Scanning Transmission Electron Microscopy Analysis Research Articles

Effects of polystyrene nanoplastics with different functional groups on the accumulation and toxicity of Pb on dandelion

Micro (Nano)plastics are ubiquitous in the environment and can potentially affect the toxic effects of other chemicals, such as heavy metals. Although the interaction of micro (nano)plastics and heavy metals as well as their effects on aquatic organisms have been widely investigated, studies on their influence on terrestrial plants are limited. Therefore, in this study, the effects of polystyrene (PS), carboxy-modified PS (CPS) and amino-modified PS (APS) nanoparticles on the accumulation and toxicity of Pb on dandelion (Taraxacum asiaticum Dahlst) were investigated using hydroponic cultivation. The presence of the three PS caused cell damage and destroyed the tertiary structure of the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and dehydrogenase (DHA) enzymes, thereby inhibiting Rubisco and root activities, which hindered nutrient uptake and photosynthesis. The inhibition of APS on the biomass of dandelion was greater than that of PS and CPS. Confocal laser scanning microscope and transmission electron microscopy analysis showed that APS was more likely to enter the roots of dandelion than PS and CPS. The presence of Pb induced more PS, CPS, and APS to enter dandelion roots, and Pb aggravated PS and CPS toxicities on dandelion rather than APS toxicity. This is because the complex formed by CPS and Pb can affect the structure of Rubisco and DHA through covalent and coordination bonds, and Pb increased the surface positive charge on CPS, according to Gaussian analysis. The presence of both PS and CPS significantly reduced Pb uptake by dandelion, and they did not exacerbate the toxicity of Pb. In contrast, APS slightly inhibited Pb accumulation, but aggravated Pb toxicity in dandelion. Our findings revealed that the changes in the uptake of nanoplastics and Pb by dandelion potentially resulted in a cascade of events that increased the toxicity and inhibited the growth of dandelion seedlings.

Manipulation of the coercivity of FeCoCr films through artificial defects engineering based on Bi doping

FeCoCr thin films have been considered as promising candidates for magnetic code disk materials used in high-precision magnetic rotary encoders. However, realizing high coercivity with a sufficient remanence is a critical issue for magnetic recording stability from the point of view of practical applications. We prepared Bi-free and Bi-doped FeCoCr(250 nm)/Ta(10 nm) films on Si substrates using magnetron sputtering followed by vacuum annealing at 650 °C for 30 min. The in-plane coercivity of Bi-free and Bi-doped FeCoCr samples are 414 Oe and 930 Oe respectively, indicating that the coercivity can be greatly enhanced by Bi doping. X-ray photoelectron spectroscopy (XPS) reveals that Bi atoms diffuse to the film surface and then sublimate during high-temperature annealing process. Positron annihilation spectroscopy (PAS) indicates that the diffusion of Bi atoms increases the density of defects in the film. Scanning transmission electron microscopy (STEM) analysis shows that the diffusion behavior of Bi atoms not only refines the grain size but also results in a uniform distribution of the Fe-Co-rich (α1 phase) phase with the Cr-rich (α2 phase) phase. Magnetic force microscopy (MFM) analysis observes that the introduction of Bi decreases the magnetic domain size and increases the magnetic domain density resulting in the enhancement of coercivity.

Efficient electrochemical CO2 reduction to CO by metal and nitrogen co-doped carbon catalysts derived from pharmaceutical wastes adsorbed on commercial carbon nanotubes

Transition metal and nitrogen doped carbon catalysts (MNC) are effective in electrochemical reduction of CO2 to CO with a high selectivity. However, scalable and cost-effective synthesis of active metal-nitrogen catalysts is yet to be developed. Herein, we report a simple and sustainable method that utilizes commercial carbon nanotubes (CNTs) to adsorb a pharmaceutical waste, sulfamethoxazole (SMX), followed by moderate pyrolysis to prepare an efficient MNC catalyst. The intrinsic metal impurities from CNTs are essential to form active metal sites, and it requires significantly less nitrogen precursor than methods using most widely nitrogen precursors such as melamine and urea. The CNT-SMX catalyst delivers high CO2RR performance with 91.5 % CO Faradaic efficiency and 14 mA/cm2 CO partial current density at −0.76 V vs RHE in a traditional H-Cell. The catalyst is also efficient in a scalable flow cell, exhibiting 97.5 % CO selectivity at 300 mA/cm2, plus stable CO2RR performance for more than 24 h at 100 mA/cm2. The scanning transmission electron microscopy (STEM) and X-ray absorption spectroscopy (XAS) analyses confirm the existence of single atomic sites primarily in the form of Fe-N bonds that are active sites for CO2RR. Density functional theory (DFT) calculations suggest a synergy between the single atomic FeNC sites and Ni nanoparticles embedded in the CNTs, which enhances CO production rate and selectivity by lowering the desorption energy of *CO intermediate. To the best of our knowledge, the results in this work are among the top performing carbon-based catalysts. Furthermore, catalysts developed in this work are synthesized at a moderate temperature without pre-oxidation or post-acid-washing and utilize cheap or waste materials, presenting a simple, sustainable, and cost-effective way to synthesize highly active catalysts.

Structural and electronic properties of SrCuO2+δ thin films

The layered structure of superconducting cuprates is considered to be a key ingredient to achieve high superconducting transition temperatures. In this work, we investigate the possibility of doping the SrCuO2 infinite-layer compound by inserting additional oxygen into its structure. We observe that the infinite-layer SrCuO2 structure is epitaxially stabilized in thin films grown by pulsed laser deposition in pure O2. Increasing the oxidizing power by introducing ozone during the growth leads to a different phase with an elongated c axis. Scanning transmission electron microscopy analysis suggests that the films with an elongated c axis are composed of SrCuO2.5 blocks separated by SrCuO2 layers arranged to match the substrate spacing. X-ray absorption spectroscopy measurements show that this SrCuO2+δ phase is associated with a more isotropic Cu orbital configuration and hole doping. This hole doping leads to a dramatic reduction in the resistivity of the films, with a magnitude that depends on the precise oxygen content in the structure.

Layered-double-hydroxide-based Ni catalyst for CO2 capture and methanation

Ni-based catalysts prepared using layered double hydroxides (LDH) as precursors containing Mg and Ca are examined as dual-function materials for CO2 capture and methanation. X-ray diffraction, thermogravimetric analysis, H2 temperature-programmed reduction, N2 adsorption, and scanning transmission electron microscopy analyses revealed that the LDH-derived Ni catalysts form porous structures of composite oxides (MgO-NiO) containing 5-nm-sized micropores and highly dispersed 5–10-nm-sized Ni-metal nanoparticles. The methanation performance is investigated under isothermal cyclic operation with an O2-containing gas (10%-CO2/5%-O2/bal.-He) and 20%-H2/bal.-He at 320 °C; the results indicate that the LDH-derived Ni catalysts containing Ca, Mg, and Al exhibit high methanation activities. Mg contributes to the stabilization of the porous structure and enhances the Ni-metal dispersion, while Ca provides effective CO2 adsorption and storage sites.

Effects of Cu additions on the precipitation activation energy and mechanical properties of prestrained Al–Mg–Si alloys

We investigated the effect of different Cu additions (0.1 wt.% and 0.3 wt.%) on the precipitation activation energy and mechanical properties of Al–Mg–Si alloys under different prestraining levels (0%, 3%, and 5%). Tensile tests were performed before and after paint baking (PB). Differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) analyses were conducted to explore the clustering and precipitation behavior. Our results show that the precipitation activation energy was reduced by higher Cu addition but increased with prestraining level. Before PB, higher Cu addition significantly improved the elongation and work-hardening behavior, and the improvement was more pronounced in the prestrained alloys than in the nonprestrained alloys. After PB, higher Cu addition slightly increased the bake hardening response (BHR) of the alloy, and this improvement was enhanced in the prestrained alloys. However, only by introducing an appropriate amount of prestraining (3%) could the high-Cu alloy increase the BHR more significantly than the low-Cu alloy. When 5% prestraining was introduced, the high-Cu alloy had no advantage in increasing the BHR. After the introduction of 3% prestraining, a small amount of pre-Q′ phases was additionally formed near the dislocation lines, but the β″ phase was still the main strengthening phase. Higher Cu addition significantly refined the β″ phase and increased its number density, thereby improving the BHR. The formation of pre-Q′ phases was more pronounced in the high-Cu alloy under 5% prestraining, which suppressed the formation of the β″ phase and limited the BHR.

Atomic-Scale Observations of Oxygen Release Degradation in Sulfide-Based All-Solid-State Batteries with Layered Oxide Cathodes.

All-solid-state batteries exhibit considerable potential for applications in electric vehicles. Understanding and controlling the oxygen release from the layered cathode active material are essential in achieving long-term operation of all-solid-state batteries because the oxygen release degrades the cathode material and the solid electrolyte, triggering capacity degradation. In this study, we verified the specific interface where the oxygen release is accelerated by atomic-scale scanning transmission electron microscopy and electron energy loss spectroscopy analyses. Oxygen release is suppressed at the interface where the LiNbO3 coating layer is sufficiently formed. Decomposition products on the solid electrolyte and the antisite defect layers on the cathode surface are formed by oxygen release at the interface where the Li2S-P2S5 solid electrolyte and Li(Ni1/3Mn1/3Ni1/3)O2 cathode are in direct contact. These irreversible passivation layers lead to capacity degradation. In addition, we found that exfoliation of the LiNbO3 coating from the cathode not only physically breaks the Li conduction path but also results in oxygen release and the deterioration of the cathode. These atomic-scale insights can further advance the development of all-solid-state batteries by suppressing oxygen release.

Elucidating Cathodic Corrosion Mechanisms with Operando Electrochemical Transmission Electron Microscopy.

Cathodic corrosion represents an enigmatic electrochemical process in which metallic electrodes corrode under sufficiently reducing potentials. Although discovered by Fritz Haber in the 19th century, only recently has progress been made in beginning to understand the atomistic mechanisms of corroding bulk electrodes. The creation of nanoparticles as the end-product of the corrosion process suggests an additional length scale of complexity. Here, we studied the dynamic evolution of morphology, composition, and crystallographic structural information of nanocrystal corrosion products by analytical and four-dimensional electrochemical liquid-cell scanning transmission electron microscopy (EC-STEM). Our operando/in situ electron microscopy revealed, in real-time, at the nanometer scale, that cathodic corrosion yields significantly higher levels of structural degradation for heterogeneous nanocrystals than bulk electrodes. In particular, the cathodic corrosion of Au nanocubes on bulk Pt electrodes led to the unexpected formation of thermodynamically immiscible Au-Pt alloy nanoparticles. The highly kinetically driven corrosion process is evidenced by the successive anisotropic transition from stable Pt(111) bulk single-crystal surfaces evolving to energetically less-stable (100) and (110) steps. The motifs identified in this microscopy study of cathodic corrosion of nanocrystals are likely to underlie the structural evolution of nanoscale electrocatalysts during many electrochemical reactions under highly reducing potentials, such as CO2 and N2 reduction.

Cyanide removal from blast furnace effluent using layered double hydroxide based mixed matrix beads: Batch and fixed bed study

Effluent tailings from steel industries contain huge amount of cyanide either in free form or as metal complex. The nanoparticle-based technologies for treatment of cyanide effluent are limited in practical application due to leaching and causes severe operational problems. In this study, the synthesized nickel aluminium layered double hydroxide (NiAl LDH) was impregnated inside the polysulfone matrix at different loadings of 2, 4, 6 and 8 wt% to form mixed matrix beads (MMBs) that serve as an alternative for the upscaling of adsorptive column and thereby overcome the shortcomings adequately. The basal spacing of the LDH impregnated inside the MMB is 8.8 Å. The characteristic peak at 2120 cm−1 in the post-adsorption FTIR indicated the successful adsorption of cyanide in LDH. The mean free energy value suggested that adsorption occurs via ion-exchange. The morphological stability of the impregnated LDH nanoparticles at elevated loading (6 and 8 wt%) was asserted using Field emission scanning electron microscopy and Transmission electron microscopy analysis. The maximum adsorption capacity of the optimum MMB was 80 mg/g at 303 K. The adsorption mechanism was established based on the speciation chemistry of cyanide present in the actual steel plant effluent. A fundamental macroscopic transport model was used to predict the adsorption kinetics to evaluate the mass transfer and diffusion time scales. The information about the effective pore diffusivity obtained from kinetic macroscopic model along with the adsorption isotherm parameters were used in a first-principle based model to simulate the breakthrough behaviour of continuous column mode experiments and axial dispersion and mass transfer coefficient were estimated in due process. These parameters were used to scale-up the adsorption columns and a performance curve was generated correlating the life of the filter, flow rate, feed concentration and amount of adsorbent required.

Study of the beneficial effects of sodium doping Cu2ZnSnS4 material

This paper reports the effect of Na doping Cu2ZnSnS4 powders on the structural, morphological and optical properties. CZTS powders were synthesized by direct melting method of the constituent elements with different sodium doping concentrations from 0.5% to 2%. The resulting CZTS:Na powders were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, scanning transmission electron microscopic and UV–visible–NIR spectrophotometer. X-ray diffraction and scanning transmission electron microscopic analysis confirmed the formation of CZTS:Na with kesterite structure and preferential orientation along (112) plane. SEM results shown the microstructure with large grains with increasing the Na doping concentration. Optical measurements revealed that the band gap of CZTS decreases from 1.66 to 1.53 eV by increasing Na-doping. In addition, electrical investigations indicated that all ingots exhibit p-type conductivity.

Antibacterial activity, cytocompatibility, and thermomechanical stability of Ti40Zr10Cu36Pd14 bulk metallic glass.

This paper envisions Ti40Zr10Cu36Pd14 bulk metallic glass as an oral implant material and evaluates its antibacterial performance in the inhabitation of oral biofilm formation in comparison with the gold standard Ti–6Al–4V implant material. Metallic glasses are superior in terms of biocorrosion and have a reduced stress shielding effect compared with their crystalline counterparts. Dynamic mechanical and thermal expansion analyses on Ti40Zr10Cu36Pd14 show that these materials can be thermomechanically shaped into implants. Static water contact angle measurement on samples' surface shows an increased surface wettability on the Ti–6Al–4V surface after 48 ​h incubation in the water while the contact angle remains constant for Ti40Zr10Cu36Pd14. Further, high-resolution transmission and scanning transmission electron microscopy analysis have revealed that Ti40Zr10Cu36Pd14 interior is fully amorphous, while a 15 ​nm surface oxide is formed on its surface and assigned as copper oxide. Unlike titanium oxide formed on Ti–6Al–4V, copper oxide is hydrophobic, and its formation reduces surface wettability. Further surface analysis by X-ray photoelectron spectroscopy confirmed the presence of copper oxide on the surface. Metallic glasses cytocompatibility was first demonstrated towards human gingival fibroblasts, and then the antibacterial properties were verified towards the oral pathogen Aggregatibacter actinomycetemcomitans responsible for oral biofilm formation. After 24 ​h of direct infection, metallic glasses reported a >70% reduction of bacteria viability and the number of viable colonies was reduced by ∼8 times, as shown by the colony-forming unit count. Field emission scanning electron microscopy and fluorescent images confirmed the lower surface colonization of metallic glasses in comparison with controls. Finally, oral biofilm obtained from healthy volunteers was cultivated onto specimens' surface, and proteomics was applied to study the surface property impact on species composition within the oral plaque.

Applications of a novel electron energy filter combined with a hybrid-pixel direct electron detector for the analysis of functional oxides by STEM/EELS and energy-filtered imaging

The performance and suitability of a new electron energy filter in combination with a hybrid pixel, direct electron detector for analytical (scanning) transmission electron microscopy are demonstrated using four examples. The STEM-EELS capabilities of the CEOS Energy Filtering and Imaging Device (CEFID) were tested with focus on weak signals and high spatio-temporal resolution. A multiferroic, multilayer structure of REMnO3 (RE = Yb, Er, Tb, Y), grown on yttria-stabilized zirconia (YSZ), is used to exemplify that this new instrumental setup produces valuable electron energy-loss spectroscopy (EELS) data at high energy losses even when using short acquisition times, providing detailed chemical information about the interfaces in this complex multilayer sample. Another functional oxide, namely a ferromagnetic La2NiMnO6 thin film grown on SrTiO3, demonstrates that atomically resolved spectrum images can be recorded, using short dwell times and moderate beam currents in order to warrant the integrity of the sample. In a third example, inhomogeneously Er-doped YSZ shows by EELS spectrum imaging that elements at low concentrations can be detected semi-quantitatively, uncovering the expected layered Er distribution but revealing substantial interdiffusion. In a final example, we simply demonstrate that the hybrid pixel detector in combination with the energy filter can also be used for energy-filtered imaging and thus for elemental mapping complementary to EELS in scanning transmission mode.

Antifungal Activity of β-Carboline Alkaloids Compound and Its Resistance Mechanism on Peronophythora Litchii

ABSTRACT Peronophythora litchii (P. litchii) is the pathogenic factor of litchi downy blight. Derivatives extracted from harmine officinalis and modified, N-(2-pyridyl)-1-phenyl-9 H-pyrido [3, 4-b] indole-3-formamide (PPPIF), could inhibited P. litchii growth and development. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analyses indicated that PPPIF severely damaged the mitochondria, cell wall and endomembrane system of P. litchii cells, thus abnormal morphology, as well as deformed mycelia. PPPIF could suppress mycelial growth, sporulation, sporangia germination and germ tube elongation as well. PPPIF also caused a series of physiological and biochemical changes of P. litchii, including the serious deviation of extracellular pH, the obvious increase of the content of extracellular reducing sugar and malondialdehyde, the notable decrease of soluble protein and the activity of NADH oxidase. Furthermore, PPPIF seriously raised openness of membrane permeability transporter (MPTP) and markedly decreased the transmembrane potential (Δψm) and the activity of enzyme complex I–complex V in respiratory chain of mitochondria. The current research suggests that PPPIF may act upon the mitochondrion of P. litchii, then respiratory chain complex activity was blocked and energy metabolism disrupted or inhibited, resulting in the growth inhibition of P. litchii. Above results have strengthened our understanding of P. litchii resistance mechanisms and may help in the development of more potent inhibitors against plant diseases in the fields.

Aerobic oxidation of isoprene glycol with platinum-bismuth nanoparticles catalysts supported on metal oxides

β-Hydroxy β-methylbutyric acid (HMB) is expected as a promising therapeutic agent or a supplement. For industrial production of HMB, Pt-catalyzed aerobic oxidation of isoprene glycol is a potent synthetic method. However, the previous report using Pt-Bi catalyst supported on active carbon suffered from low tolerance to high substrate concentration conditions, which leads to low volumetric productivity. Herein, we report aerobic oxidation of isoprene glycol using Pt-Bi catalysts supported on ZrO2 or TiO2, showing high tolerance to the high substrate concentration conditions. In addition, these catalysts exhibited high recyclability. Scanning transmission electron microscopy analyses suggested the Pt-Bi species supported on ZrO2 or TiO2 are less likely to aggregate than those supported on activated carbon. Additionally, these metal oxides supported catalysts showed lower metal leaching than the carbon supported catalysts. Besides, the results of the various control experiments indicated the prevention of dehydration of an aldehyde intermediate is important for further improvement.

On the provenance of GEMS, a quarter century post discovery

The provenance of GEMS (glass with embedded metal and sulfides) in cometary type interplanetary dust particles is investigated using analytical scanning transmission electron microscopy and secondary ion mass spectrometry. We review the current state of knowledge and closely examine the densities, elemental compositions and distributions, iron oxidation states, and isotopic compositions of a subset of GEMS in chondritic porous interplanetary dust. We find that GEMS are underdense with estimated densities that are 35–65% of compositionally equivalent crystalline aggregates. GEMS low densities result in a lower contribution to the bulk compositions of IDPs than has been assumed based on their volume fraction. We also find that element/Si ratios, assumed to be primary (indigenous), are instead perturbed by contamination and secondary alteration, including pulse heating during atmospheric entry. Fe in pyrrhotite inclusions was oxidized and Mg, S, Ca, and Fe were depleted relative to lithophile Al and Si, resulting in reduction in element/Si ratios. Because they trap outgassing elements, Fe-rich oxide rims that formed on the surface of GEMS are serendipitous “witness plates” to the changes in composition that accompany atmospheric entry. As a result of alteration, GEMS elemental compositions cannot reliably inform about their provenance. Except for highly anomalous oxygen isotope ratios measured in some large GEMS grains that indicate a contribution from circumstellar dust, oxygen isotope compositions are generally poor indicators of provenance. Prior work indicates that most GEMS fall close to the terrestrial oxygen isotope composition, which, however, does not exclude a presolar interstellar origin. Nitrogen isotopic compositions are more diagnostic. Elevated 15N/14N ratios indicate that GEMS accreted in conjunction with formation of organic matter by ion–molecule reactions in a cold (<50 K) presolar environment like the extreme outer nebula or interstellar medium. Considering all observations, we conclude that GEMS are most likely processed interstellar silicates.

The Influence of Synthesis Method on the Local Structure and Electrochemical Properties of Li-Rich/Mn-Rich NMC Cathode Materials for Li-Ion Batteries.

Electrochemical energy storage plays a vital role in combating global climate change. Nowadays lithium-ion battery technology remains the most prominent technology for rechargeable batteries. A key performance-limiting factor of lithium-ion batteries is the active material of the positive electrode (cathode). Lithium- and manganese-rich nickel manganese cobalt oxide (LMR-NMC) cathode materials for Li-ion batteries are extensively investigated due to their high specific discharge capacities (>280 mAh/g). However, these materials are prone to severe capacity and voltage fade, which deteriorates the electrochemical performance. Capacity and voltage fade are strongly correlated with the particle morphology and nano- and microstructure of LMR-NMCs. By selecting an adequate synthesis strategy, the particle morphology and structure can be controlled, as such steering the electrochemical properties. In this manuscript we comparatively assessed the morphology and nanostructure of LMR-NMC (Li1.2Ni0.13Mn0.54Co0.13O2) prepared via an environmentally friendly aqueous solution-gel and co-precipitation route, respectively. The solution-gel (SG) synthesized material shows a Ni-enriched spinel-type surface layer at the {200} facets, which, based on our post-mortem high-angle annual dark-field scanning transmission electron microscopy and selected-area electron diffraction analysis, could partly explain the retarded voltage fade compared to the co-precipitation (CP) synthesized material. In addition, deviations in voltage fade and capacity fade (the latter being larger for the SG material) could also be correlated with the different particle morphology obtained for both materials.

Defect-gradient-induced Rashba effect in van der Waals PtSe2 layers

Defect engineering is one of the key technologies in materials science, enriching the modern semiconductor industry and providing good test-beds for solid-state physics. While homogenous doping prevails in conventional defect engineering, various artificial defect distributions have been predicted to induce desired physical properties in host materials, especially associated with symmetry breakings. Here, we show layer-by-layer defect-gradients in two-dimensional PtSe2 films developed by selective plasma treatments, which break spatial inversion symmetry and give rise to the Rashba effect. Scanning transmission electron microscopy analyses reveal that Se vacancies extend down to 7 nm from the surface and Se/Pt ratio exhibits linear variation along the layers. The Rashba effect induced by broken inversion symmetry is demonstrated through the observations of nonreciprocal transport behaviors and first-principles density functional theory calculations. Our methodology paves the way for functional defect engineering that entangles spin and momentum of itinerant electrons for emerging electronic applications.

Processing-dependent stabilization of a dissimilar rare-earth boride in high-entropy (Ti0.2Zr0.2Hf0.2Ta0.2Er0.2)B2 with enhanced hardness and grain boundary segregation

This study demonstrates that 20% of a rare-earth (RE) diboride (ErB2) can be stabilized in a high-entropy transition metal (TM) diboride, despite the dissimilar chemical properties of RE and TM elements and large differences in lattice parameters of ErB2 and typical TMB2. However, the phase formation depends on the fabrication route, which is a noteworthy observation. Specifically, single-phase (Ti0.2Zr0.2Hf0.2Ta0.2Er0.2)B2 is synthesized via reactive spark plasma sintering (SPS) using elemental boron and metal elements. In contract, a specimen made by borocarbothermal reduction of binary oxides and SPS possess significant amounts of two Er-rich secondary phases. Notably, the RE addition in high-entropy TM diboride leads to improved hardness. Aberration-corrected scanning transmission electron microscopy (AC STEM) and energy-dispersive X-ray spectroscopy (EDS) elemental analyses further reveal significant Er segregation at grain boundaries. This work suggests that high-entropy ceramics can have significant solubilities of dissimilar components that may enable new, tunable, and improved properties.

Design of new, efficient, and suitable electrode material through interconnection of ZIF-67 by polyaniline nanotube on graphene flakes for supercapacitors

Metal-organic frameworks (MOFs) have been given more significant consideration in energy storage systems due to their high specific surface areas, mesoporous structures, and numerous reaction sites. To introduce additional conductive pathways and facilitate fast charge transfer, MOFs can be integrated with suitable conducting agents. In this study, we report the preparation of a novel Graphene@ZIF-67/polyaniline nanotube (PANI-NT) composite by using an easy stirring and sonication approach at room temperature. ZIF-67 rhombic dodecahedron structures are interconnected through PANI-NTs and deposited on the graphene flakes. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analysis have confirmed such individual morphology. This composite by the high surface area of 961.53 m2 g−1 exhibits a high specific capacitance of 20416.70 mF g−1 at a current density of 0.05 mA cm−2. This is due to a quick permeation of ions, easy forwarding of electrons, and excellent cooperation between the ingredients of the composite that result in reversible redox interactions. Moreover, the electrode material possesses 75% specific capacitance retention after 3000 cycles indicate good reversibility and cyclic stableness. The prepared Graphene@ZIF-67/PANI-NT composite can render outstanding electrochemical performance and is properly candidate for supercapacitors application.

Optimization of ultrasonic vibration assisted friction stir process to improve mechanical properties of AA7075-nano B4C surface composite

Ultrasonic Vibration assisted Friction Stir Processing is one of the advanced surface modification techniques developed for ductile materials like aluminium to improve their surface properties. The present study is aimed to improve mechanical properties of the AA7075-T651 surface composite by reinforcing the nano B4C particles with optimum working condition. Experiments are conducted at different levels of tool rotation speed, tool processing speed and volume percentage of nano B4C particles with and without ultrasonic vibrations and the experimental results for ultimate tensile strength, impact strength, yield strength, percentage of elongation and hardness are measured. Jaya Algorithm (JA) is used and found best optimum condition such as 1112 r/min of tool rotational speed, 43.96 mm/min of tool traverse speed and 4.02 vol % of B4C nano particles. Mechanical properties and microstructure are investigated using optical Microscope, Field emission scanning electron microscope and Transmission electron microscopy analysis. A fine grain structure and uniform distribution of reinforcement are found in the matrix with the ultrasonic vibrations and the mechanical properties of the AA7075 alloy are improved. The microstructure of the surface composite is correlated with the mechanical properties.