Showing papers on "Hematite published in 2023"

Biomass chemical looping gasification for syngas production using modified hematite as oxygen carriers

Abstract: Syngas is a clean energy carrier and a major industrial feedstock. In this paper, syngas was produced via biomass chemical looping gasification (CLG) process. Hematite, the most common Fe-based oxygen carrier (OC), was modified with different metal oxides (CeO2, CaO and MgO) by the impregnation method. The hematite modified by CeO2, CaO and MgO was namely as CeO2-hematite (CeO2-H), CaO-hematite (CaO-H) and MgO-hematite (MgO-H), respectively. The introduction of CeO2, CaO and MgO enhanced the reactivity of lattice oxygen of hematite. The optimum condition for syngas production had been explored as the mass ratio of oxygen carrier to biomass (O/B) of 0.2, the mass ratio of steam to biomass (S/B) of 0.75 and temperature of 800°C in the biomass CLG process. The CeO2-H exhibited the most wonderful performance compared to that for CaO-H and MgO-H. The crystal composition of OC influenced greatly in the CLG process. CeFeO3 had a good oxygen mobility property and lattice oxygen releasing capacity due to the most oxygen vacancy distributed on the OC surface and the most active lattice oxygen, which is conducive to the biomass chemical looping gasification process for syngas production, leading to the highest gasification efficiency of 95.86% and gas yield of 1.20 m3/kg of the three. Cyclic test proved that CeO2-H had well sintering resistance and cyclic performance.

Fully Dispersed IrOx Atomic Clusters Enable Record Photoelectrochemical Water Oxidation of Hematite in Acidic Media.

Abstract: Ir-based materials are still the benchmark catalysts for various reactions in acidic environment, but the high loading and low atom utilization limit their large-scale deployment. Herein, we report an effective strategy for implanting fully dispersed iridium-oxide atomic clusters onto hematite for boosting photoelectrochemical water oxidation in acidic solution. The resulting photoanode achieves a record-high photocurrent of 1.35 mA cm-2 at 1.23 V, corresponding to a mass activity of 172.70 A g-1 (3 times higher than electrodeposited control sample) and demonstrating the merits from the high atomic utilization of Ir. The systematically experimental and theoretical results reveal that the performance improvement correlates with the modulated electronic structure including the adjusted Fermi level and d-band center, which significantly enhances charge separation efficiency and promotes the conversion from intermediate *O into *OOH.

Multi-Technique Characterization of Painting Drawings of the Pictorial Cycle at the San Panfilo Church in Tornimparte (AQ)

Abstract: We present some results, obtained using a multi-scale approach, based on the employment of different and complementary techniques, i.e., Optical Microscopy (OM), Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS), X-ray diffraction (XRD), Raman and µ-Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy equipped with Attenuated Total Reflectance (ATR) analyses, Inductively Coupled Plasma–Mass Spectrometry (ICP-MS), and Thermal Ionization Mass Spectrometry (TIMS), of an integrated activity focused on the characterization of micro-fragments of original and previously restored paintings of the pictorial cycle at the San Panfilo Church in Tornimparte, sampled from specific areas of interest. The study was aimed, on one hand, at the identification of the overlapping restoration materials used during previous conservation interventions (documented and not), and, on the other hand, at understanding the degradation phenomena (current or previous) of the painted surfaces and the architectural structures. The study of stratigraphy allowed us to evaluate the number of layers and the materials (pigments, minerals, and varnishes) present in each layer. As the main result, the identification of blue, black, yellow, and red pigments (both ancient and modern) was achieved. In the case of blue pigments, original (azurite and lazurite) and retouching (Prussian blue and phthalo blue) materials were recognized, together with alteration products (malachite and atacamite). Traces of yellow ochre were found in the yellow areas, and carbon black in the blue and brown areas. In the latter, hematite and red ochre pigments were also recognized. The obtained results are crucial to support the methodological choices during the restoration intervention of the site, and help to ensure the compatibility principles of the materials on which a correct conservative approach is based.

Single-Atom Iridium on Hematite Photoanodes for Solar Water Splitting: Catalyst or Spectator?

Abstract: Single-atom catalysts (SACs) on hematite photoanodes are efficient cocatalysts to boost photoelectrochemical performance. They feature high atom utilization, remarkable activity, and distinct active sites. However, the specific role of SACs on hematite photoanodes is not fully understood yet: Do SACs behave as a catalytic site or as a spectator? By combining spectroscopic experiments and computer simulations, we demonstrate that single-atom iridium (sIr) catalysts on hematite (α-Fe2O3/sIr) photoanodes act as a true catalyst by trapping holes from hematite and providing active sites for the water oxidation reaction. In situ transient absorption spectroscopy showed a reduced number of holes and shortened hole lifetime in the presence of sIr. This was particularly evident on the second timescale, indicative of fast hole transfer and depletion toward water oxidation. Intensity-modulated photocurrent spectroscopy evidenced a faster hole transfer at the α-Fe2O3/sIr/electrolyte interface compared to that at bare α-Fe2O3. Density functional theory calculations revealed the mechanism for water oxidation using sIr as a catalytic center to be the preferred pathway as it displayed a lower onset potential than the Fe sites. X-ray photoelectron spectroscopy demonstrated that sIr introduced a mid-gap of 4d state, key to the fast hole transfer and hole depletion. These combined results provide new insights into the processes controlling solar water oxidation and the role of SACs in enhancing the catalytic performance of semiconductors in photo-assisted reactions.

Boosting Charge Transfer Efficiency by Nanofragment MXene for Efficient Photoelectrochemical Water Splitting of NiFe(OH)x Co-Catalyzed Hematite.

Abstract: The use of oxygen evolution co-catalysts (OECs) with hematite photoanodes has received much attention because of the potential to reduce surface charge recombination. However, the low surface charge transfer and bulk charge separation rate of hematite are not improved by decorating with OECs, and the intrinsic drawbacks of hematite still limit efficient photoelectrochemical (PEC) water splitting. Here, we successfully overcame the sluggish oxygen evolution reaction performance of hematite for water splitting by inserting zero-dimensional (0D) nanofragmented MXene (NFMX) as a hole transport material between the hematite and the OEC. The 0D NFMX was fabricated from two-dimensional (2D) MXene sheets and deposited onto the surface of a three-dimensional (3D) hematite photoanode via a centrifuge-assisted method without altering the inherent performance of the 2D MXene sheets. Among many OECs, NiFe(OH)x was selected as the OEC to improve hematite PEC performance in our system because of its efficient charge transport behavior and high stability. Because of the great synergy between NFMX and NiFe(OH)x, NiFe(OH)x/NFMX/Fe2O3 achieved a maximum photocurrent density of 3.09 mA cm-2 at 1.23 VRHE, which is 2.78-fold higher than that of α-Fe2O3 (1.11 mA cm-2). Furthermore, the poor stability of MXene in an aqueous solution for water splitting was resolved by uniformly coating it with NiFe(OH)x, after which it showed outstanding stability for 60 h at 1.23 VRHE. This study demonstrates the successful use of NFMX as a hole transport material combined with an OEC for highly efficient water splitting.

Investigating the dependence of mineral dust depolarization on complex refractive index and size with a laboratory polarimeter at 180.0° lidar backscattering angle

Abstract: Abstract. In this paper, the dependence of the particles' depolarization ratio (PDR) of mineral dust on the complex refractive index and size is for the first time investigated through a laboratory π-polarimeter operating at 180.0∘ backscattering angle and at (355, 532) nm wavelengths for lidar purposes. The dust PDR is indeed an important input parameter in polarization lidar experiments involving mineral dust. Our π-polarimeter provides 16 accurate (<1 %) values of the dust lidar PDR at 180.0∘ corresponding to four different complex refractive indices, studied at two size distributions (fine, coarse) ranging from 10 nm to more than 10 µm and at (355, 532) nm wavelengths while accounting for the highly irregular shape of mineral dust, which is difficult to model numerically. At 355 nm, the lidar PDR of coarser silica, the main oxide in mineral dust, is equal to (33±1) %, while that of coarser hematite, the main light absorbent in mineral dust, is (10±1) %. This huge difference is here explained by accounting for the high imaginary part of the hematite complex refractive index. In turn, Arizona dust exhibits higher depolarization than Asian dust, due to the higher proportion in hematite in the latter. As a result, when the strong light-absorbent hematite is involved, the dust lidar PDR primarily depends on the particles' complex refractive index, and its variations with size and shape are less pronounced. When hematite is less or not involved, the dust lidar PDR increases with increasing sizes, though the shape dependence may then also play a role. The (355, 532) nm wavelength dependence of the dust lidar PDR then allows discussing on the involved particle sizes, thus highlighting the importance of dual-wavelength (or more) polarization lidar instruments. We believe these laboratory findings will help improve our understanding of the challenging dependence of the dust lidar PDR with complex refractive index and size to help interpret the complexity and the wealth of polarization lidar signals.

How titanium and iron are integrated into hematite to enhance the photoelectrochemical water oxidation: a review.

Abstract: Hematite has been considered as a promising photoanode candidate for photoelectrochemical (PEC) water oxidation and has attracted numerous interests in the past decades. However, intrinsic drawbacks drastically lower its photocatalytic activity. Ti-based modifications including Ti-doping, Fe2O3/Fe2TiO5 heterostructures, TiO2 passivation layers, and Ti-containing underlayers have shown great potential in enhancing the PEC conversion efficiency of hematite. Moreover, the combination of Ti-based modifications with various strategies towards more efficient hematite photoanodes has been widely investigated. Nevertheless, a corresponding comprehensive overview, especially with the most recent working mechanisms, is still lacking, limiting further improvement. In this respect, by summarizing the recent progress in Ti-modified hematite photoanodes, this review aims to demonstrate how the integration of titanium and iron atoms into hematite influences the PEC properties by tuning the carrier behaviours. It will provide more cues for the rational design of high-performance hematite photoanodes towards future practical applications.

Cracking and Microstructure Transition of Iron Ore Containing Goethite in Fe-C Melt Based on the HIsmelt Process

Abstract: The phenomenon of cracking and deterioration of iron ore particles is a widespread scientific problem in the field of mineral processing and metallurgy. In this paper, the thermal decomposition properties of iron ore were investigated by a non-isothermal method using thermogravimetric equipment, and the crack evolution behavior of iron ore within Fe-C melt was investigated experimentally, by scanning electron microscopy and Micro-CT. The results show that the start decomposition temperature of #2 iron ore is 292.7 °C, which is 37.3 °C higher compared to that of #1 iron ore, because of its smaller pores and the difficulty of water vapor diffusion. The initial decomposition of iron ore is the decomposition goethite to form water vapor, and as heat transfer continues, hematite particles break into smaller particles and decompose to form Fe3O4. During the smelting reduction process, the Crack index (CI) of #1 iron ore was 5.50% at 4 s, and the CI index increased to 23.54% when time was extended to 16 s, and the internal evolved from locally interconnected holes to cracked structure. The iron ore maintains a relatively intact form during reduction within the Fe-C melt, and interfacial reduction reaction is dominant in the later stage.

Roles of Surface States in Cocatalyst-Loaded Hematite Photoanodes for Water Oxidation

Abstract: Photoelectrochemical water oxidation over bare hematite (α-Fe2O3) involved physical–chemical processes through surface states. It is found that the surface state with a higher oxidative energy (S1) served as a reaction intermediate for water oxidation, while the other surface state with a lower oxidative energy (S2) was basically catalytically inactive and induced charge recombination. Since a cocatalyst is commonly loaded on α-Fe2O3 to enhance water oxidation, the physical–chemical processes between the surface states and the cocatalyst are supposedly important but remain unclear. In the present study, we elucidated such processes by employing photoelectrochemical impedance spectroscopy. We found that, in a CoPi-loaded α-Fe2O3, S1 no longer served as an intermediate for water oxidation and was mostly passivated. At the same time, S2 became the key intermediate for water oxidation by serving as a hole reservoir, prolonging the hole lifetime, and finally transferring holes to CoPi. This study reveals the surface chemistry for optimizing cocatalyst-loaded α-Fe2O3, which is different from that for bare α-Fe2O3.

Reusable Fe2O3/TiO2/PVC Photocatalysts for the Removal of Methylene Blue in the Presence of Simulated Solar Radiation

Abstract: Currently, environmental pollution by various organic pollutants (e.g., organic dyes) is a serious, emerging global issue. The aqueous environment is highly exposed to the harmful effects of these organic compounds. Furthermore, the commonly applied conventional purification techniques are not sufficient enough. Heterogeneous photocatalysis and the photo-Fenton process are effective, low-cost and green alternatives for the removal of organic pollutants. In this study, different iron(III) oxide/titanium(IV) oxide/polyvinyl chloride (Fe2O3/TiO2/PVC) nanocomposites in tablet form were investigated in the photodegradation of methylene blue (MB) under simulated sunlight, and their possible antibacterial effects were examined. The newly synthesized nanocomposites were characterized by scanning electron microscope, X-ray diffraction, UV–Vis diffuse reflectance spectroscopy, and Raman spectroscopy. The results showed a hematite crystal form in the case of Fe2O3(2) and Fe2O3 samples, while the Fe2O3(1) sample showed a combination of hematite and synthetic mineral akaganeite. The highest photocatalytic efficiency was achieved in the presence of Fe2O3/TiO2/PVC, when 70.6% of MB was removed. In addition, the possible photo-cleaning and reuse of the mentioned photocatalyst was also examined. Based on the results, it can be seen that the activity did not decrease after five successive runs. Nanocomposites also exhibited mild antibacterial effects against the two tested Gram-positive bacteria (S. aureus and B. cereus).

Selenium Removal from Aqueous Solution Using a Low-Cost Functional Ceramic Membrane Derived from Waste Cast Iron

Abstract: The high affinity of iron-based byproducts for anion removal can facilitate wastewater treatment using membranes functionalized with such byproducts. In this study, a low-cost functional ceramic membrane (LFCM) based on waste cast iron (WCI) was fabricated and applied to remove selenium from aqueous solutions. The effect of roasting (1250 °C) on the raw material properties was analyzed by X-ray diffraction and specific surface area measurements. Upon roasting, zero-valent iron (Fe0) present in WCI was oxidized to hematite (Fe2O3), while the specific surface area of WCI increased from 2.040 to 4.303 m2/g. Raw WCI exhibited the highest Se(IV) and Se(VI) removal capacity among the prepared materials, and Se(IV) could be removed faster and more efficiently than Se(VI). The selenium removal properties of the synthesized LFCM were similar to those of WCI. This membrane could simultaneously and efficiently remove Se(IV) and turbidity-causing substances through filtration. The results are expected to provide insights into the fabrication of ceramic membranes using industrial byproducts for the removal of ionic contaminants from wastewater.

Archaeometallurgical Explorations of Bloomery Iron Smelting at Mutoti 2, an Early Iron Age Site in Venda, Northern South Africa

Abstract: When established, bloomery iron smelting profoundly transformed farming communities that settled in Africa south of the Sahara. Sustained research in the Lowveld region of northern South Africa identified multifarious evidence of metal working dating to the Early Iron Age (Common Era 200-900). Not surprisingly, the region is celebrated in oral traditions, myths, legends, and other reservoirs of local knowledge for its highly skilled metallurgists who reduced exceptionally rich magnetite (Fe3O4) and hematite (Fe2O3) ores at locales such as Tshimbupfe, Tshirululuni, Vuu, Thomo, and Thengwe. However, the technology of iron smelting and how the smelted iron (Fe) transformed producer and user communities in the region is a subject that, until recently, attracted limited archaeometallurgical work. We present the results of archaeometallurgical analyses of iron production remains from Mutoti 2 using complementary macroscopic (physical examination), microstructural (Optical Microscopy), and compositional techniques (WD-XRF). The results show that the technology of iron smelting fitted within the bloomery method. However, the quantities of iron production remains at the site suggest a scale and organization of production geared for needs beyond single villages. This embedded first-millennium CE iron production into the socio-economic, political, and environmental transformations that shaped the political economy of farming communities of the time.

Effect of the conductive substrate on the photoelectrocatalytic properties of hematite for water splitting

Abstract: In this paper, hematite photoanodes were prepared on F-doped SnO2 glass (FTO), polystyrene microspheres (PS), a three-dimensional conductive substrate prepared from a monolayer PS template (MM-TCS) and a bilayer PS template (B-TCS) by a hydrothermal method, and the effect of the different substrates on the photoelectrocatalytic (PEC) performance of hematite was investigated. At 1.23 V (vs RHE), the hematite photoanode prepared on B-TCS (B-TCS-hematite) has the optimal photocurrent response of 1.16 mA cm−2, which is 4.6 times that of the hematite photoanode prepared on FTO (FTO-hematite). The improved PEC performance of the B-TCS-hematite sample is mainly due to the thicker and more connected B-TCS layers, the high ratio of (1 0 4)/(1 1 0), the morphology of nanocoral rods with larger gaps and the increased light absorption, which significantly improve the bulk charge separation efficiency and surface charge injection efficiency. In this work, the effects of conductive substrates on the photoelectrocatalytic water of hematite were investigated by scanning electron microscopy (SEM), UV–vis spectroscopy, X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and photoelectrical measurements.

Single-atomic-site platinum steers photogenerated charge carrier lifetime of hematite nanoflakes for photoelectrochemical water splitting

Abstract: Abstract Although much effort has been devoted to improving photoelectrochemical water splitting of hematite (α-Fe 2 O 3 ) due to its high theoretical solar-to-hydrogen conversion efficiency of 15.5%, the low applied bias photon-to-current efficiency remains a huge challenge for practical applications. Herein, we introduce single platinum atom sites coordination with oxygen atom (Pt-O/Pt-O-Fe) sites into single crystalline α-Fe 2 O 3 nanoflakes photoanodes (SAs Pt:Fe 2 O 3 -Ov). The single-atom Pt doping of α-Fe 2 O 3 can induce few electron trapping sites, enhance carrier separation capability, and boost charge transfer lifetime in the bulk structure as well as improve charge carrier injection efficiency at the semiconductor/electrolyte interface. Further introduction of surface oxygen vacancies can suppress charge carrier recombination and promote surface reaction kinetics, especially at low potential. Accordingly, the optimum SAs Pt:Fe 2 O 3 -Ov photoanode exhibits the photoelectrochemical performance of 3.65 and 5.30 mA cm −2 at 1.23 and 1.5 V RHE , respectively, with an applied bias photon-to-current efficiency of 0.68% for the hematite-based photoanodes. This study opens an avenue for designing highly efficient atomic-level engineering on single crystalline semiconductors for feasible photoelectrochemical applications.

Sequential modifications of the surface of hematite (α-Fe2O3) photoanodes with amorphous nickel iron oxide (NiFeOx) and cobalt phosphate (Co-Pi)

Abstract: We prepared Hematite (α-Fe2O3)-based photoanodes, treated by either an amorphous NiFeOx coating or a cobalt-phosphate co-catalyst (Co-Pi) or both, and investigated the role of each treatment in the improvement of the PEC performances. We found that the PEC performances of the films in which both Co-Pi or NiFeOx were deposited on the surface of Hematite were much higher than that of bare Hematite regardless of the order of the treatments, which could be attributed to the synergistic effect on the enhancement of the charge transfer efficiency. Particularly, the film in which the surface of hematite was coated with NiFeOx, then Co-Pi was loaded on it, showed the excellent long-term stability, alleviating the shortcoming of the NiFeOx coating. In addition, we found that the treatments of either Co-Pi or NiFeOx resulted in the enhancement of the charge transfer efficiencies and the generation of the additional component arising from the trapped holes in Co-Pi (NiFeOx), separated from the surface states in hematite, which are beneficial for the enhancement of the PEC performance.

Structural, optical, and magnetic properties of submicron hematite (α-Fe2O3) particles synthesized from industrial steel waste

Abstract: Hematite submicron particles were synthesized using oil-contaminated ferric oxide precursor obtained from the hot-rolled steel industry in Colombia. The samples received are difficult to recycle for the steel industry, which, due to their poor disposal, causes irreparable environmental damage. Here we propose a synthetic route to obtain functional magnetic particles with this residue. First, a series of washes with solvent and alcohols were proposed, thus achieving the total removal of the oil. X-ray diffraction and Mössbauer spectroscopy show that the as received sample consists of different iron phases, with wüstite being the majority phase. After the synthesis process, the hematite phase was present as the majority phase with ∼92 wt%. FTIR, UV–Vis, and SQUID measurements was carried out to study the structural, optical and magnetic properties of the samples. This methodology is a viable alternative to give added value to this waste to improve the management of this by-product.

Characterization of a carbonatite-derived mining tailing for the assessment of rare earth potential

Abstract: Depletion of high-grade deposits of rare earth elements (REEs) has led to increased interest in reprocessing mining tailing, particularly from carbonatite-related deposits. This is because most of the world’s REEs are produced from such deposits. The objective of this study was to physically, geochemically, and mineralogically characterize a carbonatite-related tailing from an Australian mine site to assess the REEs recovery potential. The tailing sample sourced from the mine site was analyzed by dry screening, laser particle size analysis, X-ray fluorescence (XRF), X-ray diffraction (XRD), Inductively Coupled Plasma Mass Spectrometry, and Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS). The results revealed that tailing consisted of mainly fine particles with 50 wt% below 61 µm. The geochemical results showed that the tailing consisted mainly of iron (Fe), and REE accounted for over 50% and 9% of the mass, respectively. The identification of major mineral phases by XRD followed by verification by SEM-EDS found monazite and florencite were the main REE-bearing minerals. The main gangue mineral is identified as goethite. The metallurgical balance showed that over 70% of the mass, REE, and Fe were concentrated in finer particle fractions below 63 µm. The SEM-EDS-based mineral liberation analysis found that REE-minerals were primarily associated with goethite and were locked within the latter in larger particle sizes over 100 µm. However, the smaller (<50 µm) REE-mineral grains were mostly liberated. The findings of this study suggest that light grinding of the particle fractions above 63 µm would potentially liberate the locked REE-minerals and subsequent separation by gravity, magnetic, and flotation processes can be tested to make REE concentrate. Because the sample is fine-grained, direct hydrometallurgical processing could potentially be effective to recover REE from this tailing.

Advanced hematite nanomaterials for newly emerging applications

Abstract: Because of the combined merits of rich physicochemical properties, abundance, low toxicity, etc., hematite (α-Fe2O3), one of the most chemically stable compounds based on the transition metal element iron, is endowed with multifunctionalities and has steadily been a research hotspot for decades. Very recently, advanced α-Fe2O3 materials have also been developed for applications in some cutting-edge fields. To reflect this trend, the latest progress in developing α-Fe2O3 materials for newly emerging applications is reviewed with a particular focus on the relationship between composition/nanostructure-induced electronic structure modulation and practical performance. Moreover, perspectives on the critical challenges as well as opportunities for future development of diverse functionalities are also discussed. We believe that this timely review will not only stimulate further increasing interest in α-Fe2O3 materials but also provide a profound understanding and insight into the rational design of other materials based on transition metal elements for various applications.

Recycling of NdFeB magnets employing oxidation, selective leaching, and iron precipitation in an autoclave

Abstract: The increasing production of neodymium–iron–boron (NdFeB) magnets for technological applications results in disposal problems. NdFeB magnets contain a significant quantity of rare earth elements (REEs). China is the largest REEs producer, but it applies quotas and increases the export prices of REEs. To address this issue, this study aims at investigating the recovery process of REEs from scrap NdFeB magnets. After oxidation of NdFeB magnet powders, selective leaching with nitric acid was carried out to achieve high-purity REE-rich leaching liquor. First, the oxidation kinetics of NdFeB powders was studied in detail to determine the oxidation temperature and duration. Afterwards, the effects of selective leaching parameters, including acid concentration, leaching temperature, stirring speed and solid/liquid ratio, were examined by analysis of variance (ANOVA) analysis based on Taguchi method. The most substantial parameters were assigned to be the temperature and solid/liquid ratio. Eventually, the dissolution kinetics were studied to propose a model for REEs. Several universal equations for dissolution kinetics were tested, and (1 − (1 − x) = k × tn) gives the best results for REEs. The findings show that the leaching process follows the shrinking core model. Activation energy was calculated to be 40.375 kJ mol−1 for REEs. As the last step, the iron dissolved during leaching was precipitated as hematite in the autoclave. The hematite precipitation experiments were performed based on the Box–Behnken design. The effect of precipitation parameters was investigated by ANOVA analysis, and the precipitation process was optimized using response surface methodology (RSM), which resulted in the minimum iron and maximum REEs content in the leach liquor.