2 research outputs found
Titania Condensation by a Bio-Inspired Synthetic Block Copolymer
Silicatein
α, an enzyme found at the center of silica spicules in marine
sponges, is known to play a role in silica condensation from seawater.
It has also been shown to catalyze the formation of silica from various
silica precursors such as tetraethyl orthosilicate (TEOS). Inspired
by the finding that the serine-26 and histidine-165 amino acids in
the enzyme are required for silica formation from TEOS, we synthesized
polyÂ(hydroxylated isoprene-<i>b</i>-2-vinylpyridine) block
copolymers to mimic these amino acid residues. Here, we present the
results of our investigation utilizing this biomimetic polymer to
condense titania from titanium <i>iso</i>-propoxide (TiP).
Our silicatein α mimic is shown to condense titania at neutral
pH and room temperature and is compared to material produced by standard
sol–gel methods. Heats of crystallization are observed to be
72% lower for the titania made from the mimic polymer, and indistinct
X-ray diffraction peaks, even after heating well above the crystallization
temperature, suggest a higher degree of titania condensation with
the silicatein α mimic. Results from thermogravimetric analysis
show that the mimic formed titania initially contains ∼15 wt
% polymer and that the surface area increases from less than 5 to
greater than 110 m<sup>2</sup>/g when heated to 400 °C. Titania
made from the silicatein α mimic also shows a higher catalytic
activity than does commercial Degussa P25 TiO<sub>2</sub> for the
photodegradation of N-nitrosodimethylamine (NDMA), degrading 73% of
the NDMA in two hours as compared to 62% with Degussa P25. The biomimetic
system presented here offers the promise of an environmentally friendlier
method of titania production and will enable applications requiring
neutral pH and low temperatures, such as titania composite synthesis,
surface coating, or catalyst design
Stabilization of Graphene Sheets by a Structured Benzene/Hexafluorobenzene Mixed Solvent
Applications requiring pristine graphene derived from
graphite
demand a solution stabilization method that utilizes an easily removable
media. Using a combination of molecular dynamics simulations and experimental
techniques, we investigate the solublization/suspension of pristine
graphene sheets by an equimolar mixture of benzene and hexafluorobenzene
(C<sub>6</sub>H<sub>6</sub>/C<sub>6</sub>F<sub>6</sub>) that is known
to form an ordered structure solidifying at 23.7 °C. Our simulations
show that the graphene surface templates the self-assembly of the
mixture into periodic layers extending up to 30 Ã… from both sides
of the graphene sheet. The solvent structuring is driven by quadrupolar
interactions and consists of stacks of alternating C<sub>6</sub>H<sub>6</sub>/C<sub>6</sub>F<sub>6</sub> molecules rising from the surface
of the graphene. These stacks result in density oscillations with
a period of about 3.4 Ã…. The high affinity of the 1:1 C<sub>6</sub>H<sub>6</sub>/C<sub>6</sub>F<sub>6</sub> mixture with graphene is
consistent with observed hysteresis in Wilhelmy plate measurements
using highly ordered pyrolytic graphite (HOPG). AFM, SEM, and TEM
techniques verify the state of the suspended material after sonication.
As an example of the utility of this mixture, graphene suspensions
are freeze-dried at room temperature to produce a sponge-like morphology
that reflects the structure of the graphene sheets in solution