Solvothermal synthesis of greigite (Fe3S4)– Conducting polypyrrole nanocomposite and its application towards arsenic removal

In the present investigation, Greigite-conducting polypyrrole nanocomposite (GPPy nanocomposite) was prepared, characterized and used to remove arsenite and arsenate from aqueous solution. Fe₃S₄ was synthesized using solvothermal synthetic method and it was grafted to conducting polypyrrole matrix. The nanocomposite was characterized using FE-SEM, EDX, XRD, FTIR, TGA/DSC and BET surface area. Kinetic studies revealed that the removal process followed first order kinetics. Batch isotherm studies were performed to determine the binding capacity. Thermodynamic parameters were also computed and it indicated the spontaneous nature of the process. Electrophoretic studies were carried out to determine the point of zero charge.     

An overview of heavy metal removal from wastewater using magnetotactic bacteria

Considering the increase in water contamination by heavy metal discharge, water quality experts are focusing on innovative future technologies for wastewater treatment. There are a number of physical, chemical and biological processes for acquiring high‐quality effluents; however, these treatment technologies have shown some limitations regarding their specific pollutant removal efficiencies, vulnerability to environmental pollutants, higher cost and energy requirements, excessive sludge volume and toxicity issues. Therefore, this review/concept paper focuses on the application of magnetotactic bacteria (MTB) in the removal of heavy metal from wastewater and also proposes a model application of MTB‐based treatment process. The unique property of the MTB is to move along the periphery of the applied external magnetic fields due to nano sized magnetosomes (MS). MS are basically the biomineral crystals of either magnetite (Fe₃O₄) or greigite (Fe₃S₄) with a size range of 30–120 nm. Moreover, challenging aspects concerning MTB employment in the removal of heavy metal from wastewater also are discussed in detail for the consideration of experts who are involved in the development of new treatment technologies or for retrofications of existing processes. © 2018 Society of Chemical Industry     

Magnetosomal matrix: ultrafine structure may template biomineralization of magnetosomes

The organic matrix surrounding bullet‐shaped, cubo‐octahedral, D‐shaped, irregular arrowhead‐shaped, and truncated hexa‐octahedral magnetosomes was analysed in a variety of uncultured magnetotactic bacteria. The matrix was examined using low‐ (80 kV) and intermediate‐ (400 kV) voltage TEM. It encapsulated magnetosomes in dehydrated cells, ultraviolet‐B‐irradiated dehydrated cells and stained resin‐embedded fixed cells, so the apparent structure of the matrix does not appear to be an artefact of specimen preparation. High‐resolution images revealed lattice fringes in the matrix surrounding magnetite and greigite magnetosomes that were aligned with lattice fringes in the encapsulated magnetosomes. In all except one case, the lattice fringes had widths equal to or twice the width of the corresponding lattice fringes in the magnetosomes. The lattice fringes in the matrix were aligned with the {311}, {220}, {331}, {111} and {391} related lattice planes of magnetite and the {222} lattice plane of greigite. An unidentified material, possibly an iron hydroxide, was detected in two immature magnetosomes containing magnetite. The unidentified phase had a structure similar to that of the matrix as it contained {311}, {220} and {111} lattice fringes, which indicates that the matrix acts as a template for the spatially controlled biomineralization of the unidentified phase, which itself transforms into magnetite. The unidentified phase was thus called pre‐magnetite. The presence of the magnetosomal matrix explains all of the five properties of the biosignature of the magnetosomal chain proposed previously by Friedmann et al. and supports their claim that some of the magnetite particles in the carbonate globules in the Martian meteorite ALH84001 are biogenic. Two new morphologies of magnetite magnetosomes are also reported here (i.e. tooth‐shaped and hexa‐octahedral magnetosomes). Tooth‐shaped magnetite magnetosomes elongated in the [110] direction are reported, and are distinct from arrowhead‐shaped and bullet‐shaped magnetosomes. Elongation of magnetite magnetosomes in the [110] direction has not been reported previously. A Martian hexa‐octahedral magnetite particle was previously characterized by Thomas‐Keptra et al. and compared with truncated hexa‐octahedral magnetite magnetosomes. Hexa‐octahedral magnetite magnetosomes with the same morphology and similar sizes and axial ratios as those reported by Thomas‐Keptra et al. are characterized here. These observations support their claim that ALH84001 contains evidence for a past Martian biota.     

Deoxygenation of stearic acid with a novel Ni(CO)‐MoS2/Fe3S4 catalyst

Magnetically recyclable Ni(Co)‐promoted MoS₂ catalysts with greigite (G) core were synthesized and their activity and selectivity in hydrodeoxygenation of stearic acid were investigated. The activity of the catalysts tested at 320 °C and H₂ initial pressure of 3.5 MPa could be ranked as NiMo/G > CoMo/G > Mo/G. Two main products were detected, C18 (through HDO pathway) and C17 hydrocarbons (through DCO pathway). HDO was the dominant pathway for all of the catalysts. As for the C18/C17 ratio, the catalysts were found to be in the order: Mo/G > CoMo/G ≈ NiMo/G. The Paraffin/Olefin ratio was over 1 for all of the catalysts with NiMo/G showing the highest ratio. Stearic acid was found to have an inhibiting effect on the adsorption of intermediates over the active sites. Moreover, the concentrations of intermediates decreased at high conversions of stearic acid. The formation of the intermediate aldehyde is through C–O hydrogenolysis of the fatty acid following the protonation, dehydrogenation, and hydride addition steps. The same steps were suggested to be involved in the transformation of the aldehyde to the alcohol. Formation of C_n‐1 hydrocarbons was found to be via decarbonylation route. The enhancement of the DCO pathway over the promoted catalysts was related to the electron transfer from the promoting atom to an adjacent sulphur atom and reduction in sulphur‐metal bond strength.