Amorphous MoS_xO_y/h-BN_xO_y Nanohybrids: Synthesis and Dye Photodegradation

Molybdenum sulfide is a very promising catalyst for the photodegradation of organic pollutants in water. Its photocatalytic activity arises from unsaturated sulfur bonds, and it increases with the introduction of structural defects and/or oxygen substitutions. Amorphous molybdenum sulfide (a-MoS_xO_y) with oxygen substitutions has many active sites, which create favorable conditions for enhanced catalytic activity. Here we present a new approach to the synthesis of a-MoS_xO_y and demonstrate its high activity in the photodegradation of the dye methylene blue (MB). The MoS_xO_y was deposited on hexagonal boron oxynitride (h-BNO) nanoflakes by reacting h-BNO, MoCl₅, and H₂S in dimethylformamide (DMF) at 250 °C. Both X-ray diffraction analysis and high-resolution TEM show the absence of crystalline order in a-MoS_xO_y. Based on the results of Raman and X-ray photoelectron spectroscopy, as well as analysis by the density functional theory (DFT) method, a chain structure of a-MoS_xO_y was proposed, consisting of MoS₃ clusters with partial substitution of sulfur by oxygen. When a third of the sulfur atoms are replaced with oxygen, the band gap of a-MoS_xO_y is approximately 1.36 eV, and the valence and conduction bands are 0.74 eV and -0.62 eV, respectively (relative to a standard hydrogen electrode), which satisfies the conditions of photoinduced splitting of water. When illuminated with a mercury lamp, a-MoS_xO_y/h-BN_xO_y nanohybrids have a specific mass activity in MB photodegradation of approximately 5.51 mmol g^-1 h^-1, which is at least four times higher than so far reported values for nonmetal catalysts. The photocatalyst has been shown to be very stable and can be reused.