HRTEM Investigations Research Articles

Improving thermal stability and textural properties of mesoporous γ-alumina granules by Zr-La dopants

Improving the thermal stability and modifying the porous properties of γ-alumina by incorporating various transition and rare earth metals in alumina have been widely studied. However, less attention has been paid to investigating the co-doping process for increasing the alumina thermal stability and surface area in temperatures ranging from 1000° to 1200°C. In this research, pure, Zr-doped, and Zr-La doped granules with an average diameter of 1.5–2 mm were synthesized using the sol-gel granulation method. XRD results indicated that the introduction of either Zr or Zr-La dopants improves the thermal stability of transition aluminas up to 1200 °C. DTA/TG results revealed that the incorporation of 1 wt% zirconium along with 1 wt% lanthanum retarded α-Al2O3 phase transformation temperature to around 1335 °C. Compared to the pure sample, the BET surface area of alumina containing 1 wt% zirconium, 1 wt% zirconium along with 1 wt% lanthanum, and 1 wt% zirconium along with 3 wt% lanthanum increased to 234.4, 232.4, and 215.6 m2/g at 750 °C, respectively. Moreover, the sample containing 1 wt% of Zr along with 1 wt% of La dopants maintained a higher specific surface area after calcination at 1000 °C (133.6 m2/g) and 1200 °C (64.7 m2/g). According to NMR and HRTEM investigations, the capability of the co-doped Zr-La alumina to preserve the mesoporous structure and thermal stability as well as suppressing α-alumina formation up to 1200 °C is the result of zirconium and lanthanum dopants occupying tetrahedral and octahedral vacancies in the structure of transition alumina. The reported Zr-Al co-doped alumina granules in this study with high thermal and porous structural stability can be good candidates as a support for industrial catalysts.

Nano-sized aggregation induced emissive probe for highly sensitive hypochlorous acid detection

A highly sensitive aggregation-induced emissive probe KG1 was developed for detecting hypochlorous acid in an aqueous medium. The KG1 aggregates display excellent fluorescence in a THF:water (10:90) ratio, and the derived aggregates were thoroughly characterized by HRTEM and photophysical investigations. The results indicate that KG1 aggregates have a spherical in shape with an average particle size of 5 nm. Further, the light scattering capability of KG1 aggregates is validated through the Tyndall effect. The KG1 aggregates have a high fluorescence lifetime (∼6 ns) and a quantum yield of 46%, making them suitable for bio-imaging and sensing applications. The sensing ability of KG1 aggregates is evaluated by titrating various concentrations of hypochlorous acid in an aqueous medium. Notably, probe KG1 can detect hypochlorous acid without interference and has a low detection limit of 667 pM. The sensing mechanism was demonstrated through HRMS analysis. Overall, as a result of its excellent fluorescent and sensing properties, the probe KG1 was successfully applied to visualize hypochlorous acid in zebrafish. As a result, this probe is expected to be a prospective tool for investigating the biological mechanisms of hypochlorous acid in living systems.

Structural and mechanical behavior of Zr-W-Ti thin film metallic glasses prepared by multitarget co-magnetron sputtering

Zr-W-Ti thin films were deposited by magnetron co-sputtering technique with varied Ti-sputtering power between 25 and 150 W. The effect of Ti-sputtering power on their physical and mechanical properties was investigated. As a results of FE-SEM, XPS, AFM, XRD, and HR-TEM investigations, the Ti-sputtering power affected the Ti-containing structure of ZrW-based films, which exhibited an amorphous phase with a very low surface roughness layer. The mechanical properties, tested by nano-indentation, revealed the films strongest hardness and elastic modulus of 8.6 GPa and 121.3 GPa, respectively. In addition, the plastic responded, especially the serrated flow and shear banding showed that the prepared Zr-W-Ti thin films were excellent candidates for surface coating as the thin film metallic glasses (TFMGs).

Amino acid-assisted synthesis and characterization of zero-Valente iron nanoparticles for research on the bio-interactions with yeast

The wet synthesis of uniformly sized zero-Valente iron nanoparticles (NPs) for application in nanomedicine and biology is still a challenging because of magnetic interaction, oxidation and corrosion. In this study, various Fe-containing NPs were synthesized using amino acids as their size stabilizing agents to investigate their bio-interactions with Metschnikowia spp. yeast strains. For this, D-glutamic, DL-cysteine, DL-methionine, and taurine amino acids were tested. In this way, NPs in size from several to 40 nm, composed of a-Fe0, a-FeB, Fe2O3 and lepidocrocite, g-FeOOH, were synthesized and characterized using X-ray diffraction and Mössbauer spectroscopy, and HRTEM investigations. The surprising influence of amino acid nature and DL-cysteine concentration on the NP size and composition has been revealed allowing fabrication of quite pure lepidocrocite as well as a-Fe0 NPs containing boron. As-synthesized NPs were cultivated in a YEPD growth media for research on the formation of insoluble red pigment pulcherrimin by several Metschnikowia spp. yeast strains. For comparison, the behavior of M. pulcherrima yeast with metallic iron plate and Fe0 NPs has been visualized.

Combined thermal desorption spectroscopy, hydrogen visualization, HRTEM and EBSD investigation of a Ni–Fe–Cr alloy: The role of hydrogen trapping behavior in hydrogen-assisted fracture

The role of hydrogen trapping behavior in hydrogen-assisted cracking in a Ni–Fe–Cr alloy has been investigated using thermal desorption spectroscopy (TDS), hydrogen visualization, and high-resolution microstructural characterization methods. The results indicate that hydrogen resides at interstitial lattice sites, dislocations, and vacancies with the ascending order of the desorption activation energies. This study firstly shows that hydrogen is trapped reversibly at dislocations including misfit dislocations at the austenite/δ phase interface, and deformation-induced dislocations. The hydrogen trapping behavior is proved by TDS and hydrogen visualization technique. The weakly trapped hydrogen at dislocations provides sufficient hydrogen to build up a required critical hydrogen concentration at potential flaws for crack nucleation and to activate hydrogen enhanced decohesion mechanism. Further, it was found that δ phase precipitation exacerbates the hydrogen embrittlement sensitivity. For the first time, evidence for hydrogen transport by dislocations in a Ni-based alloy is observed by the hydrogen visualization technique.

Gadolinium Nitrate Decorated Reduced Graphene Oxide Structure and Morphological Studies for Battery Applications

In-situ chemical and thermal reduction method was followed to prepare reduced graphene oxide (rGO) and gadolinium nitrate doped rGO (rGO/GdN) for XRD, FTIR, Raman, SEM, HR-TEM, and AFM investigations. From XRD, rGO/GdN composite was in nano crystalline structure with diffraction peaks 19.38o, 22.49o, and 31.59o correspond to (101), (201), and (111) planes. FTIR spectrum shown oxygen containing functional groups with vibrational bands of hydroxyl (-OH), carbonyl (C-O), epoxy (O-C-O) group, and a strong peak represents stretching vibration of Gd-O. Raman spectra provides appearance of D, G, and 2D bands at 1323, 1572, and 2662 cm-1 respectively. Moreover, an additional band at 1607 cm-1 revealed in rGO/GdN represents the existence of nitrogen. Crystal d-spacing from HRTEM of rGO is found to be 0.344 nm for (002) plane and for Gd was 0.283 nm for (400) plane. Morphology indicated that GdN with particles are well anchored on rGO sheets. Furthermore, AFM studies for thickness of rGO/GdN was estimated as 32 nm with Average Roughness and Root Mean Square are 15.19 and 23.16 nm respectively. Hence, rGO/GdN nanocomposite has prospective applications for battery owing to their smaller crystallite sizes.

Self-assembly growth of electrolytic silver dendrites

The atomic level assembly of silver dendrite has never been disclosed despite the numerous studies published on fractal dendrite structures. We report for the first time an HRTEM investigation of the formation of atomic embryos (< 5 nm) and the self-assembly of atoms on an atomic plane of the tip of a dendrite arm. The mechanism of dendrite formation proceeds via the sequence of amorphous embryos aggregates (5–10 nm), nuclei, crystallites (10–20 nm), dendritelets (50–100 nm) and submicron dendrite protypes. The atomic plane is an entirely atomic-level zig-zag structure with d-spacing kink steps. The zig-zag structure triggers the self-assembly of atoms and thus directional growth to produce a dendrite arm with a high aspect ratio.

Introduced oxygen vacancies in cadmium ferrite anode materials via Zn2+ incorporation for high performance lithium-ion batteries

Cationic substitution strategy was recognized as an effective approach to create a defective structure and increase the oxygen vacancies in the crystal structure for improving the electrochemical performance of Li-ion batteries components. In this study, ZnxCd1-xFe2O4 nanoparticles were synthesized via a facile inexpensive process at low temperature. The collected XRD data confirmed the formation of cubic structure with Fd3m space group. HR-TEM investigations showed the size enlargement of spherical-like crystals with increasing the concentration of doping Zn2+ ion. FESEM and BET measurements indicated the conversion of micropores in pure CdFe2O4 into mesopores and macropores in Zn-doped CdFe2O4 samples. XPS results of O1s spectra elucidated that Zn-doped CdFe2O4 samples have higher conductivity due to the created lattice defects and oxygen species. Zn-doped CdFe2O4 anodes exhibit great improvement in their initial discharge capacities ∼1618 and 1880 mAhg−1 upon substitution of Cd with 5% and 10% Zn, respectively. Furthermore, 10% Zn-doped CdFe2O4 anode displayed the highest Li-ions diffusion coefficient and exchange current density due to the enhanced Li+ ions mobility. The increase in zinc content (0.0–0.1) led to a decrease in the DC activation energy from 0.11 to 0.09 eV.

Hybrid magnetic core-shell TiO2@CoFe3O4 composite towards visible light-driven photodegradation of Methylene blue dye and the heavy metal adsorption: isotherm and kinetic study.

Magnetic core-shell TiO2@CoFe3O4 (TCM) composite photocatalytic particles with a core-shell structure were synthesized by the co-precipitation method as a novel catalyst for methylene blue (MB) dye degradation and adsorption efficiency of heavy-metal ion Pb(II) from aqueous solution. Various analytical techniques have verified the formation of the TCM core-shell through TEM, XRD, FT-IR, Raman, PL, and UV analysis. The presence of TiO2 and cobalt magnetite in the TCM core shell is confirmed by XRD analysis. The formation of a homogenous CoFe3O4shell on TiO2 spheres is confirmed by HR-TEM investigation. TiO2 nanoparticle has a rutile structure with an average crystallite size of about 57.44 and a TCM core-shell of about 64.62nm. From UV and PL studies, it was found that the core shell absorbs the visible range of the electromagnetic spectrum, which improves the effective separation between photo carriers. This study focused on several factors that influence metal ion adsorption, including initial concentrations, adsorbent dose, pH, and contact time. The TCM nanocomposite successfully separated the heavy metal ion Pb(II) from aqueous solutions, and the model predictions exactly matched the experimental results. For TCM material, the maximum adsorption efficiency for Pb(II) was 33.09mg/g. The photocatalytic performance of TiO2 and TCM is about 12% and 91% after 60min for MB dye degradation. It was found that TiO2@CoFe3O4 core-shell nanoparticles perform better as photo catalysts than pure TiO2 and CoFe3O4due to their high efficiency and reusability. Furthermore, the analysis revealed that heavy metal adsorption from aqueous solutions could be reused over seven cycles with no adsorption capacity modification.

Unraveling the role of agro waste-derived graphene quantum dots on dielectric and mechanical property of the fly ash based polymer nanocomposite

In this study, crystalline graphene quantum dots (GQDs) is prepared using agro waste of paddy straw via hydrothermal route and GQDs reinforced fly ash polymer nanocomposites was prepared for the first time. HR-TEM and XRD investigations confirmed the formation of hexagonal GQDs with average diameter of 8 nm. Nanocomposite prepared with GQDs reinforcement in fly ash waste under epoxy system was fabricated through the compressive molding machine. Graphene quantum dots-fly ash polymer nanocomposites showed a substantial and concurrent increase in dielectric constant (ɛ') up to ~ 350 compared to fly ash based polymer composites (ɛ'~13). The GQDs-reinforced fly ash based nanocomposites possess the high flexural strength of 60 MPa, whereas pristine fly ash polymer hybrid composite exhibited flexural strength of 35 MPa. The unconventional dielectric enhancement and flexural strength of agro waste derived GQDs reinforced fly ash polymer nanocomposite is attributed to the sudden increase in the electric dipoles and improved interfacial and chemical bonding of crystalline GQDs with fly ash and epoxy.

Inducing lattice defects in calcium ferrite anode materials for improved electrochemical performance in lithium-ion batteries

Enhancing the electrical conductivity of electrode materials via a cationic substitution strategy was recognized as an effective way of improving the electrochemical performance of Li-ion batteries. Thus, LixCa1-xFe2O4 nanoparticles were synthesized via a facile inexpensive process at low temperature. XRD peaks refer to the formation of an orthorhombic structure with the Pnma space group. HR-TEM investigations reveal orthorhombic-like shape for pure CaFe2O4, nanoplatelet-like morphology for Li0.05Ca0.95Fe2O4 and irregular distorted crystals for Li0.1Ca0.9Fe2O4. Voids and pores in Li-doped CaFe2O4 were confirmed by FESEM and BET measurements. XPS spectra of O1s prove that Li-doped CaFe2O4 have higher conductivity due to the created lattice defects and oxygen species. Li-doped CaFe2O4 anodes exhibit great improvement in their initial discharge capacities ∼1219 and 1606 mAhg−1 upon substitution of Ca with 5% and 10% Li, respectively. Furthermore, 10% Li-doped CaFe2O4 anode displays the highest Li-ions diffusion coefficient and exchange current density due to the enhanced Li+ ions mobility. Moreover, the DC activation energies for the LixCa1-xFe2O4 nanoparticles decreased with increasing Li content.

From design to characterization of zirconium nitride/silicon nitride nanocomposites

ZrN/Si3N4 nanocomposites have been prepared by chemically crosslinking two polysilazanes with a zirconium-based compound and subsequent heat-treatment at temperatures ranging from 1000 to 1600 °C. The polymer synthesis has been systematically investigated using FT-IR, solid-state NMR, and elemental analyses. Then, the pyrolysis under ammonia at 1000 °C trigering the thermo-chemical polymer-to-ceramic conversion was examined, leading to X-ray amorphous ceramics with yields governed by the chemistry of the neat polysilazane. Investigations of the structural evolution of the single-phase amorphous ceramic network above 1000 °C by X-ray diffraction and Raman spectroscopy pointed out that the ZrN phase already segregated at 1400 °C and formed highly crystalline ZrN/Si3N4 nanocomposites at 1600 °C. HRTEM investigations validated the unique nanostructural feature of the nanocomposites made of ZrN nanocrystals distributed in α- and β-Si3N4 phases. Our preliminary investigations of the optical properties showed that these structural changes allowed tuning the optical properties of ZrN/Si3N4 nanocomposites.

Stacking-faulted CDO zeolite nanosheets efficient for bulky molecular reactions.

The synthesis of thin zeolite nanosheets beneficial for catalytic reactions, adsorption and diffusion involving bulky molecules remains a great challenge. Herein, we report a unique layered zeolitic nanosheet ECNU-57 with a CDO-type structure that was synthesized by employing small-molecular 1,4-bis(N-methylpyrrolidinium) cations as the organic structure-directing agent (OSDA). The ECNU-57 nanosheets are 50 nm thick along the b-axis and have an open hierarchical porosity with 486 m2 g-1 surface area. HRTEM investigation indicates that the nanosheets exhibit a stacking fault structure along the b-axis with the inclusion of the FER structure since the CDO and FER topologies possess very similar building layers. As a solid-acid catalyst, ECNU-57 exhibits promising performances in the reactions of 1,3,5-triisopropylbenzene cracking and Friedel-Crafts acylation, due to its enhanced mass transfer and more accessible active sites to bulky organic molecules.

Global popularization of CuNiO2 and their rGO nanocomposite loveabled to the photocatalytic properties of methylene blue

New advancements of photocatalytic activity with higher efficiency, low price are most important, which is challenging in industrialized and many fields. We have introduced CuNiO2 and CuNiO2/rGO nanocomposite was generally prepared by the hydrothermal treatment and tested to the photocatalytic studies. Photocatalytic measurements of CuNiO2 with different weight percentages CuNiO2/rGO (25/75), (50/50), and (75/25) are achieved to the efficiency under visible light, in this case, CuNiO2/rGO (50/50) composite have the highest performance is scrutinized. This was obeyed for a synergistic effect between CuNiO2 nanoparticles and rGO composites. Furthermore, the CuNiO2, CuNiO2/rGO (25/75), (50/50), and (75/25) nanocomposite were tested by several analyses like XRD, FT-IR, DRS UV Visible spectroscopy, Raman spectroscopy, and FESEM & HRTEM investigations. In this regard all measurements are very clear and satisfied; therefore we are encouraged for future developing environmental applications.

Synthesis and tuning the structure, morphological, optical, and photoluminescence properties of heterostructure cerium oxide and tin oxide nanocomposites

A series of Ce1-xSnxO2 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 1) nanocomposite heterostructure have been synthesized by a hydrothermal technique. The structure, composition, and morphology of samples were systematically specified by XRD, XPS, HRTEM, and FESEM. XRD manifests the composite oxide materials which comprise well-separated phases of nanocrystalline nature from both the constitutive oxides at ratios 0.2, 0.3, and 0.4. XPS studies detected the various ionization states of Ce3+/Ce4+, Sn4+, Sn2+ that were existed in the combined oxides and showed strong interactions among CeO2 and SnO2. Besides, the addition of SnO2 into CeO2 raised the amount of Ce3+ and Oα species. The HRTEM investigation illustrated the combined morphology of uniformly scattered spherical shapes observed at CTAB supported CeO2/SnO2nanocomposites. The UV effects provided that the absorption edge was shifted to higher energies in all samples described by DRS. It was found that PL spectra are very sensitive to preparation and processing conditions. From XPS, UV, and PL results of the CeO2/SnO2 nanocomposites, it is realized that the composites are promising for catalysis and optoelectronic devices.

Microstructural evaluation of iron oxide nanoparticles at different calcination temperature by Scherrer, Williamson-Hall, Size-Strain Plot and Halder-Wagner methods

ABSTRACT Ferric nitrate Fe(NO3)3 ⋅9H2O as a precursor and Ethylene Glycol as a solvent were used to prepare iron oxide nanoparticle via sol gel method. X-ray diffraction (XRD) study of IONPs at different calcination temperatures to determine the size of the crystallite was performed using various methods of calculation: Scherrer, Williamson-Hall (W-H), Halder-Wagner (H-W) and Size-Strain plot (SSP). The Scherrer and H-W methods reveal that the crystallite size decreases in the presence of a single phase (γ-Fe2O3) at lower temperature, as the contribution of other-phase (α-Fe2O3) increases size varies, but again decreases as the material converts to a single phase, while with temperature, the Size-Strain Plot and Halder-Wagner Method show increased crystallite size. FE-SEM and HR-TEM investigations confirm that the synthesized IONPs are spherical. EDX spectra and FTIR analyses have shown that synthesized particles are pure iron oxide nanoparticles. The average particle size calculated using different models below than 20 nm.

HRTEM investigations on nano precipitates in Custom 475 maraging stainless steel

In this work, nano precipitates in stainless maraging steel (Custom 475) were investigated using high-resolution transmission electron microscopy. In this steel, aging induces three transformation products, NiAl-B2 phase, R phase and austenite, which contribute various hardening effects dependent on the aging temperature. In the steel aged at 480 °C, precipitation of NiAl-B2 phase was the primary reaction and led to slow incremental hardening. No hardening effect was observed in the steel aged at 650 °C despite the presence of austenite of over 25 vol% and coarse B2 and R phases. Efficient hardening was obtained by aging at 520 °C, and the maximum hardness (601 HV) was achieved when the steel was aged for 4 h. This high strength is attributed to the formation of both B2 and R nano precipitates. Moreover, lattice images and diffractograms clarified the crystal structure of the R phase and its orientation relationship with the martensite matrix. This work provides comprehensive insights into precipitation behaviors in Custom 475 maraging steel.

Highly stable visible‐light photocatalytic properties of black rutile TiO2 hydrogenated in ultrafast flow

The hydrogenation and introducing oxygen vacancies (VO) can lead to surface lattice disorder in TiO2, which is a new form of TiO2 named black TiO2, with excellent visible-light photocatalytic activity, but this TiO2 is easy to failure because oxidation makes the concentration of surface VO decrease rapidly in a short time. In this work, black TiO2 nanoparticles with VO almost concentrated inside nanoparticles were fabricated under ultrafast hydrogen flow. These bulk VO shortened the bandgaps of black TiO2, enhanced its visible light absorption, and meanwhile provided extremely strong stability. The location of VO in black TiO2 was evident from EPR, XPS with HRTEM investigation, and other characteristics of black TiO2 were obtained by XRD, UV-Vis, SEM, PL, and photocurrent techniques. The degradation experiments on Cr6+ or rhodamine B demonstrated the good visible-light photocatalytic performance of our material. After 18 months of natural aging treatment (in the air), our samples showed no discoloration and maintained 89.5% photocatalytic efficiency, and further study exhibited that this black TiO2 also contained excellent acid resistance and moderate alkaline resistance. This work could help design lattice disorder to obtain more stable and practical black TiO2.

Constructing defect-related subband in silver indium sulfide QDs via pH-dependent oriented aggregation for boosting photocatalytic hydrogen evolution

Surface engineering of quantum dots (QDs) plays critical roles in tailoring carriers’ dynamics of I-III-VI QDs via the interplay of QDs in aggregates or assembly, thus influencing their photocatalytic activities. In this work, an aqueous synthesis and the followed pH tuned oriented assembly method are developed to prepare network-like aggregates, dispersion, or sheet-like assembly of GSH-capped Silver Indium Sulfide (AIS). FTIR, DLS, and HRTEM investigation revealed that surface protonation or deprotonation of QDs occurred at pH < 6 or pH > 12 favors the formation of network-like aggregates with various defects or sheet-like assembly with perfect crystal lattice, respectively, via the surface charge induced interaction among AIS QDs. Further UV–vis, steady and transient PL investigation confirm the narrowed band gaps and the prolonged PL lifetime of the acidic network-like aggregates. As a result, the optimized network-like aggregates (3.0-AIS) exhibits superior photocatalytic H2 evolution (PHE) rates (5.2 mmol·g−1·h−1), about 113 times that of alkaline sheet-like assembly (13.0-AIS) or 2.7 times higher than that of dispersed AIS QDs (AIS-8.0). The formation of defects and their roles in PHE mechanisms are discussed. This work is expected to give some new insight for designing efficient non-cadmium/non-novel metal I-III-VI photocatalysts for boosting PHE.

Enhanced thermoelectric performance of Bi0.5Sb1.5Te3 via Ni-doping: A Shift of peak ZT at elevated temperature via suppressing intrinsic excitation

Bi2Te3-based thermoelectric (TE) materials have been demonstrated to be a potential candidate for mainly thermoelectric cooling/refrigeration applications. However, minority charge carriers excitation at high temperature reduces thermopower which restricts these materials for the use in power generation. In present work, substitution of Ni on Sb site in Bi0.5Sb1.5-xNixTe3 (x = 0, 0.01, 0.04 and 0.08) actuates the system to supress the intrinsic excitation leading to shift in highest ZT to higher temperature regime. The Density functional theory (DFT) calculations and experimental results reveal that Ni in Bi0.5Sb1.5Te3 provides the extra holes and slightly reduces the band gap Eg which enhances the σ of Ni-doped Bi0.5Sb1.5-xNixTe3 samples and α at elevated temperature. Moreover, Ni-doping in Bi0.5Sb1.5Te3 also reduces κL which is attributed to the phonon scattering due to mass fluctuations and microstructural features such as grain boundary and strain field domain observed from HRTEM investigation. These favourable condition leads to maximum ZT∼1.38 at 433K for Bi0.5Sb1.46Ni0.04Te3 and ZTavg ∼1.1 between 300K and 503K. Interestingly the calculated theoretical TE conversion device efficiency η of Bi0.5Sb1.46Ni0.04Te3 (η∼5.5%) was achieved to be nearly twice than the efficiency of matrix Bi0.5Sb1.5Te3 (η∼3%). Experimental electronic transport is well corroborated with theoretically estimated DFT results.