Production of inorganic nanohybrids by the templating of carbon and peptide nanostructures

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Abstract

Silica and titania nanoparticles have been produced by using carbon nanotubes (CNTs) and graphene as templates in a sol-gel reaction. A range of Fmoc terminated amino-acids (Fmoc-AAs) were studied as surface modifiers to encourage the templating on the nanocarbons. After annealing the deposited structures, the carbon templates were either left in place to give hybrid structures or oxidized to leave pure inorganic nanoparticles.Absorption studies were initially conducted to identify Fmoc-AAs that would bind well to the CNTs. Fmoc-Trp had the best affinity for CNTs out of the amino acids studied. The fully reversible nature of the binding process was demonstrated via the desorption of Fmoc-AAs from CNTs in water. The equilibrium data were found to be well described by the Freundlich isotherm model. The competitive binding from a library of Fmoc-AAs on graphite was developed to efficiently identify the strongest binding candidate.The synthesis of CNT-SiO2 and CNT-TiO2 nanohybrids were successfully demonstrated. The morphology of the hybrids was found to be dependent on the CNT:precursor and Fmoc-AA:CNT ratios. Fmoc-AAs were believed to play a dual role: (1) electrostatically stabilizing the NT dispersion and (2) the functionalities from the side chains of the amino acids providing binding sites for SiO2 and TiO2 deposition. Uniform anatase nanotubes (NTs) were synthesized after calcination of the CNT-TiO2 nanohybrids. Both the inner diameter and wall thickness of the synthesized TiO2 NTs were controlled by the dimension of CNT templates and the ratio of CNT:precursor. The transition from anatase to rutile phase was found to be affected by heating temperature, pre-treatment and ramp rate. A simple route towards the production of TiO2 NT arrays was also demonstrated by using aligned CNT arrays as templates in the presence of the Fmoc-AAs.Graphene based nanohybrids were synthesized in the presence of graphene oxide (GO), Fmoc-Trp stabilized base-washed graphene oxide (bwGO) and exfoliated graphene via the sol-gel process. It was found that the morphology of the products was highly dependent on the reaction media. Graphene dispersions were prepared by direct exfoliation of graphite in Fmoc-Trp solution. Raman, TEM and AFM analyses suggested the dispersion comprised of mainly few layer graphene (<5 layers) with a broad size distribution and that the defects introduced during sonication were predominately associated with the formation of new flake edges due to sonication-induced cutting.A preliminary study was conducted on the silicification of Fmoc-Y and Fmoc-FY self-assembled hydrogels. The presence of a high density of –OH group on the nanofibers’ surface was found to promote silica deposition.

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