Tailoring size and structural distortion of Fe3O4 nanoparticles for the purification of contaminated water

Fe₃O₄ magnetic nanoparticles with different particle sizes were synthesized using two methods, i.e., a co-precipitation process and a polyol process, respectively. The atomic pair distribution analyses from the high-energy X-ray scattering data and TEM observations show that the two kinds of nanoparticles have different sizes and structural distortions. An average particle size of 6–8 nm with a narrow size distribution was observed for the nanoparticles prepared with the co-precipitation method. Magnetic measurements show that those particles are in ferromagnetic state with a saturation magnetization of 74.3 emu g⁻¹. For the particles synthesized with the polyol process, a mean diameter of 18–35 nm was observed with a saturation magnetization of 78.2 emu g⁻¹. Although both kinds of nanoparticles are well crystallized, an obviously higher structural distortion is evidenced for the co-precipitation processed nanoparticles. The synthesized Fe₃O₄ particles with different mean particle size were used for treating the wastewater contaminated with the metal ions, such as Ni(II), Cu(II), Cd(II) and Cr(VI). It is found that the adsorption capacity of Fe₃O₄ particles increased with decreasing the particle size or increasing the surface area. While the particle size was decreased to 8 nm, the Fe₃O₄ particles can absorb almost all of the above-mentioned metal ions in the contaminated water with the adsorption capacity of 34.93 mg/g, which is ∼7 times higher than that using the coarse particles. We attribute the extremely high adsorption capacity to the highly-distorted surface.     

Optimum conditions for lipase immobilization on chitosan-coated Fe3O4 nanoparticles

Magnetic Fe₃O₄-chitosan nanoparticles are prepared by the coagulation of an aqueous solution of chitosan with Fe₃O₄ nanoparticles. The characterization of Fe₃O₄-chitosan is analyzed by FTIR, FESEM, and SQUID magnetometry. The Fe₃O₄-chitosan nanoparticles are used for the covalent immobilization of lipase from Candida rugosa using N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) as coupling agents. The response surface methodology (RSM) was employed to search the optimal immobilization conditions and understand the significance of the factors affecting the immobilized lipase activity. Based on the ridge max analysis, the optimum immobilization conditions were immobilization time 2.14 h, pH 6.37, and enzyme/support ratio 0.73 (w/w); the highest activity obtained was 20 U/g Fe₃O₄-chitosan. After twenty repeated uses, the immobilized lipase retains over 83% of its original activity. The immobilized lipase shows better operational stability, including wider thermal and pH ranges, and remains stable after 13 days of storage at 25 °C.     

A seven-coordinate Fe compound: [Fe{O(CH2CO2)2}(H2O)2(NO3)]. Preparation, structure and magnetic properties

A seven-coordinate Fe^III complex, [Fe(oda)(H₂O)₂(NO₃)], was obtained after dissolving Fe(NO₃)₃ · 9H₂O in an aqueous solution of oxydiacetic acid (H₂oda) at room temperature. In the solid state, the Fe^III center adopts a pentagonal bipyramid geometry with an {FeO₇} core formed by a tridentate oda²⁻ and a bidentate in the equatorial plane, and two axial water molecules. Magnetic measurements and EPR spectra revealed the presence of S = 5/2 Fe^III centers with rhombic zero field splitting parameters (D = 0.81 cm⁻¹, E/D = 0.33 ). Weak antiferromagnetic interactions with J ≈ −0.06 cm⁻¹ operating between neighboring Fe ions connected through Fe-O-C-O?H-O-Fe paths are estimated using the molecular field approximation.     

Searching for switchable molecular conductors: Salts of [M(dcbdt)2] (M = Ni, Au) anions with [Fe(sal2-trien)] and [Fe(phen)3]

Salts of [Fe^III(sal₂-trien)]⁺and [Fe^II(phen)₃]²⁺ cations and M[(dcbdt)₂]⁻ anions with M = Ni and Au (dcbdt = dicyanobenzenedithiolate) with formula [Fe(sal₂-trien)] [M(dcbdt)₂] and [Fe(phen)₃] [M(dcbdt)₂]₂ were obtained and characterized by single X-ray diffraction and magnetic measurements. None of these salts shows a clear spin crossover behaviour and their magnetic properties are due essentially to the cations in a high spin S = 5/2 and low spin states for the Fe^III and Fe^II salts respectively. The magnetic Ni sublattices in both compounds appear to have a negligible direct contribution to the magnetization but enhance the AF interactions in the cation sublattice.     

A new example of a tetranuclear iron(III) cluster containing the [Fe4O2] core: preparation, X-ray crystal structure, magnetochemistry and Mössbauer study of [Fe4O2(O2CMe)6(N3)2(phen)2]

Two synthetic procedures have been employed that allow access to the new tetranuclear cluster [Fe₄O₂(O₂CMe)₆(N₃)₂(phen)₂] (1), where phen is 1,10-phenanthroline. Complex 1 · 3MeCN displays an unusual structural asymmetry (observed for the second time) in its [Fe₄O₂]⁸⁺ core that can be considered as a hybrid of the bent (butterfly) and planar dispositions of four metal ions seen previously in such compounds with transition metals. Complex 1 has been characterized by variable-temperature magnetic susceptibility studies, and by IR and variable-temperature ⁵⁷Fe Mössbauer spectroscopies. Magnetochemical data reveal a diamagnetic ground state (S=0) with antiferromagnetic body-body and body-wingtip interactions between the iron(III) ions of the butterfly core (J_bb=−11 cm⁻¹, J_wb=−70 cm⁻¹). Magnetochemical and Mössbauer studies on 1 show that its structural asymmetry has practically no influence on these properties compared with the more symmetric types.     

The development of an electrochemical immunosensor using a thiol aromatic aldehyde and PAMAM-functionalized Fe3O4@Au nanoparticles

In this work, a novel thiol aromatic aldehyde was synthesized. It can be used as a substrate to directly immobilize antibodies on a gold electrode, for which no additional chemical cross-linker is required. It was also applied as a linker to prepare Fe₃O₄@Au/PAMAM/Ab₂–horseradish peroxidase bioconjugates, which introduced multiple enzymes onto a sensing interface owing to the high surface-to-volume ratio of Fe₃O₄@Au nanoparticles and many functional groups of the poly(amidoamine) dendrimer (PAMAM). The introduced multiple enzymes greatly improved the detection signal. Under optimal conditions, the proposed electrochemical immunosensor exhibited desirable performance for detection of IgG in the range 0.005–50 ng ml⁻¹ with a detection limit of 3 pg ml⁻¹ based on a signal-to-noise ratio of 3. It has great potential application in the area of clinical analysis.     

The kinetics of the complex formation between iron(III)-ethylenediaminetetraacetate and hydrogen peroxide in aqueous solution

The kinetics of the formation of the purple complex [Fe^III(EDTA)O₂]³⁻, between Fe^III-EDTA and hydrogen peroxide was studied as a function of pH (8.22-11.44) and temperature (10-40 °C) in aqueous solutions using a stopped-flow method. The reaction was first-order with respect to both reactants. The observed second-order rate constants decrease with an increase in pH and appear to be related to deprotonation of Fe^III-EDTA ([Fe(EDTA)H₂O]⁻ ⇔ Fe(EDTA)OH]²⁻ + H⁺). The rate law for the formation of the complex was found to be d[Fe^IIIEDTAO₂]³⁻/dt=[(k₄[H⁺]/([H⁺] + K₁)][Fe^III-EDTA][H₂O₂], where k₄=8.15±0.05×10⁴ M⁻¹ s⁻¹ and pK₁=7.3. The steps involved in the formation of [Fe(EDTA)O₂]³⁻ are briefly discussed.     

Synthesis and characterization of [Fe(III)(qsal)2][M(III)(pds)2] (M = Cu, Au)

Salts of the Fe(III) spin crossover cation [Fe^III(qsal)₂]⁺ (qsalH = N-(8-quinolyl)salicylaldimine) and monoanions [M^III(pds)₂]⁻ (M = Cu, Au; pds = pirazine-2,3-diselenolate) with formula [Fe^III(qsal)₂][M^III(pds)₂] were prepared and characterized by single crystal X-ray diffraction and magnetic measurements. These two salts present magnetic properties essentially due to the Fe^III centres in the high-spin state (S = 5/2), and do not have any spin transition.     

Synthesis, structure and magnetic properties of an oxo-bridged dinuclear iron(III) complex [(TPyA)FFeOFeF(TPyA)](BF4)2 · 0.5MeOH (TPyA = tris(2-pyridylmethyl)amine) containing the FFeOFeF linkage

The reaction of [Fe^II(H₂O)₆](BF₄)₂ with tris(2-pyridylmethyl)amine (TPyA) and triethylamine in methanol under aerobic conditions forms [(TPyA)FFe^IIIOFe^IIIF(TPyA)](BF₄)₂ · 0.5MeOH (1), in which each Fe(III) ion is coordinated to a TPyA and an F⁻ ion as well as an oxo ion (O²⁻) linking two Fe(III) ions. 1 has offset face-to-face π-π interactions between the dimers, and possesses a supramolecular network structure. The magnetic susceptibility of 1 can be fit with g = 2.0, J/k_B = − 153 K (106 cm⁻¹), and θ = − 0.3 K [H = − 2JS_a · S_b]. These indicate that very strong antiferromagnetic interactions occur via the oxo bridge within the Fe(III) dimer and weak antiferromagnetic interactions between the dimers.     

Electrospinning of Cross-Linked Magnetic Chitosan Nanofibers for Protein Release

A poly(vinylalcohol) (PVA) electrospun/magnetic/chitosan nanocomposite fibrous cross-linked network was fabricated using in situ cross-linking electrospinning technique and used for bovine serum albumin (BSA) loading and release applications. Sodium tripolyphosphate (TPP) and glutaraldehyde (GA) were used as cross-linkers which modified magnetic-Fe₃O₄ chitosan as Fe₃O_4/CS/TPP and Fe₃O_4/CS/GA, respectively. BSA was used as a model protein drugs which was encapsulated to form Fe₃O₄/CS/TPP/BSA and Fe₃O₄/CS/GA/BSA nanoparticles. The composites were electrospun with PVA to form nanofibers. Nanofibers were characterized by field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR). The characterization results suggest that Fe₃O₄ nanoparticles with average size of 45 nm were successfully bound on the surface of chitosan. The cross-linked nanofibers were found to contain uniformly dispersed Fe₃O₄ nanoparticles. The size and morphology of the nanofibers network was controlled by varying the cross-linker type. FTIR data show that these two polymers have intermolecular interactions. The sample with TPP cross-linker showed an enhancement of the controlled release properties of BSA during 30-h experimental investigation.

Graphical Abstract

Open in a separate windowᅟKEY WORDS: cross-linker, electrospun, magnetite, mano-composite, protein loading     

Binding and direct electrochemistry of OmcA, an outer-membrane cytochrome from an iron reducing bacterium, with oxide electrodes: A candidate biofuel cell system

Dissimilatory iron-reducing bacteria transfer electrons to solid ferric respiratory electron acceptors. Outer-membrane cytochromes expressed by these organisms are of interest in both microbial fuel cells and biofuel cells. We use optical waveguide lightmode spectroscopy (OWLS) to show that OmcA, an 85 kDa decaheme outer-membrane c-type cytochrome from Shewanella oneidensis MR-1, adsorbs to isostructural Al₂O₃ and Fe₂O₃ in similar amounts. Adsorption is ionic-strength and pH dependent (peak adsorption at pH 6.5-7.0). The thickness of the OmcA layer on Al₂O₃ at pH 7.0 [5.8 ± 1.1 (2σ) nm] from OWLS is similar, within error, to that observed using atomic force microscopy (4.8 ± 2 nm). The highest adsorption density observed was 334 ng cm⁻² (2.4 × 10¹² molecules cm⁻²), corresponding to a monolayer of 9.9 nm diameter spheres or submonolayer coverage by smaller molecules. Direct electrochemistry of OmcA on Fe₂O₃ electrodes was observed using cyclic voltammetry, with cathodic peak potentials of −380 to −320 mV versus Ag/AgCl. Variations in the cathodic peak positions are speculatively attributed to redox-linked conformation change or changes in molecular orientation. OmcA can exchange electrons with ITO electrodes at higher current densities than with Fe₂O₃. Overall, OmcA can bind to and exchange electrons with several oxides, and thus its utility in fuel cells is not restricted to Fe₂O₃.     

Preparation, crystal structure and magnetic property of a binuclear oxalate-bridged iron(III) compound: Fe2(C2O4)Cl4(DMF)4 (DMF = dimethylformamide)

An oxalato-bridged binuclear iron(III) compound, Fe₂(C₂O₄)Cl₄(DMF)₄ (DMF = dimethylformamide), was obtained by electrocrystallization for three weeks at 3.4 V and it displays a strong antiferromagnetic interaction of J = −6.74(4) cm⁻¹.     

Interactions of tertiary phosphines with p-benzoquinones; X-ray structures of [HO(CH2)3]3PC6H2(O)(OH)(MeO) and Ph3PC6H3(O)(OH)

Phosphonium zwitterions of a known type were obtained in high yield via a 1:1 reaction of p-benzoquinone or methoxy-p-benzoquinone with the tertiary phosphines R₃P [R = (CH₂)₃OH, Ph, Et, Me] and Ph₂MeP, in acetone or benzene at room temperature. In all cases, attack of the P-atom occurs at a C-atom rather than at an O-atom. The products were characterized to various degrees by elemental analysis, ³¹P{¹H}, ¹H and ¹³C NMR spectroscopies, and mass spectrometry, and two of the zwitterions, the new [HO(CH₂)₃]₃P⁺C₆H₂(O⁻)(OH)(MeO) and the known Ph₃P⁺C₆H₃(O⁻)(OH), were structurally characterized by X-ray analysis. The PEt₃ reaction also produces small amounts of the ‘dimeric’, μ-oxo co-product Et₃P⁺C₆H₂(O⁻)(OH)-O-C₆H₃(O⁻)P⁺Et₃ that is tentatively characterized by 1D- and 2D-NMR data. 2,5-Di-tert-butyl- and 2,3,5,6-tetramethyl-p-benzoquinone do not react with [HO(CH₂)₃]₃P under the conditions noted above. Heating D₂O solutions of the water-soluble zwitterions R₃P⁺C₆H₃(O⁻)(OH) [R = (CH₂)₃OH, Et] at 90 °C for 72 h leads to complete H/D exchange of the H-atom in the position ortho to the phosphonium center.     

Single molecule magnet: Heterodinuclear cyano-bridged cubic cluster [(Tp)8Fe4Ni4(CN)12] (Tp = hydrotris(1-pyrazolyl)borate)

The octanuclear cyano-bridged cluster [(Tp)₈Fe₄Ni₄(CN)₁₂] · H₂O · 24CH₃CN (1) (Tp = hydrotris(1-pyrazolyl)borate) showing magnetic properties of single-molecule magnet has been synthesized by reaction of [fac-Fe(Tp)(CN)₃]⁻ with {(Tp)Ni(NO₃)} species formed from an equimolar reaction mixture of Ni(NO₃)₂ · 6H₂O and KTp in MeCN. The X-ray analysis of 1 shows molecular cube structure in which Fe^III and Ni^II ions reside in alternate corners. The average intramolecular Fe?Ni distance is 5.124 Å. Out-of-phase ac susceptibility and reduce magnetization measurements show that 1 is a single molecule magnet with ground spin state S = 6 and spin reversal energy barrier U = 14 K. Magnetic hysteresis loops were also observed by applying fast sweeping field.     

Dinitrosyl iron complexes [E5Fe(NO)2] (E = S, Se): A precursor of Roussin’s black salt [Fe4E3(NO)7]

[PPN][Se₅Fe(NO)₂] (1) and [K-18-crown-6-ether][S₅Fe(NO)₂] (2′) were synthesized and characterized by IR, UV-Vis, EPR spectroscopy, magnetic susceptibility, and X-ray structure. [PPN][Se₅Fe(NO)₂] easily undergoes ligand exchange with S₈ and (RS)₂ (R = C₇H₄SN (5), o-C₆H₄NHCOCH₃ (6), C₄H₃S (7)) to form [PPN][S₅Fe(NO)₂] and [PPN][(SR)₂Fe(NO)₂]. The reaction displays that [E₅Fe(NO)₂]⁻ (E = Se (3), S (4)) facilely converts to [Fe₄E₃(NO)₇]⁻ by adding acid HBF₄ or oxidant [Cp₂Fe][BF₄] in THF, respectively. Obviously, complexes 1 and 2′ serve as the precursors of the Roussin’s black salts 3 and 4. The electronic structure of {Fe(NO)₂}⁹ core of [Se₅Fe(NO)₂]⁻ is best described as a dynamic resonance hybrid of {Fe⁺¹(NO)₂}⁹ and {Fe⁻¹(NO⁺)₂}⁹ modulated by the coordinated ligands. The findings, EPR signal of g = 2.064 for 1 at 298 K, implicate that the low-molecular-weight DNICs and protein-bound DNICs may not exist with selenocysteine residues of proteins as ligands, since the existence of protein-bound DNICs and low-molecular-weight DNICs in vitro has been characterized with a characteristic EPR signal at g = 2.03. In addition, complex 2′ treated human erythroleukemia K562 cancer cells exposed to UV-A light greatly decreased the percentage survival of the cell cultures.     

A cyano-bridged FeRe(CN)2 cluster incorporating two high-magnetic anisotropy building units

The pentagonal bipyramidal high-spin iron(II) complex, [(TPA^2C(O)NHtBu)Fe(CF₃SO₃)]⁺, is shown to exhibit a high-anisotropy ground state, with fits to dc magnetization data providing an axial zero-field splitting parameter of D = − 7.9 cm⁻¹. The utility of this compound as a building unit is demonstrated, as its reaction with [ReCl₄(CN)₂]²⁻ affords the cyano-bridged dinuclear cluster (TPA^2C(O)NHtBu)FeReCl₄(CN)₂. dc magnetic susceptibility measurements reveal intracluster ferromagnetic exchange interactions between Fe^II and Re^IV centers, with J = +3.0 cm⁻¹, giving rise to a spin ground state of S = 7/2. Moreover, fits to dc magnetization data obtained for the FeRe cluster show the presence of strong axial anisotropy, with D = −2.3 cm⁻¹. Finally, variable-frequency ac susceptibility measurements reveal the onset of slow magnetic relaxation at low temperature, suggesting that the FeRe cluster is a single-molecule magnet.     

Study of the magnetic properties of the mixed oxide Fe2O3-Fe2(MoO4)3 in the temperature range 2-300 K with different compositions

Powdered Fe₂O₃-Fe₂(MoO₄)₃ with different amounts of iron and molybdate precursors was prepared by a solvothermal route, followed by a supercritical drying and oxidation at 500 °C. The possibility to arrange Fe or Mo precursors in excess into a methanol solution makes one accessible to the preparation of iron(III) molybdate samples with different composition. The structural parameters and relationship between different phases in the composition are obtained from Rietveld profile refinement. Our intention was to modify the magnetic properties of Fe₂(MoO₄)₃ by adding the crystalline phase of Fe₂O₃, which carries a Fe-O magnetic component. A possible contribution to the magnetization and the magnetic susceptibility by this magnetic component is analyzed in the temperature range 2-300 K. The observed higher magnetic susceptibilities are compared to those reported.     

A hexanuclear iron(III) complex [Fe6O2(OH)2(PhCOO)10(hedmp)2]·3CH3CN assembled from 2-hydroxyethyl-3,5-dimethyl pyrazole

In order to assemble polynuclear iron(III) complexes, the coordination chemistry of the 2-hydroxyethyl-3,5-dimethylpyrazole (hedmp-H) ligand has been investigated. Reaction of hedmp-H with trinuclear iron carboxylate precursor [Fe₃O(PhCOO)₆(H₂O)₃]Cl in acetonitrile yielded the hexanuclear Fe(III) complex [Fe₆O₂(OH)₂(PhCOO)₁₀(hedmp)₂]·3CH₃CN (1). This aggregate has been characterized by employing various analytical techniques, spectroscopic studies and single crystal X-ray diffraction. Detailed magnetic susceptibility measurements revealed that 1 displays an S_T = 5 ground state.     

A non-linear (2,2,2) alkoxo-bridging in a Fe4O6 core potentially relevant to iron-tunicates

The tridentate unsymmetrical ligand N-(2-hydroxymethylphenyl)salicylideneimine H₂L, derived from salicylaldehyde and 2-aminobenzylalcohol, with [ONO] donor atoms yields [L₂Fe^III₂Cl₂] (1) and [L₆Fe^III₄] (2) complexes containing alkoxide bridges, which have been structurally characterized by X-ray diffraction. In complex 1, each ferric ion is five-coordinated with a distorted square-pyramidal geometry, the basal planes of which are symmetrically bridged by two alkoxide oxygen atoms. Analysis of the susceptibility data reveals antiferromagnetic interactions with an exchange parameter J = −15.8 cm⁻¹ between the high-spin d⁵ ferric centers. The structure of 2 can be considered as “linear (2,2,2)” to specify the number of enolate oxygen atoms between four iron atoms. Variable-temperature magnetic susceptibility data are fitted to a “three-J” model, yielding pairwise antiferromagnetic exchange interactions, J₁₂ = J₃₄ = −13.4 cm⁻¹, J₁₃ = J₂₄ = −7.1 cm⁻¹, J₂₃ = −14.9 cm⁻¹, between the neighboring ferric centers; J₁₄ is assumed to be negligible. Complex 2 has a complicated low-lying magnetic structure with a non-diamagnetic ground state. In addition, the Fe-O-Fe angles at the bridging ligands seem to be determinant for the strength of the antiferromagnetic interactions.     

Rb2[B12(OH)12]·2H2O and Rb2[B12(OH)12]·2H2O2: Hydrate and perhydrolate of rubidium dodecahydroxo-closo-dodecaborate

The orthorhombically crystallizing salts Rb₂[B₁₂(OH)₁₂]·2H₂O (a = 1576.81(9), b = 813.08(5), c = 1245.32(7) pm) and Rb₂[B₁₂(OH)₁₂]·2H₂O₂ (a = 1616.54(9), b = 814.29(5), c = 1260.12(7) pm) could be prepared from Rb₂[B₁₂H₁₂] and hydrogen peroxide. Both crystal structures were determined by X-ray single crystal diffraction and refined in the space group Cmce. They are not isostructural to the other compounds containing icosahedral dodecahydroxo-closo-dodecaborate dianions [B₁₂(OH)₁₂]²⁻ and potassium, rubidium or cesium cations already known to literature, but both title compounds crystallize quasi-isotypically exhibiting Rb⁺ cations in 10-fold oxygen coordination. The hydrogen peroxide adduct (Rb₂[B₁₂(OH)₁₂]·2H₂O₂) is explosive on shock and heat, while the hydrate (Rb₂[B₁₂(OH)₁₂]·2H₂O) is not.