Size-resolved, quantitative evaluation of the magnetic mineralogy of airborne brake-wear particulate emissions

Exposure to particulate air pollution has been associated with a variety of respiratory, cardiovascular and neurological problems, resulting in increased morbidity and mortality worldwide. Brake-wear emissions are one of the major sources of metal-rich airborne particulate pollution in roadside environments. Of potentially bioreactive metals, Fe (especially in its ferrous form, Fe²⁺) might play a specific role in both neurological and cardiovascular impairments. Here, we collected brake-wear particulate emissions using a full-scale brake dynamometer, and used a combination of magnetic measurements and electron microscopy to make quantitative evaluation of the magnetic composition and particle size of airborne emissions originating from passenger car brake systems. Our results show that the concentrations of Fe-rich magnetic grains in airborne brake-wear emissions are very high (i.e., ~100-10,000 × higher), compared to other types of particulate pollutants produced in most urban environments. From magnetic component analysis, the average magnetite mass concentration in total PM₁₀ of brake emissions is ~20.2 wt% and metallic Fe ~1.6 wt%. Most brake-wear airborne particles (>99 % of particle number concentration) are smaller than 200 nm. Using low-temperature magnetic measurements, we observed a strong superparamagnetic signal (indicative of ultrafine magnetic particles, < ~30 nm) for all of the analysed size fractions of airborne brake-wear particles. Transmission electron microscopy independently shows that even the larger size fractions of airborne brake-wear emissions dominantly comprise agglomerates of ultrafine (<100 nm) particles (UFPs). Such UFPs likely pose a threat to neuronal and cardiovascular health after inhalation and/or ingestion. The observed abundance of ultrafine magnetite particles (estimated to constitute ~7.6 wt% of PM_0.2) might be especially hazardous to the brain, contributing both to microglial inflammatory action and excess generation of reactive oxygen species.

Adsorption characteristics of citric acid on Fe3O4 (001), (011), and (111) surfaces

Magnetite (001), (011), and (111) surfaces were the focus of our study. Magnetite (001) surface has two different terminations, that is, Fe_tet and 2Fe_oct4O. Magnetite (011) surface has two different terminations, that is, 2Fe_oct4O and 2Fe_tet2Fe_oct4O. Magnetite (111) surface has six different terminations, that is, Fe_tet1, Fe_oct, Fe_tet2, 3Fe_oct, 4O₁, and 4O₂. Comparing surface energies of (001), (011), and (111) surfaces, (001) has the smallest surface energy, and (111) has the largest surface energy except for Fe_oct termination, which means that (001) surface is the easiest to be cleaved, followed by (011) and (111) surfaces. Comparing adsorption energies of citric acid onto (001), (011), and (111) surfaces, (111) has the largest adsorption energies except for Fe_tet2 termination, and (001) has the smallest adsorption energies, which means that (111) surface is the most active for citric acid adsorption, followed by (011) and (001) surfaces. PDOS (partial density of states) of citric acid adsorbed onto (001), (011), and (111) surfaces with different terminations shows that 3d orbital of Fe of magnetite surface does not contribute to the adsorption, and 4s orbital of Fe of magnetite surface and 2s and 2p orbitals of O of citric acid contribute to the adsorption.

Sodium carboxymethylcellulose induced engineering a porous carbon and graphene immobilized magnetite composite for lithium-ion storage

Immobilizing nanosized electrochemically active materials with supportive carbonaceous framework usually brings in improved lithium-ion storage performance. In this work, magnetite nanoparticles (Fe₃O₄) are stabilized by both porous carbon domains (PC) and reduced graphene oxide sheets (RGO) to form a hierarchical composite (Fe₃O₄@PC/RGO) via a straightforward approach. The PC confined iron nanoparticle intermediate sample (Fe@PC) was first fabricated, where sodium carboxymethylcellulose (Na-CMC) was employed not only as a cross-linker to trap ferric ions for synthesizing a Fe-CMC precursor sample, but also as the carbon source for PC domains and iron source for Fe nanoparticles in a pyrolysis process. The final redox reaction between Fe@PC and few-layered graphene oxide (GO) sheets contributed to the formation of Fe₃O₄ nanoparticles with reduced size, avoiding any severe aggregation or excessive exposure. The Fe₃O₄@PC/RGO sample delivered a specific capacity of 522.2 mAh·g^-1 under a current rate of 1000 mA·g^-1 for 650 cycles. The engineered Fe@PC and Fe₃O₄@PC/RGO samples have good prospects for application in wider fields.

The effects of magnetite on anammox performance: Phenomena to mechanisms

Low temperature is adverse to anaerobic ammonium oxidation (anammox) reaction while proper Fe addition can enhance anammox performance. Therefore, batch assays were conducted to investigate the potential effects of magnetite (100 μm, 20 μm and 200 nm) on anammox performance which were achieved from the reactor operated at 10-25 °C. After 3 runs, the results indicated that nano-scale magnetite improved the nitrogen elimination significantly. The specific anammox activity (SAA) of the group with nano-magnetite amendments was greater than the other groups after 3 runs (13.5, 12.9, 14.3, 15.4 and 15.7 mgTN/(gVSS·h)), reaching 18.0 mgTN/(gVSS·h). The distribution of magnetite in the granules were then analyzed using X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The results indicated that nano-magnetite was more feasible to attached to the surface of the granules which might accelerate the release of Fe(II) or Fe(III) to enhance anammox performance.

A new approach on synergistic effect and chemical stability of graphene oxide-magnetic nanocomposite in the heterogeneous Fenton degradation of caffeine

Two compositions of graphene oxide-magnetite nanocomposites were studied as catalysts in the heterogeneous Fenton process. Transmission electron microscopy and X-ray diffraction revealed that the graphene oxide sheets were covered with nanoparticles of magnetite, with an average crystallite size of 7 nm. Infrared spectroscopy analysis indicated that the phases interacted through covalent Fe-O-C bonds. The composites presented significantly improved catalytic activity, compared to pure magnetite, with a synergistic effect of up to a factor of 17.1 for the Fenton degradation of caffeine, achieving total removal after 90 min. This synergistic effect was a consequence of the interaction between the phases, resulting in improved mass transfer of caffeine to the catalyst surface, adsorption and efficient degradation, with enhanced HO^• generation. The surface reaction constant increased by up to three orders of magnitude, demonstrating the important role of graphene oxide in the degradation kinetics of the heterogeneous Fenton process. The surface-bonded hydroxyl radicals were responsible for caffeine degradation, achieving 9.4 μmol L^-1. After five degradation cycles, a loss of Fe-O-C bonds and increase in oxygenated groups were associated with a small decrease of caffeine removal efficiency, from 98 to 82%, without significant iron leaching, in the dark, and with low consumption of hydrogen peroxide.

Magnetite-enhanced bioelectrochemical stimulation for biodegradation and biomethane production of waste activated sludge

Microbial electrolytic cell (MEC) and magnetite (M) have shown excellent performance in promoting anaerobic digestion (AD) of biowastes. In this study, four types of anaerobic systems (i.e. single AD, M-AD, MEC-AD, and M-MEC-AD) were developed to comprehensively investigate the potential effects of magnetite-enhanced bioelectrochemical stimulation on the biodegradation of waste activated sludge (WAS) and methane (CH₄) production. Results showed that M-MEC-AD system produced the highest cumulative CH₄ yield, 9.4% higher than that observed in MEC-AD system. Bioelectrochemical stimulation enriched electroactive Geobacter, and classical methanogens (Methanosaeta and Methanobacterium), and the proliferation was further promoted when coupling with magnetite. The relative abundance of Geobacter (6.9%), Methanosaeta (0.3%), and Methanobacterium (12.6%) in M-MEC-AD system was about 10.8, 1.2, and 1.2 times of MEC-AD system, respectively. The integration of magnetite could serve as the conductive materials, and promote inherent indirect electron transfer (IET) and emerging direct electron transfer (DET) between methanogens and fermentative bacteria, building a more energy-efficient route for interspecies electron transfer and methane productivity. This study demonstrated the positive promotion of the coupled bioelectrochemical regulation and magnetite on organic biodegradation, process stability and CH₄ productivity, providing some references for the integrated technology in sludge treatment and bioenergy recovery.

Sorption of Ce(III) on magnetic/olive pomace nanocomposite: isotherm, kinetic and thermodynamic studies

Used for various high-tech applications, cerium is an important rare earth element (REE), and its sorption on various solids also is important considering purification and environmental and radioactive waste disposal. In view of the industrial and environmental terms, it is important to remove Ce³⁺ ions from an aqueous solution. Magnetite and magnetic olive pomace nanocomposite were thus fabricated by a partial reduction co-precipitation approach. The structure and morphological properties of the prepared nano-material and nanocomposite were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-Ray diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), vibrating sample magnetometry (VSM), and BET surface area analysis. The effects of parameters such as solution pH, contact time, initial Ce(III) concentration, and temperature on the sorption efficiency were studied. The maximum sorption capacities of the magnetite (MNP) and magnetic olive pomace nanocomposite (MOP) for Ce(III) ions were found to be 76.92 and 90.90 mgg^-1, respectively. The sorption data fitted well with Dubinin-Radushkevich isotherm model and the pseudo-second-order kinetic model. Thermodynamic parameters indicated that the sorption was non-spontaneous and endothermic. This paper reports the preparation of MNP and novel MOP and their application as efficient, sustainable adsorbents alternative to commercial ones for adsorption of cerium ions from aqueous solution.

In-situ formation and self-immobilization of biogenic Fe oxides in anaerobic granular sludge for enhanced performance of acidogenesis and methanogenesis

Addition of ferric oxides into flocculent anaerobic sludge was reported to enhance methanogenesis due to accelerated direct interspecies electron transfer (DIET) between syntrophic microbial communities. However, it is generally hard to incorporate Fe oxides into already matured anaerobic granular sludge (AGS) due to its special aggregated structure. In this study, a novel method was attempted to fast incorporate Fe oxides into AGS through in-situ microbial formation and immobilization of biogenic Fe oxides. Factors influencing the formation of Fe oxides were investigated and effects of Fe oxides on the acidogenic and methanogenic performance of AGS were assessed. Results showed that AGS could form Fe oxides mainly in the form of magnetite and hematite through biological reduction of Fe(III) oxyhydroxide. A maximum loading amount of 83.9 mg Fe/g MLVSS was obtained at pH 7 after contacting with 60 mM Fe(III) oxyhydroxide. The efficiency of electron donors which supported Fe(III) reduction followed the order of pyruvate > propionate > glucose > acetate > lactate > formate. Addition of electron transfer mediators (ETMs) promoted the formation of Fe oxides and their performance followed the order of AQDS > AQC > humics > FMN > riboflavin. Presence of Fe oxides in AGS (134.6 Fe/g VSS) increased the production of volatile fatty acids (VFAs) and methane by 16.28% and 41.94% respectively, comparing to the control. The enhancement may be attributed to increased conductivity and stimulated growth of exoelectrogens (Clostridium and Anaerolinea) and methanogenic endoelectrogens Methanosaeta in granular sludge which may strengthen direct interspecies electron transfer between syntrophic microbial communities. Overall, this study provides an alternative strategy to improve the digestion performance of AGS through in-situ formation and immobilization of biogenic Fe oxides.

Fe3O4@SiO2@CeO2 as a potential nanomagnetic carrier for oral delivery system and release of Celecoxib

AIMS AND OBJECTIVES

In this study, an attempt was made to synthesize, characterize, and develop many applications of functionalized rare metal oxide nanoparticles. Herein, a new strategy for drug delivery is developed to functionalize magnetite nanoparticles to improve their performances in the delivery of celecoxib.

MATERIALS AND METHODS

Magnetite Fe₃O₄@SiO₂ nanoparticles are synthesized by the sol-gel method. The surface of the hydroxyl groups was extended by treating with cerium nitrate salt; finally, sodium hydroxide was anchored to the surface hydroxyl groups to produce cerium oxide-functionalized Fe₃O₄@SiO₂@CeO₂ magnetic nanoparticles (FSC). The synthesized sample was characterized by FT-IR, FESEM, VSM, TGA, and XRD. Afterward, the functionalized nanoparticles were examined in the delivery of celecoxib as an active drug model involving cerium oxide and hydroxyl functional groups.

RESULTS

For this purpose, the amount of loading/release of the drug was investigated in different amounts of nanocomposite and pH values.

CONCLUSION

The results of the present investigation indicate that the formulations (m_FSC=5 mg, pH=3.3) can be considered as best among various formulations with respect to particle size, entrapment efficiency, and in-vitro successful drug release.

Iron oxide minerals promote simultaneous bio-reduction of Cr(VI) and nitrate: Implications for understanding natural attenuation

Nitrate and Cr(VI) coexist in aquifers, posing a potential threat to ecological environment and public health. Iron oxide minerals (hematite and magnetite) exist ubiquitously in groundwater, which are hot spots for biogeochemical transformation. However, there is still a knowledge gap anout the effect of iron oxide minerals on bioreduction of nitrate and Cr(VI). Here we observed that iron oxide minerals can significantly improve the ability of microorganisms to simultaneously reduce nitrate and Cr(VI), the reduction rates of nitrate and Cr(VI) increased by 7.3 and 8.5 times, respectively. The addition of minerals reinforced biofilm formation and shaped microbial communities with a new dominant strain of Azoarcus. The expression levels of functional genes were also upregulated, including napA, narG, nfsA, yieF, POD, and CAT. Furthermore, nitrate and chromate reductases' activities increased by 11 and 5 folds, respectively. These results demonstrated that iron oxide minerals participated in the bio-transformation of nitrate and Cr(VI) co-contamination, alleviating oxidative stress, shaping the microbial community, and ultimately accelerating bio-transformation. These findings offer a window into the biological transformation of co-contamination in the presence of iron oxide minerals, and insights to reveal strategies for microbial detoxification and to develop promising approaches for dealing with complex pollution conditions.

Green synthesis of some 3-(α,α-diarylmethyl)indoles by bio-nanocomposite from embedding L-histidinium trichloroacetate ionic liquid on functionalized magnetite (L-His+CCl3CO2-@PEG@SiO2-nano Fe3O4)

In this research, a new multilayered magnetized bio-nanocomposite has been prepared. At first, the amino acid-based ionic liquid was obtained from L-histidine and trichloroacetic acid (L-His⁺CCl₃CO₂^-), embedded on the polyethylene glycol-functionalized silicated-nanomagnetite, to prepare the final nanostructure (L-His⁺CCl₃CO₂^-@PEG@SiO₂-nano Fe₃O₄). The bio-nanocomposite was characterized by several techniques such as FT-IR, FESEM, TGA/DTG, EDAX, TEM, VSM, and XRD. The catalytic activity of the core-shell nanostructure was examined in one-pot three-component reaction between aryl aldehydes, indoles, and β-naphthol/phenols to get some new 3-(α,α-diarylmethyl)indoles under solvent-free conditions at 75 °C. Eco-friendly protocol in the absence of hazardous solvents, no observation of by-products such as bis(indolyl)methanes (BIMs), in addition to recovery and reusability of the nanostructure within 3 runs without activity loss are some highlighted notable features of the work. The reused bio-nanocomposite was also characterized through FESEM technique.

Capacitance enhancement of nitrogen-doped graphene oxide/magnetite with polyaniline or carbon dots under external magnetic field: Supported by theoretical estimation

The effect of conductive materials (polyaniline (PA) or carbon dots (Cdots)) added to supercapacitor consisting of nitrogen-doped graphene oxide (NG) and magnetic nanoparticles (magnetite, Fe₃O₄) was assessed. Small amounts (4 wt%) of Cdots in composites of NG and Fe₃O₄ nanoparticles have shown better supercapacitor performance than the addition of PA. When the external stimulating force (magnetic field, 8.98 mT) was coupled with the electrochemical system, the specific capacitance was highest (2213 F/g at a scan rate of 5 mV/s) and the cyclic retention was 91% after 5000 cycles for the NG/Cdots/Fe₃O₄ composite electrode. These reports show that the adequate ternary composite materials effectively enhance the specific capacitance, increase the specific energy density and maintain the durability of supercapacitors under the magnet. The increase in the specific capacitance under the uniform magnetic field was proportional to the 3/5 power of bulk electrolyte concentration, although the power value was different from the theoretical estimation. The complex capacitance was almost double under the magnetic field due to the convection induced by the Lorentz force. It was also confirmed in comparison with the theoretical estimation that the Lorentz effect was responsible for the reduction of the charge transfer resistance, the increase of the relaxation time constant, the facilitation of the ion diffusion, and hence the increase of the double-layer capacitance. The present results will open a new window for the enhancement mechanisms on the capacitance efficiency under the magnetic field.

Systematic evaluation of activated carbon-Fe3O4 composites for removing and degrading emerging organic pollutants

In this study, a comparative activity assessment of several activated carbon (AC) and AC-Fe₃O₄ composites was performed to evaluate their efficiency and versatility as Fenton-like catalysts. Although many studies have demonstrated the advantages of AC-based materials as Fenton-like catalysts, most have been developed using only one oxidant and/or one pollutant. Here, untreated (AC₀) and acid-treated AC (AC_A) iron-oxide composites were synthesized, characterized, and compared in terms of activity to bare AC using several oxidants and pollutants, the activation efficiency of hydrogen peroxide (H₂O₂) and ammonium persulfate ((NH₄)₂S₂O₈), and the subsequent oxidation extent and kinetics of bisphenol-A, atrazine, and carbamazepine by the AC-based materials were studied in depth. The persulfate-based systems showed considerably higher pollutant removal in the presence of the catalysts, despite lower persulfate decomposition rates: atrazine and carbamazepine were partially degraded, mainly through a radical-dependent pathway; the highest removal of atrazine was achieved with the AC_A-iron composite, whereas carbamazepine was best removed by the AC₀-iron composite. In contrast, bisphenol A was completely mineralized, probably via a non-radical pathway, in the presence of all AC-based composites, even at very low persulfate concentrations. Furthermore, bisphenol A removal remained high for several consecutive cycles, with the most efficient removal and stability observed in the presence of AC_A. These findings reveal the high complexity of AC-based systems, with multiple binding sites and degradation pathways unique to each combination of pollutants, catalysts, and oxidants. In general, the composition of the waste stream governs the applicability of these materials. Thus, the structure-function correlations and degradation mechanisms revealed here are crucial for improving sorbent-catalyst design and accelerating the implementation of low-cost remediation and in situ regeneration technologies.

Rationally designed Shewanella oneidensis Biofilm Toilored Graphene-Magnetite Hybrid Nanobiocomposite as Reusable Living Functional Nanomaterial for Effective Removal of Trivalent Chromium

Sustainable treatment of wastewater containing trivalent chromium (Cr³⁺) remains a significant challenge owing to the several limitations of the existing methodologies. Herein, combination of biosynthesis and Response Surface Methodology (RSM) for the fabrication and optimization of Shewanella oneidensis biofilm functionalized graphene-magnetite (GrM) nanobiocomposite was adopted as a 'living functional nanomaterial' (viz. S-GrM) for effective removal of Cr³⁺ ions from aqueous solution. In the biosynthetic process, S. oneidensis cells reduced the GO-akaganeite complex and adhered on the as-synthesized GrM nanocomposite to form S-GrM hybrid-nanobiocomposite. The process parameters for fabrication of S-GrM hybrid-nanobiocomposite was optimized by RSM based on four responses of easy magnetic separation, biofilm formation along with protein, and carbohydrate contents in extracellular polymeric substances (EPS). The morphology and chemical composition of S-GrM hybrid-nanobiocomposite were investigated using various spectroscopic and microscopic analyses and subsequently explored for removal of Cr³⁺ ions. The hybrid-nanobiocomposite effectively removed 304.64 ± 14.02 mg/g of Cr³⁺ at pH 7.0 and 30 °C, which is found to be very high compared to the previously reported values. The high surface area of graphene, biofilm biomass of S. oneidensis and plenty of functional groups provided a unique structure to the S-GrM hybrid-nanobiocomposite for efficient removal of Cr³⁺ through synergistic interaction. The FTIR and zeta potential studies confirmed that electrostatic and chelation/complexation reaction played key roles in the adsorption process. The fabrication of S-GrM nanobiocomposite thus creates a novel hybrid 'living functional nanomaterial' for low cost, recyclable, and sustainable removal of Cr³⁺ from wastewater.

Magnetite drives self-dechlorination of 4-chlorophenol in anoxic aquatic sediments

The lack of available electron donors is well known as a major factor limiting the efficiency of microbial dechlorination of 4-chlorophenol (4-CP) in anoxic aquatic sediments. Considering that Fe(III) minerals largely contained in sediments can especially enrich Fe(III)-reducing bacteria and unlock the ring-like intermediates produced by dechlorination of 4-CP via dissimilatory Fe(III) reduction, a strategy of self-dechlorination of 4-CP utilizing its metabolism intermediates such as short-fatty acids (SCFAs) as the endogenous electron donors with magnetite was proposed in this study. The results showed that the removal efficiency of 4-CP increased by 156-203% in magnetite-supplemented biotic groups compared with the magnetite-free biotic group. Liquid chromatography-mass spectrometer (LC-MS) and gas chromatography (GC) revealed the possible metabolic pathway of anoxic 4-CP degradation with magnetite: 4-CP→phenol→cyclohexene-1-carboxylic acid→2-hydroxycyclohexanecarboxylic acid→hexanoic acid/valeric acid→butyric/propionic acids→CO₂. High-throughput sequencing analysis showed that the abundance of functional bacteria, Desulfuromonas, Pseudomonas and Bacillus species, were increased by 1.38-1.97, 1.50-2.04, and 11.60-17.18 folds in magnetite-supplemented biotic groups, compared with the magnetite-free biotic groups. Analysis of Fe²⁺ concentration and cyclic voltammetry (CV) suggested that the potential Fe(III)/Fe(II) transformation occurred and proceeded the anoxic 4-CP degradation continuously.

Low-cost nanoparticulate oxidation catalysts for the removal of azo and anthraquinic dyes

PURPOSE

This study aimed to test the activity of Mn ferrite, hematin-Mn ferrite and colloidal maghemite in decomposition of Orange II (O-II) and Alizarin Red S (ARS) in model aqueous solutions.

METHODS

Color removal was explored at room temperature using magnetic stirring with and without a magnetic bar, taking advantage of the solids' magnetism. Decomposition of H₂O₂ was also studied separately and as radicals provider in dye decomposition. Catalyst/dye solution was fixed at 10 mg/4 mL. pH and dye concentration were variable. Absorbance was measured during 120 min by UV-Vis. Reuse of catalysts was also performed.

RESULTS

Azo dyes such as O-II are more resistant to oxidative removal using hydrogen peroxide than anthraquinone-like ARS. CITMD5 reduced ARS absorbance up to 71.9% when dye was less than 250 mg/L. HEM-Mn-MAG completely decolorized a 62.5 mg/L O-II solution at pH 11 while CITMD5 reached half of that conversion under the same conditions. The highest color removal in O-II/ARS mixtures was obtained with HEM-Mn-MAG, 40% absorbance reduction in 2 h. Mn-MAG is not active to remove O-II in presence of hydrogen peroxide in the 3-9 pH range at rt.

CONCLUSIONS

The high activity of Mn-MAG in hydrogen peroxide decomposition may be assigned to the combination of Mn⁺²/Mn⁺³ and Fe⁺²/Fe⁺³, because the MnO_x is active in the decomposition of hydrogen peroxide. Mn-MAG can be reused, preserving high activity in this reaction. Mn-based magnetic nanoparticles should be considered as inexpensive materials to treat textile wastewaters.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40201-021-00640-x.

Heterogeneous iron oxide nanoparticles anchored on carbon nanotubes for high-performance lithium-ion storage and fenton-like oxidation

In this work, heterogeneous hematite (Fe₂O₃) and magnetite (Fe₃O₄) nanoparticles are jointly engineered on the external surface of multi-walled carbon nanotubes (CNTs) to construct a composite material (Fe₂O₃@Fe₃O₄/CNT). A simple one-step redox reaction is triggered in a hydrothermal reaction system containing functionalized CNT (FCNT) aqueous suspension and iron foils. Both Fe₂O₃ and Fe₃O₄ nanoparticles with controlled size are generated and well dispersed in the interconnected CNT framework. Controlled samples of Fe₂O₃@Fe₃O₄ and Fe₃O₄/CNT have also been prepared and used to investigate the synthetic mechanism and evaluate the lithium-ion storage performances. As an anodic active material for lithium-ion batteries, the Fe₂O₃@Fe₃O₄/CNT composite delivered a high reversible capacity of about 924 mAh·g^-1 for 200 continual charge/discharge cycles under a high current rate of 1000 mA·g^-1. As a catalyst in a Fenton-like reaction for degrading methyl orange (MO) contaminant in waterbody, the Fe₂O₃@Fe₃O₄/CNT composite exhibited an attractive decomposition efficiency (99.5% decomposition within 60 min) and good stability. The beneficial factors contributing to the inspiring performances are discussed. The effective and scalable material design and synthesis method can be regarded to have good potential in other fields.

Technetium immobilization by chukanovite and its oxidative transformation products: Neural network analysis of EXAFS spectra

The uptake of the fission product technetium (Tc) by chukanovite, an Fe^II hydroxy carbonate mineral formed as a carbon steel corrosion product in anoxic and carbonate-rich environments, was studied under anoxic, alkaline to hyperalkaline conditions representative for nuclear waste repositories in deep geological formations with cement-based inner linings. The retention potential of chukanovite towards Tc^VII is high in the pH range 7.8 to 12.6, evidenced by high solid-water distribution coefficients, log R_d ~ 6, and independent of ionic strength (0.1 or 1 M NaCl). Using Tc K-edge X-ray absorption spectroscopy (XAS) two series of samples were investigated, Tc chukanovite sorption samples and coprecipitates, prepared with varying Tc loadings, pH values and contact times. From the resulting 37 XAS spectra, spectral endmembers and their dependence on chemical parameters were derived by self-organizing (Kohonen) maps (SOM), a neural network-based approach of machine learning. X-ray absorption near-edge structure (XANES) data confirmed the complete reduction of Tc^VII to Tc^IV by chukanovite under all experimental conditions. Consistent with mineralogical phases identified by X-ray diffraction (XRD), SOM analysis of the extended X-ray absorption fine-structure (EXAFS) spectra revealed the presence of three species in the sorption samples, the speciation predominately controlled by pH: Between pH 7.8 and 11.8, TcO₂-dimers form inner-sphere sorption complexes at the surface of the initial chukanovite as well as on the surface of secondary magnetite formed due to redox reaction. At pH ≥ 11.9, Tc^IV is incorporated in a mixed, chukanovite-like, Fe/Tc hydroxy carbonate precipitate. The same species formed when using the coprecipitation approach. Reoxidation of sorption samples resulted in a small remobilization of Tc, demonstrating that both the original chukanovite mineral and its oxidative transformation products, magnetite and goethite, contribute to the immobilization of Tc in the long term, thus strongly attenuating its environmental transport.

Facile synthesis of a rod-like porous carbon framework confined magnetite nanoparticle composite for superior lithium-ion storage

This work demonstrates a streamlined method to engineer a rod-like porous carbon framework (RPC) confined magnetite nanoparticles composite (Fe₃O₄/RPC) starting from metallic iron and gallic acid (GA) solution. First, a mild redox reaction was triggered between Fe and GA to prepare a rod-shaped metal-organic framework (MOF) ferric gallate sample (Fe-GA). Then, the Fe-GA sample was calcinated to obtain a prototypic RPC supported metal iron nanoparticle intermediate sample (Fe/RPC). Finally, the Fe₃O₄/RPC composite was synthesized after a simple hydrothermal reaction. The Fe₃O₄/RPC composite exhibited competitive electrochemical behaviors, which has a high gravimetric capacity of 1140 mAh·g^-1 at a high charge and discharge current of 1000 mA·g^-1 after 300 cycles. The engineered RPC supportive matrix not only offers adequate voids to buffer the volume expansion from inside well-dispersed Fe₃O₄ nanoparticles, but also facilitates both the ionic and electronic transport during the electrochemical reactions. The overall material synthesis involves of no hazardous or expensive chemicals, which can be regarded to be a scalable and green approach. The obtained samples have a good potential to be further developed for wider applications.

Enhancing anaerobic digestion of kitchen wastes via combining ethanol-type fermentation with magnetite: Potential for stimulating secretion of extracellular polymeric substances

Magnetite, a common mineral that is abundant in the soils and sediments, has been widely documented to enhance the anaerobic digestion of organic wastes, whereas the mechanisms of magnetite promoting interspecies electron transfer are still unclear. In this study, under the conditions (ethanol-type fermentation) employed, magnetite stimulated the secretion of extracellular polymeric substances (EPS). Analysis of three-dimensional excitation emission matrix revealed that these EPS secreted in the presence of magnetite were primarily comprised of the redox-active organic functional groups. Electrochemical analysis showed that the EPS secreted with magnetite had the higher electron-accepting and electron-donating capacity than the EPS without magnetite. Syntrophomonas species capable of extracellularly transferring electron were enriched with supplementing magnetite. Together with the increased abundance of Methanospirillum and Methanobacterium species that could proceed direct interspecies electron transfer (DIET), the anaerobic digestion was likely improved due to the establishment of DIET with supplementing magnetite. As a result, anaerobic digestion of kitchen wastes was evidently enhanced. With decreasing the solid retention time to 30 d, the methane production rate only slightly declined to 18 ± 0.8 mL/g-VSS/d in the magnetite-supplemented digester, while almost no methane was detected in the digester without magnetite.

Prolific shedding of magnetite nanoparticles from banknote surfaces

Here, we use magnetic methods first to quantify the content of strongly magnetic particles of banknotes (US dollars, USD, and British pounds sterling, GBP), and then examine the possibility of their release from handled banknote surfaces. The content of magnetic particles, from magnetic remanence measurements, for the USD and paper GBP banknotes is high; greater, for example, than that in vehicle engine-exhaust emissions, and similar to that for airborne roadside particulate matter (PM). Our magnetic analyses of USD and GBP banknotes, and of the ink pigment widely used in their printing, reveal not only that the banknotes are highly magnetic, but also that strongly magnetic, nano-sized particles are readily and prolifically shed from their surfaces (especially from the USD banknotes). A common practice, prior to increased automation, was for bank tellers to count banknotes by licking a finger to adhere to each successive counted note, and thus speed up the manual counting process. Given the rate of particle shedding reported here, this traditional manual counting procedure must have resulted in prolific transfer of iron-rich nanoparticles both to the fingers and thence to the tongue. We hypothesise that, pre-automation, magnetite and other metal-bearing nanoparticles were repetitively and frequently ingested by bank tellers, and subsequently entered the brain directly via the taste nerve pathway, and/or indirectly via the systemic circulation and the neuroenteric system. This hypothesis may plausibly account for the reported and currently unexplained association between elevated neurodegeneration-related mortality odds ratios and this specific occupation.

Cerium-modified iron oxides applied as catalysts in the heterogeneous Fenton system for degradation of cephalexin

The effect of incorporation of different amounts of cerium on iron oxides and different heat treatment temperatures was evaluated for the degradation of cephalexin (CEX) using heterogeneous Fenton and photo-Fenton processes. The materials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), specific area (BET), and zeta potential (ZP). The conversion of magnetite to maghemite was observed when a 140 °C thermal treatment was applied. The insertion of cerium resulted in a loss of the uniform spherical shape of the particles. The material containing the lowest amount of cerium (0.5% w/w) presented an increase in the specific area from 91.2 to 171.6 m² g^-1 relative to the pure iron oxide, while with 2% (w/w) a decrease to 99.2 m² g^-1 was observed for the materials treated at 70 °C. The same behavior was observed for materials treated at 140 °C, however, with smaller areas. At pH 6.0, a low catalytic activity was observed contrasting to the high consumption of H₂O₂, suggesting its catalytic decomposition into water and oxygen. This was confirmed by the very low production of HO• in the degradation system. On the other hand, the high production of HO• was observed at pH 3.5, which was chosen as a working pH. The material treated at 140 °C and containing 1% Ce (w/w) was the highlight, promoting degradation of 0.052 mg of CEX per m² area of the catalyst after 150 min using 1.0 mmol L^-1 of H₂O₂. The CEX intermediates identified indicated hydroxylation as the major route of degradation.

Hydroxyapatite with magnetic core: Synthesis methods, properties, adsorption and medical applications

This review presents the actual state of knowledge and recent research results on the magnetic composite synthesized from iron oxide (γ-Fe₂O₃ or Fe₃O₄) and hydroxyapatite. It can be obtained applying some methods, i.e. chemical precipitation, hydrothermal, sol-gel, and biomimetic or combined techniques which exhibit characteristic properties affecting the form of the prepared product. More specific details are discussed in this paper. A comparison of the discussed synthesis methods is presented. On the basis of selected publications, a comparison of the results of the analysis by XRD, FTIR, SEM and EDX methods for hydroxyapatite with a magnetic core was also presented. Moreover, the characteristics large adsorption capacity and specific area allow employing nanocomposites as adsorbents particularly in removal of toxic metal ions. Nowadays this issue is extremely vital due to large amounts of pollutants in the environment and greater ecological awareness of people. Moreover, magnetic hydroxyapatite can be also applied as a catalyst in various syntheses or oxidation reactions as well as in medicine in magnetic resonance imaging, hyperthermia treatment, drug delivery and release, bone regeneration or cell therapy.

Phosphate modified magnetite@ferrihydrite as an magnetic adsorbent for Cd(II) removal from water, soil, and sediment

This work successfully fabricated a novel magnetic adsorbent, i.e., phosphate modified magnetite@ferrihydrite (Mag@Fh-P), and explored its potential application for Cd(II) removal from water, soil, and sediment. To synthesize the adsorbent, ferrihydrite-coated magnetite (Mag@Fh) was firstly developed with partially acid-dissolved natural magnetite particles, followed by in-situ synthesis of ferrihydrite on magnetite surface via alkali addition. Selection of natural magnetite as iron source for ferrihydrite synthesis and as magnetic core is believed to save the cost of adsorbent. Then, phosphate was loaded on Mag@Fh by impregnation-heating treatment to produce Mag@Fh-P. Batch adsorption experiments revealed that the Cd(II) adsorption on Mag@Fh-P could reach equilibrium within 60 min, and the calculated adsorption capacity using Langmuir model was 64.1 mg/g, which was significantly higher than that on magnetite (0.44 mg/g) and Mag@Fh (23.9 mg/g). The results from X-ray photoelectron spectroscopy analysis and batch adsorption experiments confirmed that both ligand exchange and electrostatic attraction contributed to Cd(II) adsorption. Besides, Mag@Fh-P can also be an efficient amendment for soil and sediment remediation. The spent Mag@Fh-P could be easily recovered via magnetic separation, accompanied by the significant decrease in total Cd(II) concentration in soil/sediment. At an adsorbent dosage of 2 wt%, 0.82 and 0.74 mg/kg of total Cd(II) in soil and sediment was removed, respectively. In all, the synthesized Mag@Fh-P as adsorbent has the merits of cost effectiveness, fast adsorption rate, high adsorption capacity, and easy separation, and thus it has promising application for the removal of heavy metal cations from water, soil, and sediment.

Comparative study of arsenic removal by iron-based nanomaterials: Potential candidates for field applications

Graphene oxide supported magnetite (GM) and graphene oxide supported nanoscale zero-valent iron (GNZVI) nanohybrids were compared for arsenic removal at a wide pH range (3-9). While already published work reported high process efficiency for GM and GNZVI, they cannot be compared one-on-one given the non-identical experimental conditions. Each researcher team used different initial arsenic concentration, solution pH, and adsorbent dose. This study evaluated GM and GNZVI, bare magnetite (M), and bare nanoscale zero-valent iron (NZVI) for aqueous arsenic removal under similar experimental conditions. GNZVI worked more efficiently (>90%) in a wide pH range (3-9) for both As(III) and As(V), while GM was efficient (>90%) only at pH 3 for As(V) and As(III) removal was maximum of ~80% at pH 9. GNZVI also exhibited better aqueous dispersibility with a zeta potential of -21.02 mV compared to other adsorbents in this experiment. The arsenic removal based on normalized iron content indicated that the nanohybrids recorded improved arsenic removal compare to bare nanoparticles, and GNZVI worked the best. In NZVI-based nanomaterials (GNZVI and NZVI), electrostatic attraction played a limited role while surface complexation was dominant in removal of both the arsenic species. In case of M-based nanomaterials (GM and M), As(V) removal was controlled by electrostatic attraction while As(III) adsorption was ligand exchange and surface complexation. GNZVI has the potential for field application for drinking water arsenic removal.