On the Reactivity of Graphene and MoS2 and the Preparation of their Heterostructures

Abstract

Graphene and MoS2 are two of the most popular materials in an ever widening range of two dimensional nanosheets that possess valuable and novel properties. It is not a case of if, but when, they become commonplace as components of devices such as fuel cells, solar cells, batteries, supports and catalysts worldwide. This raises its own concerns about the reactivity of two dimensional materials that have been released into the environment, as well as their bioavailability and possible bioremediation. The reactivity of graphene when exposed to a range of organic and metal-based oxidants is explored as an example of how graphene may react during the waste water treatment process and upon contact with the enzymes of soil bacteria. Incomplete degradation or functionalisation of graphene can make it significantly more bioavailable, leading to greater nanotoxicity. This can make disposing of graphene safely increasingly difficult and must be considered if graphene use is to become widespread. The combination of graphene and MoS2 in the form of heterostructures or composites has opened up an area of research into materials that possess enhanced qualities of multiple types of 2D nanosheets. However, the chemical interaction of graphene and MoS2 during heterostructure formation is often overlooked, and so, it is explored in detail here, through a series of spectroscopic techniques. The influence of this interaction on the HER properties of heterostructures is also studied. Building on this, the formation of covalently linked heterostructures has been largely ignored in favour of non-covalent structures such as van der Waals heterostructures. The formation of a graphene/MoS2 by covalently joining functionalised graphene and functionalised MoS2 is illustrated, and tested for HER catalysis. In order to explore further avenues for covalently joining graphene and MoS2 in future work, a study on the functionalisation and conversion of functional groups on graphene dispersions via wet chemistry is also demonstrated.