Current trends in the use of zero-valent iron (Fe0) for degradation of pharmaceuticals present in different water matrices

Zero-valent iron (Fe⁰) has recently been proposed as a potential candidate for the degradation of pharmaceuticals, because Fe⁰ can release dissolved iron species, activate molecular oxygen, and react with oxidant species. Additionally, due to its small particle size and large surface area, this catalyst can provide better degradation results, compared to traditional processes. This work focuses on the elimination of pharmaceuticals present in different water matrices, considering the potential harm that these substances can cause in the environment. The mechanisms of pharmaceutical removal using Fe⁰ particles include reduction, adsorption, precipitation, and oxidation processes. Most studies have focused on oxidation processes in the presence of Fe⁰ and radicals derived from oxidants such as hydrogen peroxide (H₂O₂), ozone (O₃), peroxysulfate (SO₅²⁻), peroxodisulfate (S₂O₈²⁻), and oxygen (O₂). Most of the results have shown that high percentages of pharmaceuticals can be removed, degraded, and mineralized. The mechanisms of oxidation and the parameters that influence the degradation of pharmaceuticals, as well as the possible degradation pathways, are discussed here. This review provides information on trends of different processes that use Fe⁰, considering aspects such as particle size, type of matrix, the pharmaceuticals studied, and the results obtained that can improve understanding of new advances in the field of advanced oxidation processes (AOPs) for the degradation and elimination of pharmaceuticals.     

Hydrophilic Fe3O4 nanoparticles prepared by ferrocene as high‐efficiency heterogeneous Fenton catalyst for the degradation of methyl orange

Hydrophilic Fe₃O₄ nanoparticles were prepared with ferrocene as an iron source via the thermal decomposition method and their catalytic response towards methyl orange was investigated. The effects of the pH, temperature, H₂O₂ dosage, catalyst dosage and initial dye concentration on the degradation of methyl orange were researched in detail. Furthermore, the stability of the catalyst was evaluated by measuring the degradation rate in eight successive cycles. The study demonstrates that methyl orange can be completely degraded i.e., a 99% degratation rate was obtained within 3 min. This excellent catalytic activity is attributed to the small size and good dispersibility of the nanoparticles, which stimulate the rapid and massive generation of reactive oxygen species in the heterogeneous Fenton reaction. In addition, the magnetic separation of the catalyst offers great prospects for fast and economical decontamination of dye polluted water.     

Facile preparation of Fe-Y catalyst under water-free conditions for selective catalytic reduction of NO x by ammonia

A series of Fe-Y zeolite catalysts with different Fe loading were prepared by ferrocene sublimation under solvent and water-free conditions.The dispersion,structure and morphology of the iron species on the Fe-Y catalysts were characterized by XRD,TEM and UV-Vis.The catalytic activities of Fe-Y samples were measured in selective catalytic reduction of NO with ammonia(NH3-SCR).The results showed that the iron species on the HY zeolite support were mainly made up of isolated Fe3+ions,Fex Oy oligomers and a little amount of<3 nm spherical Fe2O3particles.Isolated Fe3+ions are predominating among all the Fe-Y catalysts.The sum of isolated Fe3+ions and Fex Oy oligomers took up more than 90%percent of total iron species on the Fe-Y till 10.0 wt%loading of Fe.     

Low‐Spin Pseudotetrahedral Iron(I) Sites in Fe2(μ‐S) Complexes

Fe^I centers in iron–sulfide complexes have little precedent in synthetic chemistry despite a growing interest in the possible role of unusually low valent iron in metalloenzymes that feature iron–sulfur clusters. A series of three diiron [(L₃Fe)₂(μ‐S)] complexes that were isolated and characterized in the low‐valent oxidation states Fe^II? S? Fe^II, Fe^II? S? Fe^I, and Fe^I? S? Fe^I is described. This family of iron sulfides constitutes a unique redox series comprising three nearly isostructural but electronically distinct Fe₂(μ‐S) species. Combined structural, magnetic, and spectroscopic studies provided strong evidence that the pseudotetrahedral iron centers undergo a transition to low‐spin S=1/2 states upon reduction from Fe^II to Fe^I. The possibility of accessing low‐spin, pseudotetrahedral Fe^I sites compatible with S^2? as a ligand was previously unknown.     

Stabilization of Low‐Valent Iron(I) in a High‐Valent Vanadium(V) Oxide Cluster

Low‐valent iron centers are critical intermediates in chemical and bio‐chemical processes. Herein, we show the first example of a low‐valent Fe^I center stabilized in a high‐valent polyoxometalate framework. Electrochemical studies show that the Fe^III‐functionalized molecular vanadium(V) oxide (DMA)[Fe^IIIClV^V₁₂O₃₂Cl]³⁻ (DMA=dimethylammonium) features two well‐defined, reversible, iron‐based electrochemical reductions which cleanly yield the Fe^I species (DMA)[Fe^IClV^V₁₂O₃₂Cl]⁵⁻. Experimental and theoretical studies including electron paramagnetic resonance spectroscopy and density functional theory computations verify the formation of the Fe^I species. The study presents the first example for the seemingly paradoxical embedding of low‐valent metal species in high‐valent metal oxide anions and opens new avenues for reductive electron transfer catalysis by polyoxometalates.     

Computational Approaches for Redox Potentials of Iron(IV)-oxido Complexes

The potential of the redox couple Fe^IV=O / Fe^III–O is of interest for the reactivity of the high-valent nonheme iron oxidants in enzymes and bioinspired small molecule systems but, unfortunately, experimentally it so far is very poorly described. Discussed are three computational methods that are used in combination with available experimental data derived from titrations of Fe^IV=O species with ferrocene derivatives in dry acetonitrile, and from spectroelectrochemical titrations of Fe^III–OH complexes in wet acetonitrile, i.e. describing the Fe^IV=O / Fe^III–OH couple – both data sets are known to have some ambiguities. First, a DFT-based method is used to compute the E° values of 14 Fe^IV=O / Fe^III–O couples with an error margin of around 110 mV. A subset of four species of the original data set is used to evaluate a DLPNO-CCSD(T) based approach, and another subset of complexes, where the spectroelectrochemically determined Fe^IV=O / Fe^III–OH potentials are also known, are used for a Bordwell-Polanyi analysis, which also yield pK_a values. It is shown that the three approaches lead to a consistent picture but due to possible ambiguities with the experimental data, it currently is not possible to fully evaluate the accuracy of the used approaches.     

Oxidation triggers guest dissociation during reorganization of an FeII4L6 twisted parallelogram

A three-dimensional Fe^II₄L₆ parallelogram was prepared from ferrocene-containing ditopic ligands. The steric preference of the bulky ferrocene cores towards meridional vertex coordination brought about this new structure type, in which the ferrocene units adopt three distinct conformations. The structure possesses two distinct, bowl-like cavities that host anionic guests. Oxidation of the ferrocene Fe^II to ferrocenium Fe^III causes rotation of the ferrocene hinges, converting the structure to an Fe^II₁L₁⁺ species with release of anionic guests, even though the average charge per iron increases in a way that would ordinarily increase guest binding strength. The degrees of freedom exhibited by these new structures – derived from the different configurations of the three ligands surrounding a meridional Fe^II center and the rotation of ferrocene cores – thus underpin their ability to reconfigure and eject guests upon oxidation.

An oxidation-triggered twist in its ferrocene ligands causes an Fe₄L₆ parallelogram to release its guests and collapse into a high spin Fe₁L₁ structure.     

Synthesis and characterization of micron‐sized monodisperse superparamagnetic polymer particles with amino groups

Micron‐sized monodisperse superparamagnetic polyglycidyl methacrylate (PGMA) particles with functional amino groups were prepared by a process involving: (1) preparation of parent monodisperse PGMA particles by the dispersion polymerization method, (2) chemical modification of the PGMA particles with ethylenediamine (EDA) to yield amino groups, and (3) impregnation of iron ions (Fe²⁺ and Fe³⁺) inside the particles and subsequently precipitating them with ammonium hydroxide to form magnetite (Fe₃O₄) nanoparticles within the polymer particles. The resultant magnetic PGMA particles with amino groups were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X‐ray diffractometry (XRD), and vibrating sample magnetometry (VSM). SEM showed that the magnetic particles had an average size of 2.6 μm and were highly monodisperse. TEM demonstrated that the magnetite nanoparticles distributed evenly within the polymer particles. The existence of amino groups in the magnetic polymer particles was confirmed by FTIR. XRD indicated that the magnetic nanoparticles within the polymer were pure Fe₃O₄ with a spinel structure. VSM results showed that the magnetic polymer particles were superparamagnetic, and saturation magnetization was found to be 16.3 emu/g. The Fe₃O₄ content of the magnetic particles was 24.3% based on total weight. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3433–3439, 2005     

Magnetic poly(N‐propargylacrylamide) microspheres: Preparation by precipitation polymerization and use in model click reactions

Magnetic poly(N‐propargylacrylamide) (PPRAAm) microspheres were prepared by the precipitation polymerization of N‐propargylacrylamide (PRAAm) in a toluene/propan‐2‐ol medium in the presence of magnetic nanoparticles (oleic acid‐coated Fe₃O₄). The effects of several polymerization parameters, including the polarity of the medium, polymerization temperature, the concentration of monomer, and the amount of magnetite (Fe₃O₄) in the polymerization feed, were examined. The microspheres were characterized in terms of their morphology, size, particle‐size distribution, and iron content using transmission and scanning electron microscopies (TEM and SEM) and atomic absorption spectroscopy (AAS). A medium polarity was identified in which magnetic particles with a narrow size distribution were formed. As expected, oleic acid‐coated Fe₃O₄ nanoparticles contributed to the stabilization of the polymerized magnetic microspheres. Alkyne groups in magnetic PPRAAm microspheres were detected by infrared spectroscopy. Magnetic PPRAAm microspheres were successfully used as the anchor to enable a “click” reaction with an azido‐end‐functionalized model peptide (radiolabeled azidopentanoyl‐GGGRGDSGGGY(¹²⁵I)‐NH₂) and 4‐azidophenylalanine using a Cu(I)‐catalyzed 1,3‐dipolar azide‐alkyne cycloaddition reaction in water. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Magnetically loaded poly(methyl methacrylate-co-acrylic acid) nano particles

Magnetically loaded polymeric nano-particles carrying functional groups on their surface were prepared by a two-stage process. In the first stage, super-paramagnetic magnetite (Fe₃O₄) nano-particles were produced by a co-precipitation method from the aqueous solutions of FeCl₂·4H₂O and FeCl₃·6H₂O using a NaOH solution. The smallest size obtained was 40.9 nm with poly-dispersity index of 0.194 obtained by using a Zeta Sizer. The effects of Fe²⁺/Fe³⁺ molar ratio, stirring rate, temperature, base concentration, and pH on the particle size/size distribution and stability of the dispersions were examined. Increasing the relative concentration of Fe²⁺ ion and decreasing the stirring rate and pH increased the particle size, while the concentration of NaOH and temperature did not change the particle size significantly. Polymer coating was achieved by emulsion polymerization at high surfactant to monomer ratio of methyl methacrylate (MMA) and acrylic acid which were used as comonomers (comonomer ratio: 90/10 weight) with high surfactant to monomer ratio. The surfactant and initiator were SDS and KPS, respectively. Nano-particles in the range of 115 and 300 nm in diameter were produced depending on recipe. Increasing the Fe₃O₄/monomer and surfactant/monomer ratios, the KPS concentration caused a decrease in the average diameter. Magnetic properties of the nano-particles were obtained by electron spin resonance and vibrating-sample magnetometer. Most of the polymer-coated nano-particles exhibited super paramagnetic behavior.An erratum to this article can be found at     

Facile preparation of ferromagnetic alginate-g-poly(vinyl alcohol) microparticles

Alginate-g-poly(vinyl alcohol) was physically cross-linked with Fe(II) ion in a surfactant-free emulsion system to form microparticles via in situ precipitation. The microparticles were subjected to oxidation in aqueous of pH 13 at ambient temperature and transformed into magnetic ones within minutes. X-ray diffractometry showed that magnetic Fe₃O₄ was formed and it was further confirmed with a vibrating sample magnetometer measurement. Scanning electron microscopy examinations indicated that the iron oxide was well embedded into ferrous alginate and the size of particles was around 0.2-1.2 μm.     

Mössbauer studies of iron(III)-(indole-3-alkanoic acids) systems in frozen aqueous solutions

Summary This paper describes the M?ssbauer investigations of iron(III) salts in aqueous solutions in the presence of indole-3-alkanoic acid ligands. The measurements showed two parallel reactions between the ligands and ferric ions: a complex formation and a redox process. The oxidation process takes place in the ligands, and a part of Fe³⁺is reduced to Fe²⁺.     

Density functional based calculations for Fen (n⩽32)

We investigate magnetic and structural properties of iron clusters up to Fe₃₂, well extending into the size range accessible by experiment. A density-functional based tight-binding scheme fully incorporating the effects of spin polarisation and charge transfer in a self-consistent manner has been used. The potential hypersurfaces have been scanned by an unconstrained search using a genetic algorithm. Results for smaller clusters up to Fe₁₇ are validated against more sophisticated density functional theory calculations. Our magnetic moment data show a strong change around Fe₁₃ being unique in this size range. For the larger cluster sizes a smooth decrease of the clusters average spin magnetic moments is found in good agreement with experimental data.     

Synthesis and characterization of two binuclear iron(III) complexes of aminoethanol derivatives of aminophenol as models for non-heme iron enzymes active sites

Two aminoethanol derivatives of aminophenol ligands were synthesized and characterized by IR and ¹H NMR spectroscopies. The binuclear iron(III) complexes of these ligands have been prepared and characterized by IR, ¹H NMR and UV-Vis spectroscopic techniques, cyclic voltammetry, single crystal X-ray diffraction and magnetic susceptibility studies. X-ray analysis revealed binuclear complexes, Fe₂(L₂), in which Fe(III) centers are surrounded by two phenolate and hydroxyl oxygen atoms, and amine nitrogens of the ligands. The metal active sites of both complexes are held together by the two above mentioned hydroxyl bridges. Variable temperature magnetic susceptibility indicates antiferromagnetic coupling between the iron centers of both complexes. This exchange coupling is stronger for Fe₂(L^ae)₂, such that it shows a room temperature strong coupling between the two iron centers. The investigated complexes undergo irreversible electrochemical oxidation and reduction.     

Hydrothermal Synthesis,Crystal Structure Determination,and Magnetic Properties of a New Calcium Iron Iridium Hydrogarnet Ca3(Ir2–xFex)(FeO4)2–x(O4H4)1+x with 0 ≤ x ≤ 1

The new calcium iron iridium hydrogarnet Ca₃(Ir_2–xFe_x)(FeO₄)_2–x(H₄O₄)_1+x (0 ≤ x ≤ 1) was obtained by hydrothermal synthesis under strongly oxidizing alkaline conditions. The compound adopts a garnet‐like crystal structure and crystallizes in the acentric cubic space group I4 3d (no. 220) with a = 12.5396(6) Å determined at T = 100 K for a crystal with a refined composition Ca₃(Ir_1.4Fe_0.6)(FeO₄)_1.4(O₄H₄)_1.6. Iridium and iron statistically occupy the octahedrally coordinated metal position, the two crystallographically independent tetrahedral sites are partially occupied by iron. Hydroxide groups are found to cluster as hydrogarnet defects, i.e. partially substituting oxide anions around the empty tetrahedral metal sites. The presence of hydroxide ions was confirmed by infrared spectroscopy and the hydrogen content was quantified by carrier gas hot extraction; the overall composition was verified by energy dispersive X‐ray spectroscopy. The structure model is supported by ⁵⁷Fe‐Mössbauer spectroscopic data evidencing different Fe sites and a magnetic ordering of the octahedral iron sublattice at room temperature. The thermal decomposition proceeds via three steps of water loss and results in Ca₂Fe₂O₅, Fe₂O₃ and Ir. Mössbauer and magnetization data suggest magnetic order at ambient temperature with complex magnetic interactions.     

Synthesis and morphology of an iron oxide/polystyrene/poly(isopropylacrylamide‐co‐methacrylic acid) thermosensitive magnetic composite latex with potassium persulfate as the initiator

In this work, an iron oxide (Fe₃O₄)/polystyrene (PS)/poly(N‐isopropylacryl amide‐co‐methacrylic acid) [P(NIPAAM–MAA)] thermosensitive magnetic composite latex was synthesized by the method of two‐stage emulsion polymerization. The Fe₃O₄ particles were prepared by a traditional coprecipitation method and then surface‐treated with either a PAA oligomer or lauric acid to form a stable ferrofluid. The first stage for the synthesis of the thermosensitive magnetic composite latex was to synthesize PS in the presence of a ferrofluid by emulsion polymerization to form Fe₃O₄/PS composite latex particles. Following the first stage of reaction, the second stage of polymerization was carried out with N‐isopropylacryl amide and methacrylic acid as monomers and with Fe₃O₄/PS latex as seeds. The Fe₃O₄/PS/[P(NIPAAM–MAA)] thermosensitive magnetic particles were thus obtained. The effects of the ferrofluids on the reaction kinetics, morphology, and particle size of the latex were discussed. A reaction mechanism was proposed in accordance with the morphology observation of the latex particles. The thermosensitive property of the thermosensitive magnetic composite latex was also studied. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3062–3072, 2007     

Influence of Calcination Conditions on Structural and Solid-State Kinetic Properties of Iron Oxidic Species Supported on SBA-15

Iron oxidic species supported on silica SBA-15 were synthesized with various iron loadings using two different Fe^III precursors. The effect of varying powder layer thickness during calcination on structural and solid-state kinetic properties of Fe_xO_y/SBA-15 samples was investigated. Calcination was conducted in thin (0.3 cm) or thick (1.3 cm) powder layer. Structural characterization of resulting Fe_xO_y/SBA-15 samples was performed by nitrogen physisorption, X-ray diffraction, and DR-UV/Vis spectroscopy. Thick powder layer during calcination induced an increased species size independent of the precursor. However, a significantly more pronounced influence of calcination mode on species size was observed for the Fe^III nitrate precursor compared to the Fe^III citrate precursor. Temperature-programmed reduction (TPR) experiments revealed distinct differences in reducibility and reduction mechanism dependent on calcination mode. Thick layer calcination of the samples obtained from Fe^III nitrate precursor resulted in more pronounced changes in TPR profiles compared to samples obtained from Fe^III citrate precursor. TPR traces were analyzed by model-dependent Coats-Redfern method and model-independent Kissinger method. Differences in solid-state kinetic properties of Fe_xO_y/SBA-15 samples dependent on powder layer thickness during calcination correlated with differences in iron oxidic species size.     

Redox chemistry of [Fe2(CN)10]4−. Part I. Reaction with iodide

The iron(III) dimeric complex [Fe₂(CN)₁₀]⁴⁻ is reduced to the iron(III)iron(II) species [Fe₂(CN)₁₀]⁵⁻ by iodide ion, the equilibrium constant being strongly dependent upon the nature of the alkali metal cation, reduction being favoured in the sequence: Cs⁺>NH ₄ ⁺ ≥K⁺>Na⁺>Li⁺. The reaction kinetics are autocatalytic in character, the catalytic species being the mixed valence dimer. The rates of reactions are also strongly catalysed by alkali metal cations, in the same sequence as for the equilibrium constants. The reaction mechanism involves the formation of I ₂ ⁻ as a reactive intermediate which can be oxidised by both [Fe₂(CN)₁₀]⁴⁻ and [Fe₂(CN)₁₀]⁵⁻.     

Mössbauer Spectroscopic Investigation of FeII and FeIII 3,4,5‐Trihydroxybenzoates (Gallates) – Proposed Model Compounds for Iron‐Gall Inks

Iron gallates with iron in the oxidation states Fe²⁺ and Fe³⁺ were prepared and studied by Mössbauer spectroscopy, X‐ray diffraction, and IR spectroscopy. Fe^III 3,4,5‐trihydroxybenzoate (gallate) Fe(C₇O₅H₄) · 2H₂O, whose structure was first determined by Wunderlich, was obtained by the reaction of gallic acid and metallic iron or by oxidation of the Fe^II gallate, which was obtained by the reaction of ferrous sulfate with 3,4,5‐trihydroxybezoic acid (gallic acid) under anoxic conditions. Trials to reproduce the hydrothermal preparation method of Feller and Cheetham show that the result depends crucially on the free gas volume in the reaction vessel. If there is no free volume one obtains the same Fe^III gallate as in the other preparation methods. With a large free volume another compound was found to form whose composition and structure could not be determined. It could be specified only by Mössbauer spectroscopy. Fe^III gallate, the Fe^II gallate, and the new phase show magnetic ordering at liquid helium temperature.