-nanotube interactions in comparison to unfunctionalized PG because
of pi-pi stacking interactions. However, at higher functionalization degrees
mutual interactions between trityl groups come into play, decreasing the
surfactant efficiency, while lack of water solubility becomes an issue at very
high functionalization degrees. Low molar mass surfactants are less efficient
compared to higher molar mass species most likely because the higher bulkiness
of the latter allows for a better CNT separation and stabilization. The most
efficient surfactant studied allowed dispersing 2.85 mg of CNT in 20 mL with as
little as 1 mg of surfactant. These dispersions, remaining stable for at least
2 months, were mainly composed of individual CNTs as revealed by electron
microscopy
Molecular shape-selectivity of MFI zeolite nanosheets in n-decane isomerization and hydrocracking
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