Activation of two-dimensional MoS2 nanosheets by wet-chemical sulfur vacancy engineering for the catalytic reduction of nitroarenes and organic dyes

Two-dimensional 2H-phase MoS2 nanosheets can be used as a non-noble metal-based catalyst for nitroarene and organic dye reduction, thus being of potential utility towards the treatment of industrial wastewater. However, their activity is severely limited by the inertness of their pristine basal surface. We report here a simple approach for the catalytic activation of solvent-dispersed MoS2 nanosheets based on the introduction of sulfur vacancies by hydrazine treatment. MoS2 nanosheets boasting markedly improved catalytic activities in the reduction of 4-nitrophenol, 4-nitroaniline, methyl orange and methylene blue by NaBH4 could be obtained, outperforming many prior non-noble metal-based catalysts developed for such reactions. Notably, the improvement in catalytic activity was not compromised by the use of a proper dispersant to colloidally stabilize the activated nanosheets in the aqueous reaction medium. Substrate-supported catalysts could be prepared by immobilizing the nanosheets on melamine foam, facilitating their handling and reutilization. The chemical processes taking place between the investigated reagents and the MoS2 catalyst were also discussed and rationalized, based on which a mechanism for nitroarene/dye reduction mediated by the sulfur vacancies was proposed.