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•γ-Fe2O3 nanoparticles were synthesized by Flame Spray Pyrolysis (FSP).•γ-Fe2O3 nanoparticles were characterized and they remediated aqueous Pb2+ and Cu2+.•Maghemite adsorption ...capacities of ∼69 (Pb2+ at 45°C) and ∼34 (Cu2+ at 25°C) mg/g were obtained.•Likely Pb2+ and Cu2+ sorption mechanisms versus pH were described.•γ-Fe2O3 nanoparticle application in ground water remediation was demonstrated.
Superparamagnetic maghemite (γ-Fe2O3) nanoparticles of controllable morphology were successfully synthesized using a flame spray pyrolysis (FSP) technique. Their physico-chemical properties, size, morphology, and surface chemistries were determined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), selected area electron diffraction patterns (SAED), SEM-EDX, scanning electron microscopy (SEM), and pHZPC(6.3). Elemental contents before and after adsorption were identified using energy dispersive X-ray fluorescence (ED-XRF), energy dispersive X-ray analysis (EDX) and elemental mapping. Surface area (SBET 79.35m2/g) and size distribution analyses were conducted using a surface area analyzer and dynamic light scattering (DLS), respectively. The magnetic moment (44.5 at 300K and 50.16 at 2K) was determined using a physical properties measurement system (PPMS). The first adsorption study using γ-Fe2O3 nanoparticles synthesized by FSP to successfully remediate Pb2+ and Cu2+ from water is reported. Batch adsorption studies were carried out. An optimum pH of 5.0 was studied for Pb2+ and Cu2+ removal. Pb2+ and Cu2+ removal mechanisms by these maghemite nanoparticles were presented. The adsorption of Pb2+ and Cu2+ was highly pH-dependent. The metal ion uptake was mainly governed by electrostatic attractions. Sorption kinetic data followed the pseudo-second-order model. The Freundlich, Langmuir, Redlich–Peterson, Radke and Sips adsorption isotherm models were applied to interpret equilibrium data. The Freundlich and Langmuir isotherm equations best fit the respective equilibrium data for Pb2+ and Cu2+. The maximum Langmuir adsorption capacities of these maghemite nanoparticles were 68.9mg/g at 45°C for Pb2+ and 34.0mg/g at 25 °C for Cu2+. Thus, these maghemite nanoparticles made by FSP were readily prepared, characterized and showed promise for remediating heavy metal ions from aqueous solutions.
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•Good performance on arsenic removal is achieved with composite materials.•Chitosan beads show good mechanical properties both in batch and column experiments.•Magnetic materials are ...obtained with specific metal solution/plant extract ratios.•Magnetic properties are only observed during nanoparticle immobilization in chitosan beads.
New magnetic hybrid materials were developed by the encapsulation of iron oxide nanoparticles into a chitosan matrix. A green synthesis method to obtain metallic nanoparticles was conducted using eucalyptus extract as reducing agent. Well-formed iron oxide nanoparticles were successfully synthesized. Under precise conditions, the encapsulation of the synthesized iron oxide nanoparticles in chitosan beads leads to the formation of magnetic hybrid organic/inorganic materials. The XRD pattern of these materials shows peaks that match with structure similar to maghemite for those materials showing magnetic properties. The new hybrid materials were proved as sorbent in a complete arsenic removal study (pH dependence, kinetic and equilibrium experiments) showing good features and sorption capacity. The large scale sorption capacity of the new material was also successfully proved in a continuous flow study using a column filled with beads of the hybrid magnetic material.
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•Product film of Ni-advanced weathering steel exposed to Maldives is thoroughly studied.•The product film displays a better resistance to atmospheric corrosion due to the superior ...structure and phase compositions and distribution.•The inner film is mainly composed of fine grains’ goethite, while the outer film is constituted by maghemite, akaganeite, and hematite.•NiFe2O4 is specifically enriched in the inner film, which improves the nature of product film.
The product film formed on Ni-advanced weathering steel in a tropical marine environment was investigated in detail through outdoor exposure by using diverse surface analysis techniques combined with electrochemical impedance spectroscopy and scanning kelvin probe measurements. The results showed that the product film was mainly composed of nanophasic goethite in the inner layer and maghemite, akaganeite, and hematite in the outer layer. Moreover, the resistance to atmospheric corrosion gradually increased from the outermost product film to the innermost film. Ni was significantly enriched in the inner layer in the form of the spinel phase NiFe2O4, which transformed lepidocrocite to fine-grained goethite, withstood the invasion of chloridion, and improved the corrosion potential of the product film in a tropical marine atmosphere.
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•PPY/γ-Fe2O3 and PANI/γ-Fe2O3 MNCs can be used for the magnetic removal of Cr (VI) and Cu (II) ions from aqueous media.•These MNCs can be recovered from a polluted liquid medium by ...the application of an external magnetic field.•These MNCs can be easily recycled and reused for at least four adsorption cycles.•These MNCs can adsorb a high amount of Cr (VI) and Cu (II) ions in a relatively short time.•These MNCs are promising low-cost materials for heavy metal ions removal.
We examined the use of polypyrrole/maghemite (PPY/γ-Fe2O3) and polyaniline/maghemite (PANI/γ-Fe2O3) magnetic nanocomposites (MNCs) as active agents for removal of heavy metals ions from aqueous media. We have used chemical co-precipitation methods to prepare the maghemite nanoparticles. Subsequently, we synthesized the MNCs through emulsion polymerization of pyrrole or aniline. We estimated the efficiency of these MNCs for Cr (VI) and Cu (II) removal by using batch methods and inductively coupled plasma-optical emission spectroscopy (ICP-OES) to measure the metal content in the solutions before and after use of the MNCs. We evaluated the adsorption capacity (qe) of each MNC as a function of the solution pH and of the time allowed for its interaction with the metallic ions in solution. In the Cr (VI) Cu (II) case, we determined the value of qe as 209 171 mg/g, for the PPY/γ-Fe2O3 MNC, and 196 107 mg/g, for the PANI/γ-Fe2O3 MNC. In the PPY/γ-Fe2O3 PANI/γ-Fe2O3 MNC case, the time necessary for attaining the qe saturation limit was of the order of 15 35 min for both Cr (VI) and Cu (II). These characteristics compare favorably to those of alternative agents for removal of dissolved metal ions reported in the literature.
This study presents a new bottom-up biofabrication method to produce highly porous magnetic biochar from waste-derived fungal biomass. Neurospora crassa was grown in iron containing coagulation ...backwash (BW) diluted with primary effluent (PE) wastewater in two ratios of 1:4 (PE-BW 1:4) and 3:4 (PE-BW 3:4). The fungi encapsulated iron directly into biomass hyphae and carbonization resulted in one-step biochar preparation and maghemite (Fe2O3) formation. The morphology and structure of the materials were investigated using a suite of characterization tools. Results indicated that the physiochemical properties of each char were dependent on the blend used for fungal cultivation. PE-BW 1:4 had much larger average pore diameters (13.2 nm vs. 6.1 nm), less elemental surface carbon (2.1% vs. 23.7%), and more expansive Fe2O3 formation. Batch phosphorus adsorption experiments were conducted in the range of 0–90 mg-P/L, and a maximum adsorption density of 23.9 mg/g was achieved. Langmuir, Freundlich and Temkin isotherms were used to describe the interactions of the phosphate on the absorbents and an in-depth error analysis was conducted. Further characterization of the P-loaded chars indicated adsorption primarily via P-OH bonding on the surface of the materials. This new biofabrication method showed great potential to magnetic biochar production with excellent phosphorus adsorption, which can be effectively used in wastewater resource recovery.
•Fungi (N.crassa) can be used as a feedstock for direct magnetic biochar production.•Physiochemical properties of biochar are dependent on the fungal growth conditions.•Fungal biochar effectively adsorbed phosphorus from aqueous solution.
Alkaline oxides concerted with acidic -COOFe structure, for the one-pot esterification and transesterification of high AV Jatropha oils without saponification. Zn8@Fe-C400 nanoparticles achieved ...nearly 100% Jatropha biodiesel yield at 160 °C within 4h, and was used for at least 10 cycles with biodiesel yield of >94.3% at acid value of 6.3 mg KOH/g.
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•Biodiesel production was catalyzed with magnetic acid-base amphoteric nanoparticles (<46 nm).•Zn8@Fe-C400 nanoparticles presented good activity, stability and reusability.•Strong magnetism for Zn8@Fe-C400 nanoparticles benefitted the continuous biodiesel production.•Jatropha biodiesel yield of 100.0% was achieved for Zn8@Fe-C400 without saponification.•Zn8@Fe-C400 was cycled for at least 10 times with biodiesel yield of >94.3%.
Biodiesel production from Jatropha oils with high acid value at low temperature was catalyzed with synthesized novel magnetic acid-base amphoteric nanoparticles (<46 nm). Alkaline oxides (ZnFe2O4, ferrihydrite, zincite, maghemite and magnetite) concerted with acidic -COOFe structure, benefited the one-pot esterification and transesterification of Jatropha oils with high acid value to produce biodiesel without additional pretreatment. The strong magnetism of catalyst helped catalyst separation for recycle in continuous biodiesel production. Jatropha biodiesel yield of 100% at 160 °C within 4 h, with methanol/oil molar ratio of 40/1 and catalyst dosage of 7 wt% was achieved, while the catalyst can be cycled for at least 10 times with biodiesel yield >94.3% at acid value of 6.3 mg KOH/g. No obvious saponification was observed during the reactions and storage.
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Nowadays there is a continuously increasing worldwide concern for the development of efficient wastewaters treatment technologies. Among the heavy metal ions, chromium holds a ...distinct position due to its high toxic nature to biological systems. This study aims to assess magnetite derivatives nanoparticles for the removal of Cr(VI) species. Crystalline magnetite-rich (Magn) and pure maghemite (Magh) nanoparticles were produced by the polyol method and by subsequent heat treatment of Magn, respectively. The XRD analysis confirmed the formation of nanosized single phase cubic spinels with a cell parameter of 8.3710(2)Å for Magn and 8.3401(2)Å for Magh, consistent with those of a magnetite-rich ferrite and maghemite, respectively. TEM analysis showed that the two nanoferrites possessed comparable mean particle size of ∼15nm. Magn and Magh showed superparamagnetic behavior at room temperature and reasonable saturation magnetizations at 300K of 69 and 67emu.g−1, respectively. The Curie temperature of both nanoferrites exceeded 350°C allowing the materials to work in severe conditions. Room temperature, batch adsorption experiments of Cr(VI) onto maghemite nanoparticles were carried out at pH 2.0. Adsorption efficiency increased rapidly was the increase of the nanoparticles dose. For a 20mg.L−1 Cr(VI) solution a 100% removal was found with ∼3g.L−1 dose. Additionally, for a given dose (4.0g.L−1), the adsorption rate measured as a function of time for different Cr(VI) concentrations was very rapid; ∼90% of removable Cr(VI) species was achieved within 10min. The high rate of Cr(VI) uptake takes advantages of the high active surface chemistry of the nanoparticles. The adsorption of Cr(VI) onto Magh nanoparticles followed a pseudo-second order kinetics indicating a chemisorption process. Further, the Langmuir isotherm model was found to best describe the equilibrium data with a maximum adsorption capacity of 12.5mg.g−1 for an adsorbent dosage of 4.0g.L−1.
A nanocatalyst comprising ultra-small Pd/PdO nanoparticles (<5 nm) supported on maghemite was prepared by a co-precipitation protocol using inexpensive raw materials and was deployed successfully in ...various significant synthetic transformations, namely the Heck–Mizoroki olefination (up to 95%), the Suzuki reaction (60–95%), and the allylic oxidation of alkenes under milder conditions. The chemical nature, morphology, size, and loading of palladium nanoparticles over the magnetic support were studied by TEM/EDX, HAADF-STEM chemical mapping, XPS, AAS, and in-field 57 Fe Mössbauer spectroscopy. The cost-effective catalyst could be easily separated from the reaction mixture by using an external magnet and reused four times without any loss of activity; chemical stability and recyclability aspects of the catalyst were investigated.
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•Fe aggregated to the surface with pyrolysis temperature increases.•γ-Fe2O3 was the primary Fe species in Fe-modified biochars.•Fe(0) was observed in Fe-modified biochar pyrolyzed at ...600 or 900 °C.•FeCl3BC900 enhanced As(V), As(III), Cr(VI), and Hg(II) removal.
Characterization of the spatial distribution and speciation of iron (Fe) in Fe-modified biochars is critical for understanding the mechanisms of contaminant removal. Here, synchrotron-based techniques were applied to characterize the spatial distribution and speciation of Fe in biochars modified by FeCl3 or FeSO4 and pyrolyzed at 300, 600, and 900 °C, respectively. Confocal micro-X-ray fluorescence imaging (CMXRFI) results indicated Fe, sulfur (S), and chlorine (Cl) diffused into the basic porous structure of the biochars and aggregated to the surface as pyrolysis temperature increased. Fe K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra revealed maghemite (γ-Fe2O3) as the primary Fe species in the modified biochars and Fe(0) was observed when pyrolyzed at 600 or 900 °C. Unmodified and FeCl3-modified biochars pyrolyzed at 900 °C were evaluated in the removal of arsenate (As(V)), arsenite (As(III)), hexavalent chromium (Cr(VI)) and Hg(II) from aqueous solution and Fe-modification enhanced the removal efficiency from 42.0%, 62.5%, 19.6%, and 97.0%, respectively, to all 99.9%. X-ray absorption spectroscopy results indicate both adsorption and redox reaction contributed to the removal mechanisms. The present study provides a prospective and sustainable material and offers information relevant to tailoring Fe-modified biochars to specific environmental applications.
Iron oxide magnetic nanoparticles produced by chemical synthesis are usually composed of both magnetite and maghemite phases. Information about the phase composition is typically obtained using ...Mössbauer spectroscopy. A method that can provide information about the magnetite versus maghemite phase composition of the nanoparticles and the organization of the phases simply from magnetization curve is still missing. Here we present a simple and elegant method that for nanoparticles with a known size distribution can give information about the magnetite and maghemite phase composition and suggests a magnetite core and a maghemite shell structure for all the nanoparticles sizes. The method is based on fitting of the room-temperature magnetization curve using a Brillouin function, while considering dipolar interactions. The model predicts that the nanoparticles are composed of a single magnetic domain for sizes below 14 nm. The model is validated by Mössbauer spectroscopy.
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