Abstract
The molecular functionalization of two-dimensional MoS2 is of practical relevance with a view to, for example, facilitating its liquid-phase processing or enhancing its performance in target applications. While derivatization of metallic 1T-phase MoS2 nanosheets has been relatively well studied, progress involving their thermodynamically stable, 2H-phase counterpart has been more limited due to the lower chemical reactivity of the latter. Here, we report a simple electrolytic strategy to functionalize 2H-phase MoS2 nanosheets with molecular groups derived from organoiodides. Upon cathodic treatment of a pre-expanded MoS2 crystal in an electrolyte containing the organoiodide, water-dispersible nanosheets derivatized with acetic acid or aniline moieties (∼0.10 molecular groups inserted per surface sulfur atom) were obtained. Analysis of the functionalization process indicated it to be enabled by the external supply of electrons from the cathodic potential, although they could also be sourced from a proper reducing agent, as well as by the presence of intrinsic defects in the 2H-phase MoS2 lattice (e.g., sulfur vacancies), where the molecular groups can bind. The acetic acid-functionalized nanosheets were tested as a non-noble metal-based catalyst for nitroarene and organic dye reduction, which is of practical utility in environmental remediation and chemical synthesis, and exhibited a markedly enhanced activity, surpassing that of other (1T- or 2H-phase) MoS2 materials and most non-noble metal catalysts previously reported for this application. The reduction kinetics (reaction order) was seen to correlate with the net electric charge of the nitroarene/dye molecules, which was ascribed to the distinct abilities of the latter to diffuse to the catalyst surface. The functionalized MoS2 catalyst also worked efficiently at realistic (i.e., high) reactant concentrations, as well as with binary and ternary mixtures of the reactants, and could be immobilized on a polymeric scaffold to expedite its manipulation and reuse.
Highlights
Over the past decade, layered transition metal dichalcogenides (TMDs) in the form of nanosheets (NSs) have become one of the most intensively investigated members of the family of twodimensional (2D) materials
Because access of both electrical current and electrolyte to the expanded layers should be guaranteed under such conditions, this initial cathodic treatment was expected to set a favorable stage for any subsequent electrochemical modification of the MoS2 material.[23]
We have demonstrated that 2H-phase MoS2 NSs can be functionalized with molecular groups derived from organoiodides by a straightforward and expeditious electrolytic method
Summary
Over the past decade, layered transition metal dichalcogenides (TMDs) in the form of nanosheets (NSs) have become one of the most intensively investigated members of the family of twodimensional (2D) materials. Electrochemical strategies for molecular functionalization, and more generally for organic synthesis, are often more attractive than their classical, reagentbased counterparts in terms of, for example, atom economy and environmental friendliness (chemical redox agents being replaced by electrons) or industrial scalability, if carried out in water.[19] the availability of electrolytic routes toward chemically derivatized 2D TMDs could ease the deployment of such materials in practical uses We address this gap and report the electrolytic functionalization of 2H-phase MoS2 NSs based on their reaction with organoiodides. The present work illustrates both the feasibility of functionalizing 2H-phase TMD NSs by electrochemical means and the advantages associated with such functionalization in terms of practical utility
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