Application of Mechanoenergy in Accessing Graphene Composite Functional Nanomaterials

Author: Mohd Wahid

Wahid, Mohd, 2015 Application of Mechanoenergy in Accessing Graphene Composite Functional Nanomaterials, Flinders University, School of Chemical and Physical Sciences

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Graphene, the monoatomic layer of the graphite mineral has been a subject of intense research interest among the scientific community. Given the exceptional electrical, thermal, mechanical and optical properties of graphene, it shows huge potential for wide-ranging applications and this is further extended through functionalization. In this dissertation various hybrid materials of graphene have been synthesised, characterized in detail, and some of their potential applications explored. Multi-layers of graphene have been synthesised using a vortex fluidic device (VFD) in water and subsequently they were interfaced with the surface of microalgal cells, Chlorella vulgaris. This functionalization of microalgae with multi-layer graphene has resulted in enhanced nitrate-removal activity compared to pristine microalgal cells. Viability tests show that the graphene is non-toxic towards the cells. This work demonstrates the advantage of hybridization of microalgae with graphene.

Secondly, taking advantage of the bio-interfacing of graphene towards cells, encapsulation of microalgae, Chlorella vulgaris, with ultra-thin layers of graphene oxide (GO) using the VFD has been established. The entrapment of algal cells within GO layers enabled the temporal confinement of the growth of microalgae which is promising as an immobilization technique for the microalgal cells. Furthermore, using the VFD, improved wrapping efficiency is obtained which is evidenced by the morphology of the samples and the growth curve of the cells post wrapping. This work demonstrates for the first time the wrapping of single cell algae with graphene oxide.

GO encapsulation of two types of bacteria has been established using the VFD, for spherical shaped Staphylococcus aureus, and rod shaped Rhodococcus opacus. Similar to the previous study with microalgae, GO wrapping of the bacteria resulted in a temporal confinement of the bacterial growth and AFM, TEM and SEM microscopy images of the samples demonstrate the wrapping of bacterial cells within GO layers. This work demonstrates the effectiveness of the VFD processing on wrapping different shapes of bacteria with the scope of extending functionality of the bacterial cells.

Functionalization of graphene was also carried out using an antimicrobial agent, 1,3,5-tris[(1E)-2’-(4’-benzoic acid) vinyl]benzene, namely Ramizol®. Ramizol® is essentially a planar molecule and can interact with the surface of graphene via extended π- π interactions thus potentially stabilising the graphene in water. Moreover, the shape of Ramizol® lends itself to facilitate the exfoliation of graphene from graphite by acting as a molecular ‘wedge’ during sonication where the graphene sheets are prized apart. The ensuing stabilized composite material demonstrates antibacterial activity against Staphylococcus aureus bacteria and it has potential in biomedical applications such as wound dressing materials with the graphene acting as a drug carrier as well as enhancing the structural strength of the composite material.

The amphiphilic property of graphene oxide has been utilised as a surfactant for the stabilization of 2D monoatomic crystals, namely boron nitride and molybdenum disulphide, in water. One of the intricacies of processing 2D atomic crystals is due to their insolubility in water and common organic solvents. If they can be made soluble, this can significantly facilitate their processing. An alternative route to overcome this problem has been established, involving the use of graphene oxide. This work demonstrates a facile approach of preparing 2D atomic crystals in aqueous solution, which can be further developed for the large scale synthesis of 2D layered materials and hetero-laminar material in general.

Overall, the synthesis of novel functional materials through hybridization with graphene derivatives has been established, with the ability to gain access to various products with novel properties. The unique properties of graphene and other materials are combined to generate potentially useful materials such as water treatment agents, surface functionalized biological cells, antibacterial materials and 2D hetero-atomic materials. Moreover, samples were prepared using facile preparation methods which are scalable, and therefore have potential for industrial applications.

Keywords: graphene composite, mechanoenergy, Vortex Fluidic Device, ultrasonication

Subject: Chemistry thesis

Thesis type: Doctor of Philosophy
Completed: 2015
School: School of Chemical and Physical Sciences
Supervisor: Prof. Dr. Colin L. Raston