Active-screen plasma reduction and multi-functionalisations of graphene oxide

Jing, Zhiyuan (2021). Active-screen plasma reduction and multi-functionalisations of graphene oxide. University of Birmingham. Ph.D.

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Abstract

Graphene is a young but popular carbon material due to its attractive properties for various applications. As a derivative of graphene, graphene oxide (GO) is often used as the precursor of graphene due to its low cost, hydrophilicity and capability for modifications. Notwithstanding the fact that some methods have been explored for GO reduction, nitrogen doping or hybridisation with metal nanoparticles, each of these methods has its own limitations and none of them could fulfil all these three functions together. Therefore, a novel active-screen plasma (ASP) technique has been developed from this research by combining GO reduction, nitrogen doping and hybridising with metal nanoparticles in one treatment. The morphology, micro-structure, element composition as well as chemical bond of GO were fully characterised, and the electrical and electrochemical properties were evaluated.
The results have shown that ASP treatment using argon as a working gas was superior to annealing treatment in terms of GO reduction, lower sheet resistance and better super-capacitive performance. When a gas mixture of nitrogen and hydrogen was used in ASP, GO was reduced and nitrogen doped simultaneously, and the optimal ratio of nitrogen to hydrogen is 1:3, with the nitrogen doping configurations of pyridinic N, pyrrolic N and graphitic N. On the other hand, ASP using a gas mixture of nitrogen and argon deteriorated the electrical property.
Apart from reduction and nitrogen doping, metal nanoparticles from the active screen were sputtered and deposited on ASP treated GO at the same time when an additional noble metal lid was placed on top of the stainless-steel screen. Iron and chromium sputtered from the stainless steel were mainly in oxidised states, whilst noble metals were mainly in the form of pure metals, except for a minority of metal oxides in the cases of palladium and platinum.
With the noble metal deposition, the electrical and electrochemical properties of ASP treated GO were greatly influenced. The sheet resistances of ASP treated GO hybridised with platinum and gold were further reduced dramatically, and the super-capacitive performance of the ASP treated GO hybridised with platinum nanoparticles is the best among all the samples. However, silver nanoparticles aggregated and formed into large particles when deposited on GO surfaces, and palladium was chemically bonded with carbon, so that in these two cases, the metal hybridisation could not contribute to the improvement of electrical or electrochemical properties of GO.
It is expected that the novel ASP technology combining surface modification and metal hybridisation could open the way towards new applications of multi-functionalised GO such as GO-Ag for anti-bacterial materials, GO-Au and GO-Ag for surface-enhanced Raman scattering and GO-Pt, GO-Pd and GO-Au for catalysts.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):