Nanoparticle single-phase nickel sulfides such as NiS, NiS 2 , Ni 3 S 4 , and Ni 7 S 6 were prepared from elemental sulfur and nickel nitrate hexahydrate, using a temperature-controlled precursor injection method. The initial ratio of the concentrations of the sources was used to control the size and phase of the final product.Phase control was confirmed using X-ray diffraction and transmission electron microscopy. The synthesized nickel sulfide phases, which had metallic characteristics, were used to study the catalytic reduction of 4-nitrophenol. The results showed that the catalytic activity of the NiS nanoparticles in the reduction of 4-nitrophenol to 4-aminophenol was higher than those of the other nickel sulfide phases. In addition, the nanocrystals showed good separation ability and reusability for reduction of 4-nitrophenol.

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Cu2ZnSnS4 (CZTS) nanoparticles were synthesized by the precursor injection method using oleylamine as a solvent. Preliminary characterization indicated that the synthesized nanoparticles belonged to the kesterite structure with a bulged sphere-like morphology. Reduced graphene oxide (rGO) was synthesized by an improved Hummers method and was used for nanoparticle functionalization. CZTS nanocrystals were decorated on rGO by two different methods. One was oleylamine-based nanoparticle functionalization, and the other was in situ nanoparticle growth. Transmission electron microscopy analysis of CZTS-functionalized rGO showed that the synthesized nanoparticles were uniformly spread on the surface of rGO sheets. Single phase CZTS nanoparticles were grown on rGO without any impurity phase in the in situ growth. Tuned absorption of the pure CZTS was observed by the decoration of CZTS nanoparticles on the surface of rGO in the visible and UV regions.

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Reduced graphene oxide (rGO)‐functionalized nickel sulfide nanoparticles were synthesized using a temperature‐controlled injection method. Syntheses were carried out in single (oleylamine) and mixed (oleylamine, oleic acid, and octadecene) solvents. Phase‐controlled NiS, NiS2, or Ni3S4 nanocrystals were decorated on rGO sheets through the single‐step temperature‐controlled injection processes. Problems with the synthesis of rGO/nickel sulfide yielding mixed phases were overcome by adjusting the solvent mixture and source concentrations. X‐ray diffraction and transmission electron microscopy were used to study the crystal structures and phases of nickel sulfide on the rGO sheets. The catalytic performances of rGO/nickel sulfide structures containing different nickel sulfide phases were analyzed by measuring the degradation rate of 4‐nitrophenol. Catalytic activity of as synthesized rGO/NiS, rGO/NiS2 and rGO/Ni3S4 were higher activity than pure NiS, among them rGO/NiS was showed better activity than those of rGO/NiS2 and rGO/Ni3S4.

Hierarchical structures of nickel sulfide have been grown by the hydrothermal method. Nickel nitrate hexahydrate and thiourea were used as precursor materials to synthesize nickel sulfide. Ethylenediaminetetraacetic acid was used as a capping agent to achieve monodispersity. The different phases of nickel sulfide and its dependency on the precursor concentration were analyzed by X-ray diffractometry. Transmission electron microscopy analysis was used to confirm the phase changes and morphological behavior of the synthesized material. The morphological evolution of the hierarchical structure formation was studied systematically by scanning electron microscopy. In this study, we explore a novel method to control the synthesis of nickel sulfide hierarchical structures by varying the precursor concentration. The two mixed phases enhanced the catalytic activity in the 4-nitro phenol reduction reaction.