Preparation Of Nickel Sulfide And Iron Sulfide Nanoparticles By Solvothermal Method

FeS₂(pyrite) has been considered as one of the best absorption materials for thin film solar cell due to its suitable band gap (0.95 eV) and high light absorption coefficient (λ≤700nm,α≥5×10⁵cm^-1). However, the coexistence of FeS₂(marcasite) with a direct band gap (0.3 eV) significantly affects the properties of FeS₂(pyrite). Nickle sulfide with pyrite structure is also an interesting material of research and is currently attracting much attention. However, nickle sulfide has several crystalline phases includingα-Ni_3+xS₂,β-Ni₃S₂, Ni₄S_3+x, Ni₆S₅, Ni₇S₆, Ni₉S₈,α-NiS,β-NiS, Ni₃S₄ and NiS₂. Therefore, it is a challenging and interesting topic of research to synthesize iron sulfide and nickel sulfide with single phase by controlling the reaction process. This thesis focuses on the phase and morphology control of iron sulfide and nickel sulfide via a solvothermal process by changing experimental parameters such as the molar ratio, reaction temperature and reaction time, and by the addition of appropriate surfactants.A series of nanocrystalline iron sulfide has been successfully prepared via the reaction of Fe(NO₃)₃·9H₂O with NH₂CSNH₂in ethylene glycol in the temperature range of 200²40°C. Two single phases of Fe3S₄ and Fe_1-xS was obtained without surfactant. Using PVP as surfactant, Pyrite FeS₂ was obtained and marcasite FeS₂ was effectively inhibited. We present some results on the influence of reactant molar ratio, reaction temperature and time, and the kind of surfactants on the formation of the single-phase pyrite FeS₂ powder.Two single phases of Ni₃S₂ andα-NiS nanocrystals has been successfully prepared by the reaction of Ni(NO₃)₂·4H₂O with NH₂CSNH₂in ethylene glycol via a solvothermal process in the temperature of 160²20°C. It was found that both the temperature and the molar ratio of nickel nitrate to thiourea put a significant effect on the phase and morphology of nickel sulfide powders. In addition, Single phase cubic NiS₂ was obtained via a PVP-assisted solvothermal route. More interestingly, the phase and morphology of nickel sulfide nanocrystals could be adjusted by the addition of acrylamide as surfactant. With the amount of acrylamide increase, the products transformed from the cubic phase of NiS₂ solid ball into the rhombohedral phase ofα-NiS (acrylamide: thiourea=25:1) solid ball, eventually transformed into hexagonalβ-NiS (acrylamide: thiourea = 200:1) hollow spheres.FeS₂ thin film was deposited onto ITO glass substrates via a solvothermal method, which is mild, convenient and easy to handle compared with the conventional coating technique.