Goethite (α-FeOOH) magnetic transition by ESR, Magnetometry and Mössbauer

Valezi, Daniel F.; Piccinato, Marilene Turini; Sarvezuk, P.W.C.; Ivashita, Flávio F.; Paesano, Andrea; Varalda, J.; Mosca, D. H.; Urbano, Alexandre; Guedes, Carmen Luı́sa Barbosa; Mauro, Eduardo Di

doi:10.1016/j.matchemphys.2016.01.067

Cited by 20 publications

(18 citation statements)

References 19 publications

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“…The ESR spectra showed resonances with g ≈2.1 and Δ H pp = 84.4 ± 0.5 mT for GD and g ≈2.0 and Δ H pp = 28.1 ± 1.2 mT for GC. These parameters agree with the literature results . Some variation is expected because the resonance signal depends on several factors.…”

Section: Results and Analysissupporting

confidence: 92%

Enhanced Magnetic Component in Synthetic Goethite (α‐FeOOH) and its Relation with Morphological and Structural Characteristics

Valezi

Baú

Zaia

et al. 2019

Physica Status Solidi (b)

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Goethite (α‐FeOOH) is by definition an antiferromagnetic (AFM) material. In the present work an investigation of the magnetic properties of goethite is performed, studying the magnetic component of this material in different samples and relating these properties with its structural and morphological characteristics. Samples are synthetized in two distinct ways in order to generate solids with different degrees of structural defects and imperfections. Electron spin resonance (ESR) data show that the sample synthesized in a faster procedure, most susceptible to defects and imperfections (GC sample), shows an area under the ESR line ≈20 times higher than the sample set for a lower incidence of defects (GD sample). Experiments with heat‐treated samples at 150 °C show a reduction in the number of spins which contributed to ESR signal for the GC sample. Considering data of thermogravimetry (TGA), X‐ray diffraction (XRD), and Mössbauer spectroscopy, the differences observed in ESR analysis are attributed to a magnetic mismatch in the AFM structure caused by the incidence of local defects, more common in GC sample. Results of heat‐treated samples are associated to an increase in the exchange interaction between grains, which reduces the number of mismatched spins and favors the AFM arrangement.

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Section: Results and Analysissupporting

confidence: 92%

Enhanced Magnetic Component in Synthetic Goethite (α‐FeOOH) and its Relation with Morphological and Structural Characteristics

Valezi

Baú

Zaia

et al. 2019

Physica Status Solidi (b)

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“…At room temperature, goethite is considered as antiferromagnetic (AFM). However, several studies show that goethite has a magnetic component and relaxation effects, as it can be seen by Electron Paramagnetic Resonance (EPR) [2]. Among many studies on this subject, we cite the Superferromagnetism model (SFM) [3,4].…”

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confidence: 99%

“…While GD rods exhibit a slight surface roughness (Figure 2A), the occurrence of these irregularities in GC is more pronounced, presenting a surface containing well-defined steps ( Figure 2B). EPR analysis performed on a JEOL (JES-PE-3X) spectrometer operating in X-band (~ 9.5 GHz), have shown resonance lines characteristics of goethite [2]. However, the area over the resonance signal is at least 20 times greater in GC sample than in GD.…”

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Influence of Microstructure on the Magnetic Properties of Goethite (α-FeOOH)

et al. 2017

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Goethite (α-FeOOH) is an iron oxyhydroxide, one of the most abundant mineral in our planet [1]. Despite being a very well-known material, studied for at least half of a century, goethite still has some magnetic properties that are not fully understood. At room temperature, goethite is considered as antiferromagnetic (AFM). However, several studies show that goethite has a magnetic component and relaxation effects, as it can be seen by Electron Paramagnetic Resonance (EPR) [2]. Among many studies on this subject, we cite the Superferromagnetism model (SFM) [3,4]. In this model, the relaxation effects could arise from magnetic mismatches caused by defects in the structure as grain boundaries, dislocations and voids in the crystallites [4].In this work we conducted two different types of synthesis. Both were performed by two modified methods of Schwetmman [1,5]. For GC sample, FeCl2.4H2O was dissolved in water, then added NaHCO3 to goethite formation for 1 hour [5]. For GD sample Fe(NO)3.9H2O was dissolved in water and added KOH solution; the suspension was left to goethite formation for 52 days at 50°C [1]. With this different processing we aim at generating two different goethite samples in terms of imperfections and defects such as grain boundaries, voids and dislocations. In fact, Infra-red (IR) spectra and X-ray diffractogram of those samples are similar.Transmission electron microscopy (TEM) analysis, in a JEOL 2100F, reveals that both kinds of samples contains particles in rod-like format, as it appears in Figure 1A of GD sample (GC sample have shown similar results in terms of morphology). The atomic resolution image, Fig 1B, obtained from region indicated by the red box in Figure 1A shows the tip of superimposed rods. Most detailed analysis shows some narrow disordered regions, perhaps a low angle grain boundary, as indicated by arrows. In this HRTEM image the distance between the lattice fringes was measured as 0.25 nm. High resolution images, shown in Figure 2, indicate that the surface of some rods is not smooth but show atomic-scale steps. While GD rods exhibit a slight surface roughness (Figure 2A), the occurrence of these irregularities in GC is more pronounced, presenting a surface containing well-defined steps ( Figure 2B).EPR analysis performed on a JEOL (JES-PE-3X) spectrometer operating in X-band (~ 9.5 GHz), have shown resonance lines characteristics of goethite [2]. However, the area over the resonance signal is at least 20 times greater in GC sample than in GD. This observation is in agreement with more pronounced degree of imperfections at GC, because some kind of imperfections can generate non-compensated moments [4]. These subjects are currently under investigations [6].

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“…The formation of maghemite, at 380 °C, is confirmed by presence of a magnetically ordered component (sextet), with hyperfine field at approximately 48 T and a quadrupole shift at around zero. The presence of goethite in the spectrum may be associated with the reaction of maghemite with water from air, as 380 °C is sufficient to promote the thermal decomposition of goethite …”

Section: Resultsmentioning

confidence: 99%

Preparation of magnetic mesoporous composites from glycerol and iron(III) salt

Medeiros

Ardisson

Lago

2019

J of Chemical Tech & Biotech

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BACKGROUND A process was developed to produce mesoporous composites with magnetic cores involving the following sequential reactions: glycerol polymerization/iron(III) reduction/polyglycerol pyrolysis/activated carbon production. RESULTS Glycerol containing 1, 3, 5, or 8 mol% iron(III) was heat treated to 380, 600, or 800 °C. The scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction, Mössbauer spectroscopy, thermogravimetry/differential thermal analysis, Raman spectroscopy, and nitrogen adsorption/desorption results showed that the iron(III) salt promoted polymerization of glycerol up to 380 °C. At higher temperatures, up to 800 °C, three different processes simultaneously occurred: pyrolysis of polyglycerol, reduction of iron(III) ion (Fe3+) to Fe0 and Fe3C, and activation of the carbonaceous matrix, yielding a composite with a BET surface area of 136 m2 g−1. Moreover, to verify a possible environmental application of the prepared composites and their ability to remain suspended in aqueous solution, they were tested as adsorbents of organic contaminants such as methylene blue and indigo carmine. The test results were satisfactory: 10 mg of the prepared composite (GFe3‐800) adsorbed up to 80% of the dye [10 mL of solution (50 ppm)] within 30 min of contact, and the composite could be removed from the system by simple magnetic attraction. CONCLUSIONS Magnetic composites exhibited good dye adsorption, in addition, good resistance to acid leaching. © 2019 Society of Chemical Industry

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Goethite (α-FeOOH) magnetic transition by ESR, Magnetometry and Mössbauer

Cited by 20 publications

References 19 publications

Enhanced Magnetic Component in Synthetic Goethite (α‐FeOOH) and its Relation with Morphological and Structural Characteristics

Enhanced Magnetic Component in Synthetic Goethite (α‐FeOOH) and its Relation with Morphological and Structural Characteristics

Influence of Microstructure on the Magnetic Properties of Goethite (α-FeOOH)

Preparation of magnetic mesoporous composites from glycerol and iron(III) salt

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