Iron Sulfide Nanoparticles Synthesised from Single Source Molecular Precursors

Abstract

The interest in nanoparticles research has grown recently because of their size dependent properties which has proved to be valuable for several applications. Iron chalcogenides nanoparticles especially iron sulfides have been used in photovoltaics, Li-ion batteries and magnetic data storage devices. Iron sulfides are cheap, abundant, non-toxic and exist in several phases such as troilite (FeS), mackinawite (FeS), smythite (Fe9S11), pyrrhotite (Fe1−xS), greigite (Fe3S4), marcasite (FeS2) and pyrite (FeS2). Each of the phases has its own advantages, for instance, pyrite is the key phase for photovoltaic applications with an appropriate band gap of 0.95 eV. This thesis report cheap and easily scalable preparation methodologies enabling to obtain pure phases of iron sulfide and iron nickel sulfide nanoparticles. Two methodologies were applied in this work, the hot injection thermolysis method and an environmentally friendly and economic solventless thermolysis method. In chapter 2, iron(III) tris(alkylxanthates) [Fe(S2COR1)3] (R1 = methyl (Me), ethyl (Et), n-propyl (nPr) or iso-propyl (iPr)); iron(II) bis(alkylxanthate)tetramethylethyldiamine [Fe(S2COR2)2(TMEDA)] (R2 = Me, Et, nPr or iPr); and iron(II) bis(alkylxanthate)phenanthroline [Fe(S2COR3)2(phen)] (R3 = Me or Et) were synthesized and used as single source precursors for the preparation of iron sulfide nanoparticles (FeS NPs). FeS NPs have been synthesized via a solventless thermolysis method. A comparison between iron(II) and iron(III) single source precursors to obtain iron sulfide nanoparticles through solventless thermolysis was explored. Iron(II) precursors were found to give smaller size NPs compared to NPs obtained using iron(III) precursors which consequently impacted their magnetic properties. The differences in NPs size is because of the alkyl chain length which impacted the magnetic properties as well as the morphology of the obtained iron sulfide nanoparticles. The as-synthesized iron sulfide precursors and iron sulfide nanoparticles are characterised by XRD, SEM-EDX, TEM and Raman spectroscopy, and their magnetic properties have been studied by SQUID magnetometry. A pyrrhotite phase was obtained for all nanoparticles synthesized from [Fe(S2COR)3] and [Fe(S2COR)2(TMEDA)] precursors while troilite phase from [Fe(S2COR)2(phen)]. In chapter 3, a hot injection thermolysis method was used to prepare iron sulfide NPs from same iron(II) single source precursors that were used in chapter 2 in addition to iron(II) alkylxanthate bipyridine, [Fe(S2COR)2(bipy)]. This allowed us to study the difference between the solventless thermolysis method and hot injection method for iron sulfide NPs preparation. The iron sulfide nanoparticles obtained from hot injection have larger particle size compared to the nanocrystals obtained by solventless thermolysis. The resulting nanoparticles were characterised by several techniques, which confirmed the successful formation of iron sulfide NPs. A pure pyrrhotite phase was obtained from iron(II) alkyxanthate tetramethylethyldiamine [Fe(S2COR)2(TMEDA)] while [Fe(S2COR)2(bipy)] and [Fe(S2COR)2(phen)] gave pure troilite. All nanoparticles obtained in chapters 2 and 3 were studied by SQUID magnetometry and were found to be ferromagnetic with high coercive field energy. In chapter 4, ternary iron nickel sulfide FeNiS2 nanoparticles were prepared via the solventless thermolysis method using two single source precursors; iron(III) ethylxanthates, [Fe(S2COEt)3] and nickel(II) ethylxanthates, [Ni(S2COEt)2] mixed at different ratios. The nanoparticles were characterized using p-XRD, SEM-EDX, Elemental Mapping and Raman spectroscopy. A hexagonal FeNiS2 was obtained from 2:1, 3:1 and 4:1 ratios of Fe:Ni. The ratio of iron(III) ethylxanthates, [Fe(S2COEt)3] to nickel(II) ethylxanthates, [Ni(S2COEt)2] was found to impact the particle size. The ma