Iron Nitride Nanoparticles for Enhanced Reductive Dechlorination of Trichloroethylene.

Nitriding has been used for decades to improve the corrosion resistance of iron and steel materials. Moreover, iron nitrides (FexN) have been shown to give an outstanding catalytic performance in a wide range of applications. We demonstrate that nitriding also substantially enhances the reactivity of zerovalent iron nanoparticles (nZVI) used for groundwater remediation, alongside reducing particle corrosion. Two different types of FexN nanoparticles were synthesized by passing gaseous NH3/N2 mixtures over pristine nZVI at elevated temperatures. The resulting particles were composed mostly of face-centered cubic (γ'-Fe4N) and hexagonal close-packed (ε-Fe2-3N) arrangements. Nitriding was found to increase the particles' water contact angle and surface availability of iron in reduced forms. The two types of FexN nanoparticles showed a 20- and 5-fold increase in the trichloroethylene (TCE) dechlorination rate, compared to pristine nZVI, and about a 3-fold reduction in the hydrogen evolution rate. This was related to a low energy barrier of 27.0 kJ mol-1 for the first dechlorination step of TCE on the γ'-Fe4N(001) surface, as revealed by density functional theory calculations with an implicit solvation model. TCE dechlorination experiments with aged particles showed that the γ'-Fe4N nanoparticles retained high reactivity even after three months of aging. This combined theoretical-experimental study shows that FexN nanoparticles represent a new and potentially important tool for TCE dechlorination.

Discovering the potential of an nZVI-biochar composite as a material for the nanobioremediation of chlorinated solvents in groundwater: Degradation efficiency and effect on resident microorganisms.

Abiotic and biotic remediation of chlorinated ethenes (CEs) in groundwater from a real contaminated site was studied using biochar-based composites containing nanoscale zero-valent iron (nZVI/BC) and natural resident microbes/specific CE degraders supported by a whey addition. The material represented by the biochar matrix decorated by isolated iron nanoparticles or their aggregates, along with the added whey, was capable of a stepwise dechlorination of CEs. The tested materials (nZVI/BC and BC) were able to decrease the original TCE concentration by 99% in 30 days. Nevertheless, regarding the transformation products, it was clear that biotic as well as abiotic transformation mechanisms were involved in the transformation process when nonchlorinated volatiles (i.e., methane, ethane, ethene, and acetylene) were detected after the application of nZVI/BC and nZVI/BC with whey. The whey addition caused a massive increase in bacterial biomass in the groundwater samples (monitored by 16S rRNA sequencing and qPCR) that corresponded with the transformation of trichloro- and dichloro-CEs, and this process was accompanied by the formation of less chlorinated products. Moreover, the biostimulation step also eliminated the adverse effect caused by nZVI/BC (decrease in microbial biomass after nZVI/BC addition). The nZVI/BC material or its aging products, and probably together with vinyl chloride-respiring bacteria, were able to continue the further reductive dechlorination of dichlorinated CEs into nonhalogenated volatiles. Overall, the results of the present study demonstrate the potential, feasibility, and environmental safety of this nanobioremediation approach.

Microwave Synthesis of Magnetite Nanoparticles and Mg-Doped Magnetite Nanoparticles by Precipitation of Fe2+ Ions.

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.

Sulfidated nano-scale zerovalent iron is able to effectively reduce in situ hexavalent chromium in a contaminated aquifer.

In a number of laboratory studies, sulfidated nanoscale zero-valent iron (S-nZVI) particles showed increased reactivity, reducing capacity, and electron selectivity for Cr(VI) removal from contaminated waters. In our study, core-shell S-nZVI particles were successfully injected into an aquifer contaminated with Cr(VI) at a former chrome plating facility. S-nZVI migrated towards monitoring wells, resulting in a rapid decrease in Cr(VI) and Crtot concentrations and a long-term decrease in groundwater redox potential observed even 35 m downstream the nearest injection well. Characterization of materials recovered from the injection and monitoring wells confirmed the presence of nZVI particles, together with iron corrosion products. Chromium was identified on the surface of the recovered iron particles as Cr(III), and its occurrence was linked to the formation of insoluble chromium-iron (oxyhydr)oxides such as CrxFe(1-x)(OH)3(s). Injected S-nZVI particles formed aggregates, which were slowly transformed into iron (oxyhydr)oxides and carbonate green rust. Elevated contents of Fe0 were detected even several months after injection, indicating good S-nZVI longevity. The sulfide shell was gradually disintegrated and/or dissolved. Geochemical modelling confirmed the overall stability of the resulting Cr(III) phase at field conditions. This study demonstrates the applicability of S-nZVI for the remediation of a Cr(VI)-contaminated aquifer.

Thermally reduced fluorographenes as efficient electrode materials for supercapacitors.

There is an urgent need for a simple and up-scalable method for the preparation of supercapacitor electrode materials due to increasing global energy consumption worldwide. We have discovered that fluorographene exhibits great potential for the development of new kinds of supercapacitors aimed at practical applications. We have shown that time control of isothermal reduction of fluorographite at 450 °C under a hydrogen atmosphere led to the fine-tuning of fluorine content and electronic properties of the resulting fluorographene derivatives. Charge transfer resistances (Rct) of the thermally reduced fluorographenes (TRFGs) were decreased with respect to the pristine fluorographene; however, the Rctvs. time-of-reduction plot showed a v-shaped profile. The specific capacitance vs. time-of-reduction of TRFG followed the v-shaped trend, which could be the result of the decreasing content of sp3 carbons and increasing content of structural defects. An optimized material exhibited values of specific capacitance up to 539 F g-1 recorded at a current density of 0.25 A g-1 and excellent cycling durability with 100% specific capacitance retention after 1500 cycles in a three-electrode configuration and 96.7% of specific capacitance after 30 000 cycles in a two-electrode setup.

Preparation of Magnetite by Thermally Induced Decomposition of Ferrous Oxalate Dihydrate in the Combined Atmosphere.

This study presents an investigation of thermal decomposition of ferrous oxalate dihydrate in the combined atmosphere of inert and conversion gases to find an optimal route for a simple magnetite preparation. Homogenized precursor was isothermally treated inside the stainless-steel cells at 8 equidistant temperatures ranging from 300 to 650 °C for 1, 6, and 12 hours. The enclosure of samples inside the cells with the combined atmosphere eliminates the necessity of the inert gas to flow over the treated samples. Structural, magnetic, and morphological aspects of the prepared materials were examined by the combination of experimental techniques, such as Mössbauer spectroscopy, X-ray powder diffraction, and scanning electron microscopy.

Novel assay for the toxicity evaluation of nanoscale zero-valent iron and derived nanomaterials based on lipid peroxidation in bacterial species.

Nano-scale zero-valent iron (nZVI) began attracting research attention in remediation practice in recent decades as a prospective nanomaterial applicable to various contaminated matrices. Despite concerns about the negative effects of nanomaterials on ecosystems, the number of reliable toxicity tests is limited. We have developed a test based on the evaluation of oxidative stress (OS). The test employed the analysis of a typical OS marker (malondialdehyde, MDA), after exposure of six bacterial strains to the tested nanomaterial. We also attempted to use other OS and cell membrane damage assays, including the determination of glutathione and lactate dehydrogenase, respectively. However, we found that the components of these assays interfered with nZVI; therefore, these tests were not applicable. The MDA assay was tested using nZVI and three newly engineered oxide shell nZVI materials with different oxide thicknesses. Six different bacterial species were employed, and the results showed that the test was fully applicable for the concentrations of nanomaterials used in remediation practice (0.1-10 g/L). MDA was produced in a dose-response manner, and the bacteria showed a similar response toward pure pyrophoric nZVI, reaching EC50 values of 0.3-1.1 g/L. We observed different responses in the absolute production of MDA; however, the MDA concentrations were correlated with the cell membrane surfaces of the individual strains (R > 0.75; P < 0.09). Additionally, the EC50 values correlated with the thickness of the oxide shells (except for Escherichia coli: R > 0.95; P < 0.05), documenting the reliability of the assay, where reactivity was confirmed to be an important factor for reactive oxygen species production.

Synthesis of flower-like magnetite nanoassembly: Application in the efficient reduction of nitroarenes.

A facile approach for the synthesis of magnetite microspheres with flower-like morphology is reported that proceeds via the reduction of iron(III) oxide under a hydrogen atmosphere. The ensuing magnetic catalyst is well characterized by XRD, FE-SEM, TEM, N2 adsorption-desorption isotherm, and Mössbauer spectroscopy and explored for a simple yet efficient transfer hydrogenation reduction of a variety of nitroarenes to respective anilines in good to excellent yields (up to 98%) employing hydrazine hydrate. The catalyst could be easily separated at the end of a reaction using an external magnet and can be recycled up to 10 times without any loss in catalytic activity.

A simple high-yield synthesis of high-purity Hägg carbide (χ-Fe5C2) nanoparticles with extraordinary electrochemical properties.

Iron carbides are of eminent interest in both fundamental scientific research and in the industry owing to their properties such as excellent mechanical strength and chemical inertness. They have been found very effective in Fischer-Tropsch synthesis exploring heterogeneous catalysis for the production of chemicals such as liquid fuel and they have also been employed as successful promoters for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). However, so far there have been only a few reports on the application of iron carbide nanoparticles in the field of electrochemical sensing. Here, we present a stable form of Hägg carbide nanoparticles synthesized from a rare form of iron(iii) oxide (ß-Fe2O3). The as-prepared nanomaterial was characterized employing X-ray powder diffraction and Mössbauer spectroscopy to prove its composition as well as an extraordinary high purity level. It turned out that Hägg carbide nanoparticles prepared by thermally treated ß-Fe2O3 exhibited excellent electrochemical properties including low charge transfer resistivity (Rct) compared to the other tested materials. Moreover, the Hägg carbide nanoparticles were tested as a promising electrocatalyst for voltammetric detection of the antibiotic metronidazole proving its practical applicability.

Pharmaceuticals, benzene, toluene and chlorobenzene removal from contaminated groundwater by combined UV/H2O2 photo-oxidation and aeration.

This study was performed to test the feasibility of several decontamination methods for remediating heavily contaminated groundwater in a real contaminated locality in the Czech Republic, where a pharmaceuticals plant has been in operation for more than 80 years. The site is polluted mainly by recalcitrant psychopharmaceuticals and monoaromatic hydrocarbons, such as benzene, toluene and chlorobenzene. For this purpose, an advanced oxidation technique employing UV radiation with hydrogen peroxide dosing was employed, in combination with simple aeration pretreatment. The results showed that UV/H2O2 was an efficient and necessary step for degradation of the pharmaceuticals; however, the monoaromatics were already removed during the aeration step. Characterization of the removal mechanisms participating in the aeration revealed that volatilization, co-precipitation and biodegradation contributed to the process. These findings were supported by bacterial metabolite analyses, phospholipid fatty acid analysis, qPCR of representatives of the degradative genes and detailed characterization of the formed precipitate using Mössbauer spectroscopy and scanning electron microscopy. Further tests were carried out in a continuous arrangement directly connected to the wells already present in the locality. The results documented the feasibility of combination of the photo-reactor employing UV/H2O2 together with aeration pretreatment for 4 months, where the overall decontamination efficiency ranged from 72% to 99% of the pharmaceuticals. We recorded even better results for the monoaromatics decontamination except for one month, when we encountered some technical problems with the aeration pump. This demonstrated the necessity of using the aeration step.

Magnetically assisted surface-enhanced raman scattering selective determination of dopamine in an artificial cerebrospinal fluid and a mouse striatum using Fe(3)O(4)/Ag nanocomposite.

The dopaminergic neural system is a crucial part of the brain responsible for many of its functions including mood, arousal, and other roles. Dopamine is the key neurotransmitter of this system, and a determination of its level presents a demanding task needed for a deeper understanding of the processes, even pathological, involving this brain part. In this work, we present a method for a fast analysis of dopamine levels in samples of cerebrospinal fluid and mouse striatum. The method is based on a nanocomposite composed of magnetite and silver nanoparticles, whose surface is modified with iron nitriloacetic acid (Fe-NTA)-a dopamine-selective compound. The magnetic properties of this nanocomposite enable simple separation of targeted molecules from a complex matrix while the silver acts as a platform for surface-enhanced Raman scattering (SERS). Silver and magnetite nanoparticles are joined by carboxymethyl chitosan, useful in biological environments and enhancing the sensitivity due to the presence of carboxyl groups. This system reveals a good stability and reproducibility. Moreover, rapid and simple quantitative experiments show an improvement in the detection of dopamine levels in biological assays at low femtomolar concentrations. The comparative data performed with clinical samples of mouse striatum show that the developed magnetic SERS is a strong alternative to conventional high-performance liquid chromatography-mass spectrometry (HPLC-MS) with even several superior aspects including faster and cheaper analysis and no necessity of sample preconcentration or derivatization.

Core-shell hybrid nanomaterial based on prussian blue and surface active maghemite nanoparticles as stable electrocatalyst.

A novel core-shell nanomaterial based on prussian blue (PB) coating on peculiar surface active maghemite nanoparticles (SAMNs), was developed. The synthetic process involves the direct crystallization of Fe(II)(CN)6(4-) onto the surface of SAMNs by simple incubation in water at controlled pH, demonstrating the presence of under-coordinated Fe(III) on nanoparticle surface. The coating reaction occurs in a narrow pH range and the synthetic procedure was optimized. The resulting SAMN@PB hybrid nanostructures were characterized by transmission and scanning electron microscopy, Mössbauer, UV-vis and FTIR spectroscopy and X-ray powder diffraction. The nanomaterial, characterized by high stability in alkaline media, behave as excellent electro-catalyst for hydrogen peroxide reduction. The stability of SAMN@PB hybrid has been investigated as a function of pH, showing excellent stability up to pH 9.0 and demonstrating the feasibility of SAMNs, superficially derivatized with prussian blue, to produce an efficient and extremely stable nanostructured material. This maghemite supported nanostructured prussian blue was applied to develop a sensor, based on a simple carbon paste electrode, which was able to catalyze the electro-reduction of hydrogen peroxide, in aqueous solutions, buffered at pH 7.0, at low applied potentials (0.0 V vs. SCE).

Mixtures of L-amino acids as reaction medium for formation of iron nanoparticles: the order of addition into a ferrous salt solution matters.

Owing to Mössbauer spectroscopy, an advanced characterization technique for iron-containing materials, the present study reveals previously unknown possibilities using l-amino acids for the generation of magnetic particles. Based on our results, a simple choice of the order of l-amino acids addition into a reaction mixture containing ferrous ions leads to either superparamagnetic ferric oxide/oxyhydroxide particles, or magnetically strong Fe0-Fe2O3/FeOOH core-shell particles after chemical reduction. Conversely, when ferric salts are employed with the addition of selected l-amino acids, only Fe0-Fe2O3/FeOOH core-shell particles are observed, regardless of the addition order. We explain this phenomenon by a specific transient/intermediate complex formation between Fe2+ and l-glutamic acid. This type of complexation prevents ferrous ions from spontaneous oxidation in solutions with full air access. Moreover, due to surface-enhanced Raman scattering spectroscopy we show that the functional groups of l-amino acids are not destroyed during the borohydride-induced reduction. These functionalities can be further exploited for (i) attachment of l-amino acids to the as-prepared magnetic particles, and (ii) for targeted bio- and/or environmental applications where the surface chemistry needs to be tailored and directed toward biocompatible species.