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 poly­(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 m²/g when heated to 400 °C. Titania made from the silicatein α mimic also shows a higher catalytic activity than does commercial Degussa P25 TiO₂ 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 (C₆H₆/C₆F₆) 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 Å from both sides of the graphene sheet. The solvent structuring is driven by quadrupolar interactions and consists of stacks of alternating C₆H₆/C₆F₆ molecules rising from the surface of the graphene. These stacks result in density oscillations with a period of about 3.4 Å. The high affinity of the 1:1 C₆H₆/C₆F₆ 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