Graphene-based nanostructures such as graphene, graphene oxide, and graphene-like hexagonal boron nitride sheet have attracted significant attention because of their potential use for electronic nanodevices, biosensors and polymer composite preparation. The sensitivity and selectivity of graphene-based materials to biomolecules are deciding factors to determine the suitability of these materials as biosensor. As for nanofillers in polymer composites, the interfacial binding characteristics influence significantly the mechanical and thermal property improvements of the polymer composites. Thus, the interactions between bio-/poly- molecules and graphene-based materials are important issues for nanodevice design and nanomaterial preparation. In this thesis, the interactions between bio-/poly- molecules and graphene-based materials were studied using theoretical methods.
First, the adsorption of nitrated tyrosine on intrinsic and metal-doped graphene was studied by density functional theory (DFT) to explore the possibility of using graphene-based biosensor to detect protein tyrosine nitration (PTN). The configurations of (a) phenolic ring coordination and (b) nitro group coordination on graphene were compared. It was found that nitrated tyrosine was physisorbed on the intrinsic graphene and favored coordinating with the intrinsic graphene by phenolic ring, while chemisorption was observed on Au, Cr and Ni-doped graphene with high binding energy. In contrast, the nitrated tyrosine favored coordinating with the metal-doped graphene through metal-nitro group configuration. The electronic density of states analysis showed strong orbital hybridization between the nitro group and metal-doped graphene. The analysis results indicated that metal-doped graphene was sensitive to tyrosine nitration, thus suggesting the potential application of metal-doped graphene for PTN detection.
As a further exploration of graphene-like material as biosensors, the adsorption of hydrogen-bonded and stacked nucleobase pairs on the hexagonal boron nitride (h-BN) surface was studied by DFT and molecular dynamics (MD) methods. Eight types of nucleobase pairs (i.e., GG, AA, TT, CC, UU, AT, GC, and AU) were chosen as the adsorbates. The adsorption configurations, interaction energies, and electronic properties of the nucleobase pair on the h-BN surface were obtained and compared. The density of states analysis result shows that both the hydrogen-bonded and stacked nucleobase pairs were physisorbed on h-BN with minimal charge transfer. The hydrogen-bonded base pairs lying on the h-BN surface are significantly more stable than the stacked forms in both the gas and water phase. The molecular dynamics simulation result indicates that h-BN possessed high sensitivity for the nucleobases and the h-BN surface adsorption could revert the base pair interaction from stacking back to hydrogen bonding in aqueous environment. The h-BN surface could immobilize the nucleobases on its surface, which suggests that the use of h-BN has good potential in DNA/RNA detection biosensors and self-assembly nanodevices.
To explore the mechanism of graphene as adsorbent in the application of organic pollutant molecules extraction, the adsorption of polybrominated diphenyl ethers (PBDEs) on graphene surface was studied by DFT and MD methods. Nine types of PBDEs with different degree of bromination (i.e. BDE 15, BDE 28, BDE 47, BDE 99, BDE 153, BDE 154, BDE 183, BDE 194 and BDE 209) as well as a diphenyl ether molecule (DE) were selected as the adsorbates. The stable adsorption configurations, interaction energies, electronic properties and thermodynamic parameters of the adsorption systems were obtained. The DFT calculation results showed that for the DE, BDE 15, BDE 28, BDE 47, BDE 99, BDE 153 and BDE 194 adsorption systems, the interaction strength between the PBDE congeners and graphene increased with increasing of the substituent bromine atom. The adsorption strength of these seven systems also exhibited a positive linear correlation with the hydrophobicity of PBDEs. However, the BDE 154, BDE 183 and BDE 209 adsorption systems were inconsistent with this trend due to only mono phenyl ring forming a π-π stacking with graphene. The electronic density of states and charge transfer analysis indicated the adsorption of PBDEs on graphene is physisorption. The MD simulation showed that graphene is sensitive to PBDE and the adsorption process of PBDE on graphene is very fast.
Finally, Poly(vinyl alcohol)/graphene oxide (PVA/GO) composites were studied by molecular mechanics and MD methods to analyze the effect of GO sheets addition on PVA material. The properties of polymer/GO composites with different oxidation degree and dispersion states of GO sheets in PVA matrix were compared. The interfacial binding characteristics, mechanical properties and glass transition temperature of PVA/GO composites were obtained. It was found that the oxidation degree of GO sheet would influence the strength of interfacial binding characteristics between polymer and GO sheet. A high oxidation degree of GO would enhance the interaction between GO sheet and PVA matrix, thus improve the properties of PVA/GO composites. By reinforcing pure PVA with GO to give PVA/GO composites, its Young's modulus, bulk modulus, shear modulus, as well as glass transition temperature of the PVA/GO composites were obviously enhanced.
| Date of Award | 2 Oct 2013 |
|---|
| Original language | English |
|---|
| Awarding Institution | - City University of Hong Kong
|
|---|
| Supervisor | Lawrence WU (Supervisor) |
|---|