An attractive target for many scientists due to the alterations in the optical, magnetic  properties and catalytic activities , which occur in nanometer-sized particles. Metal sulfides have a great feature prominently among the phases investigated in nanocrystalline form especially nanocrystals of CdS[4,5] and the wideband gap semiconductor ZnS.[6-8] Interestingly, the magnetic properties of other metal sulfide nanocrystals have been studied such as iron sulfide, nickel sulfide[10,11] phase systems, MnS, AgS , and numerous copper sulfide phases.[5,12]
Nickel II complexes are very important as they detect presences of pollutants, water vapour, and they have catalytic activates. They have unique optical, electrical properties and have different applications many studies report the high capacitance of the nickel sulfides such as Shombe and co-workers studies the conversion efficiency and specific capacitance of solvent-free synthesized different nickel sulfide composites. Their results are based on X-ray diffraction, transmission, and scanning microscopy. Sajjad and Khan used nickel sulfide nanoparticles as electrode material for symmetric supercapacitor. The synthesized nanoparticles showed a uniform shape and size. Nickel sulfides electrodes showed enhanced electric properties such as high specific capacitance of 2495 F g−1 at 1 A g−1 and excellent cycling stability based on the Ragone plot shows a high energy density of 52.4 W h kg−1 and an ultra-high-power density of 13500.0 W kg−1.
Marand et al. studied electric properties of nickel sulfide reduced graphene oxide composite and reported a high specific capacitance of 305 Fg−1 at a current density of 1.1 A g−1 and high-capacity retention of 91% after 3000 cycles. The composite was synthesized using a solution combustion method. 
Nickel sulfides are also used as electrodes in the battery to enhance their electrical properties. Li et al. developed nickel sulfide nanoparticles with sulfur-doped reduced graphene oxide as dual-role anode materials for both lithium-ion battery (LIBs) and sodium-ion battery (SIBs) by increasing lithium and sodium storage efficiency. Their results showed good transition oxides/sulfides in alkali metal-ion batteries. Li and co-workers synthesized a composite of nickel sulfide nanoparticles and reduced oxide nanosheets. The composites were synthesized via a simple one-step hydrothermal method using different temperatures. These composites avoided the agglomeration of the sodium ion batteries electrode materials and enhanced reversible capacity and better capability.
The photocatalytic activities of nickel sulfides also attracted many researchers Kumari and co-workers synthesized nickel sulfide nanostructures using the precipitation method. The surface of the nanostructure was functionalized and used for selective adsorption of anionic and cationic dyes and two different types of antibiotics. The adsorption of the dyes to the nanostructure was electrostatic, whereas the adsorption with the antibiotic was due to hydrogen bonding and metal coordination. The synthesized and functionalized nanostructure can be used as recyclable adsorbate for different organic pollutants. Zhang and co-workers synthesized nickel sulfide composite for efficient photocatalytic nitrogen fixation upon sunlight irradiation. The composite system enhanced the electron transfer, increase the nickel sulfide band potential with the synergetic internal electric field and photogenerated electron-hole pairs. These results were confirmed by electrochemical impedance spectroscopy and photocurrent tests. The nickel sulfide composite system showed a good photocatalytic nitrogen reduction and produced a high NH3 rate. Dev and Singh studied nickel sulfide nanoparticles anchored graphene oxide among different metallic sulfide nanoparticles. Moreover, they tested the photocatalytic activates through methylene blue reduction. Lakshmanan et al., synthesized nickel sulfides and nickel oxide nanoparticles using solvothermal and thermal decomposition, they characterized the synthesized nanoparticles by powder X-ray diffraction (pXRD), high resolution scanning electron microscopy (HRSEM), energy dispersive spectroscopy (EDS), and UV diffuse reflectance spectroscopy (UV-DRS). The photocatalytic activities of the nanoparticles were tested by detecting the degradation of methylene blue and rhodamine 6G upon UV irradiation. Their results showed that the nickel sulfide nanoparticles are more photocatalytic active than nickel sulfide nanoparticles.
As reported nickel II complexes are very important and have variable chemistry that let them applicable in different fields such as the detection of the presences of pollutants, water vapour, and they have catalytic activates. Nickle sulfides have been used in different applications such as agriculture , solar cells [23,24] and as superconductors , pollutants degradation.
The properties of nanoparticles mainly depend on their shape and size. According to different synthesis methods nanoparticles, different nanoparticles crystalline phases and sizes can be obtained. The different applications of synthesized nanoparticles depend on their precise synthesis and characterization. Using a single-molecule precursor has many advantages if compared to multi-source synthetic protocols. Single molecules precursor synthesis resulted in constant and better composition nanoparticles and fewer crystal defects on its structure. Thus, a high-quality nanomaterial can be obtained. Synthesis of nickel sulfides using multi- sources is commonly used and reported in many studies[27-29]. Using a long organic chain was also reposted in many studies to control the size and morphology of the synthesized nanomaterials but they limit their application as they caused ligand surface chemistry complexity[30,31].
Many methods have been applied to synthesize metal sulfide nanocrystals such as hot injection[32–34] and colloidal methods, hydrothermal methods, solvothermal methods[37,38].
Solventless thermolysis method is distinguished over other routes their ease of synthesis in which solid-state decomposition of a precursor is accomplished by thermal treatment under inert conditions. The solventless thermolysis method is considered an effective way to synthesize metal chalcogenide nanomaterials with a wide range of morphologies such as nanorods, nanowires, nanospheres, and nanodisks. Interestingly, melt thermolysis can provide a simple and cost-effective way to scale up production. Another advantage of this approach is its ability to offer economic and environmental benefits reduce the requirement for harsh materials, and typically, yields are frequently high. Melt reactions was used to synthesize a wide range of different nanoparticles materials including metal sulfides such as Bi2S3, Cu2S, NiS, PbS, PdS and CdS.
For single-source precursors, the origin of transition metals and non-metals materials of the target binary compound are associated with a single precursor species. Recently, this approach has been utilized widely in nanocrystal synthesis. Typically, it offers many great features such as ease of utilizing and high-quality products under relatively mild reaction conditions. [49-51] numerous transition metal sulfide nanocrystals have been synthesized using single-source precursors e.g., ZnS[52,53], iron sulfide[54,55], and nickel sulfide nanocrystals[56,57].
Xanthates (alkyl dithiocarbonates or ROCS-2) are organic compounds that contain two groups a negatively charged group that react with metals and a hydrocarbon chain that react with non-polar solvents. Xanthates complexes are applicable in different fields such as agriculture, antimicrobial industries, and material science. Metal xanthates [M(S2COR) x] (M = transition metal, R = alkyl chain) are considered as a good choice to synthesis metal sulfides as they decomposed easily and cleanly at low temperatures. In addition, it can be used as a capping ligand for the synthesis of metal nanoparticles and self-assembly monolayer. Using xanthates for the synthesis of nanoparticles have many advantages, as the by-products generated due to xanthates decomposition are highly volatile and can easily be removed from the reaction leaving a pure and stable nanoparticle.
Here we used the melting (solvent-less) method at two different temperatures 400 and 500°C to synthesis two nickel sulfide nanoparticles using two xanthate ligands [K(S2COBu)] Potassium butyl xanthate and [K(S2COPn)] Potassium Pentyl xanthate as a single-source precursor. Two nickel sulfides nanoparticles were characterized using XRD and EDX. The crystallite size (D) is calculated using the Debye-Scherrer formula. The nanoparticles were imaged using SEM. We present a simple, low cost and feasible synthesis of pure, stable, with definite size two nickel sulfides nanoparticles using metal xanthate ligands.