Magnetite Surface Research Articles

Polydopamine-based molecularly imprinting polymers on magnetic nanoparticles for recognition and enrichment of ochratoxins prior to their determination by HPLC.

A polydopamine-based molecularly imprinted polymer was deposited on the surface of magnetite (ferroferric oxide) nanoparticles (Fe3O4@PDA MIPs) and is shown to be an efficient and fairly specific sorbent for the extraction of various ochratoxins. The MIPs were characterized by IR spectroscopy and transmission electron microscopy. The adsorption capacities, evaluated through the langmuir adsorption isotherm model, are 1.8, 0.23 and 0.17mg·g-1 for ochratoxin A, ochratoxin B and ochratoxin C, respectively. Parameters such as the amount of magnetic MIPs, pH value, time for ultrasonication, elution solvent and volume were optimized. Following desorption from the MIP with acetonitrile, the ochratoxins were quantified by HPLC with fluorometric detection. Under optimal experimental conditions, the calibration plots are linear in the range of 0.01-1.0ng·mL-1 ofOTA, 0.02-2.0ng·mL-1 ofOTB, and 0.002-0.2ng·mL-1 ofOTC. The LODs are between 1.8 and 18pg·mL-1, and the recoveries from spiked samples are 71.0% - 88.5%, with RSDs of 2.3-3.8% in case of rice and wine samples. The MIPs can be re-used for at least 7 times. Graphical abstract Schematic of the preparation of a magnetic molecularly imprinted polymer based on self-polymerization of dopamine in weakly alkaline solution. Ochratoxins are recognized owing to homologous cavities in the MIPs, and quantified by HPLC after desorption with acetonitrile.

Surface Modification of Pentlandite and Serpentine with Reagents and Magnetite for Magnetic Separation

In this study, selective magnetic coating was employed to separate pentlandite and serpentine. The surface properties of minerals with and without reagents and magnetite were characterized by zeta potential measurements, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM). Zeta potentials showed that the surfaces of serpentine and magnetite were both negatively charged with the addition of sodium hexametaphosphate. Thus, serpentine was hardly coated by magnetite due to the electrostatic repulsion between them. The results of SEM and FTIR demonstrated that a magnetic coating of magnetite was observed on the pentlandite rather than on the serpentine. The VSM measurements confirmed that the magnetism of pentlandite was increased significantly due to the selective adsorption of magnetite on its surfaces; therefore, pentlandite was successfully separated from serpentine by magnetic separation. The study shows that selective magnetic coating technology has the alternative potential to separate pentlandite from serpentine.

Assessment of pectin-coated magnetite nanoparticles in low-energy water desalination applications.

Novel magnetite nanoparticles (NPs) modified with pectin coating were fabricated, characterized, and evaluated as potential draw solute in a forward osmosis (FO) process for water desalination applications. The prepared NPs had a spherical shape with an average diameter of 200nm and saturation magnetization of 23.13emu/g. Thermogravimetric analysis (TGA) and FTIR spectra elucidated the successful pectin coating on magnetite surface. The potential use of the fabricated NPs in water desalination was conducted via a newly developed lab-scale FO system. Deionized water, saline water (0.2, 0.5, and 1g% NaCl solution), and real well water (TDS = 0.9g%) were used as feed solutions. In all experiments, the water flux gradually decreased along with the extension of experimental time and NaCl rejection rate by the FO membrane was measured to be higher than 95%. Moreover, it was found that the pectin-coated magnetite NPs demonstrated to be able to draw clean water across the FO membrane from well water with a remarkable salt rejection of 97%. Thus, it is believed that the proposed FO system using pectin-coated magnetite NPs as draw solute can be a promising technique for desalination of well waters in an environmental-friendly and energy-saving manner.

Comparative Study on the Adsorption of [AuCl<sub>4</sub>]<sup>–</sup> onto Salicylic Acid and Gallic Acid Modified Magnetite Particles

Salicylic acid-modified magnetite (Mag-SA) and gallic acid-modified magnetite (Mag-GA) particles were prepared by co-precipitation procedure. Characterization results showed the interaction that occurs between the surface of magnetite with salicylic acid (Mag-SA) and gallic acid (Mag-GA) was through hydrogen bonding. Adsorption of [AuCl4]– onto Mag-SA and Mag-GA surfaces as a function of initial pH, contact time, and initial concentration of the [AuCl4]– solution were comparatively investigated. Result showed that the optimum adsorption of [AuCl4]– onto Mag-SA or Mag-GA was found at pH 3. The adsorption process were found to allow the pseudo-second order equation, both for Mag-SA and Mag-GA. The parameters in isotherm adsorption equations conformed to the Langmuir and Freundlich isotherms very well for Mag-GA, but for Mag-SA, only conformed to the Langmuir isotherm very well. The result of this study demonstrate that the ability Mag-GA to adsorb [AuCl4]– higher than Mag-SA.

Stimulatory effect of magnetite on the syntrophic metabolism of Geobacter co-cultures: Influences of surface coating

Magnetite-mediated direct interspecies electron transfer (DIET) can facilitate syntrophic metabolism in natural microbial communities and also promote the performance of the engineered systems based on syntrophic interactions. In this study, the stimulatory effect of bare synthetic magnetite (Mt), humic acid coated magnetite, and SiO 2 coated magnetite (Mt-SiO 2 ) on DIET in defined co-cultures of Geobacter metallireducens / Geobacter sulfurreducens were studied. Magnetite coated with Aldrich humic acid (HA) and Elliott Soil humic acid (HA ES ), respectively, were prepared, and the two kinds of humic acid influenced the ability of Mt to promote syntrophic metabolism of the co-cultures in a similar way. When weight concentration was the same, pure humic acid presented the stimulatory effect on DIET similar to bare magnetite. However, the presence of HA coating on magnetite surface caused 50% and 61%, respectively, decrease in the rates of ethanol consumption ( R e ) and succinate production ( R s ) in DIET processes. Pure HA in the same weight concentration as the HA coating in Mt-HA induced the similar metabolism rates as Mt-HA. In the Mt-HA mediated DIET, most electrons from ethanol metabolism were transferred to G. sulfurreducens selectively through the HA coating, and magnetite core hardly contributed to DIET processes. The SiO 2 coating on magnetite resulted in 81% and 89%, respectively, decreases in R e and R s , mainly because the non-conductive SiO 2 layer hindered electron transfer between magnetite core and bacteria. After eight-day incubation with the co-cultures, bare magnetite nanoparticles formed relatively larger and more compact aggregates with cells than Mt-HA and Mt-SiO 2 , due to the different surface charge between bare and coated Mt. The generation of dissolved Fe(II) and HCl-extractable Fe(II) due to microbial reduction of magnetite by G. metallireducens and vivianite formation were observed along with DIET processes in all DIET experiments. Based on these results, different pathways of electron transfer in defined co-cultures of Geobacters with bare and coated magnetite nanoparticles were proposed. The findings in this study demonstrate the significant effects of surface properties on the ability of magnetite to stimulate DIET, which needs to be considered in order to comprehensively understand the role and mechanisms of mineral-mediated DIET in natural and engineered systems.

Parametric Rietveld refinement and magnetic characterization of superparamagnetic iron oxide nanoparticles

This article describes the synthesis of two superparamagnetic iron oxide nanoparticles (SPIONs) covered with different ligands – hydrophobic (oleic acid (OA)) and hydrophilic (tetraethyl ammonium (TEA)) – and the investigation of the effects of thermal treatments on the crystal structure of TEA-SPIONs or OA-SPIONs using X-ray powder diffraction data and parametric Rietveld refinements; we stablished non-crystallographic models to describe how the oxidation processes take place with increasing temperatures for the different systems. The morphological and magnetic properties revealed the nanoparticles have a mean diameter of ∼10 nm in the solid state and are superparamagnetic at room temperature. Magnetization measurements confirmed the superparamagnetic state for both systems and revealed smaller particle sizes and narrower size distribution for OA-SPIONs than for TEA-SPIONs. The thermomagnetic analyses show only the ferrimagnetic phase transition of magnetite for OA-SPIONs while in the TEA-SPIONs, besides the ferrimagnetic phase transition there is the appearance of an antiferromagnetic one disclosing the evolution of hematite phase probably on the surface of magnetite due to thermal cycles.

Formation of Fe(III)–oxides on the magnetite surfaces in the low–temperature hydrothermal reaction

Formation of Fe(III)–oxides on the magnetite surfaces in the low–temperature hydrothermal reaction

The importance of the helical structure of a MamC-derived magnetite-interacting peptide for its function in magnetite formation.

Biomineralization is the process of mineral formation by organisms and involves the uptake of ions from the environment in order to produce minerals, with the process generally being mediated by proteins. Most proteins that are involved in mineral interactions are predicted to contain disordered regions containing large numbers of negatively charged amino acids. Magnetotactic bacteria, which are used as a model system for iron biomineralization, are Gram-negative bacteria that can navigate through geomagnetic fields using a specific organelle, the magnetosome. Each organelle comprises a membrane-enveloped magnetic nanoparticle, magnetite, the formation of which is controlled by a specific set of proteins. One of the most abundant of these proteins is MamC, a small magnetosome-associated integral membrane protein that contains two transmembrane α-helices connected by an ∼21-amino-acid peptide. In vitro studies of this MamC peptide showed that it forms a helical structure that can interact with the magnetite surface and affect the size and shape of the growing crystal. Our results show that a disordered structure of the MamC magnetite-interacting component (MamC-MIC) abolishes its interaction with magnetite particles. Moreover, the size and shape of magnetite crystals grown in in vitro magnetite-precipitation experiments in the presence of this disordered peptide were different from the traits of crystals grown in the presence of other peptides or in the presence of the helical MIC. It is suggested that the helical structure of the MamC-MIC is important for its function during magnetite formation.

Magnetic mesoporous polymelamine-formaldehyde resin as an adsorbent for endocrine disrupting chemicals.

A magnetic mesoporous poly(melamine-formaldehyde) composite (Fe3O4-mPMF) was prepared via grafting poly(melamine-formaldehyde) onto the surface of amino-functionalized magnetite (Fe3O4) nanoparticles. The material was characterized by scanning electron micrography, transmission electron microscopy, X-ray diffraction, Fourier transform-infrared spectroscopy, nitrogen adsorption-desorption isotherms, and thermogravimetric analysis. It has a large surface area, a typical mesoporous structure, and a high thermal stability. It was employed as a magnetic sorbent for the solid phase extraction of the following endocrine disrupting chemicals (EDCs): Bisphenol A, 4-tert-butylphenol, 4-tert-octylphenol and nonylphenol. The EDCs were then quantified by HPLC. Under the optimized conditions, the response to the EDCs is linear in the range of 0.5-100ng·mL-1, and the limits of detection are 0.02-0.1ng·mL-1. The high adsorption capability of the Fe3O4-mPMF is mainly attributed to multiple interactions including π-stacking, hydrogen bonding, and hydrophobic interactions. The method was applied to the extraction of EDCs from spiked river water and bottled juice samples. The results demonstrated that the Fe3O4-mPMF is an efficient adsorbent for the extraction of organic compounds with large conjugated π-system, plenty of hydrogen-bonding sites, and strong hydrophobicity. Graphical abstract A magnetic mesoporous polymelamine-formaldehyde composite (Fe3O4-mPMF) was prepared and employed as a magnetic sorbent for the solid phase extraction of endocrine disrupting chemicals from river water and bottled juice samples prior to high-performance liquid chromatographic analysis.

Reactivity of CO2 on the surfaces of magnetite (Fe3O4), greigite (Fe3S4) and mackinawite (FeS).

The growing environmental, industrial and commercial interests in understanding the processes of carbon dioxide (CO2) capture and conversion have led us to simulate, by means of density functional theory calculations, the application of different iron oxide and sulfide minerals to capture, activate and catalytically dissociate this molecule. We have chosen the {001} and {111} surfaces of the spinel-structured magnetite (Fe3O4) and its isostructural sulfide counterpart greigite (Fe3S4), which are both materials with the Fe cations in the 2+/3+ mixed valence state, as well as mackinawite (tetragonal FeS), in which all iron ions are in the ferrous oxidation state. This selection of iron-bearing compounds provides us with understanding of the effect of the composition, stoichiometry, structure and oxidation state on the catalytic activation of CO2 The largest adsorption energies are released for the interaction with the Fe3O4 surfaces, which also corresponds to the biggest conformational changes of the CO2 molecule. Our results suggest that the Fe3S4 surfaces are unable to activate the CO2 molecule, while a major charge transfer takes place on FeS{111}, effectively activating the CO2 molecule. The thermodynamic and kinetic profiles for the catalytic dissociation of CO2 into CO and O show that this process is feasible only on the FeS{111} surface. The findings reported here show that these minerals show promise for future CO2 capture and conversion technologies, ensuring a sustainable future for society.This article is part of a discussion meeting issue 'Providing sustainable catalytic solutions for a rapidly changing world'.

New Features and Uncovered Benefits of Polycrystalline Magnetite as Reusable Catalyst in Reductive Chemical Conversion

Magnetite is one of the most well-characterized and used iron oxides in a variety of research and industrial fields. Its easy separation by magnetism has attracted great attention for use as a support material for various noble metallic catalysts. Here, we report for the first time that bare polycrystalline magnetite can show a remarkable catalytic activity toward p-nitrophenol reduction by sodium borohydride, while three other single-crystal magnetite samples exhibit little effect on the catalysis. Electron and atomic force microscopies and Mossbauer spectrometry showed that elemental Fe nanoparticles were formed on the surface of polycrystalline magnetite. Density functional theory calculation further elucidated that the Fe atom exposed at the high-index magnetite surface develops a significant Fe–BH3 interaction and that its leaching-out process can be substantially promoted. Surprisingly, recycling tests showed that this great activity could be fully preserved up to 10 reaction cycles, in contrast to ...

EDTA-functionalized Fe3O4 nanoparticles

This study analyzes the synthesis and characterization of functionalized Fe3O4 nanoparticles by ethylenediaminetetraacetic acid (EDTA). The syntheses were performed using the co-precipitation method under different experimental conditions: nitrogen atmosphere versus ambient atmospheric conditions, and temperatures of 25 °C versus 90 °C. X-ray diffraction techniques, Fourier transform infrared (FTIR) spectroscopy, zeta potential, and transmission electron microscopy (TEM) were used to characterize these nanoparticles. The co-precipitation method produced high homogeneity in nanostructure shape and size. The functionalization of the magnetite surface was confirmed by the FTIR analyses and the development of new bands associated with EDTA as well as by zeta potential change. The addition of EDTA was also found to change the mechanism of nucleation and nanostructure growth; EDTA was found to favor nucleation, thus decreasing nanoparticle size.

Adsorption isotherm, mechanism, and geometry of Pb(II) on magnetites substituted with transition metals

Iron oxides are abundant in natural waters and soils and have high capacities for scavenging Pb(II) by adsorption, which affects the transport and fate of Pb on the earth's surface. We investigated the adsorption of Pb(II) on magnetites substituted with commonly incorporated transition metals such as Cr, Mn, Co, and Ni. The adsorption capacity, mechanism, and local coordination of Pb(II) were investigated by traditional macroscopic studies, i.e., acid-base titration and batch adsorption experiment, complemented with X-ray absorption fine structure (XAFS) spectrum analysis and surface complexation model (SCM). The substitution increased the surface site density, while pHpzc did not vary. Pb(II) adsorption was not suppressed by the presence of background electrolyte and improved as pH increased. The isotherms were well fit to the Langmuir adsorption model. The XAFS analysis demonstrated that Pb(II) ions were adsorbed on magnetite surface predominantly via inner-sphere complexation, where the adsorbed Pb(II) species was in bidentate binuclear corner-sharing geometry, independent of the adsorption capacity. This adsorption geometry can be applied to fit the experimental adsorption data well with the diffuse layer model (DLM). The substitutions improved the adsorption capacity in the following order: Cr>Ni>Mn>Co, and were discussed regarding the measured values of active site density and local coordination of adsorbed Pb(II). This study is the first documentation of Pb(II) adsorption on magnetite with different substitutions. The obtained results are of great significance for the understanding of Pb(II) surface complexation reactions on magnetite surface.

Design of Optimally Stable Molecular Coatings for Fe-Based Nanoparticles in Aqueous Environments.

Magnetic nanoparticles are widely used in biomedical and oil-well applications in aqueous, often harsh environments. The pursuit for high-saturation magnetization together with high stability of the molecular coating that prevents agglomeration and oxidation remains an active research area. Here, we report a detailed analysis of the criteria for the stability of molecular coatings in aqueous environments along with extensive first-principles calculations for magnetite, which has been widely used, and cementite, a promising emerging candidate. A key result is that the simple binding energies of molecules cannot be used as a definitive indicator of relative stability in a liquid environment. Instead, we find that H+ ions and water molecules facilitate the desorption of molecules from the surface. We further find that, because of differences in the geometry of crystal structures, molecules generally form stronger bonds on cementite surfaces than they do on magnetite surfaces. The net result is that molecular coatings of cementite nanoparticles are more stable. This feature, together with the better magnetic properties, makes cementite nanoparticles a promising candidate for biomedical and oil-well applications.

Effective removal of phosphate from aqueous solution using humic acid coated magnetite nanoparticles

Effective removal of excess phosphate from water is critical to counteract eutrophication and restore water quality. In this study, low cost, environmentally friendly humic acid coated magnetite nanoparticles (HA-MNP) were synthesized and applied for the remediation of phosphate from aqueous media. The HA-MNPs, characterized by FTIR, TEM and HAADF-STEM showed the extensive coating of humic acid on the magnetite surface. The magnetic nanoparticles with diameters of 7–12 nm could be easily separated from the reaction mixture by using a simple hand held magnet. Adsorption studies demonstrate the fast and effective separation of phosphate with maximum adsorption capacity of 28.9 mg/g at pH 6.6. The adsorption behavior follows the Freundlich isotherm suggesting the formation of non-uniform multilayers of phosphate on the heterogeneous surface of HA-MNP. The adsorption kinetic fits the pseudo-second order model well with rate constants of 0.206 ± 0.003, 0.073 ± 0.002 and 0.061 ± 0.003 g mg−1min−1 for phosphate (P) concentrations of 2, 5 and 10 mg/L respectively. The removal of phosphate was found higher at acidic and neutral pH compared to basic conditions. The nanoparticles exhibit good selectivity and adsorption efficiency for phosphate in presence of co-existing ions such as Cl−, SO42−and NO3− with some inhibition effect by CO32−. The effect of temperature on the adsorption reveals that the process is endothermic and spontaneous. HA-MNPs are promising, simple, environmentally friendly materials for the removal of phosphate from aqueous media.

Gd(III) Adsorption on the DTPA-functionalized chitosan/magnetite nanocomposites

ABSTRACTThe method for chitosan (CS) covalent immobilization onto NH2-functionalized magnetite nanoparticles surface is presented. Covalent binding of CS to the magnetite surface proceeds using a free -CH2OH group of CS and a NH2-group of magnetite with epichlorohydrin (ECH) as a cross-linker. The obtained nanocomposites were functionalized by diethylenetriaminepentaacetic acid (DTPA)-groups. Composites were characterized by elemental analysis, FTIR, XPS and ASAP methods. The total content of organic phase (CS-DTPA) in the hybrid material, appreciated by thermogravimetric analysis (TGA), was 3.7%. Considering the atomic ratio between oxygen in CS and oxygen in ECH residue, the chemical structure of the hybrid material is proposed. The adsorption of Gd-DTPA and Gd3+ on the obtained nanocomposite was studied. The Freundlich isotherm fits all the experimental data better than the Langmuir adsorption.

Reduction removal of hexavalent chromium by zinc-substituted magnetite coupled with aqueous Fe(II) at neutral pH value

In this study, Cr(VI) removal by Zn-substituted magnetite coupled with aqueous Fe(II) through adsorption and reduction was investigated. A series of Zn-substituted magnetites (Fe3−xZnxO4, x=0, 0.25, 0.49, 0.74 and 0.99) were synthesized by a coprecipitation method, followed by systematic characterization, e.g., X-ray diffraction (XRD), thermogravimetry (TG), specific surface area and surface acid/base titration. The characterization results show that all samples had a spinel structure without an obvious alternation by Zn substitution. The BET surface area and surface site density gradually increased with Zn substitution. During Cr removal under neutral pH value, Cr(VI) was first adsorbed on the magnetite surface and then reduced to Cr(III) by Fe3−xZnxO4 and adsorbed Fe(II); finally, it was immobilized on the Fe3−xZnxO4 surface, which was verified via X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES) analyses and desorption experiment. With the increase in the Zn content in magnetite, the Cr removal efficiency initially decreased; then, it improved, which was ascribed to the decreasing Cr(VI) reduction and increasing Cr(VI) adsorption. This variation in activity by Zn substitution was discussed in terms of the reaction mechanism as well as the cationic microstructure and surface properties of Fe3−xZnxO4.

Spectroscopic and quantum chemical studies of interaction between the alginic acid and Fe3O4 nanoparticles

In this work, we present the spectral investigation of the interactions between the coverage with alginic acid (AA) and nanoparticles for three different composites containing 74, 80, and 88wt% of magnetite. These results show that the Fe3O4 nanoparticles are coated with the AA and indicate that there is an interaction between them. Moreover, we have investigated the thermal and magnetic properties of all investigated compounds. We show that bonding of alginic acid to the surface of magnetite results in better thermal stability of the polymer and in higher temperature of AA chains degradation. We find that for dense assembly of magnetite nanoparticles, at low temperatures, the intergranular coupling becomes much stronger than between nanoparticles dispersed in composites.

Effects of nano-CaCO3 on the adsorption of carboxymethyl starch onto magnetite concentrate in pelletizing

The carboxylmethyl starch modified with nano-CaCO3 has been identified as an alternative binder in iron ore pelletization. This study aims to further clarify effects of nano-CaCO3 on the adsorption of carboxymethyl starch (CMS) onto magnetite particles. Variables influencing the adsorption capacity of CMS, such as solution pH, initial concentration, the ratio of nano-CaCO3 to CMS and adsorption time, were systematically investigated. Zeta potential and solution pH results verify that nano-CaCO3 can serve as an active site, which reducing the repulsive force between the negatively charged CMS and magnetite surface. Consequently, the adsorption capacity of CMS is promoted by the addition of nano-CaCO3. Besides, both the adsorption capacity of CMS and strengths of green pellets with the addition of nano-CaCO3 decrease by increasing the pH value of binder solution. In other words, there is a positive correction between the adsorption capacity and the strength of green pellet. The equilibrium adsorption data of CMS can be described by the Freundlich isotherm. The addition of nao-CaCO3 does not change the adsorption type of CMS onto magnetite surface. For the adsorption of CMS with or without the addition of nano-CaCO3, the pseudo-second-order kinetics of chemical reaction provides the best correlation. Moreover, the adsorption rate of CMS with nano-CaCO3 is much larger than that of CMS. SEM results indicate that the cross-linked structure built by CMS+nano-CaCO3 is unique and different from that of CMS. The nano-CaCO3 can serve as the active site and skeleton, and promote the cohesion force of neighboring CMS molecules. Consequently, this unique structure gives CMS+nano-CaCO3 a high binding ability.

Effect of coexisting components on phosphate adsorption using magnetite particles in water.

In this study, we focused on the rate of adsorption of phosphate on to the surface of magnetite in the presence of coexisting anions, organic matters and heavy metals. Magnetite particles were prepared using a co-precipitation method. Iron (II) sulfate heptahydrate and iron (III) chloride hexahydrate were mixed and then a sodium hydroxide solution was added drop-wise in the mixed iron solution. Coexisting anions were found to have no effect on the decrease in phosphate adsorption. However, phosphate adsorbed on to magnetite surface decreased with increasing total organic carbon (TOC) concentration of natural organic matter (NOM) such as citric, oxalic, and humic acid. The amount of phosphate adsorbed rapidly decreased with the increase of NOM concentration; therefore, it can be noted that NOM concentration considerably affects the adsorption of phosphate due to the negative charge exiting on the surface of NOMs. Glucose and ethanol, meanwhile, were found to have no effect on the phosphate adsorption. The amount of phosphate adsorbed did not change in the presence of heavy metals, namely, Pb and Cd, under acidic conditions. However, under alkaline conditions, the amount of phosphate adsorbed decreased with increasing concentrations of Pb and Cd. In the case of coexisting As(III), the amount of phosphate adsorbed decreased at all pH levels with increasing As(III) concentrations.