Reaction Kinetics for the Covalent Functionalization of Two-Dimensional MoS₂ by Aryl Diazonium Salts

The two-dimensional transition-metal dichalcogenide molybdenum disulfide (MoS₂) has been intensely studied in the past several years due to its exceptional electronic, optical, and chemical properties in a wide range of applications. The chemical functionalization of MoS₂ allows its properties and interfacial interactions to be tuned and controlled. Recently, we reported the direct covalent functionalization of semiconducting MoS₂ with aryl diazonium salts, without the use of harsh initial treatments or phase engineering. In this paper, we confirm and expand the covalent functionalization reaction model by performing a detailed study of the reaction kinetics for monolayer MoS₂ functionalized by 4-nitrobenzene tetrafluoroborate (4-NBD). We find that both the Freundlich and Temkin isotherm models are good descriptors of the reaction due to the energetically inhomogeneous surface of MoS₂ and the indirect adsorbate-adsorbate interactions from previously attached nitrophenyl groups, respectively. The reaction kinetics was then found to be well described using a pseudo-second-order model, showing that the order of this reaction is two. This study supports our previous work and gives us a deeper understanding of the nature of the covalent functionalization of MoS₂.