Search Results (1,293)

Cobalt-free SrFeO_3−δ is an attractive mixed ionic-electronic conducting (MIEC) oxygen-electrode platform for intermediate-temperature solid oxide fuel cells (IT-SOFCs), but its electrochemical response is strongly coupled to Fe valence, oxygen non-stoichiometry, and structural phase stability. Here, B-site Ce-substituted SrFe_1−xCe_xO_3−δ (x = 0, 0.05, 0.10, 0.15, and 0.20) was prepared by a solid-state route to establish a composition-structure-defect-transport relationship. X-ray diffraction and Rietveld refinement show an initial expansion of the perovskite lattice after Ce introduction, followed by a lattice-parameter plateau and weak CeO₂/Sr₃Fe₂O_7−δ segregation at higher Ce contents. Electron microscopy confirms an interconnected granular morphology, while HRTEM/SAED of SrFe_0.85Ce_0.15O_3−δ verifies well-crystallized perovskite domains. XPS reveals a Ce-dependent redistribution of the Fe³⁺/Fe⁴⁺ and surface oxygen environments, with the x = 0.15 composition displaying the most favorable defect-associated oxygen response. Electrical conductivity follows a non-monotonic composition dependence and is maximized at x = 0.15, indicating an optimum balance between defect formation and continuity of the Fe-O-Fe transport network. A single cell employing SrFe_0.85Ce_0.15O_3−δ as the oxygen electrode delivers a peak power density of 0.53 W cm⁻² at 800 °C. The corresponding polarization resistance decreases from 0.47 Ω at 600 °C to 0.36 Ω at 800 °C, confirming strongly activated oxygen-electrode kinetics. These results identify controlled B-site Ce substitution as an effective route for tuning the electronic/defect chemistry of cobalt-free SrFeO_3−δ cathodes. Full article

Laser cladding was employed to deposit an AlCoCrFeNiTi high-entropy alloy coating on 45 steel substrate to enhance its surface properties. The coating microstructure consists of a BCC solid-solution matrix with B2-ordered precipitates and in-situ Al₂O₃@TiC core–shell nanoparticles. HRTEM reveals a semi-coherent interface between the core and shell, attributed to a low lattice mismatch of 6.43%. Mechanical and tribological tests show that the coating exhibits an average microhardness of 781 HV_0.2, about 2.3 times that of the substrate, and a 31.25% lower friction coefficient and a wear rate only 57.75% of that of the substrate. The coating primarily undergoes abrasive wear, whereas the substrate suffers severe adhesive and oxidative wear. Strengthening originates from solid-solution and second-phase strengthening, with the hard Al₂O₃@TiC phase contributing to stability, hardness, and wear resistance. These results indicate that the core–shell structured coating effectively improves the surface performance of 45 steel and offers theoretical guidance for fabricating high-entropy alloy tool coatings via laser cladding. Full article

This study synthesized graphene oxide (GO) from graphite flakes and evaluated its performance in removing methylene blue (MB) from water using modeling. Characterization was done using FTIR, FESEM, HRTEM, XRD, Raman spectroscopy, and BET. The analysis showed an amorphous nature with micro- and mesopores and the presence of aromatic rings, carbonyl, epoxy, and hydroxyl groups. Box–Behnken design (BBD) and artificial neural networks (ANNs) were used to optimize process parameters, including concentration (10–30 mg/L), pH (3–6), time (10–30 min), and dosage (0.05–0.15 g). BBD yielded a high correlation (R² = 0.9988), while ANN demonstrated superior predictive accuracy (R² = 0.9998). Isotherm models of Langmuir, Temkin, Sips, Freundlich, and Dubinin–Radushkevich had high R² values, and they were used to understand the mode. Sips best described the process (R² = 0.9953), yielding a theoretical maximum adsorption capacity of 350.4 mg/g. The experimentally observed capacity at the highest tested concentration (400 mg/L) was approximately 160 mg/g, indicating that the Sips model provides a reasonable fit but extrapolates beyond the measured concentration range. The model thus suggests that both monolayer and multilayer adsorption occur simultaneously. The kinetic models of Elovich, pseudo-second-order, intraparticle diffusion, and pseudo-first-order provided evidence for a mechanism that occurs either by chemisorption or physisorption. Both PFO (R² = 0.9978) and PSO (R² = 0.9989) confirmed both physisorption and chemisorption mechanisms. Lastly, the predominant forces in the removal of MB were due to π-π interactions, and electrostatic attractions. Full article

This study investigates the compound surface modification of 7075 aluminum alloy through the High-Speed Cutting-Solid Projectile Embedded Water Jet (HSC-SPEWJ) method. The research employed SEM, XRD, TEM, and HRTEM techniques to assess how process parameters such as jet pressure, nozzle distance, and nozzle traverse speed influence surface properties, including surface quality, roughness, microhardness, residual stress, and microstructural evolution in the alloy. The results indicate that the surface of the alloy treated with the SPEWJ process primarily exhibits features such as “craters,” microcracks, and micropores, with the lowest surface roughness recorded at 0.6214 μm. The modification leads to the formation of a plastic deformation layer with depths varying between 28 and 78 μm, with the maximum depth of 78 μm achieved at a jet pressure of 15 MPa. This treatment results in an 8.8% increase in the maximum microhardness when compared to the untreated sample. The greatest work-hardened layer observed extended to a depth of 100 μm. Furthermore, the surface residual compressive stress reached −210.37 MPa, with the stress field extending to 356 μm below the surface. The HSC-SPEWJ treatment also facilitated the formation of high-density dislocations and grain refinement in the alloy, while the size of the Precipitate-Free Zone (PFZ) was reduced by 5 to 10 nm relative to the untreated sample. Full article

Hard carbon is a leading anode candidate for sodium-ion batteries (SIBs), yet its complex microstructure has prevented consensus on sodium storage mechanisms, impeding rational electrode design. Herein, we present a computational framework that integrates image-guided atomistic modeling with reactive force field molecular dynamics (ReaxFF-MD) to systematically investigate sodium storage behaviors in hard carbon. Quantitative HRTEM analysis—employing semantic segmentation and Gabor filtering with a data throughput reaching 10⁶—enables the decomposition of carbon structures into curved (amorphous-like) and stacked (crystalline-like) basic structural units, which are then reassembled into three-dimensional atomic models. ReaxFF-MD simulations reveal three sodium storage states: intercalation, surface adsorption, and pore clustering. Crucially, this framework achieves decoupled analysis of three critical structural parameters—crystalline volume fraction (CVF), intracrystallite d-spacing (d₀₀₂), and crystallite size—thereby overcoming the inherent limitation of trial-and-error approaches in which multiple parameters co-vary with processing conditions. The results demonstrate that (i) higher CVF increases intercalation sites and enhances binding energy; (ii) within the investigated parameter ranges, a favorable d-spacing window exists at 0.37–0.38 nm; and (iii) crystallite size below approximately 20 Å exerts minimal influence. This research technology chain—spanning HRTEM analysis, automated modeling, molecular simulation, and experimental calibration—provides quantitative structure–property relationships that support the rational design of hard carbon anodes for SIBs within the investigated parameter ranges. Full article

CeO_2x-ZrO_2(100-x) mixed oxides (x = 0, 5, 15, 25 and 50 wt.%) were successfully synthesized via the sol–gel method and further promoted with 5 wt.% of different transition metals (Ni, Fe, Cu, and Co) through impregnation. XRD analysis confirmed the formation of a tetragonal Ce-Zr solid solution at low ceria loadings (5–25 wt.%), while the Ce₅₀Zr₅₀ sample showed coexistence of tetragonal and cubic solid-solution phases, consistent with the CeO₂-ZrO₂ phase diagram; crystallite size decreased systematically with increasing ceria content. Physisorption measurements revealed a mesoporous texture for all solids, with pore size and pore shape characteristics varying with ceria content, and specific surface areas increasing with increasing ceria loading. The catalysts were evaluated for formaldehyde (HCHO) oxidation. Complete HCHO conversion was achieved from 50 °C over pure ZrO₂ and Ce₅₀Zr₅₀, whereas the Ce₅Zr₉₅, Ce₁₅Zr₈₅ and Ce₂₅Zr₇₅ samples showed markedly lower activity at this temperature, revealing a non-monotonic dependence of catalytic activity on ceria content. The Ce₅₀Zr₅₀ support showed high CO₂ selectivity, indicating near-total mineralization of HCHO and reduced formation of by-products. The incorporation of Cu and Co into this optimal support maintained a high CO₂ selectivity, comparable to that of the bare support, while reducing the formation of minor by-products; the Fe-containing catalyst showed lower activity and selectivity. Oxygen storage capacity (OSC) measurements confirmed the redox ability of the cerium-containing solids; however, since pure ZrO₂, which showed no measurable OSC, was also highly active and selective, catalytic performance cannot be attributed to OSC alone and is more likely governed by a combination of textural (surface area, porosity) and structural (defect/vacancy density) properties. HRTEM analysis showed that all samples contained similar ceria–zirconia support crystallites, which were well defined, highly crystalline, and exhibited a particle size distribution of approximately 5–15 nm. H₂-TPR and XPS analyses provided insights into the presence and nature of metal species on the support surfaces. Full article

Fluoride contamination in geothermal water is a persistent water-quality concern in high-altitude regions, particularly on the Qinghai–Tibet Plateau. In this study, lightweight magnesium oxide (MgO) nanosheets were investigated for fluoride adsorption from geothermal water, with emphasis on adsorption performance and the underlying mechanism. The effects of MgO dosage, temperature, contact time, and initial fluoride concentration were systematically evaluated, while the physicochemical changes of MgO before and after fluoride adsorption were characterized using SEM, EDS, HRTEM, BET, FTIR, and XPS. The MgO nanosheets exhibited abundant surface hydroxyl groups and enabled rapid fluoride uptake under elevated-temperature conditions. At 70 °C and an MgO dosage of 3 g/L, more than 95% of fluoride was adsorbed within 10 min. The saturated adsorption capacity was 87.167 mg/g at an initial fluoride concentration of 500 mg/L. Kinetic analysis revealed rapid initial uptake followed by a slower adsorption stage, with intraparticle diffusion contributing to, but not solely controlling, the overall adsorption process. The equilibrium data were better described by the Langmuir model than by the Freundlich model (R² = 0.940 vs. 0.725), suggesting relatively homogeneous surface sites. FTIR and XPS analyses revealed pronounced changes in the surface chemical environment following water contact and fluoride adsorption. These changes suggest that water-induced hydration and hydroxylation generate reactive Mg–OH sites, which subsequently interact with fluoride through hydroxyl–fluoride exchange and the formation of Mg–F-related surface species. These findings highlight the contribution of surface chemical interactions to fluoride uptake by MgO nanosheets and their potential for rapid fluoride control in geothermal water. Full article

Electron microscopy is essential for nanoparticle research because it provides the critical structural data of particle size, morphology, crystallography, and elemental composition that are essential for tailoring and for predicting nanoparticles’ optical, electronic, catalytic, and mechanical properties. The weak scattering from nanoparticles results in low contrast in electron microscope images. Therefore, observing and interpreting such images requires special care to avoid erroneous conclusions. This study investigates the imaging contrast of diamond structures on different supporting films. When the nanodiamond is overlapped with a carbon film, particle edge details cannot be explained, and the overlapping interference lattices produce a pattern of interference fringes that is much coarser than the original pattern. Single graphene oxide (GO) sheets, as the ideal support film, are highly electron-transparent for the study of nanoparticles. As a low-background and high-transparency support to identify the dominant structural information of the nanodiamond, GO is superior to carbon support film. Quantitative contrast analysis reveals that GO film improves the contrast-to-noise ratio (CNR) by a factor of 3.0 for 8 nm particles compared with conventional amorphous carbon films. The {111} lattice-fringe detection rate increases from 35% on carbon film to 85% on GO for the same particle size. These results establish GO as a quantitatively superior support film for high-resolution electron microscopy (HRTEM) imaging of sub-10 nm nanoparticles. Full article

Post-quench natural aging can alter the response of Al–Mg–Si alloys to further artificial aging, while post-artificial-aging hardness, H_post-AA, may obscure changes in the retained artificial-aging response. Five high-purity alloys containing 0.95–0.99 mol% Mg + Si, with Mg/Si ratios of 0.52, 1.1, 1.9, 3.0, and 4.0, were solution-treated at 848 K for 3.6 ks, quenched, and artificially aged at 473 K. Under direct artificial aging, after a minimum practical delay of approximately 0.1 ks, the Mg/Si = 1.1 alloy showed the highest H_peak of approximately 72–73 HV0.1, whereas Mg/Si = 4.0 reached approximately 53–55 HV0.1. The precipitate areal density was highest near Mg/Si = 1 and decreased markedly in Mg-rich alloys. Operational HRTEM classification indicated that β″-related precipitates predominated in the Si-excess alloys, whereas β′-like and parallelogram-type precipitates were more prominent in the Mg-rich alloy. For Mg/Si ratios of 0.52, 1.9, and 4.0, quench-to-aging delays of up to 6000 ks produced non-monotonic changes in H_post-AA. However, the additional hardening increment, ΔH_AA, decreased from 38.5 to 26.1 HV0.1 at Mg/Si = 0.52 and from 33.5 to 26.9 HV0.1 at Mg/Si = 1.9. These results show that both H_post-AA and ΔH_AA are required to evaluate quench-to-aging delays. Full article

Acquiring an amphiphobic nanocalcium carbonate (NCC) is a perplexing problem in the long term because of its hydrophility. This restricts its application in self-cleaning coatings and other super-low surface energy engineering fields. This study offers a novel and simple approach that endows NCC with an amphiphobic property through surface modification using perfluoropolyether carboxylic acid in the presence of sodium hydroxide. The modification process was optimized at a 5 wt% modifier concentration, 50 °C, and a duration of 40 min. Comprehensive characterization was performed using FT-IR, TG-DTA, SEM, HR-TEM, NMR and XPS techniques, in contrast with the previous literature describing hydroxyl groups. Notably, FT-IR analysis indicates that no hydroxyl groups were detected on the NCC surface. The modification mechanism involves COO⁻ groups from the modifier forming Ca-O ionic bonds with calcium sites on the NCC surface. HR-TEM analysis revealed an exceptionally thin modifier film (2–5 nm) on the NCC surface. Despite this minimal thickness, it endows NCC with remarkable amphiphobic properties, with water and oil contact angles up to 120.4° and 139.9°, respectively. These findings expand insights into the surface modification mechanism of NCC and its potential application fields. Full article

This study investigated the biogeochemical processes governing heavy metal sequestration in Laguna Honda, a hypersaline Mediterranean wetland affected by intensive olive cultivation located in the Guadalquivir Basin River (S Spain). A network of sediment samples was analyzed from the wetland using X-ray fluorescence, ICP-MS, and high-resolution electron microscopy (FESEM/HRTEM). Geochemical data were treated with statistical factor analysis. Sediments show significant enrichment of Cu, Hg, and Au due to anthropogenic agrochemical treatments. Mineralogical characterization revealed authigenic pyrite framboids and metallic sulfide nanoparticles (CuS and HgS) within organic-rich sediments, where sequestration is primarily probably driven by the metabolic activity of sulfate-reducing microorganisms (SRMs) under reducing conditions. Additionally, Au enrichment is attributed to mechanical transport and coagulation of pesticide-derived nanoparticles, exhibiting a distinct geochemical correlation with rare earth elements (REEs). We concluded that hypersaline wetlands act as critical environmental sinks, where microbial activity, high organic matter content, and detrital transportation interact to facilitate the immobilization and stabilization of toxic trace elements through the precipitation of low-solubility sulfide phases (Cu and Hg) and the mechanical accumulation of nanoparticles (Au). Full article

Synthesis of multilayer graphene oxide (GO) was achieved through a Hummers method with meticulous control over the addition of the oxidizing agent. Precursors were immersed in an ice bath during the synthesis to maintain a temperature of approximately 275 K in oxidation stages I and II, temperature was measured with a thermocouple inside the cooling bath, in direct contact with the vacuum filter flask at the level of the reactants. In contrast to the variety of Hummers synthesis methods—where the system is maintained at certain temperature during the initial oxidation stage and heat continues to be supplied during the second stage—our setup operates at low temperature from the beginning to the conclusion of the process. A detailed analysis of the compositional, structural, and optical properties of the fabricated GO was conducted, revealing a notable photoluminescent band in the 380–480 nm region. This property is of interest for a potential future application in the field of optoelectronics. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) revealed that the structure of the material consists of a sp³ matrix with sp² domains. Raman spectroscopy revealed an I_D/I_G ratio of 2.7, which could indicate a high density of structural defects or extremely small sp² graphitic domains. Furthermore, deconvolution of the 2D band suggests the presence of multilayers in the GO. Fourier transform infrared spectroscopy (FTIR) analysis revealed the presence of all functional groups associated with the GO. Upon observation of the photoluminescence exhibited by the material, a broadband centered on the violet-blue emission, with a possible mechanism consistent with the literature associated with the transitions between sp² domains and localized states in the basal plane defects or it might be caused by quantum confinement effects. The diminished contribution from the green emission could be caused by the transitions between localized states sp² and the functional groups associated with oxygen. Full article

Co-based oxides are commonly introduced into porous ceramic membranes to add catalytic activity, but their attachment at the atomic scale remains unclear. We examined a buried Co₃O₄/Al₂O₃ interface formed by sol–gel deposition and thermal conversion. Site-specific focused-ion-beam (FIB) lift-out, scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (STEM-EDS), and high-resolution transmission electron microscopy (HRTEM) were used to access and characterize the interface. A Co-rich spinel-type domain with a (111) lattice spacing was observed next to Al₂O₃(012). The observations guided density functional theory (DFT) initial models. After structural relaxation, substrate-O-mediated Co-O contacts emerged from both starting geometries: the O-bridged-start model exhibited eight contacts across four Co sites, whereas the non-bridged-start model developed three contacts around one Co site. Around the Co-O-Al linkages, there is a clear manifertation of the interface polarization and charge redistribution, indicated by charge-density-difference and Bader analyses. In both models, projected density of states (PDOS) showed coupling between Co 3d and O 2p states, while integrated crystal orbital Hamilton population (ICOHP) analysis further indicated that O atoms retained Al-O bonds while forming occupied-state Co-O bonds. These results support a representative, laterally distributed Co-O-Al motif as an atomic-scale pathway for chemically attaching the functional oxide to porous alumina. Full article

Antimicrobial nanomaterials have attracted increasing attention as potential alternatives for controlling pathogenic microorganisms. In this study, pure ZnO and Ag-modified ZnO nanoparticles prepared using nominal Ag contents of 1 and 5 wt.% were synthesized using a reflux-assisted polyol method and evaluated to determine the influence of Ag content on their structural characteristics and antibacterial activity. The synthesized materials were characterized by UV-Vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). UV-Vis and FTIR analyses confirmed the characteristic optical response and chemical features of ZnO-based materials. XRD patterns revealed that all samples retained the hexagonal wurtzite structure of ZnO, while additional reflections corresponding to face-centered cubic (FCC) Ag were observed in the Ag-containing samples and increased in intensity with Ag content. Crystallite sizes estimated by the Scherrer equation were 16.9 ± 2.6 nm for ZnO, 12.9 ± 1.6 nm for ZnO-Ag 1%, and 32.6 ± 10.1 nm for ZnO-Ag 5%. HRTEM confirmed the formation of crystalline nanoparticles with average particle sizes of approximately 16 nm and 12 nm for ZnO and ZnO-Ag 1%, respectively. Antimicrobial activity was evaluated against the reference strains Escherichia coli ATCC 25922 and Salmonella typhimurium ATCC 14020. ZnO–Ag 5% exhibited the greatest antibacterial activity, with minimum inhibitory concentration (MIC) values of 250 ppm against E. coli and 750 ppm against S. typhimurium, and minimum bactericidal concentration (MBC) values of 750 and 1500 ppm, respectively. These findings demonstrate that increasing Ag content influences the structural properties of ZnO nanoparticles and enhances their antibacterial performance, highlighting the potential of ZnO-Ag nanomaterials for antimicrobial applications. Full article

The electrocatalytic nitrogen reduction reaction (NRR) is a key approach for synthesizing green ammonia under mild conditions. However, the high bond energy of the N≡N triple bond makes N₂ difficult to activate, limiting the Faradaic efficiency. MoS₂ offers advantages such as low cost and abundant reserves as a non-precious-metal NRR electrocatalyst. Nevertheless, pure MoS₂ suffers from insufficient conductivity and a limited number of active sites, resulting in suboptimal catalytic performance. Herein, we develop a solvent-regulated one-step hydrothermal strategy using ethylene glycol as the sole reaction medium to fabricate an oxygen-substituted amorphous MoS₂ (O-MoS₂) electrocatalyst. XRD, SEM, and HRTEM characterization revealed that, as the ethylene glycol ratio increased, the product gradually transformed from a layered crystalline structure to a completely amorphous structure. XPS confirmed that oxygen atoms were uniformly incorporated into the MoS₂ lattice via substitution doping. Electrochemical testing showed that O-MoS₂ achieved an ammonia yield of 97.16 μg h⁻¹ mg⁻¹ and a Faradaic efficiency of 46.44% in a 0.1 M Na₂SO₄ electrolyte at −0.70 V vs. RHE, significantly outperforming undoped MoS₂ and semi-doped S-MoS₂. DFT calculations indicate that O doping reduces the N₂ adsorption energy, thereby synergistically promoting N₂ adsorption and activation. This dual-modification strategy provides a facile and universal guidance for electronic structure regulation of MoS₂-based catalysts and sheds new light on the design of high-efficiency ambient nitrogen fixation electrocatalysts toward practical green ammonia synthesis. Full article