Effect of Fe_2O_3/SiO_2 ratio on maghemite-silica particulate nanocomposites

Abstract： Maghemite-silica particulate nanocomposites were prepared by modified 2-step sol-gel process. Superparamagnetic maghemite nanoparticles were successfully produced using Massart＇s procedure. Nanocomposites consisting of synthesized maghemite nanoparticles and silica were produced by dispersing the as-synthesized maghemite nanoparticles into the silica particulate form. The system was then heated at 140 ℃for 3 d. A variety of mass ratios of Fe2O3/SiO2 was investigated. Moreover, no surfactant or other unnecessary precursor was involved. The nanocomposites were characterized using XRD, BET and AGM. The XRD diffraction patterns show the reflection corresponding to maghemite nanoparticles and a visible wide band at 20 from 20° to 35° which are the characteristics of the amorphous phase of the silica gel. The patterns also exhibit the presence of only maghemite and SiO2 amorphous phase, which indicates that there is no chemical reaction between the silica particulate gel and maghemite nanoparticles to form other compounds. The calculated crystallite size for encapsulated maghemite nanoparticles is smaller than the as-synthesized maghemite nanoparticles indicating the dissolution of the nanoparticles. Very high surface area is attained for the produced nanocomposites （360-390 m^2/g）. This enhances the sensitivity and the reactivity of the nanocomposites. The shapes of the magnetization curves for nanocomposites are very similar to the as-synthesized maghemite nanoparticles. Superparamagnetic behaviour is exhibited by all samples, indicating that the size of the maghemite nanoparticles is always within the nanometre range. The increase in iron content gives rise to a small particle growth.

The Effect of Temperature on Synthesis and Stability of Superparamagnetic Maghemite Nanoparticles Suspension

Maghemite (γ-Fe2O3) nanoparticles have been synthesized using chemical co-precipitation at a different temperature. Characterizations of the sample were performed by X-ray diffraction (XRD), transmission electron microscopy (TEM), alternating gradient magnetometry (AGM) and thermogravimetryanalysis (TGA). The stability of the maghemite nanoparticles suspension was studied at different pH and time of storage by dynamic light scattering (DLS) and zeta potential measurements. The XRD patterns confirmed that the particles were maghemite. TEM observation showed that the particles have spherical morphology with narrow particle size distribution. The particles showed superparamagnetic behavior with good thermal stability. The increasing of temperature in the synthesis of maghemite nanoparticles produced smaller size particles, lower magnetization, better thermal stability and more stable maghemite nanoparticle suspension.

Absorption Studies of Arsenic Using Maghemite Crystals Synthesized from Iron Waste Extracted from Ogun State Iron Mill Dumpsite

This paper outlines the synthesis of maghemite from raw iron waste obtained in an iron mill dumpsite around Ogun state, Nigeria. Magnetite was synthesized from the ferrous precursor obtained by digesting the iron waste with concentrated H2SO4. Transformation of magnetite to maghemite was done by heating the magnetite obtained in an oven at 200°C. To determine the absorption capacity of the synthesized maghemite sample, a stock solution of As(III) was used for the absorption. Absorption spectrum shows higher absorption of γ-Fe3O4 at higher concentration of As(III). Maximum absorption obtained is 14 mg/g. Estimated yield of γ-Fe3O4 was 32%;however a low, further study promises to improve the yield value. The study shows γ-Fe3O4 to be a good absorbent for heavy metals.

Structural, Magnetic and Heating Efficiency of Ball Milled γ-Fe2O3/Gd2O3 Nanocomposite for Magnetic Hyperthermia

The preparation of γ-Fe2O3/Gd2O3 nanocomposite for possible use in magnetic hyperthermia application was done by ball milling technique. The nanocomposite was characterized by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The heating efficiency and the effect of milling time (5 h and 30 h) on the structural and magnetic properties of the nanocomposite were reported. XRD analysis confirms the formation of the nanocomposite, while magnetization measurements show that the milled sample present hysteresis with low coercivity and remanence. The specific absorption rate (SAR) under an alternating magnetic field is investigated as a function of the milling time. A mean heating efficiency of 68 W/g and 28.7 W/g are obtained for 5 h and 30 h milling times respectively at 332 kHz and 170 Oe. The results showed that the obtained nanocomposite for 5 h milling time is a promising candidate for magnetic hyperthermia due to his properties which show an interesting magnetic behavior and high specific absorption rate.

Analysis on variety and characteristics of maghemite

Maghemite (γ-Fe2O3) is a very common mineral at the earth’s surface and also an important material for making music and video tapes. Maghemite is usually synthesized from magnetite under oxidizing conditions after a few hours or a few days below a temperature of 300°C. The magnetic property of thermal instability and the chemical action after heating is an important character for maghemite. That is, it will become hematite in certain proportion after being heated above 250°C. Maghemite is therefore actually unable to have its Curie temperature measured. But late using synthetic sample, maghemite was further found partially thermal stable with a measurable Curie temperature ~645°C. During our thermally magnetic experiments for a set of synthetic magnetite, we found that extra fined grain size (pseudo single domain (PSD) and small multi-domain (MD), mainly 1-10 μm) magnetite was formed to a completely thermally stable maghemite. This maghemite can also be produced by heating the same powder up to 700°C in an oven and keeping this temperature for 10 min, then cooling it down. When the generated maghemite by these two ways is heated from room temperature to 700°C, it shows almost fully reversible, or thermally stable. We used X-ray powder diffraction and Mssbauer spectroscopy to confirm the identity of this maghemite and compared its magnetic hysteresis, high temperature magnetization, low temperature thermal demagnetization, and low temperature susceptibility with those of the original preheated magnetite. Such quickly oxidized maghemite by heating to high temperature implies some types of maghemite formed in certain natural condition can carry a thermal remnant magnetization (TRM). Four types of maghemite were characterized and discussed according to their thermal stability. Among them, partially stable and fully thermally stable maghemite after heating should possess capability of carrying TRM. There is possibly a compensation of synthetizing maghemite between heating temperature and heating duration. The thermal stability of maghemite may be affected by a few factors, such as its purity (stoichiometry), heating temperature and duration. The grain size may be one of important factors. Maghemite might be similar to magnetite, having various magnetic properties corresponding to its grain size categories such as superparamagnetic (SP), single domain (SD) and MD. Low temperature measurement for PSD fine grain of synthetic magnetite shows a phenomenon of Verwey transition 'suppressed', its fundamental causes could be that the core diameter of oxidized magnetite is actually reach or approach SD size, so that its Verwey transition is shown 'suppressed'.

Au,Pd and maghemite nanofunctionalized hydroxyapatite scaffolds for bone regeneration

Nanotechnology plays a key role in the development of innovative scaffolds for bone tissue engineering(BTE)allowing the incorporation of nanomaterials able to improve cell proliferation and differentiation.In this study,Mg-HA-Coll type I scaffolds(Mg-HA-based scaffolds)were nanofunctionalized with gold nanorods(Au NRs),palladium nanoparticles(Pd NPs)and maghemite nanoparticles(MAG NPs).Nanofunctionalized Mg-HA-based scaffolds(NF-HA-Ss)were tested for their ability to promote both the proliferation and the differentiation of adipose-derived mesenchymal stem cells(hADSCs).Results clearly highlight that MAG nanofunctionalization substantially improves cell proliferation up to 70% compared with the control(Mg-HA-based scaffold),whereas both Au NRs and Pd NPs nanofunctionalization induce a cell growth inhibition of 94% and 89%,respectively.Similar evidences were found for the osteoinductive properties showing relevant calcium deposits(25% higher than the control)for MAG nanofunctionalization,while a decreasing of cell differentiation(20% lower than the control)for both Au NRs and Pd NPs derivatization.These results are in agreement with previous studies that found cytotoxic effects for both Pd NPs and Au NRs.The excellent improvement of both osteoconductivity and osteoinductivity of the MAG NF-HA-S could be attributed to the high intrinsic magnetic field of superparamagnetic MAG NPs.These findings may pave the way for the development of innovative nanostructured scaffolds for BTE.

Green Synthesis of Magnetic Adsorbent Using Groundwater Treatment Sludge for Tetracycline Adsorption

Groundwater treatment sludge is an industrial waste that is massively produced from groundwater treatment plants.Conventional methods for treatment of this sludge,such as discharge into deep wells or the sea,or disposal at landfills,are not environmentally sustainable.Here,we demonstrate an alternative strategy to recycle the sludge by preparing a magnetic maghemite adsorbent via a one-step hydrothermal method with NaOH solution as the only solvent.With this method,the weakly magnetized sludge,which contained 33.2%iron(Fe)and other impurities(e.g.,silicon(Si),aluminum(Al),and manganese(Mn)),was converted to magnetic adsorbent(MA)with the dissolution of Si/Al oxides(e.g.,quartz and albite)into the liquid fraction.At a NaOH concentration of 2 mol L^-1,approximately 18.1%of the ferrihydrite in the Fe oxides of the sludge was converted into 11.2%maghemite and 6.9%hematite after the hydrothermal treatment.MA2(i.e.,MA produced by a 2 mol L^-1 NaOH concentration)exhibited a good magnetic response of 8.2 emu g^-1(1 emu=10^-3 A m^2),and a desirable surface site concentration of 0.75 mmol g^-1.The synthesized MA2 was used to adsorb the cationic pollutant tetracycline(TC).The adsorption kinetics of TC onto MA2 fitted well with a pseudo-second-order model,and the adsorption isotherms complied well with the Langmuir model.The maximum adsorption capacity of MA2 for TC was 362.3 mg g^-1,and the main mechanism for TC adsorption was cationic exchange.This study is the first to demonstrate the preparation of an MA from recycled sludge without a reductant and/or exogenous Fe source.The prepared adsorbent can be used as a low-cost adsorbent with high capacity for TC sorption in the treatment of TC-containing wastewater.

Magnetic properties of low-grade hematite ore after magnetizing reduction and reoxidation using a fluidized bed

Magnetizing roasting via a fluidized bed,which was recognized as an efficient method for beneficiation of low-grade iron ores,has attracted much attention in China recently due to the fluctuation of the international iron ore market.In order to examine the effects of magnetic properties on the separability and to optimize the operating parameters,magnetic susceptibility and coercivity of a low-grade hematite after magnetizing reduction and reoxidation under different conditions were investigated.It was found that the magnetic susceptibility of roasted ore increased with reduction degree and particle diameter to different degrees.The magnetite was re-oxidized to maghemite when the temperature was below 400℃,and the magnetic susceptibility decreased slightly.The recovery efficiency decreased notably with the particle size for very fine grains although no significant change was found in magnetic susceptibility.The coercivity and remanence of roasted ores decreased with increasing roasting temperature.The scanning electron microscope(SEM) study showed that more cracks were produced by the reoxidation of reduced ores,which could possibly favor the intergranular fracturing and the liberation for further treatment.

Properties of Aluminosilicate Glasses Prepared by Red Mud with Various [Al2O3]/[CaO] Mass Ratios

By introducing other oxide materials（SiO_2, Al_2O_3, CaO） into the red mud, all materials were melted into aluminosilicate glasses. On the basis of 17.2Fe_2O_3-5.7CaO-18.2Al_2O_3-50SiO_2-5.9Na_2O-3TiO_2 system glasses, [Al_2O_3]/[CaO] mass ratio changed further. For each sample, the assignment of IR absorption bands for aluminosilicate glasses was investigated by Fourier transform infrared spectroscopy and the glasstransition temperature and high temperature molten state were studied by differential scanning calorimetry. According to X-Ray diffraction and differential scanning calorimetry, the behavior of crystallization was analyzed. The results show that the glass structures of three-dimensional network are depolymerized and the amount of non-bridging oxygens increases gradually with network modifier CaO replacing network intermediate Al_2O_3 when [Al_2O_3]/[CaO] ratio of aluminosilicate glass decreases from 4.05 to 0.66, resulting in decreasing density, melting temperature, crystallization peak temperature and glass-transition temperature. As [Al_2O_3]/[CaO] mass ratio decreases, the concentration of crystallized phase maghemite（γ-Fe_2O_3） will increase which provides the possibility for production of black glass-ceramic further.

Mechanism of magnetic property changes of serpentinites from ODP Holes 897D and 1070A

Serpentinites have great implications for the oceanic crust, subduction zones, island arc magmatism activity, and the formation of nickel ore deposits. To further determine the mechanism of magnetic property changes of serpentinites, samples from ODP Holes 897 D and 1070 A were investigated by integrating both magnetic and non-magnetic methods. Detailed rock magnetic results demonstrate that magnetite prevails in the entire serpentinite section, while maghemite is present in the upper and altered parts. The concentration of Fe in the fresh peridotite is inhomogeneous; nonetheless, the magnetic properties are generally determined by the serpentinization process. The formation and state of the magnetite depend on the fracture conditioning and fluid activities which are controlled by the serpentinization process. By comparing these two holes, we found that the production of magnetite is consistent with the serpentinization process; serpentinization is a multi-stage process which involves early high-temperature serpentinization and later low-temperature oxidation. As the serpentinization continues, the fine magnetic particles become coarser, combined with the formation of new SP particles, and the later low-temperature oxidation leads to the maghemitization of the magnetites. The duration of oxidation also contributes to the differences of remanent magnetization between these two holes. These results greatly improve our understanding of the magnetic enhancement during the serpentinization process, and provide constraints on the interpretation of the paleomagnetic and aeromagnetic anomalies in this area.