The present study reports on the preparation and physico-chemical investigation of a 2 mu m thick film produced from AISI 304 stainless steel by DC magnetron sputtering. A phase transformation from the conventionally nonmagnetic Face-Centered Cubic (FCC) phase of austenite (gamma-Fe) nature to a predominantly Body-Centered Cubic (BCC) ferromagnetic single phase (alpha-Fe) during the deposition is observed upon the deposition process. The deposited films are characterized by various experimental techniques including Scanning Electron Microscopy (SEM) with Energy-Dispersive X-ray spectroscopy (EDX), X-Ray powder Diffraction (XRD), Grazing-Incidence X-Ray powder Diffraction (GIXRD), and Mossbauer Spectroscopy (MS) in both transmission and back-scattered geometry. For interpretation of the Mossbauer spectra of the film, a physico-chemical model based on distinct micromagnetic environments evolved due to alloying elements is suggested. The results, presented within this study, may stimulate further and detailed research in identifying the causes for the phase transition from both theoretical and experimental perspectives and understanding the underlying mechanisms.

Meropenem, a last-resort antibiotic, is frequently detected in wastewater, but research on its removal remains limited. This study introduces molybdenum-modified iron oxides (MFx), synthesized via a simple solution combustion method, to activate peroxydisulfate (PDS), for enhanced oxidation of meropenem in heterogeneous advanced oxidation processes. The physicochemical and magnetic properties of MFx were systematically analyzed, revealing that sodium molybdate and polyvinyl alcohol (PVA) play key roles in forming Mo-incorporated maghemite. M & ouml;ssbauer spectroscopy and magnetic characterization further validated the successful incorporation of molybdenum into maghemite. Among the synthesized MFx at different iron to molybdenum molar ratios (x), MF 1.0 demonstrated superior catalytic performance due to its higher molybdenum content and larger surface area, achieving >99 % meropenem removal under optimal conditions (0.25 g L-1 catalyst dosage, 1.0 mM PDS, pH 4.0). Mechanistic investigations identified sulfate radical (SO4 center dot-) and hydroxyl radical (HO center dot) as primary reactive species, with EPR and XPS measurements confirming the role of Fe2+/Fe3+ and Mo5+/Mo6+ redox transitions in the activation of PDS. The MF 1.0/PDS system exhibited promising recyclability, maintaining over 90 % meropenem removal efficiency even after five consecutive cycles, highlighting its potential applicability in practical water treatment systems. This study highlights the potential of molybdenum-modified iron oxides for achieving pharmaceutical remediation, contributing to improved environmental and public health outcomes.

Mössbauer spectra of FeIII complex salts with urea-related ligands show a broadened line due to magnetic relaxation. The origin of the relaxation is not known, mostly spin–spin type is considered. A study of a large number of compounds can be helpful to show differences in the Mössbauer parameters and to see the infuence of the chemical environment on the relaxation. We have evaluated the Mössbauer spectra of 13 compounds recorded at various temperatures with the Blume–Tjon two-state relaxation model and with the (unrestricted) Afanasev–Gorobchenko model. The latter showed significant differences between some salts, and proved the presence of spin–lattice relaxation.

Acetaminophen (APAP) is a well-known type of over-the-counter painkillers and is frequently found in surface waterbodies, causing hepatotoxicity and skin irritation. Due to its persistence and chronic effects on the environment, innovative solutions must be provided to decompose APAP, effectively. Innovative catalysts of tungsten-modified iron oxides (TF) were successfully developed via a combustion method and thoroughly characterized using SEM, TEM, XRD, XPS, a porosimetry analysis, Mössbauer spectroscopy, VSM magnetometry, and EPR. With the synthesis method, tungsten was successfully incorporated into iron oxides to form ferrites and other magnetic iron oxides with a high porosity of 19.7 % and a large surface area of 29.5 m2/g. Also, their catalytic activities for APAP degradation by activating peroxymonosulfate (PMS) were evaluated under various conditions. Under optimal conditions, TF 2.0 showed the highest APAP degradation of 95 % removal with a catalyst loading of 2.0 g/L, initial APAP concentration of 5 mg/L, PMS of 6.5 mM, and pH 2.15 at room temperature. No inhibition by solution pHs, alkalinity, and humic acid was observed for APAP degradation in this study. The catalysts also showed chemical and mechanical stability, achieving 100 % degradation of 1 mg/L APAP during reusability tests with three consecutive experiments. These results show that TFs can effectively degrade persistent contaminants of emerging concern in water, offering an impactful contribution to wastewater treatment to protect human health and the ecosystem.

The phase transition of austenitic stainless steel of commercial label CL20ES and zinc ferrite nanoparticles was studied in an oxidative atmosphere of dry air to develop a low-cost, effective technique for covering-layer fabrication. CL20ES powder and zinc ferrite powder were mechanically mixed. This mixture was studied in an atmosphere of dry air at different annealing temperatures from room temperature to 900 °C. The employed characterization techniques are X-ray powder diffraction, Mössbauer spectroscopy in the transmission geometry, and scanning electron microscopy with elemental mapping. The fabricated layers were also characterized by surface-specific techniques such as conversion electron Mössbauer spectroscopy and grazing incidence X-ray powder diffraction. The analyzed powder mixture shows resistance against oxidation in dry air and high temperatures. These results were employed to produce zinc ferrite covering layers on 3D-printed cylinders of CL20ES. The results show a predisposition of zinc ferrite to be recrystallized at temperatures above 350 °C without the production of corrosive substances on steel. The zinc ferrite layers were analyzed by an ultrasonic hardness tester as well, which proved the hardness enhancement.

57Fe transmission Mossbauer (TMS) spectroscopy and powder X-ray diffractometry (XRD), as well as scanning electron microscopy (SEM-EDX) measurements were used to study the effect of swift heavy ion irradiation on powdered hematite mixed with epoxy resin. TMS, XRD and EDX of the samples indicated no significant changes neither in the crystal structure nor in the composition of hematite irradiated with 148 MeV Xe ions with a fluence of 1 x 1013 cm-2 as compared to those of non-irradiated ones. However, about a quarter of the total iron content of the hematite detected by TMS was converted to w & uuml;stite and to magnetite superparamagnetic at room temperature upon irradiation with a fluence of 5 x 1013 cm-2. The presence of w & uuml;stite was evidenced by XRD in agreement with TMS measurements. Temperature dependence of the hematite TMS measurements indicated a significant change in the Morin transition after irradiation with a fluence of 5 x 1013 cm-2. The results are discussed in terms of the defects produced by irradiation and corresponding changes in the Morin transition and for the hematite to w & uuml;stite and magnetite transformation. (c) 2017 Elsevier Inc. All rights reserved.

The effect of swift heavy ion irradiation on sol–gel-prepared maghemite nanoparticles was studied by 57Fe transmission Mössbauer spectroscopy and X-ray diffractometry (XRD). The room temperature Mössbauer spectra of the non-irradiated nano-maghemite showed poorly resolved magnetically split, typical relaxation spectra due to the superparamagnetic state of the nanoparticles. Significant changes in the line shape, indicating changes in the superparamagnetic state, were found in the Mössbauer spectra upon irradiation by 160 MeV and 155 MeV 132Xe26+ ions with fluences of 5 × 1013 ion cm−2 and 1 × 1014 ion cm−2. XRD of the irradiated maghemite nanoparticles showed a significant broadening of the corresponding lines, indicating a decrease in the crystallite size, compared to those of the non-irradiated ones. The results are discussed in terms of the defects induced by irradiation and the corresponding changes related to the change in particle size and consequently in the superparamagnetic state caused by irradiation.

Citric acid plays an ubiquitous role in the complexation of essential metals like iron and thus it has a key function making them biologically available. For this, iron(III) citrate complexes are considered among the most significant coordinated forms of ferric iron that take place in biochemical processes of all living organisms. Although these systems hold great biological relevance, their coordination chemistry has not been fully elucidated yet. The current study aimed to investigate the speciation of iron(III) citrate using Mössbauer and electron paramagnetic resonance spectroscopies. Our aim was to gain insights into the structure and nuclearity of the complexes depending on the pH and iron to citrate ratio. By applying the frozen solution technique, the results obtained directly reflect the iron speciation present in the aqueous solution. At 1:1 iron:citrate molar ratio, polynuclear species prevailed forming most probably a trinuclear structure. In the case of citrate excess, the coexistence of several monoiron species with different coordination environments was confirmed. The stability of the polynuclear complexes was checked in the presence of organic solvents.

57Fe transmission and conversion electron Mössbauer spectroscopy as well as XRD were used to study the effect of swift heavy ion irradiation on stress-annealed FINEMET samples with a composition of Fe73.5Si13.5Nb3B9Cu1. The XRD of the samples indicated changes neither in the crystal structure nor in the texture of irradiated ribbons as compared to those of non-irradiated ones. However, changes in the magnetic anisotropy both in the bulk as well as at the surface of the FINEMET alloy ribbons irradiated by 160 MeV 132Xe ions with a fluence of 1013 ion cm−2 were revealed via the decrease in relative areas of the second and fifth lines of the magnetic sextets in the corresponding Mössbauer spectra. The irradiation-induced change in the magnetic anisotropy in the bulk was found to be similar or somewhat higher than that at the surface. The results are discussed in terms of the defects produced by irradiation and corresponding changes in the orientation of spins depending on the direction of the stress generated around these defects.

The application of microwave irradiation for rapid synthesis of magnetic biochar from agricultural waste with the subsequent modification of carbon matrix by magnetic nanoparticles was performed. The magnetic biochar was characterized by 57Fe Mo center dot ssbauer spectroscopy, X-ray diffraction, a low-temperature nitrogen adsorption method, and electron microscopy. Except of magnetic properties, modification of biochar brings surface texture increase (SBET = 21.1 m2/g for char precursor versus 139.1 m2/g for magnetic biochar), and therefore better adsorption properties. The magnetic biochar was tested as an adsorbent of As5+ oxyanion and methylene blue (MB) to study the sorption mechanism and regeneration process. Magnetic biochar is the excellent adsorbent of arsenic (Qm = 24.9 mg/g; pH = 3.8). In the regeneration procedure, fast-acting microwave irradiation (10 s) significantly increases the value of the As5+ desorption rate constant as well as the initial desorption rate. The adsorption of MB on the magnetic biochar (Qm = 55.0 mg/g; pH = 10.2) was realized to study microwaveinduced thermal regeneration. After short microwave treatment (30 s), a degradation of MB was observed (no absorption in the UV/VIS spectrum), whereas six degradation products were detected (HPLC/ESI-MS) and proposed formulas were revealed. Longer irradiation (60 s) caused total degradation of MB.

Two series of ZnFe2O4 mixed cubic spinel nanoparticles were prepared by a coprecipitation method, where a solution of Fe3+ and Zn2+ was alkalised by a solution of NaOH. While the first series was prepared by a careful mixing of the two solutions, the microwave radiation was used to enhance the reaction in the other series of samples. The effect of the microwave heating on the properties of the prepared particles is investigated. X-ray powder diffraction (XRD), 57Fe Mössbauer spectroscopy and magnetometry were employed to prove the cubic structure and superparamagnetic behavior of the samples. The particle size in the range of nanometers was investigated by a transmission electron microscopy (TEM), and the N2 adsorption measurements were used to determine the BET area of the samples. The stoichiometry and the chemical purity were proven by energy dispersive spectroscopy (EDS). Additionally, the inversion factor was determined using the low temperature Mössbauer spectra in the external magnetic field. The microwave heating had a significant effect on the mean coherent length. On the other hand, it had a lesser influence on the size and BET surface area of the prepared nanoparticles.

Covering layers might have very important role in improving performance of many mechanical parts. These layers are usually designed to protect a substrate from the environment and enhance mechanical properties such as hardness. Blackening is a classical approach that is very demanding on resources. This process is based on the alkalisation of surface atoms and the transformation of formed hydroxides to oxides. Such an approach inspired us to carry out experiments resulting in preparation of protective layers with similar properties, by using stoichiometric spinel ferrite nanoparticles (MeFe2O4). Thus mechanical parts were covered with ferrite nanoparticles and heated in a furnace. Ferrite samples, which were used as precursor for the preparation of layers, were analysed with X-ray powder diffraction, energy dispersive X-ray spectroscopy and Fe Mössbauer spectroscopy. The samples were analysed with ultrasonic hardness test, electron microscopy, and Mössbauer spectroscopy. The protection layers showed a higher hardness compared to untreated parts.

This study is focused on a simple and fast synthesis of nonstoichiometric magnetite nanoparticles with the chemical formula Fe3-XO₄ and magnesium ferrite nanoparticles (Mg1-XFe2+XO₄). The nanoparticles were prepared with Fe2+ ions (FeSO₄ · H₂O) alkalised by KOH under oxidative conditions and in a microwave field. X-ray powder diffraction (XRD) and 57Fe transmission Mössbauer spectroscopy were used to determine the phase composition and crystal structure in detail. The presence of synthetic magnetite, maghemite, goethite, and magnesium ferrite was observed. Room temperature Mössbauer spectroscopy revealed the existence of ferromagnetic sublattices and superparamagnetic fraction. The superparamagnetic component corresponds to magnesium ferrite nanoparticles. Low temperature Mössbauer spectroscopy was used to locate the blocking temperature of superparamagnetic nanoparticles and to separate the sublattices. The presumed spherical morphology of nanoparticles and their size under 100 nm have been confirmed by transmission electron microscopy (TEM). The obtained results were used to provide possible reaction scheme, which serves to tailor the synthesis to a desired application.

Over the past decades, soluble compounds with iron in high oxidation state(s) (so-called ferrates) have turned out to be a highly promising and "green" oxidants deployed in water treatment technologies. Ferrates(IV, V, VI) have good oxidation properties, as indicated by the magnitude of the oxidation-reduction potential (an acidic reaction with an oxidation-reduction potential of 2.20 V, in the basic environment it is 0.72 V), making them interesting for oxidation of inorganic compounds including metals, the decomposition of broad range of organic pollutants including various types of micropollutants found in wastewater (pesticides, pharmaceuticals, and drugs), and for disinfection. The important advantage of ferrates is also their minimal environmental load as the reactions result in the formation of benign iron hydroxides. The only limitation of using ferrates in practice is their demanding production as well as their instability due to the high electron affinity of hexavalent iron.

We achieved sputter deposition of silver atoms onto liquid alcohols by injection of solvents into vacuum via a liquid microjet. Mixing silver atoms into ethanol by this method produced metallic silver nanoparticles. These had a broad, log-normal size distribution, with median size between 3.3 ± 1.4 nm and 2.0 ± 0.7 nm, depending on experiment geometry; and a broad plasmon absorption band centred around 450 nm. We also deposited silver atoms into a solution of colloidal silica nanoparticles, generating silver-decorated silica particles with consistent decoration of almost one silver particle to each silica sphere. The silver-silica mixture showed increased colloidal stability and yield of silver, along with a narrowed size distribution and a narrower plasmon band blue-shifted to 410 nm. Significant methanol loss of 1.65 × 10-7 mol MeOH per g per s from the mature silver-silica solutions suggests we have reproduced known silica supported silver catalysts. The excellent distribution of silver on each silica sphere shows this technique has potential to improve the distribution of catalytically active particles in supported catalysts.

Two Prussian blue (PB) samples with different morphologies (spheres, mean size 160 nm; cubes, mean size 1.48 mu m) and variable content of potassium (K-free and K-bearing) were used as a precursor material for the preparation of iron(III) oxides by solid state thermal decomposition method. A mixture of iron(III) oxide polymorphs (alpha-Fe2O3, beta-Fe2O3, and gamma-Fe2O3 nanoparticles) or pure maghemite (gamma-Fe2O3 nanoparticles) were obtained by thermal decomposition of the cubic (K-bearing) or spherical (K-free) PB particles, respectively, at 350 degrees C in air. The particle's morphology of the starting material (i.e. PB) was mostly retained after the thermal decomposition. The PB samples and the as-formed iron(III) oxides were characterized by using X-ray powder diffraction (XRD), Fe-57 Mossbauer spectroscopy, and scanning electron microscopy (SEM). A high amount (50 wt%) of beta-Fe2O3 polymorph was produced when K-bearing PB was used, simultaneously cubic clusters of maghemite were formed. A single phase (maghemite) clustered nanoparticles with spherical morphology were obtained when we used a K-free PB. The maghemite nanoparticles (4 nm) have proven to be superparamagnetic.

Fenton processes are promising wastewater treatment alternatives for bio-recalcitrant compounds. Three different methods (i.e., reverse microemulsion, sol-gel, and combustion) were designed to synthesize environmentally friendly ferrites as magnetically recoverable catalysts to be applied for the decomposition of two pharmaceuticals (ciprofloxacin and carbamazepine) that are frequently detected in water bodies. The catalysts were used in a heterogeneous solar photo-Fenton treatment to save the cost of applying high-energy UV radiation sources, and was performed under a slightly basic pH to avoid metal leaching and adding salts for pH adjustment. All the developed catalysts resulted in the effective treatment of ciprofloxacin and carbamazepine in both synthetic and real domestic wastewater. In particular, the sol-gel synthesized ferrite was more magnetic and more suitable for reuse. The degradation pathways of both compounds were elucidated for this treatment. The degradation of ciprofloxacin involved attacks to the quinolone and piperazine rings. The degradation pathway of carbamazepine involved the formation of hydroxyl carbamazepine and dihydroxy carbamazepine before yielding acridine by hydrogen abstraction, decarboxylation, and amine cleavage, which would be further oxidized.

The kinetics and mechanism of ferrate(iv), (v) and (vi) transformations in water and in polar organic solvents (namely ethanol and tetrahydrofuran) have been investigated by the method of 57Fe Mössbauer spectroscopy of frozen solutions. Ethanol with a very limited amount of water under an inert atmosphere, significantly slows down the transformation reactions of ferrates(iv and v) and provides direct proof of the existence of intermediate states. Simultaneously, ethanol is oxidized to caboxylates in the close vicinity of the surface of ferrate crystallites as proven by X-ray photoelectron spectroscopy. On the contrary, any transformation of ferrate(vi) in pure ethanol (with a very limited amount of water) was not observed. Mössbauer spectroscopy of frozen solutions enabled us to experimentally identify and quantify intermediates of ferrate(iv) and ferrate(v) transformations for the first time. Sodium ferrate(iv) in its tetrahedral form, Na4FeO4, undergoes a two-step charge disproportionation to Fe(iii) and Fe(vi) via a Fe(v) intermediate without any evolution of oxygen in polar protic and aprotic solvents, specifically 2Fe(iv) → Fe(iii) + Fe(v), and Fe(iv) + Fe(v) → Fe(iii) + Fe(vi), i.e. in sum 3Fe(iv) → 2Fe(iii) + Fe(vi). Ferrate(v) (K3FeO4) transforms to Fe(iii) and Fe(vi) without any indication of the Fe(iv) intermediate within the detection limit of the method. In addition to a charge disproportionation reaction proceeding in polar liquids, 3Fe(v) → Fe(iii) + 2Fe(vi), a competitive reduction of Fe(v) directly to Fe(iii) accompanied by oxygen evolution takes place in water. Oxygen evolution was also measured for ferrate(iv and vi) transformations in water, but to a higher and a smaller extent compared to ferrate(v), respectively. The thermodynamics of the suggested ferrate(iv) and ferrate(v) transformation pathways was examined by DFT calculations.

Fe uptake machinery of chloroplasts prefers to utilise Fe(III)–citrate over Fe–nicotianamine complexes.

We report the synthesis of pristine and nickel containing iron oxide (-Fe2O3) nanocrystallites by facile environmentally benign wet chemical process. The magnetic behaviour of the samples has been found to change progressively with nickel content. The Mossbauer spectra revealed the precipitation of secondary phase of nickel ferrite (NiFe2O4) at approximate to 2wt% nickel contents. The transmission electron micrographs together with asymmetric magnetic hysteresis loop have confirmed the formation of core-shell structure. The Morin temperature of nanostructured -Fe2O3 as estimated by superconducting quantum interference device has been found to be 257, 245, 247 and 242K at nickel content of 0, 1, 2 and 4wt%, respectively. The similar trends of increase/decrease in Morin temperature have been noticed by Mossbauer analysis. Furthermore, below Morin temperature, the temperature range of coexisted antiferromagnetic and ferromagnetic states has been found to increase with increase in nickel content.