Iron Oxyhydroxide Particles Research Articles

Hybrid Materials Based on Magnetic Iron Oxides with Benzothiazole Derivatives: A Plausible Potential Spectroscopy Probe.

Rare diseases affect a small part of the population, and the most affected are children. Because of the low availability of patients for testing, the pharmaceutical industry cannot develop drugs for the diagnosis of many of these orphan diseases. In this sense, the use of benzothiazole compounds that are highly selective and can act as spectroscopy probes, especially the compound 2-(4′-aminophenyl)benzothiazole (ABT), has been highlighted. This article reports the design of potential contrast agents based on ABT and iron to develop a new material with an efficient mechanism to raise the relaxation rate, facilitating diagnosis. The ABT/δ-FeOOH hybrid material was prepared by grafting (N-(4’-aminophenyl) benzothiazole-2-bromoacetamide) on the surface of the iron oxyhydroxide particles. FTIR spectra confirmed the material formations of the hybrid material ABT/δ-FeOOH. SEM analysis checked the covering of nanoflakes’ surfaces in relation to the morphology of the samples. The theoretical calculations test a better binding mode of compound with iron oxyhydroxide. Theoretical findings show the radical capture mechanism in the stabilization of this new material. In this context, Fe3+ ions are an electron acceptor from the organic phase.

Partition of Cd, Cu, Pb and Zn among mineral particles during their sorption in soils

Heterogeneity of soil mineral particles may lead to the misinterpretation of bulk sorption data on their role in metal sorption, which may be resolved through the direct observation of metal distribution among the soil particles after the sorption. Analytical transmission electron microscopy was used to study metal (Cd, Cu, Pb, Zn) sorption characteristics of clay minerals, Fe-oxyhydroxides and their natural assemblages in soils with contrasting pH under single element and competitive situations. Iron-oxyhydroxides sorbed higher metal amounts than clay mineral particles mostly, and the sorption capacity of the latter phases were more affected by competition. Iron-oxyhydroxide particles acted as effective metal sorbents in soils not only as individual particles but also as coatings on other mineral particles, and the structural Fe in clay minerals may also resulted in higher metal sorption in some cases. Besides the direct observation of metal sorption onto soil mineral particles, metal precipitates could be identified directly, and the role of organic surfaces in metal sorption could be inferred indirectly in certain cases. Comparison of metal affinity sequences and their partition characteristics between the bulk soil and different mineral particles were found to be an effective tool to specify the most active mineral components in metal sorption at given soil and sorption condition.

Assembly of Protein Stacks With in Situ Synthesized Nanoparticle Cargo.

The ability of proteins to form hierarchical structures through self-assembly provides an opportunity to synthesize and organize nanoparticles. Ordered nanoparticle assemblies are a subject of widespread interest due to the potential to harness their emergent functions. In this work, the toroidal-shaped form of the protein peroxiredoxin, which has a pore size of 7 nm, was used to organize iron oxyhydroxide nanoparticles. Iron in the form of Fe2+ was sequestered into the central cavity of the toroid ring using metal-binding sites engineered there and then hydrolyzed to form iron oxyhydroxide particles bound into the protein pore. By precise manipulation of the pH, the mineralized toroids were organized into stacks confining one-dimensional nanoparticle assemblies. We report the formation and the procedures leading to the formation of such nanostructures and their characterization by chromatography and microscopy. Electrostatic force microscopy clearly revealed the formation of iron-containing nanorods as a result of the self-assembly of the iron-loaded protein. This research bodes well for the use of peroxiredoxin as a template with which to form nanowires and structures for electronic and magnetic applications.

Nutrient Fluxes From Profundal Sediment of Ultra‐Oligotrophic Lake Tahoe, California/Nevada: Implications for Water Quality and Management in a Changing Climate

AbstractA warming climate is expected to lead to stronger thermal stratification, less frequent deep mixing, and greater potential for bottom water anoxia in deep, temperate oligotrophic lakes. As a result, there is growing interest in understanding nutrient cycling at the profundal sediment‐water interface of these rare ecosystems. This paper assessed nutrient content and nutrient flux rates from profundal sediment at Lake Tahoe, California/Nevada, USA. Sediment is a large reservoir of nutrients, with the upper 5 cm containing reduced nitrogen (∼6,300 metric tons) and redox‐sensitive phosphorus (∼710 metric tons) equivalent to ∼15 times the annual external load. Experimental results indicate that if deep water in Lake Tahoe goes anoxic, profundal sediment will release appreciable amounts of phosphate (0.13–0.29 mg P/m2·d), ammonia (0.49 mg N/m2·d), and iron to overlaying water. Assuming a 10 year duration of bottom water anoxia followed by a deep‐water mixing event, water column phosphate, and ammonia concentrations would increase by an estimated 1.6 µg P/L and 2.9 µg N/L, nearly doubling ambient concentrations. Based on historic nutrient enrichment assays this could lead to a ∼40% increase in algal growth. Iron release could have the dual effect of alleviating nitrate limitation on algal growth while promoting the formation of fine iron oxyhydroxide particles that degrade water clarity. If the depth and frequency of lake mixing decrease in the future as hydrodynamic models suggest, large‐scale in‐lake management strategies that impede internal nutrient loading in Lake Tahoe, such as bottom water oxygen addition or aluminum salt addition, may need to be considered.

Iron Oxide Nanoparticles Supported on Mesoporous MCM-41 for Efficient Adsorption of Hazardous β-Lactamic Antibiotics

In this work, the effect of crystallite size, defects, and surface area of iron oxyhydroxide particles supported on mesoporous MCM-41 on the adsorption of hazardous β-lactamic antibiotics was investigated. Different adsorbents were prepared by impregnation of 5, 10, 20, and 50 wt% of Fe followed by treatment at 150–400 °C. Mossbauer, XRD, BET, TG, FTIR, and Raman analyses suggested that treatment at 150 °C produced a mixture of α-Fe2O3, FeOOH, and highly dispersed Fe3+ species. At higher temperatures, different phases were gradually converted to hematite with crystallite sizes varying from 1 to 5 nm. Both, Fe content and temperature, strongly affected the amoxicillin, cephalexin, and ceftriaxone adsorption at pH 5, 7, and 9, with the best results obtained for the sample 20Fe150 (20% Fe treated at 150 °C), ca. 25 mgAMX g−1 which decreased to 17, 6, and 4 mgAMX g−1 (AMX = amoxicillin) upon treatment at higher temperatures. These results combined with competitive adsorption using AMX/phosphate and H2O2 decomposition experiments suggested that the antibiotic molecules are likely adsorbing by complexation on Fe3+ surface species of poorly crystallized small particles of Fe oxyhydroxide phases. It was observed that below a critical crystallite size of 3 nm, the AMX adsorption was very sensitive and strongly increased.

Redox Transformations of Iron in the Presence of Exudate from the Cyanobacterium Microcystis aeruginosa under Conditions Typical of Natural Waters.

Interaction of the exudate secreted by a toxic strain of the cyanobacterium Microcystis aeruginosa with Fe(II) and Fe(III) was investigated here under both acidic (pH 4) and alkaline (pH 8) conditions. At the concentrations of iron and exudate used, iron was present as dissolved iron (<0.025 μm) at pH 4 but principally as small (<0.45 μm) iron oxyhydroxide particles at pH 8 with only ∼3-27% present in the dissolved form as a result of iron binding by the organic exudate. The formation of strong Fe(III) exudate and relatively weak Fe(II) exudate complexes alters the reduction potential of the Fe(III)-Fe(II) redox couple, facilitating more-rapid oxidation of Fe(II) at pH 4 and 8 than was the case in the absence of exudate. Our results further show that the organic exudate contains Fe(III)-reducing moieties, resulting in the production of measurable concentrations of Fe(II). However, these reducing moieties are short-lived (with a half-life of 1.9 h) and easily oxidized in air-saturated environments. A kinetic model was developed that adequately describes the redox transformation of Fe in the presence of exudate both at pH 4 and pH 8.

Synthesis, Structural Characterization, and Thermal Properties of the Poly(methylmethacrylate)/δ-FeOOH Hybrid Material: An Experimental and Theoretical Study

Theδ-FeOOH/PMMA nanocomposites with 0.5 and 2.5 wt.% ofδ-FeOOH were prepared by grafting 3-(trimethoxysilyl)propyl methacrylate on the surface of the iron oxyhydroxide particles. The FTIR spectra of theδ-FeOOH/PMMA nanocomposites showed that the silane monomers were covalently attached to theδ-FeOOH particles. Because of the strong interaction between the PMMA andδ-FeOOH nanoparticles, the thermal stability of theδ-FeOOH/PMMA nanocomposites was improved compared to the pure PMMA. The SEM analysis conferred the size agglomerate of particles regarding the morphology of samples. The theoretical study enabled a better understanding of the interaction of the polymer with the iron oxyhydroxide. The DFT-based calculations reinforce the radical trapping mechanism of stabilization of nanocomposites; that is, Fe3+species might be able to accept electrons coming from the organic phase that decomposes via radical unzipping. The radical scavenge effect delays the weight loss of polymer.

Synthesis of Goethite α-FeOOH Particles by Air Oxidation of Ferrous Hydroxide Fe(OH)2 Suspensions: Insight on the Formation Mechanism

Iron oxide and iron oxyhydroxide particles, particularly, the goethite α-FeOOH phase, are environmentally friendly materials and are used in various technological applications as adsorbents, precursors of Fe powders for magnetic recording media, and pigments. In this work, the formation process of α-FeOOH by air oxidation of Fe(OH)2 suspensions has been studied. The effects of the air flow rate, as well as of the reactant concentration ratio, R (=[(OH)−]/[Fe(II)]), on the reaction product were analyzed. It has been found that the morphology and the size of the α-FeOOH particles can be modified by means of the air flow rate. Furthermore, by performing a detailed microscopic analysis of the morphology of the initial, intermediate, and final reaction products, we have obtained evidence of epitaxial growth of α-FeOOH on the Fe(OH)2 substrate. It is suggested that the similarity between the anion arrangements in both phases facilitates this process. Based on these results, a pathway for the formation of α-FeOO...

Influence of iron content, surface area and charge distribution in the arsenic removal by activated carbons

Abstract Due to the high number of toxicological issues, the presence of asenic (V) in water supplies is a major problem of public concern. Adsorption by iron modified activated carbons stands as an interesting alternative for the removal of arsenic (V) from aqueous solutions. However, the question of which of the activated carbon properties have impact during arsenic (V) uptake has arisen. The influence of textural and chemical features of several activated carbons (AC), un-modified and modified with iron oxyhydroxide nanoparticles, for the removal of arsenic (V) from aqueous solution was studied. The surface area ( S BET ), micropore volume, surface charge and iron content of 28 ACs were determined. Results showed that the S BET of materials range from 388 to 1747 m 2 /g, the point of zero charge (PH PZC ) from 3 to 11 and the iron content range from negligible to around 2%. A detailed data analysis demonstrated that the most important parameter of AC when removing arsenic (V) from water is the pH PZC (52.5% of contribution); however, the presence of iron is indispensable for enhancing the adsorption capacity (by 36.5%). An empirical model indicated that in order to effectively remove arsenic from water a basic AC with an iron content of about 1% is desirable. Arsenic (V) adsorption isotherms under normal conditions demonstrated that the materials studied have a great potential for water polishing. Finally it is suggested that the arsenate uptake by iron-modified AC is conducted by two simultaneous mechanisms: ligand interchange with iron oxyhydroxide particles and electrostatic attraction on basic AC.

Mineral ecophysiological data provide growing evidence for microbial activity in banded-iron formations

The phosphorus composition of banded-iron formations (BIFs) has been used as a proxy for Precambrian seawater composition and the paleoeredox state of Earth's surface environment. However, it is unclear whether the phosphorus in BIFs originally entered the sediment as a sorbed component of the iron oxyhydroxide particles, or whether it was incorporated into the biomass of marine phytoplankton. We conducted high-resolution mineral analyses and report here the first detection of an Fe(III) acetate salt, as well as nanocrystals of apatite in association with magnetite, in the 2.48 Ga Dales Gorge Member of the Brockman Iron Formation (a BIF), Hamersley, Western Australia. The clusters of apatite are similar in size and morphology to biogenic apatite crystals resulting from biomass decay in Phanerozoic marine sediments, while the formation of an Fe(III) acetate salt and magnetite not only implies the original presence of biomass in the BIF sediments, but also that organic carbon likely served as an electron donor during bacterial Fe(III) reduction. This study is important because it suggests that phytoplankton may have played a key role in the transfer of phosphorus (and other trace elements) from the photic zone to the seafloor.

Interfacially active particles in droplet/matrix blends of model immiscible homopolymers: Particles can increase or decrease drop size

Particles have been shown to adsorb at the interface between immiscible homopolymer melts and to affect the morphology of blends of those homopolymers. We examined the effect of such interfacially active particles on the morphology of droplet/matrix blends of model immiscible homopolymers. Experiments were conducted on blends of polydimethylsiloxane and 1,4-polyisoprene blended in either a 20:80 or 80:20 weight ratio. The effects of three different particle types, fluoropolymer particles, iron particles, and iron oxyhydroxide particles, all at a loading of 0.5 vol.%, were examined by rheology and by direct flow visualization. Particles were found to significantly affect the strain recovery behavior of polymer blends, increasing or decreasing the ultimate recovery, slowing down or accelerating the recovery kinetics, and changing the dependence of these parameters on the applied stress prior to cessation of shear. These rheological observations were found to correlate reasonably well with particle-induced changes in drop size. The particles can both increase as well as decrease the drop size, depending on the particle type, as well as on which phase is continuous. The cases in which particles cause a decrease in drop size are analogous to the particle stabilization of “Pickering emulsions” well-known from the literature on oil/water systems. We hypothesize that cases in which particles increase drop size are analogous to the “bridging–dewetting” mechanism known in the aqueous foam literature.

Antimony Mobilization through Two Contrasting Gold Ore Processing Systems, New Zealand

Antimony, a toxic metalloid similar to arsenic, is present at variable levels in most gold-bearing rocks. Antimony is soluble in the surface environment, so antimony (Sb) mobilization in mine waters is an environmental issue around gold mines. The Reefton gold mine was originally developed in gold-bearing quartz veins; Sb concentrations were low ( 1,000 mg/kg), and the mine waters had low dissolved Sb (<0.1 mg/L). A second stage of gold mineralization at Reefton involved brecciation and cataclasis of quartz veins and wall rocks, with addition of stibnite (Sb2S3). Processing of this ore has resulted in higher dissolved Sb in mine waters (0.1–1 mg/L), even after water treatment that removes most dissolved As (to 0.01 mg/L) by adsorption to suspended iron oxyhydroxide. Competition between As and Sb for adsorption sites on iron oxyhydroxide particles may have resulted in partial exclusion of the more weakly adsorbed Sb. The high rainfall (2,000 mm/year) at Reefton ensures adequate dilution of mine waters after discharge. The Macraes gold mine has no stibnite, and most Sb is in solid solution in the abundant arsenopyrite (Sb up to 2,000 mg/kg). Pit waters have both Sb and As dissolved up to 0.1 mg/L, partly because of evaporative concentration in a low-rainfall environment. Macraes tailings waters have high As (up to 3 mg/L) but negligible Sb (<0.001 mg/L). Reefton mine gold-bearing concentrate, containing stibnite, is transported 700 km to be processed by autoclave oxidation and cyanidation at the Macraes mine. This introduction of additional Sb to the Macraes site substantially increases the Sb content of the process stream periodically. Tailings from this process have up to 3 wt% Sb, dispersed through As-rich iron oxyhydroxides that are formed in the autoclave. The Sb-rich tailings are strongly diluted (approximately 100:1) by the Macraes tailings, and adsorption of Sb to iron oxyhydroxides in the tailings piles ensures that there has been no increase in the Sb content of the tailings water since the Reefton concentrate has been added at Macraes.

Dietary iron-loaded rat liver haemosiderin and ferritin: in situ measurement of iron core nanoparticle size and cluster structure using anomalous small-angle x-ray scattering

The morphology, particle size distribution and cluster structure of the hydrated iron(III) oxyhydroxide particles associated with haemosiderin and ferritin in dietary iron-loaded rat liver tissue have been investigated using transmission electron microscopy (TEM) and anomalous small-angle x-ray scattering (ASAXS). Rat liver tissue was removed from a series of female Porton rats which had been fed an iron-rich diet until sacrifice at various ages from 2–24 months. Hepatic iron concentrations ranged from 1 to 65 mg Fe g−1 dry tissue. TEM studies showed both dispersed and clustered iron-containing nanoparticles. The dispersed particles were found to have mean sizes (±standard deviation) of 54 ± 8 Å for the iron-loaded animals and 55 ± 7 Å for the controls. Superposition of particles in TEM images prevented direct measurement of nanoparticulate size in the clusters. The ASAXS data were modelled to provide a quantitative estimate of both the size and spacing of iron oxyhydroxide particles in the bulk samples. The modelling yielded close-packed particles with sizes of 60 to 78 Å which when corrected for anomalous scattering suggests sizes from 54 to 70 Å. Particle size distributions are of particular importance since they determine the surface iron to core iron ratios, which in turn are expected to be related to the molar toxicity of iron deposits in cells.

Magnetic energy-barrier distributions for ferrihydrite nanoparticles formed by reconstituting ferritin

The spherical cage-like protein ferritin was reconstituted with varying numbers of iron atoms per protein shell (ranging from approximately 20 to 1100) at temperatures of both 25 and 50 °C to produce iron(III) oxyhydroxide (ferrihydrite) particles with different average particle sizes and degrees of crystallinity. After characterization of the structural properties of the resulting iron-oxyhydroxide nanoparticles with transmission electron microscopy and Mössbauer spectroscopy, magnetic viscosity measurements were made in zero applied magnetic field and the resulting data were used to calculate the apparent magnetic-moment-weighted energy barrier distributions for the samples. The distributions measured were typically comprised of both a lognormal distribution and an exponential decay of barrier frequency with increasing barrier height. Evidence that the lognormal component of this distribution arises from the distribution of particle volumes and moments within the ensemble is strongly supported by the increase in the mode of the energy barrier distribution with increasing particle size. The exponentially decaying distribution has a relatively higher contribution to the overall distribution for the more crystalline reconstituted ferritin samples suggesting that it may be associated predominantly with uncompensated spins at particle surfaces.

Precipitated iron Fischer-Tropsch catalyst: Effect of carbidization on the morphology of iron oxyhydroxide nanoneedles

The effect of carbidization on the morphology of iron oxyhydroxide particles has been studied. Homogeneous oxidation of iron(II) sulfate results in predominantly γ-FeOOH particles which have a rod-shaped crystalline structure. Carbidization of the prepared iron oxyhydroxide particles at 270 °C and atmospheric pressure without mechanical stirring was found to produce iron carbides with spherical layered structure residing in close proximity. HRTEM, EDS and electron microdiffraction analysis revealed that carbidization alters the initial nanoneedle-type morphology and generates ultrafine carbide particles with irregular spherical shape. When carbidization was performed under severe mechanical stirring, formation of spherical carbide particles completely separated from each other was obsrved. Initial activity of iron oxyhydroxide for Fischer-Tropsch synthesis was found to be high (a CO conversion of about 84%) which declined steadily with synthesis time (26% CO conversion after 340 h of synthesis). The effect of carbidation on the morphology of iron hydroxide oxide (γ-FeOOH) particles with a three dimensional crystalline nanoneedle structure has studied. Carbidation of γ-FeOOH with CO at atmospheric pressure produced iron carbides with spherical layered structure. HRTEM and EDS analysis revealed that carbidation changes the initial nanoneedles morphology and generates ultrafine carbide particles with irregular spherical shape.

Paleozoic and Mesozoic silica-rich seawater: Evidence from hematitic chert (jasper) deposits

Laterally extensive beds of highly siliceous, hematitic chert (jasper) are associated with many volcanogenic massive sulfide (VMS) deposits of Late Cambrian to Early Cretaceous age, yet are unknown in analogous younger (including modern) settings. Textural studies suggest that VMS-related jaspers in the Ordovician Lokken ophiolite of Norway were originally deposited as Si- and Fe-rich gels that precipitated from hydrothermal plumes as colloidal silica and iron-oxyhydroxide particles. Rare earth element patterns and Ge/Si ratios of the jaspers reflect precipitation from plumes having seawater dilution factors of 10 3 to 10 4 , similar to modern examples. We propose that silica in the ancient jaspers is not derived from submarine hydrothermal fluids-as suggested by previous workers-but instead was deposited from silica-rich seawater. Flocculation and precipitation of the silica were triggered inorganically by the bridging effect of positively charged iron oxyhydroxides in the hydrothermal plume. A model involving amorphous silica (opal-A) precursors to the jaspers suggests that silica contents of Cambrian-Early Cretaceous oceans were at least 110 mg/L SiO 2 , compared to values of 40-60 mg/L SiO 2 estimated in other studies. The evolution of ancient silica-rich to modern Fe-rich precipitates in submarine-hydrothermal plumes reflects a changeover from silica-saturated to silica-depleted seawater through Phanerozoic time, due mainly to ocean-wide emergence of diatoms in the Cretaceous.

Chemical Force Microscopy Investigation of Phosphate Adsorption on the Surfaces of Iron(III) Oxyhydroxide Particles

Phosphate-modified AFM tips were prepared by the deposition of self-assembled monolayers (SAMs) of bis(11-thioundecyl) phosphate on Au-coated silicon nitride cantilevers. The properties of the PO 2H-terminated SAMs were investigated by studying the pH-dependent force interactions of the tips with phosphate- and carboxylic acid-terminated SAM control surfaces. The PO 2H functional groups had a p K a of ≈5.0. A chemical force microscopy (CFM) study was conducted on the interactions between the probes and the surfaces of hydrous ferric oxide particles prepared in our laboratory by hydrolytic precipitation from FeCl 3. The forces between PO 2H probes and the hydrous ferric oxide surfaces were seen to exhibit a strong pH dependence, with maximum attractive forces occurring for pH values between 5 and 8. The effects of postprecipitation of the hydrous ferric oxide colloids with orthophosphate, H 2PO 4 −, dimethylphosphate, (CH 3O) 2PO 2H (DMP), and tannic acid (TA) on the adhesive interactions between the PO 2H tips and the solids were also investigated. Attenuated total reflectance infrared spectroscopy (ATR-IR) was used to verify the presence of surface-adsorbed species and zeta potentiometric measurements to determine surface charge on the colloids. We show that the method of chemical force titration using phosphate-terminated tips can differentiate between these various colloids and that it shows promise as a general method for studying this environmentally important class of compounds.

Influence of Phosphate on Bacterial Adhesion onto Iron Oxyhydroxide in Drinking Water

The transport and storage of drinking water in water distribution systems can modify its initial composition and properties. The accumulation of bacteria on corroded pipes is prejudicial and may lower the microbiological quality of the water. Previous results have shown that when pipes are highly corroded, the addition of phosphate, used as an anticorrosion treatment, decreases the bacterial concentration in the water. We studied the possibility of using phosphate to reverse the surface charge of iron oxyhydroxide (FeOOH) to limit bacterial adhesion. Iron oxyhydroxide (IOH) particles and Escherichia coli SH 702 were used as models of corrosion products and bacterial contamination, respectively. Electrophoresis was used to characterize the initial surface charges of both types of particles and the modifications that occurred after the addition of phosphate anions. Flow cytometry and adhesion assays were used to build adsorption isotherms of bacteria on IOH versus (phosphated-) IOH. X-ray photoelectron spectroscopy permitted to determine the chemical composition of the E. coli envelope and to discuss on functional groups responsible for bacterial surface properties. In the present conditions, adding phosphate to water allowed a decrease of 75% of the bacteria adhering to IOH.

Mercury Speciation in Drainage from the New Idria Mercury Mine, California

Little is known about the amount and form of mercury released from inoperative mercury mines in the western United States. To address this, we measured mercury concentrations and speciation in water impacted by the New Idria mine. Total unfiltered mercury concentrations (UHgT) in acid mine drainage (AMD) (5.2 to 41 ng/L) were comparable to concentrations upstream from the mine (4.2 to 13 ng/L). We measured substantially higher UHgT concentrations (2900 to 12 400 ng/L) in water 1.2 km downstream from the AMD input and estimate that the creek transports a baseline flux of 1.5 kg of Hg/yr from the mine site. We hypothesize that tailings are the primary source of mercury to this creek. We attribute the decrease in UHgT along a downstream transect to Hg(II) scavenging by iron oxyhydroxide particles that precipitate and settle out of the water. Likewise, dissolved gaseous mercury concentrations decreased with increasing distance from the mine (2.8 ng/L at 1.2 km; 0.56 ng/L at 7.5 km). We regard abiotic atmospheric evasion as the primary mechanism driving this loss. The released mercury is biologically available, evidenced by high (1.1 to 1.7 ng/L) unfiltered monomethylmercury concentrations downstream from the mine. We attribute the relatively uniform downstream monomethylmercury concentrations to a balance between microbial methylation and demethylation.

Iron oxyhydroxide colloids stabilized with polysaccharides

Neutralization of iron salts in aqueous solutions of κ-carrageenan and cellulose sulfate results in iron oxyhydroxide–polysaccharide hybrid colloids with unusual pH stability up to pH 13. It is shown that both polysaccharides form a tight polymer layer surrounding the inorganic particles, which in the case of κ-carrageenan is cross-linked by helical domains forming a self-assembled nanoreactor. The stabilized iron oxyhydroxide particles can undergo further reactions, for example, it is possible by a chemical reaction to produce stabilized magnetite particles. Repetition of the loading/neutralization steps in the reaction results in hybrids with iron contents much higher than the stoichiometric balance of iron and functional groups of the polymer (greater than 100% Fe/SO4−). This combination of high iron content with a natural polysaccharide stabilizer makes these colloids interesting for a number of applications, for example, for nutritional purposes or as contrasting agents for tomography.