Synthesis of MoS2 Nanoflowers for Photocatalytic Degradation of Organic Dyes

The MoS2 nanostructures have been synthesized with the variation of Mo/S molar ratios of 1:2, 1:3, 1:4, 1:5, and 1:6 using a simple hydrothermal method. The (002) peak at 2θ ∼ 14° in the X-ray diffraction (XRD) pattern confirms the hexagonal phase of the synthesized MoS2 nanostructures, which agrees well with Raman and high-resolution transmission electron microscopy study. Furthermore, field emission scanning electron microscopy analysis reveals that the synthesized MoS2 with Mo/S molar ratios of 1:5 and 1:6 exhibits a nanoflower-like structure, significantly enhancing the photocatalytic activity. The methylene blue (MB) and phenolphthalein dye degradation efficiencies and rate constants of MoS2 are enhanced with the rise of Mo/S molar ratio under sunlight illumination. Specifically, MoS2 nanoflowers with a 1:5 molar ratio showed the maximum MB dye degradation efficiency of 98% and a rate constant of 0.132 cm–1 in 25 min of sunlight illumination. In addition, a maximum photocurrent density of 22 mA/cm2 has been achieved at −0.6 V vs Ag/AgCl for a 1:5 molar ratio sample. Moreover, the lowest charge-transfer resistance, highest carrier density, and carrier mobility enhance the photocatalytic activity of the 1:5 molar ratio sample with better separation of charge carriers and reduced carrier recombination rate. Hence, the synthesized MoS2 nanostructures with a 1:5 molar ratio of Mo/S are the optimized sample with enhanced photocatalytic and photoelectrochemical performances. The electronic and photocatalytic properties of MoS2 have been investigated theoretically with the variation of the layer number.