Iron Sulfide Nanoparticles Research Articles

Immobilization of mercury in sediment using stabilized iron sulfide nanoparticles

Mercury (Hg) immobilization using stabilized iron sulfide (FeS) nanoparticles was investigated through a series of batch and column experiments. The nanoparticles were prepared using a low-cost, food-grade cellulose (sodium carboxymethyl cellulose, CMC) as the stabilizer. The hydrodynamic diameter of fresh FeS–CMC nanoparticles was measured to be 38.5 ± 5.4 nm. Batch tests showed that the nanoparticles can effectively immobilize Hg in a clay loam sediment. The Hg distribution coefficient for the nanoparticles was determined to be 8930 ± 1480 L/g, which is >4 orders of magnitude greater than for the sediment. When the Hg-laden sediment was treated at an FeS-to-Hg molar ratio of 26.5, the Hg concentration leached into water was reduced by 97% and the TCLP (toxicity characteristic leaching procedure) leachability of Hg was reduced by 99%. Column tests showed that water-leachable mercury from the sediment containing 3120 mg/L Hg was reduced by 67% and the TCLP leachability by >77% when the sediment was treated with 67 pore volumes (PVs) of a 0.5 g/L FeS nanoparticle suspension. Column tests proved that the stabilized nanoparticles were highly mobile in the sediment and full breakthrough of the nanoparticles occurred at ∼18 PVs.

Morphological Stability of Pyrite FeS2 Nanocrystals in Water

By replicating biological processes, it is hoped that many nanomaterials may be tailored for specific applications, but a detailed knowledge of the underlying mechanisms is imperative. A perfect example of this synergy is the similarity between the intracellular biomineralization of single nanocrystals of the nonmagnetic mineral iron pyrite in multicellular magnetotactic bacterium, and the solvo-thermal synthesis of iron sulfide nanoparticles in the laboratory. Although both processes occur in aqueous solutions, the relationship between the morphological stability of the individual nanocrystals and the chemistry of the nanoparticle−water interface is still largely unknown. In the present work, we use a theoretical model capable of describing the stability of nanocrystals as a function of size, shape, temperature, and chemical environment, and use it to examine the morphological stability of pyrite nanocrystals exposed to water, or formed during biomineralization.

Bacteria-Mediated Precursor-Dependent Biosynthesis of Superparamagnetic Iron Oxide and Iron Sulfide Nanoparticles

The bacterium Actinobacter sp. has been shown to be capable of extracellularly synthesizing iron based magnetic nanoparticles, namely maghemite (gamma-Fe2O3) and greigite (Fe3S4) under ambient conditions depending on the nature of precursors used. More precisely, the bacterium synthesized maghemite when reacted with ferric chloride and iron sulfide when exposed to the aqueous solution of ferric chloride-ferrous sulfate. Challenging the bacterium with different metal ions resulted in induction of different proteins, which bring about the specific biochemical transformations in each case leading to the observed products. Maghemite and iron sulfide nanoparticles show superparamagnetic characteristics as expected. Compared to the earlier reports of magnetite and greigite synthesis by magnetotactic bacteria and iron reducing bacteria, which take place strictly under anaerobic conditions, the present procedure offers significant advancement since the reaction occurs under aerobic condition. Moreover, reaction end products can be tuned by the choice of precursors used.

Bacterial synthesis of silicon/silica nanocomposites

The synthesis of silicon/silica nanoparticle composites by the bacterium Actinobacter sp. is demonstrated. More specifically, the formation of silicon/silica nanocomposite is shown to occur when the bacterium is exposed to K2SiF6 precursor under ambient conditions. Based on the earlier reports where this bacterium has been shown to synthesize iron oxide and iron sulfide nanoparticles, it is hypothesized that this bacterium secretes reductases and oxidising enzymes, which lead to the Si/SiO2 nanocomposite synthesis. The particles obtained by bacterial synthesis were thoroughly characterized. The cytotoxicity studies revealed that the particles do not display any cytotoxicity to human skin cells. The synthesis of silica nanoparticles by bacteria in the present study demonstrates the versatility of the organism, and the formation of elemental silicon by this environmentally friendly process expands further the scope of microorganism based nanomaterial synthesis.

Degradation of lindane from aqueous solutions using iron sulfide nanoparticles stabilized by biopolymers

Lindane (γ-hexachlorocyclohexane) is an organochlorine pesticide and a Persistent Organic Pollutant (POP). Lindane residues have been detected in drinking water sources and development of viable methods for their removal is a global priority. Iron based nanomaterials have been shown to effectively transform chlorinated organic compounds. However, their uses in the treatment of drinking water and beverages have toxicity concerns. In the present study, FeS nanoparticles were synthesized by the wet chemical method and were stabilized using a polymer from the basidiomycetous fungus, Itajahia sp. The stabilized nanoparticles could degrade lindane (5 mg/l) with an efficiency of 94% in 8 h. In a subsequent microbiological treatment, residual lindane, its partially degraded intermediates as well as the stabilizing polymer could be completely degraded in 1 h. The latter process facilitated aggregation of FeS, which could be easily removed by filtration. This novel integrated nano-biotechnological method holds the promise of providing an efficient, safe, and cost-effective solution to the problem of removal of chlorinated pollutants from water sources.

Synthesis of FeS 2 and FeS nanoparticles by high-energy mechanical milling and mechanochemical processing

High-energy mechanical milling of the FeS 2 pyrite led to the formation of sub-micron particles with nano-scaled grains. FeS 2 nanoparticles were obtained, when NaCl was used as the dispersion medium. FeS 2 pyrite and FeS troilite phases could be formed after high-energy mechanical milling. The formation of FeS 2 pyrite required a long milling time. The resultant powders consisted of nano-scaled particles. The use of the solid dispersion medium (NaCl) can promote dispersion of nanoparticles. This work has shown that iron sulfide nanoparticles can be synthesized by mechanochemcial process with a solid dispersion medium.

Structural and magnetic studies on heavy-metal-adsorbing iron sulphide nanoparticles produced by sulphate-reducing bacteria

In previous and in work to be published, it has been shown that iron sulphide material, produced by sulphate-reducing bacteria (SRB), is an excellent adsorbent for a wide range of heavy metals. The material adsorbs between 100 and 400 mg g −1 and residual levels in solutions can be of the order of pg per litre. Further, strongly magnetic forms of this material can now be produced which can be effectively and cheaply removed from suspension together with the adsorbate by magnetic separation. This paper examines the structure of weakly magnetic and strongly magnetic iron sulphide material produced by SRB with a view to increasing the understanding of its adsorbent and the magnetic properties. The structural properties have been examined using high-resolution imaging and electron diffraction in a transmission electron microscope (TEM), the measurements of magnetisation versus field and temperature, extended X-ray absorption fine-structure (EXAFS) spectroscopy, X-ray absorption near-edge structure (XANES) spectroscopy and neutron diffraction. Before drying the surface area of both the weakly magnetic and the strongly magnetic iron sulphide is of the order of 400–500 m 2 g −1 as revealed by the magnetic properties, neutron scattering and the adsorption of a number of heavy metals. After freeze-drying the surface area falls to between 18 and 19 m 2 g −1. The initial inocula came from a semi-saline source and when fed with nutrient containing Fe 2+ and Fe 3+ produced a weakly magnetic iron sulphide (Watson et al., Minerals Eng. 8 (1995) 1097) and a few % of a more strongly magnetic material. Further work using a novel method (Keller-Besrest, Collin, J. Solid State Chem. 84 (1990) 211) produced a strongly magnetic iron sulphide material. EXAFS and XANES spectroscopy revealed (Keller-Besrest and Collin, 1990) that the weakly magnetic iron sulphide material had the Ni–As structure in which the Fe is tetrahedrally coordinated with the composition Fe 1− x S. The strongly magnetic iron sulphide was composed of some greigite (Fe 3S 4) and mackinawite (Fe 1+ x S), however, the bulk of the material at room temperature probably consists of disordered greigite and mackinawite. The weakly magnetic and strongly magnetic iron sulphide are good adsorbents for heavy metals and halogenated hydrocarbons.