Synthesis And Properities Of Iron Sulfide Nanomaterials

The sulfides of iron, especially nanoclusters, exhibit a wide range of properties including electron transfer, substrate binding/activation, ultra-high-density magnetic storage, magnetic separation, catalysis, biomedicine, sensors, and so on. The applications have been foreseen for nontoxic, magnetic iron sulfide nanomaterials. However, the Fe-S compounds present the high activity in atmosphere condition, it makes them very unstable. Usually, the Fe-S compounds were synthesized at rigorous condition, such as, anaerobic. Therefore, it is very valuable to develop a facile method to synthesize Fe-S compounds. They were mostly synthesized by pyrolyzing single-source precursors. In this thesis, iron sulfide nanomaterials were synthesized by the organic precursor decomposition method, hot injection method and thermal decomposition method, respectively. The structure and morphology of the products were characterized using various modern analytical techniques and magnetic properties and electrical properties of the samples were also investigated. The following results were obtained in this thesis:1. Shape-controlled synthesis and properties of iron sulfide nanostructures by pyrolyzing precursorsIron sulfide (Fe7S8) nanostructures were synthesized by pyrolyzing the organometallic precursor in oleylamine. The images of Scan Electron Microscopy (SEM) illuminated that the iron source and sulfer source have strong influence on the size, shape of the Fe7S8 products, the three different morphologies of Fe-S nanostructures (spike-like, hexagonal nanoplate and dendrite nanosheet structures) can be synthesized by only changing iron sources (FeSO4·7H2O, FeCl3·6H2O, respectively). The magnetism of iron sulfide (Fe7S8) nanostructures transforms from ferromagnetism to paramagnetism with the different assemblies of Fe-S products. For dendrite nanosheet of Fe-S products, the conductivity is nearly 3 orders higher than that of other two kinds of Fe-S nanostructures (spike-like, hexagonal nanoplates).2. Synthesis of iron sulfide nanostructures by hot injection methodMagnetic pyrrhotite (Fe7S8) and greigite (Fe3S4) nanostructures were successfully prepared by simple hot injection method. From TEM images, we can see the temperature can obviously effect the morphology and size of the product when Fe (NO3)3·9H2O as the iron source. Further XRD measurements revealed that the temperature played a critical role in determining the crystalline structure of the resultant nanosheets. In the reaction temperature range of 180-260℃, a higher reaction temperature generally favored the transformations of cubic Fe3S4 to hexagonal Fe7S8 when FeCl3·6H2O as the iron source. The magnetic properties were investigated by using a superconducting quantum interference device (SQUID) magnetometer (MPMS XL5). The magnetic properties of the resultant nanosheets were altered with the crystalline structure and the chemical composition. The electrical properties demonstrated that the conductivity of Fe7S8 nanostructure is nearly 1 order higher than that of Fe3S4 nanostructure.3. Synthesis of iron sulfide nanostructures via a thermal decomposition methodIron sulfide nanostructures are synthesized via a thermal decomposition method using ferric hexadecylxanthate as the precursor. We have successfully synthesized iron sulfide nanostructures without the solvent or inert gas protection. The characterization results indicate that the unique morphologies of the different iron sulfide nanostructures are the consequence of a temperature-dependent oriented attachment growth mechanism.