Synthesis, Functionalisation and Reactivity of Reduced 2D 2H-MoS2

Abstract

2D 2H-MoS2 is a thermodynamically stable, semiconducting material which is commonly explored for electronics, photoelectronic, sensing, bioimaging and therapeutics applications. However, one of its main drawbacks is the inert basal plane, which hampers its catalytic performance, and hinders functionalisation of its surface. The main objective of this Thesis was to activate the surface of 2H-MoS2 towards functionalisation as well as improve its catalytic performance in desulfurisation and hydrogen evolution reactions. The surface was activated through the reduction followed by the reoxidation of the material, which was discussed in Chapter 2. This was achieved in the reaction with NaBH4 and H2O and allowed for the isolation of 2H-MoS2 with a delocalised partial negative charge, denoted as n-2H-MoS2. n-2H-MoS2 displayed good stability in H2O and other solvents with a high dielectric constant. The mechanism of the introduction of that negative charge was explored in Chapter 3. It was demonstrated that the reaction with NaBH4 led to the H- and Na+ transfer, which facilitated the formation of the metastable Nax[Hx-MoS2] adduct, denoted as r-2H-MoS2, which displayed numerous signs of reduction. In the following chapters, the reactivity of 2H-MoS2, n-2H-MoS2 and r-2H-MoS2 was explored. In Chapter 4, it was demonstrated that dibenzothiophene can adsorb at the edges and corners of 2H-MoS2, forming both physisorption and chemisorption interaction in solution. In Chapter 5, it was established that both n-2H-MoS2 and r-2H-MoS2 can react with electrophiles like organoiodides, which led to the covalent functionalisation of the surface of the material. In Chapter 6, 2H-MoS2, n-2H-MoS2 and r-2H-MoS2 were functionalised with Cu(OAc)2 and Sc(OTf)3. The functionalisation of 2H-MoS2 and n-2H-MoS2 with Cu(OAc)2 caused a deterioration in the hydrogen evolution reaction performance, however, the functionalisation of 2H-MoS2 and r-2H-MoS2 with Sc(OTf)3 displayed an enhancement in the catalytic performance.