The Effect of Adding Phosphate on the Size of Extremely Fine Needle‐like Lepidocrocite Particles Prepared by Oxidizing an Aqueous Suspension of Ferrous Hydroxide

Fine particles of needle‐like lepidocrocite (γ‐FeOOH) were synthesized by the oxidation of aqueous suspensions of ferrous hydroxide using a bubble column with draft tube at a constant temperature ranging from 20°C to 30°C. The oxidation steps leading to green rust (an intermediate) and lepidocrocite (final product), termed Step I and II, respectively, could be described apparently as first order, with respect to oxygen, and zero order, with respect to total ferrous species. When the concentration of oxygen in the feed stream was varied under a constant gas velocity, the mean size based on the major axis of needle‐like particle decreased from 0.60 to 0.35 μm with increasing oxidation rate. When the gas velocity was varied under a constant oxygen concentration, the particle size was almost independent of the oxidation rate and was equal to ca. 0.6 μm. By the addition of a small amount of sodium dihydrogenphosphate (NaH2PO4), the major axis could be reduced to 0.2 μm with the minor axis and the oxidation rate almost unchanged.

This study addresses the bacterial inactivation mechanism by photo-Fenton process at near-neutral pH, focusing on iron-oxides and iron-citrate as photocatalysts for solar water disinfection and using E. coli as a bacteria model. Cell envelope damage during bacterial inactivation by photo-Fenton and TiO2 photocatalysis were investing providing evidence for lipid peroxidation and cell permeability. TiO2 photocatalysis induced significant cell membrane damage, in contrast to the photo-Fenton process, but the inactivation kinetics for both disinfection processes was similar. A higher efficiency of photo-generation of reactive oxygen species (ROS) in the presence of TiO2 photocatalyst compared with the photo-Fenton system was observed. The bactericidal effect of Fe3+/hv seems possible due to the adsorption of Fe3+ ions on the bacterial cell wall followed by photosensitization of iron-bacteria exciplexes oxidizing the cell membrane. In contrast, the effect of Fe2+/hv was associated with diffusion into the cell giving raise to intracellular dark Fenton?s reactions. We suggest that cell envelope damage might not necessarily be a unique pathway in bacterial inactivation by photo-Fenton treatment. In particular, the enhancement of an internal (photo)-Fenton process by the synergistic action of UVA and the external Fenton's reactants appears to be an important contribution to bacterial inactivation. Bacterial inactivation by the heterogeneous photo-Fenton process was carried out via iron (hydr)oxide particles, i.e. hematite, goethite, wustite and magnetite. We found that, the iron (hydr)oxides act as photocatalytic semiconductors and catalysts in the heterogeneous photo-Fenton process with the exception of magnetite, which needs H2O2 as electron acceptors. The Hydroxyl radical and superoxide radical were the principal ROS produced by iron (hydr)oxide particles under light in the absence or presence of H2O2. Natural organic matter (NOM) and inorganic substances did not interfere with the photocatalytic semiconducting action of hematite during bacterial inactivation, but enhanced bacterial inactivation mediated by hematite used as the photo-Fenton reagent. Our results demonstrated, for the first time, that low concentration of iron (hydr)oxides (0.6 mg/L) under sunlight, acting both as semiconductors or catalysts of the heterogeneous photo-Fenton process, may serve as a disinfection method for waterborne bacterial pathogens. Bacterial inactivation by the homogeneous photo-Fenton process was carried out using Fe?citrate complex as a source of iron. The efficiency of the homogeneous photo-Fenton process using Fe-citrate complex strongly improved bacterial inactivation as compared with the FeSO4 and goethite as sources of iron. The bacterial inactivation rate increased in the order of goethite < FeSO4 < Fe-citrate, which agreed with the ?OH radicals detected by ESR. Encouraging results were also obtained while applying this treatment for bacterial inactivation in natural water samples at pH 8.5. No bacterial reactivation and/or growth were observed showing that Fe-citrate-based photo-Fenton process efficiently inactivate bacteria using a low iron concentration of Fe-citrate, while avoiding precipitation of ferric hydroxides. The application of the photo-Fenton process at near-neutral pH is a promising technique for bacterial inactivation, due to its simplicity, the use of the sun, the low concentration of reagents and does not produce toxic waste.

In this study, models were used for the first time to investigate the fate and transport of rare earth elements (REE) in the presence of hydrous manganese and ferric oxides in groundwaters from the coastal Bohai Bay (China). Results showed that REE sorption is strongly dependent on pH, as well as hydrous manganese and ferric oxide content. Higher proportions of REE were sorbed by hydrous manganese oxide as compared to hydrous ferric oxides, for example in the presence of neodymium. In this case, a mean 28% of this element was sorbed by hydrous manganese oxide, whereas an average 7% sorption was observed with hydrous ferric oxides. A contrasting REE sorption behavior was observed with hydrous manganese and ferric oxide for all investigated groundwaters. Specifically, REE bound to hydrous manganese oxides showed decreasing sorption patterns with increasing atomic number. The opposite trend was observed in the presence of hydrous ferric oxides. In addition, these results suggested that light REE (from La to Sm) rather than heavy REE (from Eu to Lu) are preferentially scavenged by hydrous manganese oxide. However, the heavy REE showed a greater affinity for hydrous ferric oxides compared to light REE. Therefore, both hydrous manganese and ferric oxide are important scavengers of REE. This study shows the implication of hydrous manganese and ferric oxide sorption for the sink of REE in groundwater.

Reactions of monosilicic acid and boric acid with hydrous oxides of aluminum and iron were studied. Adsorption of B by hydrous iron oxides was satisfactorily described by the Langmuir equation over the range of equilibrium solution concentrations investigated (0–14m M ). Adsorption by hydrous aluminum oxides conformed to the Langmuir equation at equilibrium solution concentrations less than 6m M B. Maximum adsorption of boric acid by aluminum hydrous oxides was found to occur at approximately pH 7.5. Aging freshly precipitated hydrous aluminum and iron oxides up to 12 hours markedly reduced B adsorption; beyond 12 hours the effects of aging diminished. Successive treatments with 1.4m M solutions of Si(OH) 4 were applied to freshly precipitated aluminum‐ and ironhydrous oxides until an apparent saturation was attained. The adsorption of Si followed the Langmuir equation, with maximum adsorption of 2.96 and 2.67 millimoles of Si per gram of aluminum and iron hydrous oxide, respectively. Boric acid at concentrations of 1.85 and 18.5m M were applied to individual samples after each Si(OH) 4 treatment. Aluminum‐ and iron‐Si complexes retained less B as the amount of adsorbed Si on these hydrous oxides increased.

Major concerns about the effects of increasing fossil fuel consumption on the environment and energy security have prompted the development of sustainable and environmentally-friendly energy conversion and storage technologies based on electrochemical processes (e.g. water electrolysers, batteries and supercapacitors). Electrode materials are a key component of these technologies, and high-performance electrode systems are essential for the realization of a clean-energy-based economy. Numerous efforts have been made to develop advanced electrode materials for energy conversion and storage applications. However, current electrode synthesis methods are usually energy-intensive, not environmentally friendly, difficult to scale, or costly to produce. This thesis aims to utilize electrode structure engineering to develop highperformance electrodes based on earth-abundant materials via low-cost, energy-efficient and green synthesis strategies. Further, the applications of these electrodes in various energy conversion and storage applications are explored. Nickel-iron oxides or hydroxides are considered promising electrocatalysts for the oxygen evolution reaction, featuring a high activity and long cycling life in alkaline solution. A room temperature, electroless method has been developed here to grow nickel-iron hydroxides on a nickel foam current collector. The activity of nickel foam for the oxygen evolution reaction can be remarkably enhanced by simply immersing the nickel foam in a ferric nitrate solution at room temperature. During this process, the oxidation of the nickel foam surface by ferric nitrate ions increases the near-surface concentration of hydroxide ions, which results in the in situ deposition of a highly active, amorphous nickel-iron hydroxide layer. This phenomenon is described in Chapter 2 of this thesis. Carbon cloth is a widely-adopted current collector for the fabrication of electrodes. A facile, two-step method has been investigated here to turn commercial carbon cloth into a high-performance electrode for zinc-air batteries. Mild acid oxidation followed by air calcination directly activate carbon cloth to generate uniform, nanoporous and superhydrophilic surface structures with optimized, oxygen-rich functional groups and dramatically increased surface area. This two-step-activated carbon cloth exhibits superior bifunctional oxygen electrocatalytic activity and durability. A rechargeable, flexible zinc-air battery using the activated carbon cloth as a binder-free, flexible air electrode yields a remarkably high peak power density, high flexibility, and good cycling performance, with a small charge-discharge voltage gap. This work is elaborated in Chapter 3. Cost-effective synthesis of large-scale, uniform electrode materials with high activity and cycling stability is challenging. In Chapter 4, a reaction environment confinement strategy for scalable and reproducible production of nanostructured materials is proposed. Nickel foam is simply immersed in metal nitrate aqueous solution, with the volume of solution per unit area of nickel foam kept very low. A precisely designed reactor with a spiral tunnel ensures the same width of solution on each side of the nickel foam. The reaction environment is confined to ensure reproducible and uniform synthesis of nanostructured materials across the Ni foam. This approach has the largest REAVC (ratio of electrode area to precursor volume consumption) value reported so far, 2.0 cm2 mL-1. The synthesized nickel-iron hydroxides/nickel foam electrodes with uniformity in both microstructure and electrochemical properties exhibit remarkable activity for both the oxygen evolution reaction and hydrogen evolution reaction. Manganese oxides are a class of promising electrode materials for high performance supercapacitors. However, not all types of manganese oxides with different phases are electrochemically active, and their crystal structures have a considerable effect on their capacitance. In Chapter 5, a facile strategy is developed for the transformation of manganese oxide from the orthorhombic to birnessite crystal structure. The product exhibits significantly enhanced electrochemical performance as a supercapacitor electrode. This work opens up new possibilities for changing the crystal structure of manganese oxides towards optimized properties in electrochemical applications. This thesis makes significant contributions to our understanding of electrode structure engineering, materials science and electrochemical energy conversion and storage through: (i) designing novel nanostructured nickel-foam-based electrode systems with high electrocatalytic activity towards water oxidation via a simple immersion strategy at ambient temperature; (ii) developing facile activation procedures to endow commercially available, inactive carbon cloth with oxygen-rich functional groups and high oxygen electrocatalytic activity; (iii) controlling ion diffusion in a confined zone for uniform deposition of active materials over large-size electrodes, electrodes useful for various electrochemical applications; (iv) probing the phase transformation of manganese oxides from orthorhombic to birnessite, a material with enhanced electrochemical performance; (v) investigating the growth mechanisms of these advanced electrode materials to understand the origin of their exceptional activity.

The oxidation of Mn(II) by oxygen in the presence of goethite (α-FeOOH), lepidocrocite (γ-FeOOH), silica and alumina was studied. All the solids, except perhaps alumina,enhanced the rate of Mn(II) oxidation. The degree of enhancement was as follows: lepidocrocite > goethite > silica > alumina. At constant pO2 Mn(II) oxidation on goethite, lepidocrocite and silica can be described by the following equation [Equation; see abstract in scanned thesis for details.] where is the concentration of the surface hydroxyl group and a is the solids concentration. Mn(II) oxidation in the presence of goethite or lepidocrocite is first order in pO2. Both these reactions are strongly temperature dependent (apparent activation energy ~100 kJ/mol). Normal laboratory lighting has no effect on the rate of these reactions. The rate of Mn(II) oxidation in the presence of lepidocrocite is about 4 times slower in 0.7M NaClO4, than in 0.1M NaClO4. This reaction is inhibited by the following ions; Mg2+, Ca2+, silicate, salicylate, phosphate, chloride, and sulfate. Phthalate has little or no effect on the rate of this reaction. The adsorptive behaviour of Mn(II) on the metal oxides studied could be described using a surface complexation model. Using this model it was shown that the rate of Mn(II) oxidation on the metal oxides studied is described by the equation [Equation; see abstract in scanned thesis for details.] where (≡SOH)2Mn is a bidentate surface complex. It is possible that a hydrolyzed surface complex (≡SOMnOH) rather than the bidentate complex is involved in the reaction. The results of the laboratory studies indicate that in natural waters the important factors which influence Mn(II) on metal oxides are pH, iron oxide concentration, temperature, [Mg2+], [Cl-], and ionic strength. These studies predict that at pH

Parenterale Ernährung mit stabilitätsgeprüften, modularen Standardnährlösungen in der Neonatologie

Anodic oxidation of ferrous ion on passive iron

Adsorption onto hydrous iron oxide (HIO) was compared as a function of pH for a variety of organophosphorus compounds (OPs), including phosphate esters of ethanolamine, hydroxyamino acids and sugars, phosphonates with methyl and aminoethyl substituents, and nucleotides. The percentage adsorption versus pH curves could be classified into four types according to an empirical rule, viz., that the adsorptivity of OPs depended primarily on the number of unsubstituted P–O moieties in the tetrahedral structure around the P atom of the compound. The rule predicted that a large group of OPs containing more than three unsubstituted P–O moieties should be collected quantitatively by HIO from waters of pH 5.0–6.5. The OPs collected by adsorption onto HIO did not show appreciable degradation during storage for at least 2 weeks. In addition, they could be released from the HIO by using pentane-2,4-dione [acetylacetone (Hacac)] so that they entered a small-volume awueous phase which was derived from the HIO by the following reaction: Fe2O3·nH2O·(OPs)+ 6Hacac → 2Fe(acac)3+(n+ 3)H2O +(OPs). The whole procedure, involving adsorption of OPs onto HIO from a 1 l water sample, separation of the HIO from water by filtration and release of the OPs from the HIO into a 2.5 ml aqueous phase, realized a 400-fold concentration with efficiencies ranging from 45%(for adenosine-5′-triphosphate) to 92%(for 2-aminoethylphosphonate).

The major limitations of the Fenton process are the working pH range (2–5) and the high cost of H2O2. These limitations were unraveled using the Fe2+-air oxidation process, in which ferrous ions were used with continuous aeration without H2O2 at a higher pH (pH = 10). This paper studies the effect of the initial hydrous ferric oxide (HFO) concentration on the Fe2+-air process. The enhancement in degradation of the dye [Reactive Black 5 (RB5)] was observed using the Fe2+-air process in the presence of initial HFO, as compared to the Fe2+-air process in the absence of initial HFO. The enhancement is possibly attributable to the adsorption of ferrous ions, dye, and oxygen onto the HFO surface and leading to effective utilization of reactive oxidizing species. The oxidizing entities appear to be generated during oxidation of adsorbed ferrous ions under oxic conditions—probably on the surface of HFO. Furthermore, the Fe2+-air process in the presence of HFO reduces the concentration of ferrous ions requ...

Bioenergetic challenges of microbial iron metabolisms

The available information regarding the pathways of processes leading to precipitation of iron (hydrous) oxides in aqueous salt solutions is reviewed. The importance of the early hydrolysis stages in determining the nature and the morphology of the solid phases is discussed. In the second part, the phase transformation between various oxides and oxohydroxides in aqueous suspensions is described with emphasis on mechanistic considerations. Such phase transformations may proceed under milder conditions (e.g., at lower temperatures) by a dissolution-recrystallization mechanism than in dry powders, which can also influence the morphology and the size of the resulting particles. A proper control of experimental parameters has resulted in a number of well defined colloidal iron (hydrous) oxides with respect to their composition, structure, morphology, and size.

Synthesis and characterisation of homogeneous porous titanosilicate catalyst supports for carbon dioxide conversion

The present thesis is concerned with the development and characterization of new diferric purple acid phosphatase (PAP) model systems, which include functional groups that are meant to act as a second coordination sphere in phosphoester hydrolysis. A short review on purple acid phosphatases, including the postulated reaction mechanisms in phosphoester hydrolysis, and published PAP model complexes is given in Chapter 2. Furthermore, important data of published bridged diferric complexes are presented, in order to have a basis for interpretation of the analytical data in the results part. In Chapter 3, the results on the new model complexes are presented and discussed. At first, the cyclam-based ligand L1 and its coordination chemistry are described (Chapter 3.1). The most important findings are the following: Ligand L1 predominantly forms a μ-oxo bridged diferric complex when reacted with [FeCl4]- in situ. This complex, called K1, can readily coordinate phosphate and inactive phosphoesters, also in partly aqueous solution. Interestingly, the inactive phosphodiester diphenylphosphate (DPP) coordinates in a monodentate mode to one FeIII, whereas the monoesters para-nitrophenylphosphate (pNPP) and 1-naphthylphosphate (1-NP) bind in a bridging mode to both FeIII centers. The monodentate coordination of DPP is encouraging in terms of the intended reactivity in phosphoester hydrolysis, as this coordination mode is believed to be the active one, leading to a terminal hydroxide as a possible nucleophile. Chapter 3.2 deals with the phenolatebased ligands HL2 and H3L3 and their coordination chemistry. These ligands are derivatives of the published HBPMP ligand and incorporate amino and amido functional groups as second coordination sphere mimics. Diferric complexes, called K2 and K3, are obtained by in situ reaction of the ligands with a ferric salt. A spectrophotometric pH titration was performed and revealed the pH dependent species distribution and the corresponding pKa values of the complex solutions. K2 has three quilibria between pH 4.6 and 11, where the second equilibrium is the deprotonation of the second coordination sphere amines. In contrast, K3 has only two equilibria due to the low pKa of the amido protons. Regarding the coordination of phosphoesters, K2 shows a similar behavior to K1. DPP is coordinated monodentately to one FeIII, whereas pNPP and 1-NP form bridging complexes. This is not observed with K3, which shows bridging coordination with both, mono- and diesters, possibly due to the lack of hydrogen bond donors in the second coordination sphere. The complexes K1, K2 and K3 were tested for hydrolytic activity towards the activated phosphoester substrates bis-(2,4-dinitrophenyl)phosphate (BDNPP) and 2,4-dinitrophenylphosphate (DNPP). The results of these experiments are presented in Chapter 3.3. K1 and K2 are the first examples of PAP model complexes that catalyze the hydrolysis of the phophomonoester DNPP. So far, only diester hydrolysis with PAP model complexes has been reported in literature, while the inactive bridging coordination mode is observed for phosphomonoesters. We draw the fact, that K1 and K2 can hydrolyze monoesters, back to the hydrogen bonding interaction of the coordinated substrates to the remote ligand parts. A closer analysis of the reactivity of K1 towards DNPP and BDNPP, based on DFT calculations, shows that 1) BDNPP is stabilized by the interaction with the protonated cyclam in the monodentate coordination mode, 2) the hydrolysis of DNPP has a significantly lower activation barrier with the hydrogen bonding interactions than without and 3) this barrier is lower than the energy barrier to a bridging coordination mode. As a conclusion, a mechanism is proposed, where the substrate binds in a monodentate coordination mode and is subsequently attacked by a terminal hydroxide. This active species is in equilibrium with the inactive bridging complex. In the case of the diester BDNPP, the equilibrium is shifted to the active species, while the monoester DNPP is more stable in the bridging coordination mode. The hydrolysis product remains bound to K1 and inhibits catalysis.

This thesis concerns the biological process of iron reduction mediated by microbially produced extracellular redox-active organic molecules. Two different iron reducing bacteria were studied: Shewanella oneidensis and Pseudomonas chlororaphis. S. oneidensis can grow by reducing ferric iron [Fe(III)] as a terminal electron acceptor in anaerobic respiration (i.e. dissimilatory iron reduction). Previous studies had suggested that it produces extracellular electron shuttles as a strategy for reducing poorly crystalline iron (hydr)oxides, however this had not been shown. To investigate this, a new method was developed to measure iron reduction at a distance using Fe-coated porous glass beads. Given this assay, it was shown that Fe(III) reduction at a distance is an active process that requires anaerobic conditions and coincides with biofilm formation. The possibility that S. oneidensis excretes a soluble quinone derived from the menaquinone biosynthetic pathway as a mediator was ruled out, but it was shown that such molecules are present in culture fluids and can be used by the cells to make menaquinone. Regardless of the nature of the mediator, it appears to act locally within the biofilm-bead environment for S. oneidensis. P. chlororaphis is a plant root isolate that cannot respire iron but produces redox active secondary metabolites (e.g. phenazine carboxamide, PCN) that promote microbial mineral reduction. P. chlororaphis can reductively dissolve poorly crystalline iron and manganese oxides whereas a mutant in one of the phenazine biosynthetic genes (phzB) cannot. PCN functions as an electron shuttle rather than an iron chelator. Multiple phenazines and the glycopeptidic antibiotic, bleomycin, can also stimulate mineral reduction by S. oneidensis MR-1. Because diverse bacterial strains that cannot grow on iron can reduce phenazines, and thermodynamic calculations suggest that phenazines have lower redox potentials than poorly crystalline iron (hydr)oxides in a range of relevant environmental pH (5 to 9), it seems likely that natural products like phenazines promote microbial mineral reduction in the environment. Whether cycling of microbially produced extracellular redox-active organic molecules serves a physiological function remains to be determined.