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A facile magnetosensitive catalyst fabrication of palladium/platinum coated maghemite nanocomposites and characterization are presented here. Firstly, the maghemite nanoparticles (NPs) are modified by 3-aminopropyltriethoxysilane ...
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A facile magnetosensitive catalyst fabrication of palladium/platinum coated maghemite nanocomposites and characterization are presented here. Firstly, the maghemite nanoparticles (NPs) are modified by 3-aminopropyltriethoxysilane (APTES) to form surface-amino-groups-terminated APTES-maghemite NPs. Then the chloroplatinic acid/palladium chloride is added into the former solution and the Pt~(4+)/Pd~(2+) is absorbed via coordination and adsorption interaction on the modified NPs surface. Finally, the hydrazine hydrate (HHA) is added to reduce and turn the Pt~(4+)/Pd~(2+)-complexed NPs into magnetic palladium/platinum coated maghemite nanocomposites (γ-Fe_2O_3/M, M = Pt/Pd) under ultrasonic exposure. The morphology, microstructure, composition and magnetic properties of the γ-Fe_2O_3/M nanocomposites are investigated by various characterizations of X-ray diffraction (XRD), transmission electron microscopy (TEM) with selected area electron diffraction (SAED), High Resolution Transmission Electron Microscopy (HRTEM) and superconducting quantum interference device (SQUID) magnetometry. The results show that the diameters of precursor maghemite NPs are about 20 nm, and those of the γ-Fe_2O_3/Pt and γ-Fe_2O_3/Pd NPs are about 68 nm and 36 nm, respectively. Their saturation magnetizations (Ms) are 29.4 emu·g~(-1) and 31.2 emu·g~(-1) at ambient temperature, respectively. The combination of noble mental coating and inherent magnetic response enables the γ-Fe_2O_3/M nanocomposites for magnetosensitive catalyst system application and relevant catalytic activity needs further and considerable investigation. These magnetic NPs fabrication have opened a new way for recovering of Pt and Pd in magnetosensitive catalyst system.
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A maghemite-like phase referred to here as “hydromaghemite” was obtained as an intermediate product in the hydrothermal transformation of phosphated 2-line ferrihydrite into hematite. In this study, we used magnetic and non-magn...
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A maghemite-like phase referred to here as “hydromaghemite” was obtained as an intermediate product in the hydrothermal transformation of phosphated 2-line ferrihydrite into hematite. In this study, we used magnetic and non-magnetic (e.g., X-ray Absorption Near Edge Structure, XANES) techniques in combination to characterize a series of the intermediate products obtained in the aging of phosphated ferrihydrite (P/Fe atomic ratio = 0.03) at 150°C for 120 days. Particle size calculated from both the specific surface area and average unblocking temperature increased with time. XANES spectra revealed the presence of some tetrahedrally coordinated iron, which is consistent with the formation of hydromaghemite (the dominant magnetic phase in the intermediate products). Thus grain size in newly formed hydromaghemite particles increased with time from the initial values in the superparamagnetic region to others in the single-domain region. Further transformation of hydromaghemite into hematite, which was complete by day 120, was probably due to hydromaghemite becoming unstable relative to hematite when the surface to volume ratio fell below a given threshold. The relationships between pedogenically produced maghemite and hematite contents in various soils and paleosols suggest that the ferrihydrite → hydromaghemite → hematite transformation may constitute a major pathway accounting for the magnetic enhancement in many soils.
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The oxidation process from magnetite to hematite through maghemite was investigated by X-ray diffraction (XRD) and X-ray absorption spectroscopic techniques. The XRD pattern of magnetite heated at 100 ℃ for 3 h showed small refle...
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The oxidation process from magnetite to hematite through maghemite was investigated by X-ray diffraction (XRD) and X-ray absorption spectroscopic techniques. The XRD pattern of magnetite heated at 100 ℃ for 3 h showed small reflections of maghemite with partially ordered distribution of vacancy (space group P4_132 or P4_332). Thereafter, the XRD pattern of magnetite heated at 250 ℃ for 3 h exhibited extra reflections corresponding to the tetragonal maghemite with fully ordered distribution of vacancy (space group P4_12-12 or P4_32_12). Diffraction peaks of hematite occurred from the magnetite heated at 250 ℃, in which maghemite and hematite coexisted with magnetite. Diffraction peaks of magnetite subsequently disappeared at 300 ℃. Instead, maghemite and hematite dominated the XRD pattern, but the amount of maghemite reduced from 300 ℃. The maghemite completely disappeared at 500 ℃, and hematite finally dominated the XRD pattern. Rietveld fitting results clearly showed that the a lattice parameter and site occupancy factor of Fe at the octahedral site continuously decreased at the temperatures from 25 to 300 ℃. The X-ray absorption near edge structure (XANES) result showed that the Fe~(3+)/ΣFe increased up to 300 ℃ and remained constant until 500 ℃, indicating that Fe~(2+) in oxidized magnetite was completely oxidized to Fe~(3+) at 300 ℃. Furthermore, the intensities of radial structure function (RSF) peaks at 1.7 and 3.1 A corresponding to the Fe-0 bonds in octahedral site and the Fe-Fe interaction between the octahedral sites reduced continuously from 25 to 300 ℃. The fitting results of the first shells indicated that the coordination number and site occupancy factor at the octahedral site continuously decreased at the temperature range from 25 to 300 ℃, which were approximately consistent with those of Rietveld fitting analysis. The a lattice parameter of the oxidized magnetite displayed a linear trend between stoichiometric magnetite and stoichiometric maghemite with a relationship of a = 0.0985x+ 8.3397 (x = Fe2+/Fe3+). It was clearly confirmed that during the magnetite oxidation, Fe was continuously removed from the octahedral sites, which resulted in the formation of maghemite with partially ordered distribution of vacancy. Just after magnetite oxidation was completed, the vacancy ordering further progressed by the diffusion of Fe~(3+) within the structure, leading to the formation of maghemite with fully ordered distribution of vacancy.
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Magnetic nanoparticles of pure and substituted iron oxides are prepared by single step autocombustion or by wet chemical methods. The nanoparticles prepared by the first process had mixed phase of hematite and maghemite whereas th...
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Magnetic nanoparticles of pure and substituted iron oxides are prepared by single step autocombustion or by wet chemical methods. The nanoparticles prepared by the first process had mixed phase of hematite and maghemite whereas the later essentially gives maghemite phase. XRD patterns and TEM micrographs of the pure and substituted maghemites samples suggest about their monophasic nature and inverse spinel structure. Further, the size of the particles for the above iron oxide samples was found to be in the range of 4 to 30 nm. Saturation magnetization value for the samples was observed to be varying with the type and the amount of substitution. For example, magnetization value initially increased and then decreased for Al- and Mn-substitutions but it continuously decreased for Cr- and Zn-substitutions. Contrary to the saturation magnetization value, the Curie temperature decreased continuously with increased substitutions irrespective of the type of substitutions. Due to higher magnetization value of Mn-substituted maghemite (for x = 0.2, 78 Am~2/kg), it has higher heating ability and specific absorption rate compared to Al-substituted maghemite (for x = 0.07, 70 Am~2/kg) and pure maghemite (62 Am~2/kg).
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In the present study,Eucalyptus camaldulensis bark/maghemite composite(ECMC)was used for potential application as a low-cost adsorbent for the removal of Cr(VI)from aqueous solution.The structural characterization,morphology and e...
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In the present study,Eucalyptus camaldulensis bark/maghemite composite(ECMC)was used for potential application as a low-cost adsorbent for the removal of Cr(VI)from aqueous solution.The structural characterization,morphology and elemental analysis of ECMC were performed by Scanning Electron Microscopy(SEM),Energy-Dispersive X-ray(EDX)and X-ray Diffraction(XRD).The effects of various independent parameters,contact time,initial Cr(VI)concentration,temperature,pH,and adsorption were investigated.It was found that the adsorption capacity of ECMC increases with increasing Cr(VI)concentration and temperature.The optimum pH was found to be 2 for the removal of Cr(VI)by ECMC.The adsorption capacity was found to be 70.1 mg/g with 0.1 g ECMC at pH 2 and 30 ℃.Additionally,10 and 50 mg/L Cr(VI)were removed from 100 mL aqueous solution by 0.1 g ECMC with 99 % and 93.46 % removal efficiencies,respectively.Langmuir,Freundlich,Temkin,Dubinin-Radushkevich,Jovanovic,Smith,Koble Korringen,Vieth-Sladek and Sips Isotherm Models were applied to the experimental data to understand the adsorption mechanism better.The Freundlich Isotherm Model described the adsorption process better(R2 = 0.991)among the other isotherms studied.
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The present manuscript elucidated the ameliorative potential of nano-maghemite (FeNPs) against the hazardous effects of fluoride toxicity in the sensitive rice cultivar, IR-64. Fluoride pollution triggered bioaccumulation in root,...
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The present manuscript elucidated the ameliorative potential of nano-maghemite (FeNPs) against the hazardous effects of fluoride toxicity in the sensitive rice cultivar, IR-64. Fluoride pollution triggered bioaccumulation in root, shoot and spikelets which inhibited reproduction, agronomic development and mineral uptake. Suppressed activity of enzymatic antioxidants and excessive cobalt translocation manifested severe ROS-induced oxidative injuries. Seedling priming with FeNPs reduced fluoride bioaccumulation and promoted efficient uptake of macroelements and micronutrients like potassium, calcium, iron, zinc, copper, nickel, manganese, selenium and vanadium and reduced the translocation of cobalt in mature seedlings during stress. This altogether triggered growth and activated the enzymes like SOD, CAT, APX and GPOX. High accumulation of non-enzymatic antioxidants like proline, anthocyanins, flavonoids, phenolics along with stimulated GSH synthesis (determined from high GR, GST and GPX activity) and glyoxalase activity enabled FeNP-pulsed plants to efficiently scavenge ROS, O<sub>2</sub><sup>-</sup>, H<sub>2</sub>O<sub>2</sub> and methylglyoxal, and mitigate oxidative injuries. The ROS production was also lowered due to suppressed NADPH oxidase activity. This ensured subsequent revitalization of Hill activity and the level of photosynthetic pigments. Due to reduced fluoride partitioning and improved nutritional sink, the grain and panicle development in FeNP-primed, stressed seedlings were more stimulated than even control sets. Overall, our findings supported by statistical modelling established the potential of iron-nanotechnology in promoting safe rice cultivation even in fluoride-polluted environments.
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In environmental, soil, and sediment magnetism, it is important to be able to estimate the degree of oxidation of magnetite grains. We report a new method for finding the oxidation parameter z semiquantitatively from cooling-warmi...
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In environmental, soil, and sediment magnetism, it is important to be able to estimate the degree of oxidation of magnetite grains. We report a new method for finding the oxidation parameter z semiquantitatively from cooling-warming cycles of room temperature remanences. We measured magnetization M continuously for stoichiometric and partially oxidized magnetites with average grain sizes of 37 and 220 nm during zero-field cycling of 2.5 T saturation isothermal remanent magnetization (SIRM) from 300 K to 20 K and back to 300 K. Oxidized magnetites were obtained by heating stoichiometric magnetite in air at 100°C, 150°C, and 200°C. In other experiments, SIRM was given at 10 K, and M was monitored during zero-field warming to 300 K. In the oxidized magnetites, SIRM at first increases in cooling from 300 K and then decreases in approaching the Verwey transition. The hump-like form is even more pronounced in the warming curves above Tv. For maghemite, the fully oxidized end member, we found reversible cooling-warming curves with no Verwey transition. In partially oxidized grains, consisting of a maghemite surface layer and a largely unoxidized core, a Verwey transition is resolvable up to high degrees of oxidation. Hallmarks of maghemitization include (1) a smeared-out Verwey transition shifted to lower temperatures when warming 20 K SIRM, (2) a shifted and broadened transition region in both cooling and warming of 300 K SIRM, and (3) humped cooling and warming curves of 300 K SIRM between 300 K and T. Property 3 has excellent diagnostic value. It results from the combination of a slowly increasing M of maghemite and the rapid and nonlinear decrease in M of magnetite during cooling and is seen even for the slight initial oxidation of the reduced 37 nm magnetite. Certain properties, such as the change in M in warming from 20 K to Tv and the change in initial and final M values in a complete cooling-warming cycle, are roughly proportional to the oxidation parameter z. However, the proportionality factors also depend on grain size d, which would have to be known independently in order to estimate z.
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Magnetic nanoparticles have been proposed as interesting tools for biomedical purposes. One of their promising utilization is the MRI in which magnetic substances like maghemite are used in a nanometric size and encapsulated withi...
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Magnetic nanoparticles have been proposed as interesting tools for biomedical purposes. One of their promising utilization is the MRI in which magnetic substances like maghemite are used in a nanometric size and encapsulated within locally biodegradable nanoparticles. In this work, maghemite has been obtained by a modified sol-gel method and encapsulated in polymer-based nanospheres. The nanospheres have been prepared by single emulsion evaporation method. The different parameters influencing the size, polydispersity index and zeta potential surface of nanospheres were investigated. The size of nanospheres was found to increase as the concentration of PLGA increases, but lower sizes were obtained for 3 min of sonication time and surfactant concentration of 1%. Zeta potential response of magnetic nanospheres towards pH variation was similar to that of maghemite-free nanospheres confirming the encapsulation of maghemite within PLGA nanospheres. The maghemite entrapment efficiency and maghemite content for nanospheres are 12% and 0.59% w/w respectively.
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The present study aimed at research of phosphate adsorption onto poly(vinyl-alcohol) PVA alginate beads in comparison with maghemite modified beads from wastewater. The characterisation of material was performed by Fourier transfo...
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The present study aimed at research of phosphate adsorption onto poly(vinyl-alcohol) PVA alginate beads in comparison with maghemite modified beads from wastewater. The characterisation of material was performed by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. The influence of pH and the quantity of maghemite nanoparticle was studied. The results of phosphate adsorption onto PVA-alginate beads showed 45 % of initial PO43- concentration removal from wastewater while the maghemite PVA-alginate beads showed better adsorption activity at 70 % of initial PO43- removal. The optimal dose was determined at 0.9 g of PVA-M beads (containing 0.01 g maghemite) added to the 50 mL wastewater. The efficiency of phosphate removal from wastewater was relatively low due to content of coexistent anions, including SO42?, CO32?, NO3? and Cl?, which compete with phosphate for the binding sites, hindering PO43? to form inner sphere complexes.
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Magnetic particles of maghemite (spinel γ-Fe_2O_3) are synthesized by means of aerosol pyrolysis, making it possible to produce chemically uniform highly-dispersed single-phase materials. The magnetic properties of synthesized pa...
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Magnetic particles of maghemite (spinel γ-Fe_2O_3) are synthesized by means of aerosol pyrolysis, making it possible to produce chemically uniform highly-dispersed single-phase materials. The magnetic properties of synthesized particles for temperatures ranging from helium temperature up to room temperature and higher are investigated using a SQUID magnetometer. The experimental curves are compared to the results from calculations performed by the Monte Carlo method. It is found that the Curie temperature is lower for γ-Fe_2O_3 nanoparticles than for bulk samples. Several parameters of the material are estimated by comparing the experimental and calculated results.
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