Decrease In Surface Area Research Articles

Insights into the low-temperature NH3-SCR of NO performance and mechanism over manganese tailings-derived catalyst

Manganese carbonate ore is ascertained as the most abundant manganese ore in China, while its mining and beneficiation generated a large amount of manganese tailings which is regarded as a hazardous waste. Owing to great catalytic performance of manganese oxides, it is double-benefit to employ manganese tailings as catalyst to eliminate harmful nitrogen oxides from flue gas. In this study, the effects of calcination temperature on the low-temperature denitration performance and physicochemical properties of manganese tailings were systematically investigated via XRF, XRD, XPS, H2-TPR, NH3-TPD and DRIFTS, aiming at exploring the effective utilization of manganese tailings. The results revealed the best catalytic activity can be obtained at a calcination temperature of 500 °C with over 95 % NO conversion attained in the denitration temperature range of 75–225 °C. Lower calcination temperature led to the incomplete decomposition of MnCO3, while higher calcination temperature led to the decrease in specific surface area, surface acidity and oxidation performance. The denitration reaction was followed by Eley-Rideal pathway, in which the absorbed NH3 species was reacted with the gaseous NO and NO2. Based on the results in this study, the effective utilization of manganese tailings for NO emission reduction could promise for wide applications.

Fractal Characteristics of Deep Shales in Southern China by Small-Angle Neutron Scattering and Low-Pressure Nitrogen Adsorption

The occurrence and flow of shale gas are substantially impacted by nanopore structures. The fractal dimension provides a new way to explore the pore structures of shale reservoirs. In this study, eight deep shale samples from Longmaxi Formation to Wufeng Formation in Southern Sichuan were selected to perform a series of analysis tests, which consisted of small-angle neutron scattering, low-pressure nitrogen adsorption, XRD diffraction, and large-scale scanning electron microscopy splicing. The elements that influence the shale fractal dimension were discussed from two levels of mineral composition and pore structures, and the relationship between the mass fractal dimension and surface fractal dimension was focused on during a comparative analysis. The results revealed that the deep shale samples both had mass fractal characteristics and surface fractal characteristics. The mass fractal dimension ranged from 2.499 to 2.991, whereas the surface fractal dimension ranged from 2.814 to 2.831. The mass fractal dimension was negatively correlated with the surface fractal dimension. The mass fractal dimension and the surface fractal dimension are controlled by organic matter pores, and their development degree significantly affects the fractal dimension. The mass fractal dimension increases with the decrease of a specific surface area and pore volume and increases with the increase of the average pore diameter. The permeability and surface fractal dimension are negatively correlated, but no significant correlation exists between the permeability and mass fractal dimension, and the internal reason is the dual control effect of organic matter on shale pores. This study comprehensively analyses the mass fractal characteristics and surface fractal characteristics, which helps in a better understanding of the pore structure and development characteristics of shale gas reservoirs.

Synthesis and characterization of kaolinite-based granular adsorbents for the removal of Cu(II), Cd(II), Co(II), Zn(II), and Cr(VI) from contaminated water

The object of this study is granular adsorbents based on kaolinite and zero-valent iron. The ceramic mass for their preparation contained polyvinyl alcohol as a powder-forming additive. It was established that its addition in quantities of 1.8–3.3 % practically does not change the porosity of the granules but increases their strength. X-ray phase and chemical analyzes confirmed the presence of a layer of zero-valent iron on the surface of the granules. The structural and sorption characteristics of sorption materials have been studied and the calculations of the main parameters of their porous structure were carried out. It is shown that when modifying granules with zero-valent iron, there is a decrease in the specific surface area and micropores volume for samples without a powder-forming additive by almost 2 times compared to the original granules. Moreover, these values almost do not change for samples obtained with the addition of polyvinyl alcohol. It was found that the application of the reaction layer to the granules leads to a significant increase in their sorption capacity with respect to heavy metal ions Cu(II), Cd(II), Co(II), Zn(II), and Cr(VI). It has been shown that the resulting adsorbents can be used for wastewater treatment containing a mixture of these toxicants. It was found that the values of maximum sorption on modified samples are 10–20 times higher than those for the original granules. A feature of the obtained adsorbents is the ability to simultaneously remove metal ions, both in the form of cations and anions. A significant increase in the sorption values of Cr(VI) anionic forms, which are difficult to remove from water by natural ion exchangers, has been established. It has been shown that granules based on kaolinite and zero-valent iron are effective adsorbents for water purification from heavy metal ions. The resulting materials can be used for wastewater treatment of electroplating industries and hydrometallurgical industry

A study of the precipitation of cerium oxide synthesized from rare earth sources used as the catalyst for biodiesel production

Abstract This work aimed to study the preparation of cerium oxide (CeO2) used as the catalyst for biodiesel production from palm oil. The precipitation method was used in the catalyst synthesis. The effects of oxalic concentrations and stirring rates in the precipitation process were investigated. Oxalic acid was added into cerium (Ce) in ethylenediaminetetraacetic acid solution to form Ce oxalate before the Ce oxalate was calcined to obtain CeO2. The results showed that oxalic concentrations and stirring rates slightly affect the morphology of CeO2. However, these parameters considerably affect the amount of basic sites of CeO2. The basicity of CeO2 plays the main role in catalyzing the transesterification reaction for biodiesel production. When CeO2 was used as the catalyst in biodiesel production from palm oil under operating conditions using a 5% catalyst, methanol-to-oil molar ratio of 30:1, reaction temperature of 150°C, 13.8 bars, and 3-h reaction time, CeO2 obtained from 3% oxalic concentration and 400 rpm stirring rates in the precipitation process provided the highest %FAME in the range of 93.9–94.2% since it had higher basicity. In addition, the decrease in surface area of CeO2 after the use was less severe than that of basicity due to catalyst deactivation.

Lysosome exocytosis is required for mitosis in mammalian cells

Mitosis, the accurate segregation of duplicated genetic material into what will become two new daughter cells, is accompanied by extensive membrane remodelling and membrane trafficking activities. Early in mitosis, adherent cells partially detach from the substratum, round up and their surface area decreases. This likely results from an endocytic uptake of plasma membrane material. As cells enter cytokinesis they re-adhere, flatten and exhibit an associated increase in surface area. The identity of the membrane donor for this phase of mitosis remains unclear. In this paper we demonstrate how lysosomes dynamically redistribute during mitosis and exocytose. Antagonism of lysosomal exocytosis by pharmacological and genetic approaches causes mitosis failure in a significant proportion of cells. We speculate that either lysosomal membrane or luminal content release, possibly both, are therefore required for normal mitosis progression. These findings are important as they reveal a new process required for successful cell division.

Effects of ultrafiltration on Co-Metal Organic Framework/pre-hydrolysis solution carbon materials for supercapacitor energy storage.

Here, a Co-Metal Organic Framework/pre-hydrolysis (Co-MOF/pre-hydrolysis) solution carbon material is prepared by a mild and environmentally-friendly hydrothermal carbonization technique using a pulping pre-hydrolysis solution as the raw material and Co-MOF as the metal dopant. The stable hollow structure provide sufficient space for particle shrinkage and expansion, while the low density and large specific surface area of the long, hairy tentacle structure provide a greater contact area for ions, which shorten the transmission path of electrons and charges. The materials exhibit excellent specific capacitance (400 F/g, 0.5 A/g) and stability (90%, 10,000 cycles). The Change of different concentration ratios in the structures significantly affect the electrochemical performance. The specific surface area of the carbon materials prepared by ultra-filtration increased, but the specific surface area decrease as ultrafiltration concentration increase. The specific capacitance decrease from 336 F/g for C-ZIF-67-1/3 volume ultrafiltration to 258 F/g for C-ZIF-67-1/5 ultrafiltration. The results indicate that energy storage by the carbon materials relied on a synergistic effect between their microporous and mesoporous structures. The micropores provide storage space for the transmission of ions, while the mesopores provide ion transport channels. The separation of large and small molecules after ultrafiltration concentration limit the ion transmission and energy storage of the pores.

Mineral surface area accessibility and sensitivity constraints on carbon mineralization in basaltic aquifers

Estimating mineral reactive surface areas in geologic media remains one of the key challenges limiting the accuracy of reactive transport modeling (RTM) predictions of subsurface processes, particularly those controlling the fate of carbon dioxide (CO2) during geologic storage. Although there have been numerous attempts to combine imaging and experimental techniques to estimate mineral reactive surface area for use in RTM predictions of geologic CO2 storage, these techniques have yet to be adapted to basaltic reservoirs, which have pore structure, mineralogy, and chemical composition that is unique compared to their more often-studied sedimentary counterparts. Here, we address this issue by quantifying fluid-accessible mineral surface areas through image analysis of scanning electron microscope (SEM) backscatter electron images (high-resolution 500 nm/pixel) and Raman spectroscopic mapping of a basaltic rock sample from the Eastern Snake River Plain, Idaho. To evaluate whether the determined pore fluid-accessible mineral surface area accurately reflects reactive surface area, a micro-continuum scale RTM was developed and compared with a high-temperature, high-pressure flow-through CO2 mineralization experiment conducted on the characterized basalt. Importantly, simulations employing the image-derived pore fluid-accessible mineral surface areas match the experimental effluent chemistry well within uncertainties. These mineral surface areas were then used to parametrize a field-scale model representative of the Cascadia basin, Northeastern Pacific, to evaluate impacts of surface area variations on mineral carbonation. Simulations were carried out using variations in image-derived surface areas that cover one to two orders of magnitude increase and decrease in surface area, analogous to previously reported magnitudes of difference between total and reactive surface areas. Carbonation efficiency in terms of CO2 volume mineralized over the simulated period was tracked and compared. Simulations with surface area increased and decreased by two orders of magnitude show basalt carbonation efficiency that is three times faster and six times slower, respectively, than predictions with image-derived mineral surface area. These sensitivity analyses demonstrate that accurate quantification of mineral surface area is crucial for efforts to predict CO2 mineralization, and that efforts such as those employed here can dramatically reduce the uncertainty of field-scale predictions of basalt carbonation.

Defining Spatial and Temporal Resolution of Edema following Rhinoplasty: A Three-Dimensional Topographical Analysis.

Defining Spatial and Temporal Resolution of Edema following Rhinoplasty: A Three-Dimensional Topographical Analysis.

Capacitance of edge-free three-dimensional graphene: New perspectives on the design of carbon structures for supercapacitor applications

The current target for expanding the application scope of supercapacitors is to increase their energy density (E) beyond 20 Wh kg−1. In this regard, edge-free carbon materials show considerable potential because of their high working voltage (U) in organic electrolytes; however, their capacitance (C) remains limited. In this study, we synthesized edge-free three-dimensional (3D) graphene materials with different numbers of graphene stacking layers (nstack). These carbon materials have similar pore morphologies and an edge-free structure because a template method and annealing at 1800 °C were applied, respectively. These features allowed C to remain unaffected by the pore size effect, wettability, parasitic side reactions, and pseudocapacitance. Our results suggested that increasing nstack slightly enhances the areal C; however, such an increase cannot compensate for the decrease in C attributed to the decrease in the specific surface area. We also confirmed that the C of 3D graphene materials has a quantum origin, which results in a “butterfly shaped” cyclic voltammetry curve; we also successfully quantified the quantum capacitance (CQ) for the complete understanding of the origin of C. Based on this knowledge, we estimated that this 3D graphene material can yield a high E of 43 Wh kg−1 once CQ is optimized.

Puerarin attenuates isoproterenol‑induced myocardial hypertrophy via inhibition of the Wnt/β‑catenin signaling pathway.

Myocardial hypertrophy (MH) is an independent risk factor for cardiovascular disease, which in turn lead to arrhythmia or heart failure. Therefore, attention must be paid to formulation of therapeutic strategies for MH. Puerarin is a key bioactive ingredient isolated from Pueraria genera of plants that is beneficial for the treatment of MH. However, its molecular mechanism of action has not been fully determined. In the present study, 40 µM puerarin was demonstrated to be a safe dose for human AC16 cells using Cell Counting Kit-8 assay. The protective effects of puerarin against MH were demonstrated in AC16 cells stimulated with isoproterenol (ISO). These effects were characterized by a significant decrease in surface area of cells (assessed using fluorescence staining) and mRNA and protein expression levels of MH-associated biomarkers, including atrial and brain natriuretic peptide, assessed using reverse transcription-quantitative PCR and western blotting, as well as β-myosin heavy chain mRNA expression levels. Mechanistically, western blotting demonstrated that puerarin inhibited activation of the Wnt signaling pathway. Puerarin also significantly decreased phosphorylation of p65; this was mediated via crosstalk between the Wnt and NF-κB signaling pathways. An inhibitor (Dickkopf-1) and activator (IM-12) of the Wnt signaling pathway were used to demonstrate that puerarin-mediated effects alleviated ISO-induced MH via the Wnt signaling pathway. The results of the present study demonstrated that puerarin pre-treatment may be a potential therapeutic strategy for preventing ISO-induced MH and managing MH in the future.

Rationally control the path of hydrodeoxygenation of palmitic acid over Ni/red-mud catalysts by surface decoration of oxophilic MoOx species

Red mud supported Ni (Ni/RM) catalysts have been explored to the hydrodeoxygenation (HDO) of palmitic acid, however, the decarbonylation (DCO)/decarboxylation (DCO2) is dominant. Therefore, the modification the oxophilic nature of catalysts can significantly impact their path of HDO and selectivity to aim products. Herein, MoOx-decorated Ni-Mo/RM catalysts with a hierarchical flower-like micro/nanostructure were prepared and applied in the HDO of palmitic acid. The effect of MoOx addition was investigated to control the path of HDO, resulting in the changing of carbon number distribution of the product. Combined with several comprehensive structural characterizations and catalytic HDO test, it is shown that the surface defective MoOx species and FeOx species near the metallic sites could significantly facilitate the C-O bond weakening, generated more direct deoxygenation product (hexadecane). Whereas the excessive Mo loading leads to clear altering of surface chemistry (i.e., decrease of specific surface area, pore volume and Mo0 species, increase of reduction temperature and CO2 adsorption, uneven dispersion, and agglomeration of Ni species), resulting in the decrease of palmitic acid conversion. As the main oxide in RM, Fe2O3, Al2O3 and SiO2 were used as supports to load Ni-Mo bimetals respectively to explore the contribution of different components in RM to the distribution of hydrodeoxygenation products of palmitic acid.

Dynamic adsorption of diclofenac onto a magnetic nanocomposite in a continuous stirred-tank reactor

In this study, a waste-based magnetic activated carbon (MAC) was used for the first time in a continuous-flow stirred tank reactor (CSTR). The aim was to evaluate the dynamic removal of diclofenac (DCF) from water and wastewater. Firstly, the breakthrough curves corresponding to DCF adsorption from distilled water at different feed flow rates and doses of MAC were determined. After selecting the most favourable conditions, namely 0.18 h L−1 flow rate and 400 mg L−1 of MAC, the effect of different aqueous matrices was studied, with the breakthrough curves evidencing a performance decline in wastewater in comparison with distilled water. Finally, the exhausted MAC was magnetically recovered, regenerated by microwave-assisted heating and applied in two subsequent adsorption cycles. The regeneration studies pointed to a decrease of the specific surface area and an improvement of the magnetic retrievability of MAC. After the first regeneration step, just mild effects were observed in the dynamic adsorptive performance of MAC. However, after a second regeneration step, the performance declined ca. 50%. Overall, the results highlight the feasibility of producing waste-based magnetic composites that simultaneously combine high adsorption efficiency under dynamic operation in a CSTR, with easy retrievability and successful one-stage regeneration for further reutilization.

Synthetical designing of solid oxide fuel cell electrodes: Effect of particle size and volume fraction

Solid oxide fuel cell (SOFC) electrode microstructures composed of catalyst, electrolyte and pore phases with various microstructural features are synthetically generated and the effects of the mean particle size and volume fraction of each phase on three/triple phase boundaries (TPBs) are computed. For mono-sized particles with an equal volume fraction, the active and total TPB density are found to decrease with increasing the mean particle size due to decreased surface area. However, both are found to be inversely related to the square of the mean particle size. Active TPB densities of 37.62 μm μm−3, 9.27 μm μm−3 and 4.11 μm μm−3 are obtained from the electrode microstructures with mono-sized particles of 0.25 μm, 0.50 μm and 0.75 μm mean particle size, respectively. Moreover, ∼94% of the total TPB density is determined to be active regardless of the mean particle size. TPBs for the polydisperse particles with the same volume fraction also show a decreasing trend with the mean particle size in general. However, no significant change is observed in inactive TPB formations even for the largest particle size investigated, revealing almost fully percolated phases can be achieved when the volume fraction of each phase is equal (∼33.3%). On the other, when the volume fractions are also varied, the active TPB is shown to be strongly depended on the volume fraction of the phase having the highest mean particle size. In this regard, among the related cases studied, the lowest active TPB density is computed as 0.25 μm μm−3, whereas the highest one is measured as 26.64 μm μm−3.

Image processing tools in the study of environmental contamination by microplastics: reliability and perspectives

Microplastic pollution is one of the greatest environmental concerns for contemporary times and the future. In the last years, the number of publications about microplastic contamination has increased rapidly and the list is daily updated. However, the lack of standard analytical approaches might generate data inconsistencies, reducing the comparability among different studies. The present study investigates the potential of two image processing tools (namely the shapeR package for R and ImageJ 1.52v) in providing an accurate characterization of the shape of microplastics using a restricted set of shape descriptors. To ascertain that the selected tools can measure small shape differences, we perform an experiment to verify the detection of pre-post variations in the shape of different microplastic types (i.e., nylon [NY], polyethylene [PE], polyethylene terephthalate [PET], polypropylene [PP], polystyrene [PS], and polyvinylchloride [PVC]) treated with mildly corrosive chemicals (i.e., 10% KOH at 60 °C, 30% H2O2 at 50 °C, and 15% H2O2 + 5% HNO3 at 40 °C; incubation time ≈ 12 h). Analysis of surface area variations returns results about the vulnerability of plastic polymers to digestive solutions that are aligned with most of the acquired knowledge. The largest decrease in surface area occurs for KOH-treated PET particles, while NY results in the most susceptible polymer to the 30% H2O2 treatment, followed by PVC and PS. PE and PP are the most resistant polymers to all the used treatments. The adopted methods to characterize microplastics seem reliable tools for detecting small differences in the shape and size of these particles. Then, the analytic perspectives that can be developed using such widely accessible and low-cost equipment are discussed.

Effect of the Internal Humidity of Concrete on Frost Resistance and Air Void Structure under Different Low Temperature Conditions.

From the perspective of combining macroscopic and microscopic properties, this paper simulates the freeze–thaw cycle process at different freezing low temperatures based on the climate simulation equipment and by setting the curing conditions with different temperatures and relative humidity to produce different moisture conditions in concrete. The frost resistance properties and microscopic air void performance of concrete with different internal water content under different freezing low temperatures in freeze–thaw cycles were systematically studied. The results show that the higher the internal water content of concrete, the more obvious the mass loss rate and dynamic elastic modulus loss of concrete in the freeze–thaw process, and the more serious the deterioration of the air void parameter performance of the air-entraining agent introduced into concrete, which is manifested as the average bubble diameter and bubble spacing factor become larger and the bubble specific surface area decreases. In addition, in the case of the same internal moisture content of concrete, the freezing temperature used in the freeze–thaw cycle also has an important impact on the frost resistance of concrete and air void parameters; the lower the freezing temperature used, the more significant the decline in the frost resistance of concrete, the more obvious the deterioration of air void parameters.

How Metabolic Rate Relates to Cell Size.

Simple SummaryThe metabolic conversion of resources into living structures and processes is fundamental to all living systems. The rate of metabolism (‘fire of life’) is critical for supporting the rates of various biological processes (‘pace of life’), but why it varies considerably within and among species is little understood. Much of this variation is related to body size, but such ‘metabolic scaling’ relationships also vary extensively. Numerous explanations have been offered, but no consensus has yet been reached. Here, I critically review explanations concerning how cell size and number and their establishment by cell expansion and multiplication may affect metabolic rate and its scaling with body mass. Numerous lines of evidence suggest that cell size and growth can affect metabolic rate at any given body mass, as well as how it changes with increasing body mass during growth or evolution. Mechanisms causing negative associations between cell size and metabolic rate may involve reduced resource supply and/or demand in larger cells, but more research is needed. A cell-size perspective not only helps to explain some (but not all) variation in metabolic rate and its body-mass scaling, but may also foster the conceptual integration of studies of ontogenetic development and body-mass scaling.Metabolic rate and its covariation with body mass vary substantially within and among species in little understood ways. Here, I critically review explanations (and supporting data) concerning how cell size and number and their establishment by cell expansion and multiplication may affect metabolic rate and its scaling with body mass. Cell size and growth may affect size-specific metabolic rate, as well as the vertical elevation (metabolic level) and slope (exponent) of metabolic scaling relationships. Mechanistic causes of negative correlations between cell size and metabolic rate may involve reduced resource supply and/or demand in larger cells, related to decreased surface area per volume, larger intracellular resource-transport distances, lower metabolic costs of ionic regulation, slower cell multiplication and somatic growth, and larger intracellular deposits of metabolically inert materials in some tissues. A cell-size perspective helps to explain some (but not all) variation in metabolic rate and its body-mass scaling and thus should be included in any multi-mechanistic theory attempting to explain the full diversity of metabolic scaling. A cell-size approach may also help conceptually integrate studies of the biological regulation of cellular growth and metabolism with those concerning major transitions in ontogenetic development and associated shifts in metabolic scaling.

Encapsulation of NiS and ZnS in analcime nanoparticles as novel nanocomposites for the effective photocatalytic degradation of orange G and methylene blue dyes

ABSTRACT Encapsulation of semiconductor materials in zeolites is one of the important types of composites that have been used as photocatalysts in the degradation of several organic dyes. The high surface area and uniform porous structure of the zeolite particles prevent the coagulation of the catalyst and ensure its stability and dispersion. The strong polarised electrostatic field of zeolites can decrease the energy consumption needed to facilitate the electrons transfer from the valence band to the conduction band. So, in this paper, ethylenediaminetetraacetic acid disodium salt dihydrate was used as an organic template to hydrothermally synthesise analcime nanoparticles. Besides, NiS and ZnS were encapsulated in the analcime nanoparticles as novel photocatalysts for the efficient degradation of orange G and methylene blue dyes. EDX, XRD, FE-SEM, FT-IR, HR-TEM, diffuse reflectance spectrophotometer, and nitrogen gas sorption instruments were used to characterise the novel photocatalysts. The XRD results confirmed that the encapsulation of NiS or ZnS in the analcime nanoparticles led to a decrease in the intensity of the peaks only without affecting their positions. The FE-SEM images confirmed that the encapsulation of NiS or ZnS in the analcime nanoparticles changed the surface of the analcime from small spherical particles into large spherical particles, in addition to the presence of irregular shapes. Besides, the nitrogen gas sorption analyser confirmed that the encapsulation of NiS or ZnS in the analcime nanoparticles led to an increase in average pore radius and total pore volume and a decrease in BET surface area. The percentage of photocatalytic degradation of orange G dye using NiS/analcime and ZnS/analcime composites is 63.60 and 70.50%, respectively. The percentage of photocatalytic degradation of methylene blue dye using NiS/analcime and ZnS/analcime composites is 88.76 and 98.31%, respectively.

Structure Specific Adsorbate Interactions at Electrodepositing Cu Interfaces

Mechanistic understanding of interfaces during additive based electrochemical deposition of thin films is limited by lack of tools to discretely probe given features of deposits. Modern spectroelectrochemical methods that have enabled significant understanding, like surface-enhanced Raman and infrared spectroscopies (SERS and SEIRAS, respectively), are restricted by specimen geometry; SERS is closely linked to the use of rough plasmonically active surfaces while SEIRAS measurements is constrained to thin IR transparent metal films. More recently, the application of Au@SiO2 core-shell nanoparticles as “vibrational reporters” on plasmonically inactive surfaces has enabled collection of site-specific vibrational data on well-defined single crystal surfaces whereby the nanoparticle serves to channel the plasmonic energy to the nanoparticle-substrate interface. The present work utilizes this technique, Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy (SHINERS) to track relative coverages of sulfonate, chloride and methylene moieties following super-conformal Cu electrodeposition on a patterned interface (Figure 1 a,b,d). Corroborated by computational finite-element results (Figure 1 c,d) and x-ray photoelectron spectroscopy measurements, the SHINERS measurements demonstrate that during early stages of electrodeposition, on an accelerator functionalized surface, the regions with more deposition have higher coverage of sulfonate species. As deposition continues dilation of the sulfonate concentration occurs following the continual decrease in surface area of the interface. Ultimately, this work reveals the benefit from the combined use of SHINERs, photoelectron spectroscopy and computational models to further our understanding of composite electroplating and resolve complex site-specific interfacial interactions. Figure 1

Multimodal Synchrotron X-Ray Tools for Studying Spinel Oxide Nanocrystals-Based Mg Cathodes

Magnesium battery has huge potential to meet the future needs of large-scale energy storage due to the high abundance of Mg element, high volumetric and gravimetric capacities, and improved safety compared to Li metal battery. The complex solid-electrolyte interface (SEI) formed on Mg anode surface and slow diffusion rate of magnesium ion in cathode bulk are two critical challenges to achieve high capacity and energy density of Mg battery. Nanostructured spinel oxides with well-defined morphology and crystalline structures are promising candidates for Mg battery cathodes, but their dynamic evolutions of chemical composition and electronic/geometric structure during charging and discharging are still on the early stage, which hinders understanding of the interaction and degradation mechanisms on spinel oxide-based cathodes. Herein, in-situ/or ex-situ soft X-ray absorption spectroscopy (sXAS) and small/wide-angle X-ray scattering (SAXS/WAXS) to track the changes of structure and surface/bulk chemistry of spinel oxide nanocrystals during Mg intercalation/deintercalation processes at both local and macroscopical levels. The Mg0.5Fe2.5O4 (MFO) nanocrystals were tested in a Swagelok cell with an electrolyte of 0.3 M Mg(TFSI)2 and 0.15 M MgCl2 at room temperature. An initial discharge capacity of 187 mAh g-1 was achieved and 83% capacity was retained after 20 cycles. sXAS results reveal that Fe3+/Fe3+ redox is highly reversible during charge/discharge process, and MgF2 slowly formed on the surface as well. In-situ WAXS shows that rocksalt phases of FeO and MgO were both observed during discharge process, and the former one quickly disappeared and the latter one slowly converted to pristine phase during charge process. Moreover, MFO with small size (~5 nm) delivered double specific capacity but poorer cyclability compared to large size (~18 nm), which is ascribed to the nanocrystal aggregation and decrease of active surface area and formation of interfacial crystal boundary based on in-situ SAXS and ex-situ STEM. More structural features of shape and crystallinity degree of MFO were also investigated and correlated to their battery performance. This work highlight the powerful role of multimodal in-situ synchrotron X-ray techniques in understanding the structure-performance of spinel oxide nanocrystals-based Mg cathodes. Figure 1

Effects of Impregnated Amidophosphonate Ligand Concentration on the Uranium Extraction Behavior of Mesoporous Silica.

A series of solid-phase uranium extractants were prepared by post-synthesis impregnation of a mesoporous silica support previously functionalized with octyl chains by direct silanization. Five materials were synthesized with 0, 0.2, 0.3, 0.4 and 0.5 mmol of the amidophosphonate ligand DEHCEBP per gram of functionalized solid, and the effect of the ligand concentration on the uranium extraction efficiency and selectivity of the materials was investigated. Nitrogen adsorption–desorption data show that with increasing ligand loadings, the specific surface area and average pore volume decrease as the amidophosphonate ligand fills first the micropores and then the mesopores of the support. Acidic uranium solutions with a high sulfate content were used to replicate the conditions in ore treatment leaching solutions. Considering the extraction kinetics, the equilibration time was found to increase with the ligand concentration, which can be explained by the clogging of micropores and the multilayer arrangement of the DEHCEBP molecules in the materials with their highest ligand contents. The fact that the equilibrium ligand/uranium ratio is about 2 mol/mol regardless of the ligand concentration in the material suggests that all the ligand molecules remain accessible for extraction. The maximum uranium extraction capacities ranged from 30 mg∙g−1 at 0.2 mmol∙g−1 DEHCEBP to 54 mg∙g−1 in the material with 0.5 mmol∙g−1 DEHCEBP. These materials could therefore potentially be used as solid-phase uranium extractants in acidic solutions with high sulfate concentrations.