X-ray Diffractometry Analysis Research Articles

Bluish-green emission of novel BaAl2Ge2O8:Eu2+ phosphors under near-ultraviolet excitation

A new class of phosphor samples, denoted as Ba1–xAl2Ge2O8:xEu2+ (BAGO:xEu2+) was synthesized using a Pechini-type sol–gel technique and subsequent thermal reduction in CO atmosphere. The morphology and structural characteristics of both the BAGO host lattice and the Eu2+ ions activated BAGO phosphors were investigated through field-emission scanning electron microscopy and X-ray diffractometry analyses, respectively. The BAGO host lattice has micro-sized particles and the Rietveld refinement reveals the presence of a monoclinic crystal phase, characterized by the space group I2/c (No. 15). Introducing Eu2+ ions into Ba2+ sites under CO condition reduces the particle size, switching from microscale to nanoscale. Within the near-ultraviolet spectrum (353 nm), the BAGO:xEu2+ phosphors exhibit a broadband bluish-green photoluminescence (PL) emission characterized by a peak band at 492 nm. This phenomenon is attributed to the 4f65d1 → 4f7 electronic transition. The BAGO:0.02Eu2+ phosphor shows the strongest bluish-green PL emission, and a comprehensive description of the concentration quenching mechanism between Eu2+ ions is revealed. Additionally, the thermal stability of the optimized BAGO:0.02Eu2+ phosphor was investigated, and its activation energy was estimated. Therefore, the synthesized bluish-green BAGO:0.02Eu2+ phosphor holds the promise of being a novel and potential candidate for utilization in white light-emitting diode applications.

DETECTION AND CHARACTERIZATION OF SOME GLAZE FAULTS ENCOUNTERED IN SANITARYWARES

The use of suitable glaze compositions, which enable ceramic sanitaryware (such as sink, toilet bowl, toilet bowl, etc.) to have better hygienic, aesthetic and technical properties, is of great importance as in other ceramic products. Glaze compositions, which provide durability to sanitaryware materials, reduce impact resistance and give ceramic material a hygienic appearance, are produced as ~97% white color depending on the preferences of the consumers, therefore, surface defects attract more attention in glazing and post-glazing process applications. When faults occurred during the different stages of manufacture detected on the final product, failure to detect faults on the final product by passing many production stages poses a problem in terms of intervention in the process. Faults that occur during glaze preparation are important in terms of cost. Since it is a stage in which many economic evaluations have been made in production, eliminating the faults caused from glaze preparation prevents further financial loss. In this study, the appearance of the faults in the sanitaryware items and the change in their regions (occured as a result of the oils contaminations from the machinery and components used in the preparation of glaze, the pipes of the tanks used in the glaze transport tanks and the glaze transfer or the impurities contaminated from the environment, the splashing of the impurities by the colored glazes in the glazing cabinets etc.) were characterized by means of SEM (Scanning Electron Microscopy), XRF (X-ray fluorescence spectrometry), XRD (X-Ray Diffractometry) and color measurement (L a* b*) analyses. According to the data derived from the final defected products, the faulty products were imitated by using the same components and methods on the plates under the laboratory conditions. Finally, the solutions for the problems were determined on the basis of faulty products obtained in the laboratory.

Peculiarities of Structuring of Ultrafine hBN Particles on the Surfaces of Polyamide Filaments

Purpose. Establishment of the mechanism of formation of nanofilms from ultrafine two-dimensional crystals of hexagonal boron nitride.Methods. Film structures from ultrafine two-dimensional crystals of hexagonal boron nitride were created both on the surface of a filament separated from a PA-6 polyamide yarn and on a silicon substrate. Ultra sonication was used to fix UC hBN from an aqueous colloidal system on surfaces. The characterization of UC hBN and films made from them was performed by the following methods: сщт scanning electron with energy dispersive elemental analysis, probe atomic force microscopy, vibrational Fourier IR spectroscopy (and Raman (Raman) scattering, as well as fluorescence spectroscopy, X-ray diffractometry and X-ray phase analysis, small-angle X-ray scattering.Results. The dependence of the intensity of the E2g line (I = 1362.8 cm–1) in the RS spectrum of a film structure deposited on the surface of aqueous CS UC hBN filaments on the time UST – tUST has been studied. Based on the results of the analysis of confocal, SEM and AFM images, RS and FS spectroscopy, the multilayer nature of the UC hBN film structures on the surface of the filaments and the silicon wafer was proved. The FS spectrum contains excitations on lines lying inside the band gap.Conclusion. The formation of structures on the surfaces of filaments and a silicon plate from an aqueous CS of UC hBN particles after UST occurs due to either covalent bonds in the plane of hexagons with abnormal sizes up to 1 μm, or van der Waals and ionic-covalent bonds with the formation of multilayer structures with heights from 3.6 to 340 nm.

VNIR-SWIR Spectroscopy, XRD and Traditional Analyses for Pedomorphogeological Assessment in a Tropical Toposequence

Tropical climate conditions favor landscape evolution and the formation of highly weathered soils under different pedogenic processes due to certain differential properties. Traditional analysis coupled with VNIR-SWIR reflectance spectroscopy and X-ray diffractometry (XRD) analyses can reveal such characteristics. Several researchers cited throughout this study already discussed the possible applications of analyses in this field. All agree that integrated knowledge (holistic) can drive the future of the soil sciences. However, few refer to the potential of soil spectroscopy in deriving pedogenetic information. Thus, this paper aimed to assess pedomorphogeological relationships in a representative toposequence of the Brazilian Midwest using traditional analyses and geotechnologies. We performed landscape observations and soil sampling in the field. The laboratory’s physical, chemical, spectral, and mineralogical determinations supported the soil classification according to the World Reference Basis (WRB/FAO) system. Based on the analysis results, we divided five profiles into two soil groups (highly and slightly weathered soils) using Pearson’s correlation and hierarchical clustering analysis (HCA). Traditional analyses determined the diagnostic attributes. Spectroscopic readings from 0.35 to 2.5 µm wavelengths and XRD supported identifying soil attributes and properties. Finally, all soil classes were correlated according to correspondent reflectance spectra and primary pedological attributes. There was a strong correlation between spectral oxide features and X-ray diffraction peaks. The HCA based on oxide content and mineral composition validated the previous soil grouping. Thus, we could assess the pedomorphogeological relationships through VNIR-SWIR spectroscopy, XRD, and traditional analyses concerning pedogenic processes through their correlation with soil properties resulting from these processes. However, periodic measurements are required, making orbital sensing a continuous data source for soil monitoring.

One-pot synthesis of In2O3/ZnO nanocomposite photocatalysts and their enhanced photocatalytic activity against cationic and anionic dye pollutants

An In2O3/ZnO nanocomposite was synthesized by co-precipitation and applied in the photocatalytic degradation of cationic and anionic dyes. The nanocomposite was characterized by X-ray diffractometry (XRD), Raman spectroscopy, X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectrometry (EDS), surface area analysis and UV–visible diffuse reflectance spectrometry (UV–Vis DRS). The XRD, Raman and XPS analyses revealed that the nanocomposite was composed of two phases (In2O3 and ZnO). SEM images showed agglomerations of In2O3 and ZnO, and TEM images confirmed the adhesion of In2O3 nanoparticles to the surface of ZnO. The specific surface area of the nanocomposite increased from 5.86 to 8.41 m2/g with increments of In2O3 content. The optical bandgap energies of ZnO and In2O3 powders were 3.12 and 2.90 eV, respectively. The best photocatalyst was 2%In2O3/ZnO nanocomposite and the optimal dosage was 150 mg. Under UV irradiation, 92.17, 55.54 and 38.61% of MB, RhB and MO, respectively, were degraded over the 2%In2O3/ZnO nanocomposite. Since the point of zero charge of 2%In2O3/ZnO was about 6.6, MB and RhB were more completely degraded under basic conditions while MO was more completely degraded under acidic conditions. The possible charge transfer mechanism for photocatalytic degradation over the 2%In2O3/ZnO nanocomposite was proposed based on an active species test. The results showed that h+, •OH and •O2- species were the reactive species responsible for the photocatalytic degradation of MB, RhB and MO. The In2O3/ZnO nanocomposite could remove the cationic dyes from water in a neutral condition and exhibited good stability.

Experimental study on thermal runaway characteristic and residue of Li(Ni0.8Co0.1Mn0.1)O2 lithium-ion batteries induced by overcharge

Overcharge is one of the most common triggers of thermal runaway in lithium-ion batteries. The process and mechanism of overcharging are not clarified. In particular, little research has been done on thermal runaway residues. Accident investigators require a method to identify thermal runaway residue. In this study, the thermal runaway induced by 1C (12 A) current overcharge in 12 Ah pouch Li(Ni0.8Co0.1Mn0.1)O2 lithium-ion batteries was investigated. The battery residue was disassembled. Scanning electron microscopy, X-ray diffractometry, and other analysis methods were used to investigate macro characteristics, micromorphology, and phase composition of the residue. The analysis of the residues revealed that the layered electrode adhesion was severe, the current collectors at the rupture were damaged and ejected, and copper molten beads were observed in the ejecta. Numerous fracture and breaking were observed in the residue cathode material particles, and the explanatory hypothesis was proposed. New phase C, Li2CO3, LiF, MnO, NiO, Co and Ni were found. Also, the mechanisms of the phenomena and characteristics were discussed. Accident investigators would be helped if these overcharge characteristics were widely validated.

Phase Transformation of Anhydrous to Dihydrate Carbamazepine: Preparation and Comparative Characterization

Carbamazepine, an anticonvulsant drug is one of the suitable activecompounds for the study of crystal and polymorphism study. Hydrate formation or dehydration of a given hydrate may affect the overall performance of the ultimate formulations and it has been estimated that more than 30 % available active drug compound can form a hydrate. The anhydrous form of the compound always shows higher aqueous solubility and dissolution parameter as compared to hydrates. This ultimately led to improved bioavailability when the rate limiting step for the absorption is dissolution rate. The purpose of the present investigation was to compare various techniques for the formation of Carbamazepine dihydrate from anhydrates and also to discriminate crystal forms of Carbamazepine by Melting point, FTIR, DSC, Powder X-ray diffractometry analysis, NMR, scanning electron microscopy, solubility and intrinsic dissolution testing. Carbamazepine phase transformation of solid state occurs when exposed to the environmental condition, which can affect the performance of the drug and the formulations.

The Influences of Forest Fires on the Repellency, Mineralogy and Thermogravimetry of Soils in a Mountainous Area of the Atlantic Forest Biome - the Study Case of São Pedro da Serra, Rio de Janeiro (Brazil)

Landscapes are systems undergoing constant transformation, associated with different forms of environmental disturbances. Among these disturbances are fires, which depending on the magnitude and frequency can have effects with different severities. In the district of São Pedro da Serra, in the municipality of Nova Friburgo, located in the mountain region of the state of Rio de Janeiro, Brazil, controlled burning is often used to prepare areas for farming. However, in certain atmospheric conditions, type of vegetation and soil moisture levels, among others, these fires can escape control. This study reports the analysis through X-ray diffractometry and thermogravimetric analysis of the characteristics of the soils in two distinct areas Area 1 (Benfica) and Area 2 (Bocaina), in the same pedological regime within the Macaé de Cima Environmental Protection Area. These two areas were affected by forest fires in different periods. We also sought to identify the severity of these fires, for which purpose we collected undeformed soil samples from depths of 0-5, 5-10, 10-15, 15-20 and 20-25 cm. The data obtained showed that the mineralogy of the sand fraction was homogeneous, but the clay fraction in Area 2, unlike Area 1, was characterized by the presence of smectite and goethite. Fire tended to have the greatest impact on the top 5 cm of soil, possibly related to the hydrophobic characteristics, which are not directly linked to the timing of the fires, but rather to their magnitudes.

Laurus nobilis essential oil nanoemulsion-infused chitosan: A safe and effective antifungal agent for masticatory preservation

The present study reports the first time investigation on encapsulation of Laurus nobilis essential oil into chitosan nanoemulsion (CS-Ne-LNEO) and assessment of its efficacy to inhibit fungal infestation and aflatoxin B1 (AFB1) contamination in stored masticatories food system. Gas chromatography mass spectrometry (GC-MS) analysis revealed m-Eugenol (46.23%) and D-Limonene (8.89%) as the most abundant components of LNEO. The CS-Ne-LNEO was physico-chemically characterized through scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), and x-ray diffractometry (XRD) analyses. The CS-Ne-LNEO exhibited broad range of antifungal activity against food contaminating fungi including inhibition of toxigenic Aspergillus flavus (AF-LHP-PE-4) and AFB1 production at lower concentrations as compared to unencapsulated LNEO. The CS-Ne-LNEO caused impairment in ergosterol biosynthesis and enhancement in leakage of Ca2+, Mg2+, K+ ions and 260, 280 nm absorbing materials along with inhibition of methylglyoxal production suggesting the antifungal and antiaflatoxigenic mechanism of action. The DPPH antioxidant activity of CS-Ne-LNEO was noted with IC50 value of 0.004 µL/mL. In addition, the CS-Ne-LNEO caused complete protection of stored Phyllanthus emblica (model masticatories) fruit samples against fungal and AFB1 contamination without altering their sensory characteristics and exhibited high LD50 value (13,504 µL/Kg body weight) mammalian system. Overall, these results indicated that LNEO loaded chitosan nanoemulsion could be promoted as an eco-friendly preservative for complete protection of stored plant masticatories against fungal and AFB1 contamination.

Evaluation of Retained Austenite in Carburized Bearing Steel Using Magneto-Inductive Method

The present work explores the magneto-inductive method to evaluate different levels of retained austenite content in carburized 20NiCrMo7 bearing steel while comparing the corresponding measurements by X-ray diffractometry and image analysis by optical microscope. The content of retained austenite in carburized 20NiCrMo7 steel was modified with additional tempering to yield three samples with distinct ranges of retained austenite profiles in the carburized region of the steel. The retained austenite measured at different depths in these samples using the magneto-inductive method had an outcome comparable to other methods. Further discussion based on data suggests that the magneto–induction method yields precise (with an average deviation of 0.5%) results with sufficient sensitivity at different levels (including below 5 vol. %.) of retained austenite.

Angelica archangelica essential oil loaded chitosan nanoemulsion as edible coating for preservation of table grape fruit against Botrytis cinerea contamination and storage quality deterioration

The present study deals with the encapsulation of Angelica archangelica essential oil into chitosan nanoemulsion (AAEO-NE) and evaluation of its effectiveness as novel coating agent with innovative controlled release delivery system for protection of table grape (Vitis vinifera L.) fruit against Botrytis cinerea contamination, and quality deterioration over 30 d of storage (25 ± 2 °C, Relative humidity 85%). The AAEO-NE was characterized through dynamic light scattering (DLS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The mean particle size was tended to increase from 53.69 to 98.63 nm, while ζ-potential was decreased from + 32.3 to + 23.5 mV. Fourier transform infrared spectroscopy (FTIR), and X-ray diffractometry (XRD) analyses suggested intermolecular interaction followed by effective encompassment of AAEO into chitosan nanomatrix. In vitro release study confirmed the biphasic and controlled delivery of AAEO, essentially required for its long term effectiveness in view of maintaining postharvest quality of the treated fruit. The antifungal efficacy of unencapsulated AAEO against B. cinerea was found as 5.5 g L−1, and noticed to be enhanced (2.5 g L−1) after encapsulation into chitosan nanoemulsion. The inhibition of ergosterol biosynthesis followed by subsequent enhancement of ions leakage after treatment of B. cinerea cells with AAEO-NE suggested plasma membrane as major site of antifungal activity. During in vivo investigation, AAEO-NE coating inhibited the contamination of B. cinerea and maintained the quality attributes like weight, titrable acidity, total soluble solids, phenolic content, and pH of table grape fruit. Additionally, the preservation of enzymatic antioxidants, reduced respiration rate, and better sensory qualities of coated table grape fruit recommend the functional potentiality of chitosan as biocompatible wall matrix to encapsulate AAEO and application as novel nano-green smart coating based fungitoxicant and shelf-life enhancer in fruit and agricultural industries.

Core/shell structured Ti/Si/C composite for high-performance zinc-ion hybrid capacitor

Zinc-ion capacitors (ZnIC) have focused great attention due to high intrinsic safety and their advantages in terms of environmental protection and price. However, the increase in energy and power densities still remains a challenge. Therefore, this study aims to design and fabricate novel low-cost and environmentally-friendly nanocomposite based on titania/silica/carbon used as cathode in ZnIC. The fabrication procedure involves the functionalization of TiO2 nanoparticles with APTES and glucose, followed by a hydrothermal reaction and carbonization at 600, 700, and 800 °C (Ti/Si/C-Tx, where Tx is the temperature of carbonization) to result in carbon-coated titania/silica with a core/shell architecture. In-situ Raman and X-Ray Diffractometry (XRD) analyses were conducted to elucidate the electrochemical behaviour of the material during charge-discharge cycles. The nanocomposites were electrochemically tested using cyclic voltammetry (CV), galvanostatic cycling with potential limitation (GCPL), and potentio electrochemical impedance spectroscopy (PEIS). The designed nanocomposite showed improved performance in terms of specific capacity, power, and energy densities with values of 295 F/g, 160 W/kg, and 210 Wh/kg, respectively. Ti/Si/C-700 also demonstrated a high stability retention of 85% after 10′000 cycles, indicating its potential for use in energy storage devices. Despite these promising results, further research is required to improve capacity retention at increased current densities. The key implication of this study is the potential for the development of low-cost and high-performance energy storage devices for various applications, contributing to the growth of renewable energy sources.

Monitoring crystallite fusion of nanocellulose during colloid condensation

The crystallinity of cellulose decreases when bundled microfibrils are dispersed in water as cellulose nanofibers (CNFs) or physically separated into finer nanoscale fibrils or single microfibrils. The crystallinity of these CNFs is recovered when they become densely assembled through the dehydration of the dispersion. In this process, multiple CNFs are assumed to partially fuse, leading to the enlargement of crystallite widths. The mechanism of this CNF fusion is, however, not well understood. In this study, the recovery process of the crystallinity of CNFs was monitored by sampling wet CNF gels during condensation from a dilute dispersion to a dense aggregate, followed by wide-angle X-ray diffractometry (WAXD) and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy analyses after supercritical drying. In the WAXD analysis, a two-step enlargement in the (2 0 0) crystal size was observed: the first step was a rapid increase in the range of solid content up to 1%, followed by a gradual increase in the range of 1–85%. The crystallinity index estimated by NMR hardly changed in the range of 0.5–30% but gradually increased in the range of 30–85%. A portion of the CNF samples, without drying, were also subjected to small-angle X-ray scattering and viscoelasticity analyses, indicating that the inter-CNF contact points in water significantly increased until reaching a solid content of 1%, and then at solid contents higher than 1%, the contact areas of each point gradually expanded. Finally, a mechanism of CNF fusion was proposed based on these results.

Physico-chemistry and Cytotoxicity of Tenofovir-Loaded Acid Phosphatase-Responsive Chitosan Nanoparticles.

This study assesses the in vitro release of tenofovir (TFV)-loaded triphosphate (TPP) cross-linked chitosan nanoparticles (NPs) catalyzed by human prostatic acid phosphatase (hPAP) for 24h. The physico-chemical characterization of the NPs included particle mean diameter (PMD), zeta potential (ζ), percent drug encapsulation efficiency (% EE), Fourier transform infra-red (FTIR)spectroscopy, powder X-ray diffractometry analysis (PXRD), and drug release kinetics. The first-order rate constant (k) and activation energy (Ea) of the cross-link (TPP) are determined by the integrated rate law and Arrhenius's equations. The hPAP Michaelis-Menten constant (Km) is determined by theLineweaver-Burk's equation. The NP's safety profile is evaluated on vaginal epithelial cells (VK2/E6E7). The lyophilized drug-loaded NPs' PMD, ζ, and PDI are 149.97nm, 4.4mV, and 0.3, respectively. The % EE after lyophilization is 93.7 ± 4.4%. These NPs released drug at faster rate (63% of TFV within 6h) under the enzyme's influence. The similarity and difference factors of drug release profiles (absence vs presence of hPAP) are 56.5 and 40.3, respectively. The hPAP's Km value of 0.019mM suggests it has a good affinity for TPP at physiological pH ~ 7.4. The enhanced hydrolysis of TPP or degradation of chitosan NPs is fundamentally due to a decrease of TPP's activation energy by hPAP. In fact, the Ea value is 22.50 ± 3.06kJ/mol or 16.33 ± 0.62kJ/mol in the absence or presence of hPAP, respectively. The NPs are non-cytotoxic to the treated vaginal cell line. These hPAP-responsive NPs are promising topicalnanomicrobicides for HIV/AIDS prevention.

Incorporation of Fly Ash in Flame-Retardant Systems of Biopolyesters.

The incorporation of fly ash in polybutyl succinate (PBS) and polybutyl adipate terephtalate (PBAT) in the partial replacement of ammonium polyphosphate and/or melamine polyphosphate is evaluated in the present work. Furthermore, the influence of the surface modification of fly ash with two silanes and titanate coupling agents was also studied. Cone calorimeter experiments, pyrolysis combustion flow calorimeters (PCFCs), and UL94V tests were used to assess the fire performance of the composites. Scanning electronic microscopy, X-microanalysis, and X-ray diffractometry analysis were carried out on cone calorimeter residues in order to access the fire-retardant mode of action. The formation of new components due to the presence of fly ash was highlighted by X-ray diffractometry, indicating the synergistic effects between the flame-retardant system and fly ash. The X-microanalysis results showed that the main fraction of initial phosphorous is present in the cone calorimeter residue, indicating that the proposed system acts in a condensed phase.

Diagenetic History and Timing of Cu and Zn-Pb Sulfide Mineralization in the Permian Kupferschiefer System, Saale Subbasin, Eastern Germany

Abstract The Southern Permian basin in central Europe contains a number of important high-grade sediment-hosted Cu deposits. Laterally extensive stratabound Cu and Zn-Pb sulfide mineralized rocks are located at a major stratigraphic redox boundary, where coarse-grained continental sandstones of the uppermost Rotliegend Group are overlain by carbonaceous mudstones (T1) and limestones (Ca1) of the Zechstein Formation. This study investigates the diagenetic evolution and style of sulfide mineralization in three drill cores that intersect Cu and Zn-Pb sulfide mineralized rocks at three locations (Sangerhausen, Allstedt, and Wallendorf) in the Saale subbasin (Eastern Germany), which is located at the southern margin of the Southern Permian basin. We combine macro- to microscale petrographic data (binocular, transmitted and reflected light, and scanning electron microscopy) with quantitative X-ray diffractometry and bulk-rock geochemical analyses. Petrographic results show extensive, primary-porosity-occluding, early diagenetic calcite cementation that predates both the diagenetic alteration of detrital clasts and sulfide mineralization. The highest-grade Cu and Zn-Pb sulfides (bornite, sphalerite, and galena) replace the calcite cement, with subordinate replacement of dolomite and detrital clasts. Quantitative mineralogical and geochemical data demonstrate that the highest base metal (Cu, Zn, and Pb) concentrations are associated with carbonate-rich samples, mostly as disseminated mineralization in the middle T1. Bulk-rock geochemical results show enrichment and covariation of redox-sensitive trace elements (RSTEs, e.g., Mo) with total organic carbon content toward the lower T1, consistent with highly reducing depositional conditions. Overall, the distribution and dissolution of calcite cement across this stratigraphic redox boundary provided the main control on the lateral migration of base metal-bearing fluids and high-grade Cu and Zn-Pb sulfide mineralization in the Saale subbasin.

Synthesis of Ketjenblack Decorated Pillared Ni(Fe) Metal-Organic Frameworks as Precursor Electrocatalysts for Enhancing the Oxygen Evolution Reaction.

Metal-organic frameworks (MOFs) have been investigated with regard to the oxygen evolution reaction (OER) due to their structure diversity, high specific surface area, adjustable pore size, and abundant active sites. However, the poor conductivity of most MOFs restricts this application. Herein, through a facile one-step solvothermal method, the Ni-based pillared metal-organic framework [Ni2(BDC)2DABCO] (BDC = 1,4-benzenedicarboxylate, DABCO = 1,4-diazabicyclo[2.2.2]octane), its bimetallic nickel-iron form [Ni(Fe)(BDC)2DABCO], and their modified Ketjenblack (mKB) composites were synthesized and tested toward OER in an alkaline medium (KOH 1 mol L-1). A synergistic effect of the bimetallic nickel-iron MOF and the conductive mKB additive enhanced the catalytic activity of the MOF/mKB composites. All MOF/mKB composite samples (7, 14, 22, and 34 wt.% mKB) indicated much higher OER performances than the MOFs and mKB alone. The Ni-MOF/mKB14 composite (14 wt.% of mKB) demonstrated an overpotential of 294 mV at a current density of 10 mA cm-2 and a Tafel slope of 32 mV dec-1, which is comparable with commercial RuO2, commonly used as a benchmark material for OER. The catalytic performance of Ni(Fe)MOF/mKB14 (0.57 wt.% Fe) was further improved to an overpotential of 279 mV at a current density of 10 mA cm-2. The low Tafel slope of 25 mV dec-1 as well as a low reaction resistance due to the electrochemical impedance spectroscopy (EIS) measurement confirmed the excellent OER performance of the Ni(Fe)MOF/mKB14 composite. For practical applications, the Ni(Fe)MOF/mKB14 electrocatalyst was impregnated into commercial nickel foam (NF), where overpotentials of 247 and 291 mV at current densities of 10 and 50 mA cm-2, respectively, were realized. The activity was maintained for 30 h at the applied current density of 50 mA cm-2. More importantly, this work adds to the fundamental understanding of the in situ transformation of Ni(Fe)DMOF into OER-active α/β-Ni(OH)2, β/γ-NiOOH, and FeOOH with residual porosity inherited from the MOF structure, as seen by powder X-ray diffractometry and N2 sorption analysis. Benefitting from the porosity structure of the MOF precursor, the nickel-iron catalysts outperformed the solely Ni-based catalysts due to their synergistic effects and exhibited superior catalytic activity and long-term stability in OER. In addition, by introducing mKB as a conductive carbon additive in the MOF structure, a homogeneous conductive network was constructed to improve the electronic conductivity of the MOF/mKB composites. The electrocatalytic system consisting of earth-abundant Ni and Fe metals only is attractive for the development of efficient, practical, and economical energy conversion materials for efficient OER activity.

Orientation and Grain Size in MAPbI3 Thin Films: Influence on Phase Transition, Disorder, and Defects

In recent years, record efficiencies of halide perovskite-based devices have been achieved by processing high-quality thin films, where small morphology differences seem to be relevant for optimized optoelectronic functionality. However, a detailed understanding on how small morphological changes in perovskite films affect their structural and optoelectronic properties is still missing. Here, we investigate the influence of small morphology differences (i.e., increased grain size and crystallographic orientation), which are induced by hot-pressing methylammonium lead iodide (MAPbI3) thin films, on the structural properties, phase transition behavior, energetic disorder, and defects. To this end, detailed temperature-dependent photoluminescence (PL) and absorption analyses from 300 K down to 5 K are performed. The morphology differences, confirmed by scanning electron microscopy and X-ray diffractometry analyses, result in an increased phase transition temperature for hot-pressed (HP) films, which we attribute to less strain. Moreover, fluence-dependent and transient PL measurements reveal a lower defect density in HP films. Here, besides grain size, also the degree of orientation appears to enhance the charge carrier lifetimes. The identified interdependence of strain and defect properties with film morphology suggests small differences in the perovskite’s energetic disorder. Our work thus emphasizes the importance that even small structural differences in halide perovskites have on their optoelectronic functionality, spurring their further optimization.

An Invitation on Characterization of H2-Reduced Bauxite Residue and Recovering Iron through Wet Magnetic Separation Processes

Recovering iron from the bauxite residue (BR) is one of the long-standing challenges in the mining industry. However, there is a substantial lack of information in the literature regarding sample properties and iron extraction by reducing hydrogen. The present study aims at reducing a Greek BR using hydrogen, its characterization, and separating iron by magnetic separation processes. To this end, the reduced sample was characterized using X-ray diffractometry analysis (XRD), X-ray fluorescence spectrometer analysis (XRF), thermomagnetic analysis (TMA), automated mineralogy (AM), and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The effect of particle size (−200 + 100 µm, −100 + 75 µm, and <75 µm) was investigated through a medium-intensity magnetic separation (MIMS, Davis Tube) at 1000–2500 Gauss and a Slon® magnetic separator (1000 G). The effects of solid content (3% and 10% w/w) in a wet low-intensity magnetic separation (WLIMS, 350 G) and a two-stage MIMS followed by WLIMS were investigated. It was revealed that through reduction at 500 °C and 2 h with 20 wt% NaOH under 5 vol.% H2 + 95 vol.% N2, iron oxides and ferric oxyhydroxide (Fe2O3 and FeOOH) were converted into magnetite (Fe3O4), whereas aluminum (oxy)hydroxides (Al(OOH), Al(OH)3) were reacted with Na+ towards sodium aluminates (NaAlO2). The AM observations indicated that only 3% of iron was in the phase of liberated magnetite, and the remaining was associated with Na, Al, and Ti phases with different intensities. The dissemination of iron throughout the matrix of the sample was recognized as the principal challenge in the physical separation processes. It was found that increasing magnetic intensity from 1000 G to 2500 G resulted in improved recovery for all studied particle size fractions in Davis Tube tests. The particle range of −106 + 74 µm was chosen as the most appropriate size to achieve the maximum Fe content of 41%. The results of WLIMS (350 G) showed the maximum Fe grade but revealed less recovery of 52% and 27% at 10% and 3% solid contents, respectively, compared to the Davis Tube trials.

Phytomediated-Assisted Preparation of Cerium Oxide Nanoparticles Using Plant Extracts and Assessment of Their Structural and Optical Properties.

Cerium oxide nanoparticles were obtained using aqueous extracts of Chelidonium majus and Viscum album. X-ray diffractometry analysis confirmed the crystalline structure of the synthesized cerium oxide nanoparticles calcined at 600 °C. Scanning electron microscopy, UV-Vis reflectance and Raman spectroscopy, XPS, and fluorescence studies were utilized to interpret the morphological and optical properties of these nanoparticles. The STEM images revealed the spherical shape of the nanoparticles and that they were predominantly uniform in size. The optical band gap of our cerium nanoparticles was determined to be 3.3 and 3.0 eV from reflectance measurements using the Tauc plots. The nanoparticle sizes evaluated from the Raman band at 464 cm-1 due to the F2g mode of the cubic fluorite structure of cerium oxide are close to those determined from the XRD and STEM data. The fluorescence results showed emission bands at 425, 446, 467, and 480 nm. The electronic absorption spectra have exhibited an absorption band around 325 nm. The antioxidant potential of the cerium oxide nanoparticles was estimated by DPPH scavenging assay.