Magnetite Surface Research Articles

Synthesis and Characterization of Fe<sub>3</sub>O<sub>4</sub> Coated on APTES as Carriers for Morin-Anticancer Drug

Morin (MR) is an anticancer drug present in fruits and Chinese herbs. Fe3O4 magnetic nanoparticles (MNPs) coated on 3-aminopropyl triethoxysilane (APTES) were synthesized (MNPs-APTES) as carriers for MR. The characterization of drug delivery system was confirmed by Fourier Transform Infrared (FTIR), Transmission Electron Microscope (TEM), X-Ray Diffraction (XRD), dynamic light scattering (DLS), and vibrating sample magnetometer (VSM). The adsorbed APTES on the magnetite surface (MNPs-APTES) was examined by FTIR. The TEM image showed that the average particle size is obtained to be about 26.7 nm for MNPs-APTES. The MR loading and release behavior of MNPs-APTES were studied and the results showed that up to 60% of the adsorbed drug was released within 4 h. In summary, the MNPs-APTES nanocarriers are based on the results, promising for targeted morin drug delivery.

Metallurgical By-Product Transformation and Its Plasma Modification to Increase HDPE Thermal Conductivity

ABSTRACTA metallurgical by product mostly constituted of Wustita (FeO) was transformed to Magnetite (Fe3O4) spheres using a flame treatment. Then magnetite spheres surface was modified by cold plasma treatment with ethylene, where a thin polyethylene film was deposited on the spheres surface. Finally, HDPE composites with modified spheres were obtained by melt mixing and its thermal conductivity was determined by MDSC. It was found that spheres surface modification helps to increase composites thermal conductivity.

Trichloroethylene degradation by persulphate with magnetite as a heterogeneous activator in aqueous solution

Iron oxide-magnetite (Fe3O4) as a heterogeneous activator to activate persulphate anions for trichloroethylene (TCE) degradation was investigated in this study. The experimental results showed that TCE could be completely oxidized within 5 h by using 5 g L−1 magnetite and 63 mM indicating the effectiveness of the process for TCE removal. Various factors of the process, including. and magnetite dosages, and initial solution pH, were evaluated, and TCE degradation fitted well to the pseudo-first-order kinetic model. The calculated kinetic rate constant was increased with increasing and magnetite dosages, but it was independent of solution pH. In addition, the changes of magnetite morphology examined by scanning electron microscopy and X-ray powder diffraction, respectively, confirmed the slight corrosion with α-Fe2O3 coated on the magnetite surface. The probe compounds tests clearly identified the generation of the reactive oxygen species in the system. While the free radical quenching studies further demonstrated that and •OH were the major radicals responsible for TCE degradation, whereas contributed less in the system, and therefore the roles of reactive oxygen species on TCE degradation mechanisms were proposed accordingly. To our best knowledge, this is the first time the performance and mechanism of magnetite-activated persulphate oxidation for TCE degradation are reported. The findings of this study provided a new insight into the heterogeneous catalysis mechanism and showed a great potential for the practical application of this technique in in situ TCE-contaminated groundwater remediation.

Design and construction of polymerized-chitosan coated Fe3O4 magnetic nanoparticles and its application for hydrophobic drug delivery.

In this study, a novel hydrogel, chitosan (CS) crosslinked carboxymethyl-β-cyclodextrin (CM-β-CD) polymer modified Fe3O4 magnetic nanoparticles was synthesized for delivering hydrophobic anticancer drug 5-fluorouracil (CS-CDpoly-MNPs). Carboxymethyl-β-cyclodextrin being grafted on the Fe3O4 nanoparticles (CDpoly-MNPs) contributed to an enhancement of adsorption capacities because of the inclusion abilities of its hydrophobic cavity with insoluble anticancer drugs through host-guest interactions. Experimental results indicated that the amounts of crosslinking agent and bonding times played a crucial role in determining morphology features of the hybrid nanocarriers. The nanocarriers exhibited a high loading efficiency (44.7±1.8%) with a high saturation magnetization of 43.8emu/g. UV-Vis spectroscopy results showed that anticancer drug 5-fluorouracil (5-Fu) could be successfully included into the cavities of the covalently linked CDpoly-MNPs. Moreover, the free carboxymethyl groups could enhance the bonding interactions between the covalently linked CDpoly-MNPs and anticancer drugs. In vitro release studies revealed that the release behaviors of CS-CDpoly-MNPs carriers were pH dependent and demonstrated a swelling and diffusion controlled release. A lower pH value led to swelling effect and electrostatic repulsion contributing to the protonation amine impact of NH3(+), and thus resulted in a higher release rate of 5-Fu. The mechanism of 5-Fu encapsulated into the magnetic chitosan nanoparticles was tentatively proposed.

Stabilization of the surfaces of magnetite

Surface Structure Accurate structures of iron oxide surfaces are important for understanding their role in catalysis, and, for oxides such as magnetite, applications in magnetism and spin physics. The accepted low-energy electron diffraction (LEED) structure for the surface of magnetite, in which

Subsurface cation vacancy stabilization of the magnetite (001) surface.

Iron oxides play an increasingly prominent role in heterogeneous catalysis, hydrogen production, spintronics, and drug delivery. The surface or material interface can be performance-limiting in these applications, so it is vital to determine accurate atomic-scale structures for iron oxides and understand why they form. Using a combination of quantitative low-energy electron diffraction, scanning tunneling microscopy, and density functional theory calculations, we show that an ordered array of subsurface iron vacancies and interstitials underlies the well-known (√2 × √2)R45° reconstruction of Fe3O4(001). This hitherto unobserved stabilization mechanism occurs because the iron oxides prefer to redistribute cations in the lattice in response to oxidizing or reducing environments. Many other metal oxides also achieve stoichiometry variation in this way, so such surface structures are likely commonplace.

Heterogeneous activation of Oxone by substituted magnetites Fe3−xMxO4 (Cr, Mn, Co, Ni) for degradation of Acid Orange II at neutral pH

In this study, the effect of incorporation of transition metals (i.e., Co, Mn, Cr, and Ni) into the magnetite on the reactivity towards Oxone activation was investigated at neutral pH. The magnetite samples were characterized by XRD and EXAFS. Co, Cr, and Ni were in the valences of +2, +3, and +2, respectively, while Mn was in the valences of +2 and +3. These cations occupied the octahedral sites of magnetite, but the distribution of Mn and Ni on the octahedral sites of magnetite surface increased with an increase of substitution extent. The activity of magnetites in Oxone activation was investigated through Acid Orange II (AOII) degradation at an initial pH of 7.0 with or without phosphate-buffered solution. In neutral medium, the AOII degradation by Mn, Cr, and Ni substituting magnetites followed pseudo-first-order kinetics. The incorporation of Co, Mn, and Ni improved the catalytic activity of magnetite in the order Mn<Ni<Co, while Cr showed an inert effect. The dominant reactive radicals were indicated through the scavenging effect of ethanol and tert-butyl alcohols. The different effects of studied substitutions on the reactivity of magnetite were discussed in views of reactive radical species and microstructural environment.

Force interactions between magnetite, silica, and bentonite studied with atomic force microscopy

Iron ore pellets consist of variety of mineral particles and are an important refined product used in steel manufacturing. Production of high-quality pellets requires good understanding of interactions between different constituents, such as magnetite, gangue residues, bentonite, and additives. Much research has been reported on magnetite, silica, and bentonite surface properties and their effect on pellet strength but more scant with a focus on a fundamental particle–particle interaction. To probe such particle interaction, atomic force microscopy (AFM) using colloidal probe technique has proven to be a suitable tool. In this work, the measurements were performed between magnetite–magnetite, bentonite–magnetite, silica–bentonite, and silica–magnetite particles in 1 mM CaCl2 solution at various pH values. The interaction character, i.e., repulsion or attraction, was determined by measuring and analyzing AFM force curves. The observed quantitative changes in interaction forces were in good agreement with the measured zeta-potentials for the particles at the same experimental conditions. Particle aggregation was studied by measuring the adhesion force. Absolute values of adhesion forces for different systems could not be compared due to the difference in particle size and contact geometry. Therefore, the relative change of adhesion force between pH 6 and 10 was used for comparison. The adhesion force decreased for the magnetite–magnetite and bentonite–silica systems and slightly increased for the magnetite–bentonite system at pH 10 as compared to pH 6, whereas a pronounced decrease in adhesion force was observed in the magnetite–silica system. Thus, the presence of silica particles on the magnetite surface could have a negative impact on the interaction between magnetite and bentonite in balling due to the reduction of the adhesion force.

Fe adsorption on hematite (α-Fe2O3) (0001) and magnetite (Fe3O4) (111) surfaces

The structure and electronic properties of different terminations of hematite (0001) and magnetite (111) surfaces upon submonolayer Fe adsorption were studied using the spin-polarized density functional theory (DFT) including the Hubbard correction term U (DFT+U). On both oxides the Fe atoms were adsorbed on the most stable iron and oxygen terminated surfaces. The results show that Fe atoms bind strongly both to hematite and magnetite surfaces, however, the binding is distinctly stronger at the oxygen than at the iron terminated surfaces. For both oxides and surface terminations the binding energy of the Fe decreases with increasing coverage, which indicates substantial repulsive interactions between Fe adatoms. On the hematite surface, the most stable sites for Fe adsorption are bulk continuation sites which result in formation of the Fe-rich terminations. On the magnetite surface, the bulk continuation site is favored only for Fe adsorption on the oxygen terminated surface while on the iron terminated one Fe adsorbs in a position closer to the surface iron layer. Submonolayer coverages of Fe modify substantially the surface electronic structure of the oxides and, depending on the termination, can change its character from half-metallic to insulating one, and vice versa.

Enhanced Reactivity toward Oxidation by Water Vapor: Interactions of Toluene and NO2 on Hydrated Magnetite Nanoparticles

In the atmosphere, water vapor affects the interaction of trace gases and particles, influencing key processes including cloud nucleation, radiation, and heterogeneous chemistry. In this study, the effect of water vapor on the reactions of toluene and NO2 on magnetite, a component of atmospheric dust particles, is investigated using a suite of analytical techniques, namely, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF SIMS). Adsorption isotherms show that water vapor reduces the adsorption of toluene on magnetite. XPS spectra reveal that exposure to water vapor results in limited dissociation and molecular adsorption of water, and partial oxidation of magnetite. When toluene is added, enhanced dissociation of water and oxidation of the magnetite surface are observed, strongly suggesting the importance of intermolecular interactions between water molecules and the interaction of toluene with the H-bonded network of adsorbed water. Upon addition of NO2, enhanced oxidation and NO3 are observed in XPS and TOF SIMS spectra, respectively. In contrast, on oxidized magnetite, less dissociation and sorption of water is observed, and no enhanced oxidation is observed. Our results show that hydrated magnetite surfaces inactive toward further water dissociation can be reactivated depending on the surface chemistry, due to Fe2+. We show that the effect of water vapor on the interaction of toluene and NO2 on magnetite depends on the Fe2+/Fe3+ ratio, which can vary under environmental conditions. Different reactivity of the Fe3O4 in dust can thus be expected, with implications on the fate of pollutants in the atmosphere.

Inulin-based polymer coated SPIONs as potential drug delivery systems for targeted cancer therapy

This paper deal with the synthesis and characterization of PEGylated squalene-grafted-inulin amphiphile capable of self-assembling and self-organizing into nanocarriers once placed in aqueous media. It was exploited as coating agent for obtaining doxorubicin loaded superparamagnetic iron oxide nanoparticles (SPIONs) endowed with stealth like behavior and excellent physicochemical stability. Inulin was firstly modified in the side chain with primary amine groups, followed in turn by conjugation with squalenoyl derivatives through common amidic coupling agents and PEGylation by imine linkage. Polymer coated SPIONs were so obtained by spontaneous self-assembling of inulin copolymer onto magnetite surface involving hydrophobic–hydrophobic interactions between the metallic core and the squalene moieties. The system was characterized in terms of hydrodynamic radius, zeta potential, shape and drug loading capacity. On the whole, the stealth-like shell stabilized the suspension in aqueous media, though allowing the release of the doxorubicin loaded in therapeutic range. The cytotoxicity profile on cancer (HCT116) cell line and in vitro drug uptake were evaluated both with and without an external magnetic field used as targeting agent and uptake promoter, displaying that magnetic targeting implies advantageous therapeutic effects, that is amplified drug uptake and increased anticancer activity throughout the tumor mass.

Employment of a novel magnetically multifunctional purifying material for determination of toxic highly chlorinated polychlorinated biphenyls at trace levels in soil samples

In this study, we developed a magnetically multifunctional purifying material for efficient removal of matrix interferences, especially certain organochlorine pesticide (DDT, DDE, and DDD), during the determination of toxic highly chlorinated polychlorinated biphenyls (PCBs) at trace levels in soil samples. The multifunctional adsorbent (CMCD-NH2-MNPs) was prepared by grafting carboxymethyl-β-cyclodextrin on the surface of amino-functionalized magnetite (Fe3O4) nanoparticles. CMCD-NH2-MNPs has stronger host–guest complexation with DDT, DDE, and DDD, but the same adsorbent shows weaker adsorption ability toward highly chlorinated PCBs (from tetra- to octa-chlorinated PCBs) owing to their steric hindrance effect. Based on this principle, a simple and rapid gas chromatography–mass spectrometry (GC–MS) method was developed for six indicator PCBs (PCB28, PCB52, PCB101, PCB138, PCB153, and PCB180) in soil. Comparative studies were conducted to determine the clean-up efficiency of the following three techniques: (i) Oasis-HLB, (ii) multi-layer silica column, and (iii) dSPE employing CMCD-NH2-MNPs. The results indicate that CMCD-NH2-MNPs as the purification material can easily and effectively remove DDT, DDE, and DDD in soil samples within a short duration of time. The recoveries for highly chlorinated PCBs were in the range of 85.4–102.2%, with RSDs varying between1.0 and 6.5%. The proposed method was verified as one of the most effective clean-up procedures for the analysis of highly chlorinated PCBs in real soil samples

Nano- TiO2/Nd Deposited on -Fe2O3 as a Magnetically Separable Photocatalyst

TiO2/Magnetit and TiO2/Nd/Magnetit were prepared and used for photocatalytic decomposition of the methylorange as a pollutant. TiO2 and TiO2/Nd were prepared by sol gel method and were characterized using XRD, FT IR and TEM. The prepared catalysts were deposited on magnetite surface to have a catalyst with magnetite core. So the catalyst can be separated easily from the waste solution by a magnet. Comparing the photocatalytic activity of TiO2/Magnetit and TiO2/Nd/Magnetit showed that doping the TiO2 by Nd increases the catalytic activity. Acidity of the waste has also promising effect on catalytic activity and the time needed for methylorange decomposition was decreased in low pHs. Complete decomposition of the methylorange was confirmed by LC MS.

Adsorption of Ni, Pd, Pt, Cu, Ag and Au on the Fe3O4(111) surface

The interaction of Group 10 and 11 transition metals with the magnetite (111) surface has been investigated using the GGA+U density functional theory and periodic slab surface models. It was found that these transition metals adsorb stronger on an oxygen-terminated magnetite (111) surface than on an iron-terminated surface. On an oxygen-terminated surface, the adsorption strength is in the order of Ni>Pt~Cu>Pd>Ag~Au. In contrast, the order on an iron-terminated surface is Ni>Pt~Cu>Au>Pd~Ag. The adsorption strength was found to correlate well with the average lengths of metal–oxygen bonds. The magnetite (111) surfaces largely modify the electronic structures of the transition metals. Compared to their density of states in bulk structures, the atomically adsorbed transition metals have narrower d bands, and their d-band centers are closer to the Fermi levels. This implies the higher activities of the atomically adsorbed transition metals.

ChemInform Abstract: Palladium on Magnetite: Magnetically Recoverable Catalyst for Selective Hydrogenation of Acetylenic to Olefinic Compounds.

Abstract Palladium on carbon (Pd/C) is the most widely available heterogeneous hydrogenation catalyst both in academia and industry, however catalyst selectivity is poor and product purification and catalyst recycling can be difficult. Here we explored magnetite (Fe3O4) as a catalyst support for palladium because of its interesting magnetic properties. Magnetite nanoparticles were chemically modified with N- and S-donor groups by alkoxyorganosilane grafting and they were used as support for the preparation of magnetically recoverable Pd catalysts. We investigated the influence of different functional groups grafted on the surfaces of magnetite on the catalytic properties of palladium with special attention on the hydrogenation of alkyne and alkene groups. The discrimination between carbon–carbon triple and double bonds is a very important feature of those catalysts and was also observed in competitive experiments containing alkyne–alkene mixtures. No hydrogenation of olefinic bonds was observed as far as an acetylenic compound is present. Even though the hydrogenation of pure olefins occurs with reaction rates comparable with Pd/C, the commercial catalyst deactivates upon recycle and our catalyst is active for several successive reactions.

Hydrophobicity of Minerals Determined by Atomic Force Microscopy – A Tool for Flotation Research

AbstractThe mineral separation process flotation is fundamentally relying on hydrophobic interactions, which are still not entirely understood and heavily discussed in literature. Here, various possibilities to determine hydrophobic properties of mineral surfaces in water using the concept of colloidal probe atomic force microscopy are introduced. The method is based on the accepted theories of the hydrophobic effect of hydrophobic surfaces in water. Additionally, the hydrophobic parameters are correlated with microflotation experiments for magnetite and quartz surfaces.

The distinct effects of Mn substitution on the reactivity of magnetite in heterogeneous Fenton reaction and Pb(II) adsorption

In this study, a series of Mn substituted magnetites were synthesized and used in catalyzing the heterogeneous Fenton degradation of acid orange II and Pb(II) adsorption, in order to investigate the effect of Mn substitution on the reactivity of magnetite. The valence and local environment of both Fe and Mn in the spinel structure of magnetite were investigated by X-ray absorption fine structure (XAFS) spectroscopy. The incorporation of Mn did not change the valence and local structure of Fe in the synthetic magnetite, while Mn was in the valences of +2 and +3. The Mn distribution on the octahedral sites of magnetite surface increased with the increase in Mn content. The Mn introduction led to an improvement of catalytic activity of magnetite. The sample with the minimum Mn content displayed the best efficiency in OH production and the degradation of acid orange II, while the other substituted samples did not show obvious difference in their catalytic performance. The adsorption capacity of magnetite samples toward Pb(II) gradually increased with the increase in Mn content. The above influences of Mn substitution on the reactivity of magnetite were discussed in views of the variations in microstructural environment and physicochemical properties.

Photo-Fenton oxidation of phenol with magnetite as iron source

In this work, magnetite-catalyzed Fenton reaction was investigated under UVA irradiation for the degradation of phenol as model compound. Four kinds of magnetite were used having different particle size, surface area and FeII content. Different kinetic behaviors were observed, thereby underscoring the strong implications of surface and chemical properties of magnetite. The size and surface area of the particles seemed to be less important, while the FeII/FeIII ratio played some role. Despite the link between magnetite reactivity and its structural FeII content, light-induced reduction of FeIII to FeII was found necessary to promote the Fenton-based reactions. As surface FeII may be oxidized or otherwise unavailable, initial photoactivation may be needed to trigger the Fenton reactivity. Two major driving forces were highlighted that account for the photoactivity of magnetite at pH 3: (i) the formation of intermediates such as hydroquinone that are able to reduce FeIII to FeII, and (ii) the accumulation of dissolved Fe due to magnetite dissolution, both in dark and under irradiation. Very interestingly, the photo-Fenton degradation of phenol was also observed under neutral conditions. In this case, for two out of four samples, the degradation rates were quite near those found at pH 3, which is usually reported as the optimum pH value of the process. The magnetite ability to promote photo-Fenton reactions even under circumneutral pH conditions, the limited iron leaching and its easy magnetic separation makes magnetite a promising catalyst in wastewater treatment applications.

Size control in the formation of magnetite nanoparticles in the presence of citrate ions

A one-pot synthesis method for the controllable growth of magnetite nanoparticles directly during the process of co-precipitation using citrate ions was developed. The effects of the concentration of citrate ions and the solution pH on the characteristics of magnetite particles with sizes in the range of 4–10 nm synthesized by the method of co-precipitation were studied. The results showed that the specified concentration of citrate ions allowed the preparation of magnetite particles with a definite size that exhibited superparamagnetic behaviour in a particular temperature range. As the concentration ratio of citrate to iron ions was increased from 0 to 0.11, the average size of the prepared magnetite particles decreased from 10.5 to 4.4 nm. As a result, the superparamagnetic blocking temperature decreased from 300 to 20 K, the saturation magnetisation decreased from 50 to 20 emu g−1, and the average magnetic moment decreased from 8000 μB to 340 μB (at T = 300 K).The obtained experimental data proved that the size effects of the magnetite nanoparticles can be attributed to the capping of the magnetite surface by adsorbed citrate ions. Thus, the suggested approach allows magnetite nanoparticles to be prepared with an optimum particle size around superparamagnetic threshold that prevents their irreversible agglomeration and simultaneously allows them to be removed from a solution at an acceptable rate.

Surface Complexation of Oxytetracycline by Magnetite: Effect of Solution Properties

Few studies have reported on the sorptive interactions of oxytetracycline (OTC), a veterinary antibiotic frequently detected in wastewater, surface water, and soils, with common Fe oxide minerals. The primary objective of this study was to investigate the sorption behavior of OTC on magnetite (Fe3O4) as a function of different solution properties such as pH, ionic strength, and initial OTC concentration. Results indicated that sorption of OTC by magnetite was rapid and complete within 24 h. The effect of ionic strength on sorption was negligible at low OTC surface coverage. The sorption envelope indicated that with increasing pH, OTC sorption on Fe3O4 decreased. Surface complexation modeling of magnetite–OTC interactions suggested the interactions of divalent anionic species of OTC with the magnetite surface. Four possible surface complexation reactions were postulated to explain the pH dependence of OTC sorption, indicating a rather complex potential sorption mechanism. Our results suggest that magnetite has the capability of immobilizing OTC in the environment, which may be of use to scientists in predicting the fate of OTC in Fe‐oxide‐rich soil.