NiS2-NiS nanocrystalline composite synthesized by mechanochemistry and its performance for methylene blue dye adsorption

Nanocrystalline nickel disulfide, NiS2, was mechanochemically prepared using ball milling procedures in inert atmosphere, starting from 34:66 Ni:S powder mixtures. X-ray powder diffraction (XRPD) patterns showed that 6 h of milling are enough to allow the formation of the NiS2 phase, which is accompanied by a small fraction of the hexagonal NiS phase. Rietveld analysis indicates that the average crystallite size is about 22 nm for NiS2 and 12 nm for NiS after 9 h milling. Transmission Electron Microscopy (TEM) analyses reveal that the composite is mainly composed of large particles of hundreds of nanometers formed by crystalline agglomerates along with a few squared nanocrystals. The as prepared material slowly reacts with air, being converted to sulfates along with elemental sulfur as given by XRPD. The fresh and aged composite was used for the adsorption of methylene blue (MB) from aqueous solutions. Adsorption of MB was faster in the aged material probably due to its higher surface area when compared to the fresh sample. [Display omitted]