Hematite α-Fe2O3 Research Articles

Microbial Reduction of Geogenic and Synthetic Goethite and Hematite

The microbial reduction of Fe(III) is a major component of Fe cycling in terrestrial and aquatic environments and is affected by the Fe(III) mineralogy of the system. The majority of the research examining the bioreduction of Fe(III) oxides by Fe(III)-reducing bacteria (IRB) has focused on the reduction of poorly crystalline Fe(III) phases, primarily ferrihydrite; however, crystalline Fe(III) oxides like goethite (α-FeOOH) and hematite (α-Fe2O3) comprise the majority of Fe(III) oxides in soils. This study examined the bioreduction of goethite and hematite of geogenic and synthetic origin by Shewanella putrefaciens CN2, a well-studied model IRB, in laboratory incubations. Overall, the rate and extent of Fe(II) production were greater for goethite than for hematite, and for geogenic Fe(III) oxides relative to their synthetic analogs. Although there was substantial production of Fe(II) (i.e., >5 mM Fe(II)) in many of the systems, X-ray diffraction analysis of the solids at the end of the incubation did not indicate the formation of any Fe(II)-bearing secondary minerals (e.g., magnetite, siderite, green rust, etc.). The results of this study demonstrate the variability in the extent of bioreduction of geogenic goethite and hematite, and furthermore, that synthetic goethite and hematite may not be good analogs for the biogeochemical behavior of Fe(III) oxides in aquatic and terrestrial environments.

Snowflake Iron Oxide Architectures: Synthesis and Electrochemical Applications

The synthesis and characterization of iron oxide nanostructures, specifically snowflake architecture, are investigated for their potential applications in electrochemical sensing systems. A Raman spectroscopy analysis reveals phase diversity in the synthesized powders. The pH of the synthesis affects the formation of the hematite (α-Fe2O3) and goethite (α-FeOOH). Scanning electron microscopy (SEM) images confirm the distinct morphologies of the particles, which are selectively obtained through recrystallization during the elongated reaction time. An electrochemical analysis demonstrates the differing behaviors of the particles, with synthesis pH affecting the electrochemical activity and surface area differently for each shape. Cyclic voltammetry measurements reveal reversible dopamine detection processes, with snowflake iron oxide showing lower detection limits than a mixture of snowflakes and cube-like particles. This research contributes to understanding the relationship between iron oxide nanomaterials’ structural, morphological, and electrochemical properties. It offers practical insights into their potential applications in sensor technology, particularly dopamine detection, with implications for biomedical and environmental monitoring.

Capacity augmentation strategy in α-Fe2O3 nanoparticles through multifaceted structural and electrochemical analyses

Hematite (α-Fe₂O₃) has garnered significant research interest for supercapacitor applications, but capacity fading and limited cyclic life remain serious challenges. In this context, the present research provides a comprehensive study of the factors that significantly impact charge kinetics within the electrode and at the solid/electrolyte interface. By integrating structural and electrochemical analyses, this study offers an effective strategy to enhance the capacity of α-Fe₂O₃ nanoparticles through rigorous scientific analysis and identification of various qualitative and quantitative factors that influence charge storage capacity. A simple one-step co-precipitation method was adopted to synthesize porous α-Fe₂O₃ nanoparticles. The quantitative analysis of charge kinetics demonstrated the domination of diffusion-controlled charge storage as the main contributor to the total charge storage. The α-Fe₂O₃ nanoparticles-based electrode delivered a high energy density of 24.6 Wh kg⁻1 at an impressive power density of 478.7 W kg⁻1. Additionally, it displayed a capacity retention of 79 % over 10,000 cycle operations. The choice of electrode material and the superior porous nanoarchitecture have proven to be advantageous for high-performance supercapacitor applications, offering fast electron/ion transport.

In-situ synthesis of Fe phosphate layer on the porous hematite nanocube for efficient photoelectrochemical water splitting

Hematite (α-Fe2O3) is considered as an ideal photoanode material in photoelectrochemical (PEC) water splitting system due to its suitable band gap, excellent stability and abundant reserves. However, the actual PEC water oxidation performance of α-Fe2O3 is greatly limited by its severe charge recombination and sluggish water oxidation kinetics. Here, an in-situ generated Fe phosphate (Fe-Pi) coating strategy is applied on the surface of porous hematite nanocube (Fe2O3 NC) to realize PEC water oxidation effectively. The obtained Fe-Pi/Fe2O3 NC photoanode exhibits a remarkable PEC property with a photocurrent density of 2.7mAcm-2 at 1.23V vs. RHE, which was about 5.7-fold enlarged compared to the pristine nanorod-like hematite (Fe2O3 NR) photoanode. Detailed studies have shown that the porous Fe2O3 NC possesses an enhanced ability in light absorption and charge separation than the traditional Fe2O3 NR photoanode. In addition, the in-situ loading of Fe-Pi layer as a co-catalyst can not only effectively passivate the surface trapping states of Fe2O3 NC and suppress interfacial charge recombination, but also quickly extract the holes to participate in the water oxidation reaction. Our study suggests that the further surface modification based on morphological engineering is an effective strategy to improve the PEC performance of hematite.

Engineering Zinc Ion Hybrid Supercapacitor Performance of Graphitic Carbon Nitride Embedded Iron Oxide (Hematite)

Zinc-ion hybrid supercapacitors (ZHSC) gain high traction due to the prosperous unification of batteries and supercapacitors. Especially with graphene discovery nano carbonaceous materials have been the most investigated types in energy storage (ES) utilization including ZHSC. Among carbonaceous materials, graphitic carbon nitride (g-C3N4) possessing polymeric layers, quasi graphene arouses extreme interest due to its low-impact structure with economical yet chemical and mechanical stability inflicted by high nitrogen contents. Herein, we aim to examine the g-C3N4 doping effect on the electrochemical performance of hematite (α-Fe2O3) for ZHSC application. The assembled ZHSC device managed to reach the potential window of 2.0 volts with an efficient specific capacitance (Sc) of 280 F g-1 at a current density of 1 A g-1. Moreover, the highest energy and power densities were 38.8 Wh kg-1 and 20 kW kg-1 respectively. With this remarkable efficiency, the α-Fe2O3/g-C3N4 composite material can be considered a promising cathode material for ZHSC

Adsorption and C-C bond cleavage of benzene on hematite α-Fe2O3 surfaces: a DFT mechanistic study.

Reforming tar molecules into smaller gaseous molecules has been a critical challenge for biomass energy utilization. Hematite (α-Fe2O3) has been demonstrated as an effective catalyst for the catalytic reforming of tar, nevertheless, the detailed mechanism of α-Fe2O3 catalyzed tar reforming remains unclear. In this work, we apply the density functional theory method to investigate this problem. Specifically, we study both (0001) and (01[Formula: see text]2) surface structures of α-Fe2O3 and then use the structures to investigate the adsorption and C-C bond cleavage of benzene on these surfaces. Our results show that the dominant interactions between benzene and a single Fe-terminated (0001) surface are van der Waals forces, yet benzene could be chemisorbed on the Fe and O co-exposed (01[Formula: see text]2) surface via strong C-O interactions. As a result, the (0001) surface is not active towards benzene cleavage, whereas the (01[Formula: see text]2) surface can promote the aromatic C-C bond breaking. Furthermore, our calculations indicate that chain-like alkene species and carbonyl species are the two types of potential products that form after the C-C bond cleavage of benzene on the α-Fe2O3 (01[Formula: see text]2) surface, with the activation energy of 1.78eV and 2.62eV, respectively. In summary, we reveal the importance of co-adsorption on both Fe and O centers and oxidative addition on C-C bond cleavage of aromatic compounds on the α-Fe2O3 surface, which provides novel insights into the mechanisms of tar cracking on oxide catalysts.

Synthesis and optimization of chitosan-incorporated semisynthetic polymer/α-Fe2O3 nanoparticle hybrid polymer to explore optimal efficacy of fluorescence resonance energy transfer/charge transfer for Co(II) and Ni(II) sensing

Initially, four synthetic fluorescent polymers (SFPs) are synthesized from α-methacrylic acid and methanolacrylamide monomers carrying –C(=O)OH and –C(=O)NH subfluorophores, respectively. Among SFPs, ∼1:1 incorporation of subfluorophores in the optimum SFP3 is explored by spectroscopic analyses. Subsequently, chitosan is incorporated in SFP3 to produce five semi-synthetic fluorescent polymers (SSFPs). The maximum incorporation of chitosan in SSFP4 is supported by different spectroscopies. In SSFP4, strong electrostatic interactions among polar functionalities of chitosan and synthetic polymer favor resonance-associated charge transfer (RCT) from SSFP4-(amide) to SSFP4-(canonical). Finally, three hybrid fluorescent polymers (HFPs) are fabricated encapsulating iron-oxide nanoparticle within SSFP4. The maximum proportion of hematite (α-Fe2O3) phase in HFPs is explored by spectroscopic, magnetometric, microscopic, and light scattering studies. HFP2 shows local/RCT/fluorescence resonance energy transfer (FRET) emission at 393/460/570 nm. In HFP2, FRET, RCT, and ratiometric pH-sensing within 3.0–6.5 phenomena are explored by solvent polarity effects, time-correlated single photon counting, quantum yield measurements, alongside I431/I460 vs pH plots. RCT and FRET emissions of HFP2 are utilized for selective sensing of Co(II)/Ni(II) with limits of detection of 4.990 ppb (460 nm)/4.353 ppb (570 nm) and 45.041 ppb (428 nm)/29.617 ppb (527 nm) in organic and aqueous solutions, respectively.

Water purification and biological efficacy of green synthesized Co/Zn-Doped α-Fe2O3 nanoparticles

In the present study, Co/Zn doped α-Fe2O3 (Hematite) nanoparticles (NPs) were synthesized using polyvinylpyrrolidone (PVP) and Azadirachta indica (AI) leaves aqueous extract. The analytical techniques including XRD, UV, SEM, EDX, VSM, Raman, and FTIR, we were able to identify and characterize the structural, morphological and magnetic attributes of the synthesized NPs. The findings demonstrated that the synthesized NPs exhibit homogeneous spherical shapes with particle sizes ranging from 8.64 to 15.32 nm. The NPs have rhombohedral crystal lattices, with crystallite sizes of 23.25 nm for chemically synthesized doped α-Fe2O3 NPs and 12.52 nm for those synthesized using green methods. The magnetic study has shown that the saturation magnetization (Ms) value of NPs, which ranges from 36 to 45 emu/g at ambient temperature, exhibits superparamagnetic properties (300 K). The treatment of industrial wastewater and its reuse for agricultural purposes are the subjects of the current study. Different concentrations of doped α-Fe2O3 NPs were used as photocatalysts to degrade dyes in a bioreactor under UV light in a heterogeneous mixture. The degradation rates achieved were 96.42 % for Congo Red (CR) and 98.36 % for Eosin Yellow (EY). DPPH assays were conducted to evaluate the antioxidant activity of the synthesized doped α-Fe2O3 NPs. The percentage inhibition of DPPH radicals ranged from 71.13 % to 90.35 %. Our findings indicate that AI leaf extract holds promise as a valuable resource for the development of bioactive compounds and environmentally friendly approaches to synthesizing green NPs. This is primarily attributed to the increased accessibility of bioactive components with potent antioxidant properties. The combination of these benefits provides opportunities for novel uses in environmental cleanup, biological applications, and energy conversion.

Synthesis and evaluation of iron oxide nanoparticles from banana peel (Musa spp.) extract for the delivery of ciprofloxacin against resistant Escherichia coli

Background and objectiveResistance to antimicrobials is one of our most significant worldwide challenges. In Africa, around 31 % of the infections of urinary tract (UTIs) initiated by Escherichia coli (E. coli) have been observed to develop ciprofloxacin (CIP) resistance. As a result, significant efforts have been made to investigate novel and improved antibiotics. This study aimed at synthesizing iron oxide nanoparticles (IONPs) using banana peels (Musa Spp.) extract for delivery of CIP against resistant E. coli. MethodsA green synthesis method was used for the synthesis of IONPs using FeCl3.6H2O as a precursor and banana peel extract as a reducing and stabilizing agent. The physicochemical characteristics of the formed nanoparticles (NPs) were characterized using different methods. ResultsThe formation of hematite (α-Fe2O3) was confirmed with its FTIR characteristic peak at 461 cm−1, 542 cm−1, and 1131 cm−1. The size of synthesized IONPs was found to be 10.4 nm ± 1.98, 48 nm ± 0.9, and 67.3 nm ± 0.9 under XRD, SEM, and DLS measurements respectively. CIP-IONPs had almost the maximum drug loading capacity (33.3 % ± 0.67) with fast and slow drug release patterns at gastric and intestinal or blood pH respectively, and it had a promising resistant reversal with a zone of inhibition (ZOI) 22 mm ± 0.15 against resistance E. coli. ConclusionThe green synthesis of IONP using banana peel extract represents a novel and eco-friendly approach for the delivery of ciprofloxacin, with potential applications in addressing antimicrobial resistance.

Cathodic shift in flatband potential of hematite based photoelectrodes: Evaluating and correlating the redshift to solar driven photocatalysis

As a promising metal oxide semi-conductor, hematite (α-Fe2O3) has interesting optical properties to be regarded as photoactive material. In this study, we evaluated the cathodic shift in onset potential (Eonset) and the negative shift in flat band potential (Efb). It was observed that the Eonset value of −0.457 V for α-Fe2O3 based electrode shifted to −0.638 V for the ternary nanocomposite (PNFC) [Pani/Ni-α-Fe2O3/CNT] based electrode. The flat band potential for α-Fe2O3 in 1 M NaOH is at −0.49 V which shifts to −0.68 V for the ternary nanocomposite (PNFC). This photoelectrochemical enhancement appears due to electron-hole pair separation. Therefore, it apparently increases the photocurrent trace for PNFC at −0.60 V to 7.04 mA cm-2, compared to the photocurrent of 4.52 mA cm-2 observed for pristine α-Fe2O3. According to the Mott-Schottky plot, the donor concentration (Nd) for the α-Fe2O3 is 4.83 × 109 cm-3, whereas for the ternary nanocomposite (PNFC) is 7.68 × 109 cm-3, respectively. As evident, the Nd value increase for the ternary nanocomposite PNFC points to the proximity of the Fermi (Ef) level below the CB edge when Ni doped α-Fe2O3 comes in contact with polyaniline (Pani). Indeed, the ternary nanocomposite PNFC with lower Eg value (1.32 eV) and higher photocurrent (7.04 mA cm-2) show higher photo-activity with percent degradation of 98.42 % for photocatalytic degradation of Sunset Yellow under visible light irradiation. The aforementioned correlations of the energetic levels of band edges with the shifting of Efb to more negative potentials provide insight into the high photo-activity observed.

Enhanced PEC generation of hydrogen from seawater driven by efficient and stable Ti-Fe2O3 photoanode

Incorporation of Ti4+ ions into the hematite (α-Fe2O3) photoanodes has garnered significant consideration for the photoelectrochemical water splitting process since it improves the charge transport and optical properties of pristine hematite material. Herein, we have approached a facile route to fabricate the thin films of Ti-Fe2O3 by spray pyrolysis treatment. The Ti-Fe2O3 photocurrent density delivers 1.34 mA/cm2 at 1.23 V RHE in an alkaline seawater environment, showing its excellent performance for photoelectrochemical water- splitting applications. Moreover, it offers outstanding stability in seawater (0.5 M NaCl + 1 M KOH) at applied 1.23 V for 20 h and produces 21.79 µmol/cm2.h of hydrogen. Hence, it will hold a tremendously promising electrode within this area for efficient solar hydrogen generation.

Thermally synthesized hematite (α-Fe2O3) nanoparticles as efficient photocatalyst for visible light dye degradation.

In recent years, water pollution has become a pressing global issue because of the continuous release of organic dyes from various industries. Therefore, finding an easy way to remove these harmful dyes from water has drawn the attention of researchers. This study investigates the removal of toxic Rose Bengal (RB) dye using hematite nanoparticles as a visible light photocatalyst without any additive. It is observed that by controlling particle size, quantity of the nanoparticles and reaction temperature, the dye degradation can be improved up to 95.33% with a half-life of 26 min. To understand photodegradation kinetic behavior, the Langmuir-Hinshelwood kinetic equation can be employed. The scavenger test indicated that the OH* radicals majorly led to the photodegradation process. The reaction rate values strongly depended on the size, quantity of the nanoparticles and reaction temperature. Controlling the optimizing condition, faster reaction rate (k = 0.027 min-1) can be achieved as compared to earlier reports. It is also noted that the change in the degradation efficiency of the reused catalyst is negligible when compared to the fresh one. Here, the dye degradation mechanism is discussed. Overall, this study reveals that hematite nanoparticles can be used as efficient photocatalyst for dye degradation applications by optimizing the controlling factors. These observations provide novel perspectives on the development of effective and sustainable photocatalytic technologies for pollution control and water treatment applications.

Effects of mechanical alloying methods on structural phase stability, chemical state, optical, electrical and ferroelectric properties in Sc-doped α-Fe2O3 system

The development of metal doped α-Fe2O3 (hematite) based wide band gap semiconductors with high electrical conductivity, high electrical polarization and wide optical band gap is a challenging problem and also useful for application point of view. In this work, a substantial enhancement of electrical conductivity, optical band gap and ferroelectric polarization have been recorded at room temperature for Sc doped α-Fe2O3 system. Two different methods of the mechanical alloying and subsequent heat treatment have been used to synthesize the samples of α-Fe2-xScxO3 oxide (x = 0.2–1.0). The X-ray diffraction patterns have confirmed formation of single-phased Rhombohedral structure for low Sc doping content (x = 0.2), whereas a mixture of Rhombohedral-structured α-Fe2O3 type phase and cubic-structured Sc2O3 type phase has been formed for the higher Sc contents (x = 0.5 and 1.0). The phase fractions varied depending on the amount of Sc content, chemical reaction during mechanical alloying of the elementary oxides and solid-state reaction during the heat treatment. Response of the Sc2O3 type phase in Raman spectra is sensitive depending on the methods of inter-mixing the α-Fe2O3 and Sc2O3 by mechanical alloying. X-ray photoelectron spectroscopy (XPS) confirmed the metal (Fe, Sc) ions in +3 charge state, although the samples for low Sc content x = 0.2 showed a signature of Fe+2 and Sc+4 states. A detailed analysis of the Fe 3s XPS band confirmed a strong 3s-3d spins exchange coupling of strengths 1.18 eV–1.34 eV.

Non-destructive identification of iron oxide crystals in 15th century A.D. Chinese imperial red overglaze decoration

Red overglaze decoration is one of the earliest and most important colorful overglaze decorations in China, which had a remarkable influence on the successful firing and development of polychrome overglaze porcelains. The uncontrollability of red overglaze decoration led to a certain proportion of defective porcelain products in the Ming Dynasty (1368–1644 CE). To investigate and identify the coloring effect of iron oxide crystals in red overglaze decoration, three groups of samples with different color appearance were non-destructively analyzed and observed by OM, spectrophotometer, XRF, Raman spectroscopy, XRD and SEM. The results show that the hue of red overglaze decoration was caused by the different crystal forms of iron oxide. Hematite (α-Fe2O3) displays red color, while maghemite (γ-Fe2O3) and magnetite (Fe3O4) yield orange-red and dark red colors. With the similar raw materials and manufacturing processes, the presence of maghemite and magnetite are relatedto subtle differences in processing raw materials and firing them.

Synthesis and Characterization of Hematite (α-Fe<sub>2</sub>O<sub>3</sub>) from Iron Sand Using Coprecipitation Method

Hematite (α-Fe2O3) has been synthesized from iron sand using the coprecipitation method. This study aims to determine the morphology and mineral content using SEM-EDX, crystal structure and phases formed using XRD, and magnetic properties using VSM on iron sand before and after synthesis. SEM-EDX results show that the average particle size of iron sand before and after synthesizing is 356.23nm and 12.40 µm, respectively. XRD results show that iron sand before synthesizing has multipahase including Hematite, magnetic, and ilmenite and after synthesizing produces Single Phase hematite. VSM results show that iron sand before synthesizing has saturation, remanence, and coercivity of 47.56 emu/g, 5.97emu/g, and 121.03 Oe respectively, and after synthesizing has saturation, remanence, and coercivity of 9.47 emu/g, 1.53 emu/g and 102.97 Oe respectively.

Analyzing the Impact of Annealed Steel Sludge Doses on the Physicochemical Properties of Biochar Obtained from Waste Date Palm Frond

Large quantities of date palm frond waste generated from the pruning process are accumulated or burned in burn barrels, harming the environment and having very little economic value. However, because of the lack of data revealing the characteristic magnetic properties of biochar derived from date palm fronds, further research on low-cost and sustainable strategies could offer a new composite material and serve to extend the way for novel applications. In this study, we prepared biochar derived from palm fronds via pyrolysis under a limited-oxygen atmosphere at a lower temperature of 300 °C for 2 h. We introduced a facile strategy for the production of magnetic biochar with various doses of annealed steel sludge material via ball milling. Various amounts of annealed steel sludge material (5%, 15%, and 25% w) were added to date palm frond biochar, and the obtained product was fabricated by ball milling. The physicochemical characteristics of the magnetic biochar composite were subsequently analyzed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) spectroscopy, and UV-vis spectroscopy. Our findings showed that the ball milling method is a successful step for producing date palm fronds with magnetic biochar material possessing rough and packed pores, as shown by SEM. XRD patterns assumed the existence of magnetic phases of iron oxide (magnetite (Fe3O4), hematite (α-Fe2O3), and maghemite (γ-Fe2O3) at different generated peaks. FTIR outputs exhibited the abundant presence of various oxygen-containing functional groups (- COOH and -OH) on the surface of magnetic biochar material, which help to create chemically reactive sites to adsorb potential surrounding species. The UV spectra showed a noticeable enhancement of the optical properties of the magnetic biochar with an increase in the sludge dose for light absorption in the visible region from wavelengths of 400 – 700 nm . This result signifies the synthetic optimization and potential application of magnetic biochar materials for composites that could be employed in targeted uses including soil amendment, water remediation and energy applications.

Synthesis and investigation of polyvinylpyrrolidone-polymer content on magnetic and electromagnetic properties of electrospun BiFeO3, SrFe12O19, α-Fe2O3 nanostructures

A one-pot electrospinning technique was employed to synthesize polyvinylpyrrolidone (PVP)-based nanofibers containing bismuth ferrite (BiFeO3), strontium hexaferrite (SrFe12O19), and hematite (α-Fe2O3). The influence of PVP polymer concentration on structural properties revealed the formation of pure phases in all samples, except for BiFeO3 nanofibers, which contained an impurity Bi2Fe4O9 phase. Field-emission scanning electron microscope images showed that higher PVP concentrations resulted in longer, thicker nanofiber chains for all samples. Vibrating sample magnetometer analysis indicated that SrFe12O19 nanofibers exhibited strong ferrimagnetic properties with high saturation magnetization (60 emu g−1) and coercivity (5000 Oe), while the other samples displayed weaker magnetic properties. To address the fragility of nanofibers produced via the one-pot method, the highest PVP concentration nanofibers were incorporated into low and high concentrations of paraffin matrices. Electromagnetic testing showed that paraffin concentration significantly increased the real part of electrical permittivity for BiFeO3 nanofibers (from ∼2 to ∼4.5) compared to other compositions (∼2 to ∼3). Impedance results revealed that BiFeO3 nanofibers had the lowest resistance and likely higher reflectivity. Lastly, the real permittivity of nanofibers decreased with increasing frequency, aligning with Koop’s dielectric relaxation theory.

Small polaron hopping and tunneling mechanisms in Ba0.9La0.1Fe12O19 hexaferrite ceramic at low temperatures

The correlation between dielectric relaxation and conduction mechanisms in the Ba0.9La0.1Fe12O19 ceramic hexaferrite, at temperatures below 100 K was investigated. The sample was prepared using the conventional solid-state reaction method. X-ray diffraction analysis indicated that the sample is composed of a hexagonal BaFe12O19 phase (lattice parameters a = 5.8778(6) Å and c = 23.170(3) Å) and a small proportion of hematite (α-Fe2O3). The average grain size is 1.48 ± 0.4 μm, with irregular hexagonal and agglomerated grains. The magnetic hysteresis curve shows characteristics typical of ferro and ferrimagnetic materials, with an effective magnetic anisotropy coefficient of 0.960×106 emu/cm3 and an anisotropy field of 1.587×104 Oe. A dielectric relaxation process is observed between 50 and 100 K, with an activation energy of 60.4 ± 0.4 meV and a characteristic relaxation time of 2.09 ×10−10 s, mainly attributed to the electrical behavior of the grains. Two conduction mechanisms were identified: small polaron tunneling (high temperatures and low frequencies) and correlated barrier hopping of electrons (low temperatures and high frequencies). The activation energy for free polaron formation, according to the Komine-Iguchi hopping polarization model, was 7.12 ± 0.02 meV. In the dielectric modulus relaxation process between 30 and 54 K, the activation energy was 40.8 ± 0.9 meV, with a characteristic relaxation time of 2.41×10−10 s. The small polaron conductivity in the grain region was 67.52 meV and 54.0 meV in the grain boundary region. The results highlight that the polarization and conduction mechanisms in this ceramic at low temperatures are dominated by small polaron hopping and tunneling, and emphasize the influence of La3+ doping on the structural, magnetic, and electrical properties of barium hexaferrite.

Biodiesel photoelectrocatalytic synthesis employing α-Fe2O3 film decorated with Pt nanoparticles as photoanode

In this work, photoelectrochemical route for biodiesel production using an electrochemical cell configured with platinum and α-Fe2O3 modified with Pt nanoparticles as electrodes was investigated. XRD patterns registered for film prepared by modified hydrothermal method revealed a trigonal structure of the hematite (α-Fe2O3) phase. The α-Fe2O3 film surface was decorated by metallic Pt nanoparticles (PtNP) in order to reduce the charge recombination and improve the photocatalytic efficiency. The band gap energy (EBG) of the α-Fe2O3 and PtNP/α-Fe2O3 films was estimated by UV-Vis spectroscopy at approximately 2.1 eV. Electrochemical measurements showed that the oxide is an n-type semiconductor adequate to be used as a photoanode in biodiesel synthesis. Under polarization conditions, the electrochemical cell changed the pH from 7 to 14 when the system was polarized at 5.0 V. In the synthesis of biodiesel by esterification reaction, oleic acid, 300 µL of 0.1 mol L−1 aqueous KCl solution and methanol were used as precursor reagents. The reaction was carried out free of strong base, such as KOH or NaOH, as a supporting electrolyte. In this route, the reduction of the water molecule occurred on the cathode, with the formation of hydroxyl (OH-) species, methoxy, and consequently fatty acid methyl esters (FAMEs). Thermogravimetric analysis (TGA) and Gas chromatography coupled to mass spectrometry (CG-MS) were performed to evaluate the catalysis products. GC-MS analyzes show that the reaction has a yield of about 7 % with the formation of FAMEs, such as methyl 9-octadecenoate, methyl hexadecanoate and methyl hexadecanoate.

Hematite (Fe2O3)-modified biopolymer for Rhodamine B degradation under visible light

This study deals with the preparation of a novel biomaterial by incorporating the hematite α-Fe2O3 onto crushed leaves of the Washingtonia filifera palm tree in their raw state and in extracted cellulose from the same plant. The incorporation of α-Fe2O3 was accomplished by hydrothermal route at 200 °C. The palm leaves, extracted cellulose, and synthesized products were characterized by thermal analysis (TG) and FT-IR spectroscopy. The latter revealed peaks at 524 and 449 cm−1 for the synthesized material, attributed to vibrational deformation of the inorganic Fe-O bond. In contrast to the TG profile of raw palm leaves, the thermogram of the composite degrades in a single step at 343 °C. This one-step decomposition clearly indicates the chemical modification of our cellulose matrix and confirms the successful incorporation of the hematite α-Fe2O3 into the lignocellulose. The second part is devoted to α-Fe2O3 working as sensitizer in photocatalysis, it was characterized optically (Eg = 1.94 eV) and electrochemically with a flat band potential of −0.53 VSCE. The conduction band (−0.73 V SCE ) is more cathodic than the potential of the O2/O2 •− couple (−0.52 V SCE ) and should reduce dissolved oxygen into reactive O2 •− radical. The as-prepared materials were successfully tested in the photocatalytic degradation of Rh B (10 ppm) and the result gave an abatement of 60% on α-Fe2O3/lignocellulose under visible light irradiation (LED lamp) with a flux of 23 mW cm−2. The kinetic obeys a first-order model with a half photocatalytic-life of ∼ 7 h.