Preparation And Properties Of Nanostructured Bismuth/Iron Sulfides

Due to their particular optical, electrical, thermal and magnetic properties, nanostructured metal sulfides have great potential applications in the field of thermoelectronics, optoelectronics, catalysis, sensors, superconductor and solar cells. In this dissertation, various morphologies of nanostructured bismuth sulfide and iron sodium sulfide have been prepared by different chemical methods. The possible formation mechanism for them has been proposed and the optical and humidity-sensing properties have been studied.Large-scale and uniform Bi₂S₃ microrings and nanotubes have been successfully prepared and characterized. When Bi(NO3)3·5H2O is hydrolyzed via a hydrothermal way at 100oC, disk-like precursors can be obtained; when it is hydrolyzed at room temperature, rod-like precursors can be obtained. Then with the as-prepared precursors as sacrificial templates, precursor / Bi₂S₃ core/shell structures are obtained by immersing the precursors in S2? source solution, and finally Bi₂S₃ microrings and nanotubes are prepared after completely dissolving the inner precursor cores by immersing the core/shell structures in the sulfuric acid solution. The as-prepared Bi₂S₃ microrings with outer diameters of 1.5–2μm and inner diameters of 1–1.5μm are assembled by many nanocrystals with an average size of about 100 nm. The cross-section of the Bi₂S₃ nanotube is a square with a side length of about 400–1000 nm and the wall thickness of the nanotubes is estimated to be about 100 nm. PL properties of as-prepared different Bi₂S₃ nanostructures have been studied.Ultra-long NaFeS₂·2H₂O nanowire bundles and radial-shaped nanofibers have been successfully prepared and characterized. Ultra-long NaFeS₂·2H₂O nanowire bundles with uniform diameters of 50–100 nm and lengths of tens of micro-meters are prepared by evaporating the mixture of FeSO₄ and S2- aqueous solution without use of any surfactants and organic solvents. The radial-shaped NaFeS₂·2H₂O which are assembled by many NaFeS₂·2H₂O nanofibers with diameters of about 300 nm and lengths of about 10μm are prepared by hydrothermal method. The results show that the growth process of NaFeS₂·2H₂O nanowire bundles involves three typical stages, which include the formation of NaFeS₂·2H₂O microflower, NaFeS₂·2H₂O nanorods and ultra-long NaFeS₂·2H₂O nanowires. The mechanism may follow both of the crystal splitting and crystal orientation effect. The evaporation temperature plays an important role in the growth of NaFeS₂·2H₂O nanowire bundles. The formation mechanism of the radial-shaped NaFeS₂·2H₂O nanofibers may belong to the crystal splitting. NaFeS₂·2H₂O nanowire bundles are successfully used as photoluminescence-type humidity sensors for the first time at room temperature, which shows good performance.