Current Inorganic Chemistry (Discontinued) - Volume 6, Issue 2, 2016

Layered double hydroxides (LDH) with iron(II) and iron(III) as the diand trivalent metal cations of the hydroxide layers (green rusts; GRs) can be intercalated by surfactants combining strong sorption of hydrophobic compounds with the strong reducing strength of the GRs. In addition the surfactant-intercalated GRs are interesting precursors for engineering of GRs and in particular for delamination and synthesis of new GRs starting from single-sheet iron oxides. Surfactant-GRs can be synthesized via ion exchange and coprecipitation while care should be paid to prevent formation of byproducts such as surfactant salts. Fatty acids and linear alkylbenzene sulfonates adopt a bilayer structure in the GR interlayer. Surfactantintercalated LDHs and GRs show strong sorption of hydrophobic compounds characterized by linear sorption isotherms and organic-matter-normalized distribution coefficients (logKom) in the range 1.92 to 3.32. When fatty acid intercalated GRs are used for reductive dehalogenation of tetrachloromethane, fully dehalogenated products are obtained at high rates in contrast to the much slower rates and incomplete dehalogenation observed for GRs with simple inorganic anions in the interlayer. The surfactant interlayer is expected to play a key role for reductive dehalogenation of halogenated solvents through strong sorption of the substrates, as a transport medium in contact with the iron(II)- iron(III) hydroxide layers and for stabilization of intermediates.

Green rust (GR) is an intermediate product during the process of iron corrosion. Due to its special kind of layered structure, it can easily exchange anions from its gallery part, and can be used in water treatment. It also has the ability to incorporate cations in the gallery. In addition, several hazardous cations can be adsorbed and finally bonded to the hydroxide part, or replace the iron cations in the crystal lattice, and be captured. All these properties lead GR to be efficiently advantageous for water purification applications. In this article, we provide an overview and literature survey on electrochemical generation of GR and modified GR, and their applications for water treatment.

Under anoxic conditions, a novel nanoparticulate green rust with carbonate (nano GR) was synthesised by the addition of methanol to degassed switchable ionic liquid (SWIL) solution composed of 1-hexanol, diazabicycloundec- 7-ene (DBU), CO2 and Fe(C2H3O2)2. Variable temperature Mössbauer spectroscopy studies indicated the product to be predominantly GR while transmission electron microscopy selected area diffraction confirmed it was nanoparticulate in nature. Experiments with and without methanol in the SWIL medium suggest that methanol may be responsible for the Fe(II) oxidation to Fe(III) necessary for GR formation. Studies with Ar instead of CO2 trigger gas indicated that CO2 is essential for GR formation. Conditions to generate CO32- anions were most likely provided by the basic environment of the medium. The nano GR suspension was very reactive and instantaneously oxidised completely to a reddish brown precipitate upon exposure to ambient atmosphere. The nature of the oxidised product is not certain. The oxidised product, however, appears to be a mix of ferric green rust [GR(CO32-*); major] and ferrihydrite- like mineral. To our knowledge, this is the first a) example of synthetic nanoparticulate GR, and b) report of use of environmentally friendly SWIL reagents to synthesise GR materials.

Background: The activated sludge treatments combined to the addition of ferric chloride is commonly used to eliminate nitrate and phosphate from waste water in urban area. These processes that need costly infrastructures are not suitable for rural areas and passive treatments (lagoons, reed bed filters…) are more frequently performed. Reed bed filters are efficient for removing organic matter but are not suitable for treating phosphate and nitrate as well. Passive water treatments using various materials (hydroxyapatite, slag…) were already performed, but those allowing the elimination of both nitrate and phosphate are not actually available. Methods: The goal of this work is to identify the most suitable iron based materials for such treatments and to determine their optimal use conditions, in particular in hydrodynamic mode. The reactivity of the iron based minerals was measured either by using free particles in suspension or by depositing these particles on a solid substrate. Results: Pozzolana, a volcanic rock, that is characterized by a porous sponge-like structure suits for settling a high amount of iron oxides. In addition, the experimental conditions enabling to avoid any ammonium formation when green rust encounters nitrate were also determined within the framework of a full factorial design. The dephosphatation and denitrification process is divided into two steps that will be performed inside two separated reactors. Indeed, the presence of phosphate inhibits the reduction of nitrate by green rust and the dephosphatation process must precede the denitrification process. Conclusion: In order to remove phosphate, ferrihydrite coated pozzolana is the best materials. The kinetics of reaction of green rust with nitrate is relatively slow and often leads to the formation of ammonium. In this process, it is interesting to favor the accumulation of nitrite in a first step, these species react much more quickly with green rust and do not transform into ammonium.

Background: Recently, the innate capability of nitrate-reducing bacteria (NRB) to oxidize ferrous iron in the presence of nitrate was found to involve the combination of abiotic and biotic reactions. Biogenic nitrite from nitrate respiration reacts with FeIIbearing minerals (here, siderite and vivianite) to produce hydroxycarbonate green rust (GR, FeII4FeIII2(OH)12•CO3) in a first step, as a transient compound, before oxidizing into goethite (α-FeOOH) in a second step. However, the conditions leading to GR formation instead of goethite were not well defined, especially the influence of the nature and the concentration of the organic electron donor. Results: In this study, the maximum amount of electron equivalents leading to GR was determined by screening the potential of various organic electron donors: glucose, glycerol, methanoate, lactate and trypcase soy medium. FeII-bearing minerals were oxidized to GR when the amount of equivalents of electrons released per mole of organic electron donor was lower than two, whereas goethite was obtained beyond four equivalents of electrons delivered. Conclusion: A fuzzy limit was defined between these two values of equivalents of electrons released per mole of organic electron donor representing the co-existence of GR and goethite. The sequence of FeII oxidation by NRB was also discussed and compared to that of iron-oxidizing nitrate-reducing bacteria.

Background: Arene metal complexes with acyl hydrazine derived ligands exhibit serendipitous bonding modes and cytotoxic properties. The aim of this paper is to synthesize arene ruthenium, rhodium and iridium metal complexes of N, N’- Bis(picolinoyl)hydrazine ligand which exhibits discrete bonding modes. Structural elucidation of the complexes and the evaluation of their in vitro antibacterial and antitumor properties are also carried out. Methods: Complexes are synthesized and characterized by spectroscopic and crystallographic studies. The electronic properties are explored by density functional theory calculations. The antibacterial activity is evaluated by agar well diffusion method and antitumor activity is carried out by fluorescence based apoptosis study. Docking analysis is used to know the interaction between the complexes and proteins under consideration. Results: Arene ruthenium, rhodium and iridium complexes are isolated in good yields as yellow and orange solids. Various bonding modes in complexes are justified by spectroscopic and crystallographic studies. The preliminary investigation of these complexes revealed their antibacterial and antitumor activities. The ligand acts as tri and tetradentate donor forming mono and dinuclear complexes. Fascinating differences were observed in bonding modes among the complexes of ruthenium, rhodium and iridium. Conclusion: Ligand under study forms dinuclear complexes with ruthenium as tetradentate nitrogen donor. It forms mononuclear complexes with rhodium and iridium as nitrogen donor and dinuclear complexes with rhodium and iridium as nitrogen and oxygen donor. Complexes under study exhibited significant growth inhibition of Salmonella enterica ser. Paratyphi better than that of Amoxicillin. The cytotoxicity of the complexes on normal cells is lesser than that of cisplatin which is a significant feature of the complexes under study.