High-resolution Transmission Electron Microscopy Data Research Articles

Design of Magnetic Fe3O4/CeO2 "Core/Shell"-Like Nanocomposites with Pronounced Antiamyloidogenic and Antioxidant Bioactivity.

"Core/shell" nanocomposites based on magnetic magnetite (Fe3O4) and redox-active cerium dioxide (CeO2) nanoparticles (NPs) are promising in the field of biomedical interests because they can combine the ability of magnetic NPs to heat up in an alternating magnetic field (AMF) with the pronounced antioxidant activity of CeO2 NPs. Thus, this report is devoted to Fe3O4/CeO2 nanocomposites (NCPs) synthesized by precipitation of the computed amount of "CeO2-shell" on the surface of prefabricated Fe3O4 NPs. The X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy data validated the formation of Fe3O4/CeO2 "core/shell"-like NCPs, in which ultrafine CeO2 NPs with an average size of approximately 3-3.5 nm neatly surround Fe3O4 NPs. The presence of a CeO2 "shell" significantly increased the stability of Fe3O4/CeO2 NCPs in aqueous suspensions: Fe3O4/CeO2 NCPs with "shell thicknesses" of 5 and 7 nm formed highly stable magnetic fluids with ζ-potential values of >+30 mV. The magnetization values of Fe3O4/CeO2 NCPs decreased with a growing CeO2 "shell" around the magnetic NPs; however, the resulting composites retained the ability to heat efficiently in an AMF. The presence of a CeO2 "shell" generates a possibility to precisely regulate tuning of the maximum heating temperature of magnetic NCPs in the 42-50 °C range and stabilize it after a certain time of exposure to an AMF by changing the thickness of the "CeO2-shell". A great improvement was observed in both antioxidant and antiamyloidogenic activities. It was found that inhibition of insulin amyloid formation, expressed in IC50 concentration, using NCPs with a "shell thickness" of 7 nm was approximately 10 times lower compared to that of pure CeO2. For these NCPs, more than 2 times higher superoxide dismutase-like activity was observed. The coupling of both Fe3O4 and CeO2 results in higher bioactivity than either of them individually, probably due to a synergistic catalytic mechanism.

Thick p-type Mg2Si film on Si: Growth, structure and transport properties

A ∼ 0.8–0.9 µm thick Mg2Si film was grown by pulsed deposition of Mg on Si(111) at 340 °C in UHV. The X-Ray Diffraction (XRD) and cross-sectional High-resolution Transmission Electron Microscopy (x-HRTEM) data demonstrate the high crystal quality and nearly 100% texture of the film. Energy Dispersive X-ray spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS) depth profiling show that the synthesized Mg2Si contains some oxygen. Hall measurements reveal the p-type conductivity of 130 S/cm and carrier concentration of 6 × 1018 cm−3 at room temperature (RT), the acceptor concentration of ∼ 1.4 × 1018 cm−3 at 190 K, hole activation energy Ea ≈ 26 meV, mobility μ∼5050 cm2/V∙s at 75 K and μ∼134 cm2/V∙s at RT. The p-type conductivity is related to either unintentional doping with oxygen or/and Mg vacancies occurred during the non-equilibrium process of silicide ultra-fast formation. The outstanding transport parameters of the film are explained by its high crystal quality and texture. The films with such thickness and transport properties are suitable for photovoltaic and thermoelectric applications.

Synergistic coupling {101}-{111} facet of N-doped TiO2 film enhance spatial charge separation for methylene blue photodegradation

The synthesis of N-doped TiO2 film with co-exposed {101} and {111} facets via a one-pot facile hydrothermal method had proven to enhance the photocatalytic activity of TiO2. The high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS) data show the incorporation of N ions into the TiO2 accomplishes the facet modification. The shifting of the N-doped TiO2 photocatalyst adsorption bandgap toward a higher wavelength was identified as the TiO2 band gap was reduced. Up to 66 % methylene blue had successfully been degraded with the aid of N-doped TiO2 as an active photocatalyst. The enhanced photodegradation of N-doped TiO2 film is mainly attributed to the presence of {101} and {111} facets, leading to the efficient separation of carriers and lengthening the life of photogenerated carriers, consequently improving its photocatalysis potential.

Correlation between cation order/disorder and the electrocaloric effect in the MLCCs of complex perovskite ferroelectrics

The physical properties (dielectric, ferroelectric, piezoelectric, etc.) of complex perovskite ferroelectrics depend on the degree of order/disorder and the scale of the ordered domains. In this study, the electrocaloric (EC) properties of three representative complex perovskite ferroelectrics, Pb(Mg1/3Nb2/3)O3–8PbTiO3 (PMN-8PT), 1mol% Sm-doped Pb(Mg1/3Nb2/3)O3–8PbTiO3 (1S-PMN-8PT) and Pb(Sc1/2Ta1/2)O3 (PST) are evaluated. Multi-layer ceramic capacitors (MLCCs) with identical structural configurations were fabricated for these three compounds, and their EC properties were characterized by direct measurement using a thermocouple. The EC temperature change ΔT of PMN-8PT, 1S-PMN-8PT and PST MLCCs under 20 V μm−1 at room temperature were found to be 1.42 K, 1.54 K, and 3.10 K, respectively. X-ray diffraction and high-resolution transmission electron microscopy data suggests that the high EC performance of PST is related to the ordering of B-site cations (Sc3+ and Ta5+) with the ordering parameter S = 0.82 and a long coherence length of ∼100 nm, such that the sample transitioned from a relaxor ferroelectric to a normal ferroelectric. These results provide pathway towards design of high performance EC materials required for solid state refrigeration and air-conditioning technologies.

Sensitivity enhancement of gold nanospheres assisted CO2 laser tapered optical fiber for refractive index sensor

Tapered optical fibers (TOFs) have been intensively used as sensors due to their high sensitivity, simple structure, and excellent coupling efficiency. In this paper, we reported the successful rapid tapering of single mode and multimode fibers using CO2 laser beam at working wavelength of 10.6 μm. Clean and symmetric tapers could be produced in just 5 s using this method. Arduino-based microcontroller was included in the tapering set-up to precisely control the fiber pulling speed and distance. Smaller waist diameters that were observed in multimode than in single mode fibers generated more evanescent waves on the cladding of tapered multimode fibers (TMMFs). This implied that TMMFs performed better refractive index (RI) sensitivity, within the range of 1.3325–1.4266, than tapered single mode fibers (TSMFs). Furthermore, localized surface plasmon resonance (LSPR) effect was coupled with evanescent wave through AuNSs immobilization on the TOF surface. The AuNSs having average particle diameter of 12.70 nm was synthesized by citrate reduction route. The formation of AuNSs was confirmed by (ultraviolet–visible) UV–vis and high-resolution transmission electron microscopy (HRTEM) data. Self-assembly monolayer approach was conducted to immobilize AuNSs on the 3-mercaptopropyl trimethoxysilane (MPTMS)-functionalized surface of the TOFs. The AuNSs immobilization on TMMFs could improve the sensitivity up to 122 %. Besides sensitive to RI changes, the sensors were also excellent in terms of repeatability and reversibility performances. Finally, this paper described the amplitude modality-based RI sensing mechanism due to evanescent wave and LSPR effects.

Studies of Synthesis Temperature Effects on Cubic Lithated-Spinel to Layered Phase Transformation and Electrochemical Performance of LiMn0.5Ni0.5O2 Cathode Materials

Recently, our group has reported a novel Li-ion battery cathode, ‘LT-LiMn0.5Ni0.5O2’, where LT refers to its relatively low synthesis temperature (400 °C). By collecting high energy X-ray diffraction and high-angle, annular-dark-field (HAADF) scanning-transmission electron microscopy (STEM) data, we confirm that the LT-LiMn0.5Ni0.5O2 features a unique partially disordered rock salt structure with predominant lithiated-spinel-like character. The electrochemical data indicates that the Li/LT-LiMn0.5Ni0.5O2 cells shows good cycle stability when operate between 2.5-5.0V. The 1st cycle specific discharge capacity was determined to be 225mAh/g. Two distinct voltage plateaus can be identified at approximately at ~4.6 V and ~3.5 V during discharge. The ~1 voltage separation of the plateaus is caused by the octahedral and tetrahedral site energy difference during lithium extraction and insertion.1 The discovery of LT-LiMn0.5Ni0.5O2 not only expand the compositional space for the known lithated-spinel family but also provide a practical way to increase the operational capacity of traditional spinels such like LiMn2O4 and LiMn1.5Ni0.5O2.2-5 It is well known that when synthesized at 900°C, LiMn0.5Ni0.5O2 features a layered structure.6 The existence of lithated-spinel like LiMn0.5Ni0.5O2 at low temperature (400°C) immediately raise another question: How does the synthesis temperature affect the structure and electrochemical performance of LiMn0.5Ni0.5O2? We synthesized a series of different temperature of LiMn0.5Ni0.5O2 powders. By collecting high energy X-ray diffraction and high-resolution transmission electron microscopy (HR-TEM) data, we confirm that, the LiMn0.5Ni0.5O2 exhibits a lithated spinel → disordered layered → ordered layered structure transformation as temperature increase from 400-900 °C. The Rietveld refinements results also reveals a gradual decrease of the Li/Ni exchange ratio accompanied by the synthesis temperature changes. The evolution of specific discharge capacity for different temperature LiMn0.5Ni0.5O2 shows a parabola-like curve behavior with the lowest discharge capacity at 700 °C. This unique behavior is likely to be related to the diffusion channels reconstruction along with the structure changes. 3D diffusion channels are incorporated with 2D diffusion channels at low temperature (400°C) for lithated-spinel LiMn0.5Ni0.5O2. Within the middle temperature range (500°C-700°C), the 3D channels destroy rapidly while 2D diffusion channels are not well established due to the highly disorder ratio resulting in a decrease of capacity. At higher temperature (800-900°C), the 2D diffusion channels are more well established enabling an increase of the capacity. Shi, B.; Gim, J.; Li, L.; Wang, C.; Vu, A.; Croy, J. R.; Thackeray, M. M.; Lee, E., LT-LiMn 0.5 Ni 0.5 O 2: a unique co-free cathode for high energy Li-ion cells. Chemical Communications 2021, 57 (84), 11009-11012.Thackeray, M. M.; Lee, E.; Shi, B.; Croy, J. R., Review–From LiMn2O4 to Partially-Disordered Li2MnNiO4: The Evolution of Lithiated-Spinel Cathodes for Li-Ion Batteries. Journal of The Electrochemical Society 2022, 169 (2), 020535.Gummow, R.; Thackeray, M.; David, W.; Hull, S., Structure and electrochemistry of lithium cobalt oxide synthesised at 400 C. Materials research bulletin 1992, 27 (3), 327-337.Lee, E.; Blauwkamp, J.; Castro, F. C.; Wu, J.; Dravid, V. P.; Yan, P.; Wang, C.; Kim, S.; Wolverton, C.; Benedek, R., Exploring lithium-cobalt-nickel oxide spinel electrodes for≥ 3.5 V Li-ion cells. ACS applied materials & interfaces 2016, 8 (41), 27720-27729.Lee, E.; Kwon, B. J.; Dogan, F.; Ren, Y.; Croy, J. R.; Thackeray, M. M., Lithiated Spinel LiCo1–x Al x O2 as a Stable Zero-Strain Cathode. ACS Applied Energy Materials 2019, 2 (9), 6170-6175.Yang, X.-Q.; McBreen, J.; Yoon, W.-S.; Grey, C. P., Crystal structure changes of LiMn0. 5Ni0. 5O2 cathode materials during charge and discharge studied by synchrotron based in situ XRD. Electrochemistry communications 2002, 4 (8), 649-654

The role of parent lithology in nanoscale clay-mineral transformations in a subtropical monsoonal climate

Abstract Clay minerals are among the most important reactive components of soil systems, acting as a bridge linking organic and inorganic components. Lithology is a key factor in clay-mineral genesis and transformation, yet it has received scant attention to date at the nanoscale. Inferences regarding pedogenic clay-mineral transformations based on X-ray diffraction (XRD) are sometimes speculative, whereas mineralogic relationships documented by high-resolution transmission electron microscopy (HRTEM) are more robust due to direct evidence from lattice-fringe observations. In this contribution, the mineralogical and geochemical characteristics of four soils derived from different parent rock types (a gneiss, an Fe-rich siltstone, a sandstone, and a dolostone) from subtropical China were determined using HRTEM, XRD, and geochemical elemental data. The predominance of 2:1 clay minerals and kaolinite in the investigated soils is typical of subtropical climatic settings. Lattice-fringe images suggest the prevalence of topotactic transformations during clay-mineral alteration. Two distinct alteration pathways were observed in the investigated soils, one starting with chlorite and the other with illite, with convergence of mineralogic compositions toward kaolinite and crystalline iron and aluminum (oxyhydr)oxides. In the early stages of weathering, chlorite transformed into expandable clays through a continuous, solid-state mechanism with corrensite and/or randomly interstratified chlorite-vermiculite/chlorite-smectite as intermediate products. Unlike chlorite, which tends to form a 1:1 regularly interstratified phase, the weathering of illite commonly starts at layer edges. Under subtropical monsoonal climates, the precursor minerals in host rocks and aeolian materials determine the starting composition and, to a certain extent, the trajectory of clay-mineral transformation over time. With advanced weathering, mineralogic convergence toward kaolinite and Fe/Al-(oxyhydr)oxides tends to obscure the initial substrate composition. This study advances our understanding of the role of parent lithology in clay-mineral evolution at the nanoscale.

Large-scale Automated Analysis of High-Resolution Transmission Electron Microscopy Data Assisted by Deep Learning Neural Networks

Large-scale Automated Analysis of High-Resolution Transmission Electron Microscopy Data Assisted by Deep Learning Neural Networks

A comparative study of Cu-anchored 0D and 1D ZnO nanostructures for the reduction of organic pollutants in water.

In this work, Cu NPs were loaded at a fixed percentage (5 wt%) on 1D, (1D + 0D) and 0D ZnO nanostructures to investigate the effect of the support morphology on the reduction of organic pollutants in water. The synthesized materials were characterized by high-resolution transmission electron microscopy (HR-TEM), ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), N2 adsorption–desorption and X-ray photoelectron spectroscopy (XPS). The results reveal that the loading of Cu NPs decreases the optical band gap, and a slight change in the crystallite sizes increases the specific surface area value of the nanocomposites. The TEM images reveal that 1D ZnO has an average width of 44.7 nm and an average length of 211 nm, while 0D ZnO has an average diameter of 54.5 nm. The HR-TEM and XPS data confirm the loading of metallic Cu NPs on the surface of the ZnO nanostructures. The pure ZnO and nanocomposites were tested for 4-nitrophenol (4-NP) reduction in the presence of NaBH4 at room temperature. The obtained results show that pure ZnO nanostructures have no catalytic performance, while the nanocomposites showed good catalytic activities. The catalytic reduction efficiency of 4-NP was found to follow the order of Cu/0DZnO > Cu/(1D + 0D)ZnO > Cu/1DZnO. The complete reduction of 4-NP has been observed to be achievable within 60 s using the Cu/0DZnO nanocomposite, with a kapp value of 8.42 min−1 and good recyclability of up to five cycles. This nanocomposite was then applied in the reduction of organic dyes in water; it was found that the reduction rate constants for the methylene blue, Congo red, and acriflavine hydrochloride dyes were 1.4 min−1, 1.2 min−1, and 3.81 min−1, respectively. The high catalytic performance of this nanocomposite may be due to the small particle size, high specific surface area, and the high dispersion of Cu NPs on the surface of ZnO.

Janus Layers in the TiSe2–TiS2 System

Our experimental results indicate the formation of extended ordered S–Ti–Se layers (Janus layers) in the Ti(Se1–xSx)2 system. The presence of these layers is observed as a folding of the typical Fermi surface of TiS2 and TiSe2. High-resolution transmission electron microscopy (HRTEM) allows us to observe these layers by a typical rotation of the moiré fringe images. Analysis of the dependence of the electromotive force of the electrochemical cell on the S:Se ratio, angle-resolved photoelectron spectroscopy, resonant photoelectron spectroscopy, Fermi surface mapping, and HRTEM data allows us to conclude that the structure of the solid solution consists of S–Ti–Se and TiCh2 (Ch = S or Se) Janus layers.

Quasi-freestanding graphene on SiC(0001) via cobalt intercalation of zero-layer graphene

Modification of the electronic and crystal structure of zero-layer graphene grown on $6H$-SiC(0001) after Co intercalation is reported. Using a wide range of techniques including angle-resolved photoelectron spectroscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, low-energy electron diffraction, we found that zero-layer graphene on SiC transforms into graphene monolayer as a result of cobalt intercalation. The Dirac cone of $\ensuremath{\pi}$ band characteristic of quasi-freestanding graphene is observed. In combination with high-resolution transmission electron microscopy and atomic force microscopy data, we conclude that ultrathin silicide $\mathrm{CoSi}\text{/}{\mathrm{CoSi}}_{2}$ structure is formed between graphene and SiC substrate. Investigation of magnetic properties reveals ferromagnetic behavior with open hysteresis loop. The results of this work are the basis for further implementation of magneto-spin-orbit graphene on a semiconducting substrate and are important for the future application of such graphene in spintronics.

A study of γ-Al2O3 from the viewpoint of 3D nanostructure

In this work, we investigate commercially available γ-Al2O3 oxides with regard to their nanostructure. A deep analysis of high-resolution transmission electron microscopy data as well as total X-ray scattering data, including both Bragg peaks and defect-related diffuse scattering, is performed. The atomistic models of 3D nanostructured γ-Al2O3 nanoparticles are constructed and validated by the Debye function analysis and atomic pair distribution function analysis. It is revealed that the specific defects lying on {100} and {111} planes fragment the γ-Al2O3 nanoparticles into nanosized crystalline blocks. The interblock interfaces are partially coherent because the planar defects locally disturb the cation sublattice and keep anion sublattice intact. The observed shape and mutual arrangement of the primary crystalline blocks are specified by the revealed planar defects. The work shows that the γ-Al2O3 oxides can differ in the density of the defects causing the particle nanostructuring. The proposed models of 3D nanostructure complement the recent crystallographic models of γ-Al2O3 structure by providing further insights into the nature of non-spinel cations. The non-spinel cations are concentrated near the interblock interfaces formed by the planar defects.

Application of pair distribution function analysis to structural investigation of alumina supported MoS2 catalysts

Total X-ray scattering and atomic pair distribution analysis (PDF) were used to study structure of anisotropic two-dimensional (2D) MoS2 nanoparticles in MoS2/Al2O3 catalysts. We demonstrated that PDF analysis can be used not only to determine the atomic ordering but also to assess the geometry and size of 2D MoS2 nanoparticles in the catalysts. In refinement of PDFs, discrete atomistic modeling was used to account for finite size and shape effects. The values of MoS2 slab length elucidated from the PDF data were smaller than values obtained from high-resolution transmission electron microscopy (HRTEM) data due to defectiveness and multi-domain structure of the MoS2 nanoparticles. It was suggested that increase in the temperature of heat treatment of oxide precursors leads to decrease in deformation of the MoS2 nanoparticles in sulfided catalysts.

Machine Learning Pipeline for Segmentation and Defect Identification from High-Resolution Transmission Electron Microscopy Data.

In the field of transmission electron microscopy, data interpretation often lags behind acquisition methods, as image processing methods often have to be manually tailored to individual datasets. Machine learning offers a promising approach for fast, accurate analysis of electron microscopy data. Here, we demonstrate a flexible two-step pipeline for the analysis of high-resolution transmission electron microscopy data, which uses a U-Net for segmentation followed by a random forest for the detection of stacking faults. Our trained U-Net is able to segment nanoparticle regions from the amorphous background with a Dice coefficient of 0.8 and significantly outperforms traditional image segmentation methods. Using these segmented regions, we are then able to classify whether nanoparticles contain a visible stacking fault with 86% accuracy. We provide this adaptable pipeline as an open-source tool for the community. The combined output of the segmentation network and classifier offer a way to determine statistical distributions of features of interest, such as size, shape, and defect presence, enabling the detection of correlations between these features.

Formation of β-Be3N2 nanocrystallites in Be-implanted GaN

A small Be ion dose of 5 × 1014 cm−2 was implanted in a 2 μm thick GaN epilayer at an energy of 50 keV. The sample was characterized by high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy techniques after a post-implantation rapid thermal annealing (RTA) treatment. The HRTEM images show the crystallographic (1 1 0) and (0 0 2) planes of β-Be3N2. Two characteristic parallelograms drawn in Fast Fourier transform (FFT) image support the formation of β-Be3N2 nanocrystallites in RTA treated sample. Two Raman peaks at 168 and 199 cm−1 are observed in the Raman spectrum of the sample that are assigned to β-Be3N2 on the basis of group theory and HRTEM data. The Raman peak at 168 cm−1 is found close to the K point in the first Brillouin zone of β-Be3N2 while the peak at 199 cm−1 is assigned as a combination mode of the fundamental Raman modes of β-Be3N2.

Causal analysis of competing atomistic mechanisms in ferroelectric materials from high-resolution scanning transmission electron microscopy data

Machine learning has emerged as a powerful tool for the analysis of mesoscopic and atomically resolved images and spectroscopy in electron and scanning probe microscopy, with the applications ranging from feature extraction to information compression and elucidation of relevant order parameters to inversion of imaging data to reconstruct structural models. However, the fundamental limitation of machine learning methods is their correlative nature, leading to extreme susceptibility to confounding factors. Here, we implement the workflow for causal analysis of structural scanning transmission electron microscopy (STEM) data and explore the interplay between physical and chemical effects in a ferroelectric perovskite across the ferroelectric–antiferroelectric phase transitions. The combinatorial library of the Sm-doped BiFeO3 is grown to cover the composition range from pure ferroelectric BFO to orthorhombic 20% Sm-doped BFO. Atomically resolved STEM images are acquired for selected compositions and are used to create a set of local compositional, structural, and polarization field descriptors. The information-geometric causal inference (IGCI) and additive noise model (ANM) analysis are used to establish the pairwise causal directions between the descriptors, ordering the data set in the causal direction. The causal chain for IGCI and ANM across the composition is compared and suggests the presence of common causal mechanisms across the composition series. Ultimately, we believe that the causal analysis of the multimodal data will allow exploring the causal links between multiple competing mechanisms that control the emergence of unique functionalities of morphotropic materials and ferroelectric relaxors.

The growth processes and crystal structure of Ca silicides films grown by MBE at 500 °C on a Si(001) substrate

This article investigates the growth of calcium (Ca) silicides on the Si(001)2x1 surface during molecular beam epitaxy (MBE) from two sources of Ca and Si with a variable flow ratio from three to 10 at a fixed substrate temperature of 500 °C. According to atomic force microscopy (AFM), the grown films consist of grains with a mutually perpendicular orientation and have pronounced grain boundaries with an inhomogeneous relief. The best crystalline qualities of the films, both CaSi and CaSi2, were confirmed for the minimum ratio (about 3.0) of Ca to Si deposition flows by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) data in both cross-sections and in planar sections. At the same time, according to XRD and HRTEM data, for all formed films over the CaSi(010) layer on Si(001), the growth of hR3-CaSi2 was observed with epitaxial relationships: hR3-CaSi2(001)//CaSi(010)//Si(001). An analysis of these studies showed that calcium monosilicide (CaSi) is the first silicide phase in the Ca–Si(001) system at 500 °C due to (1) the maximum modulus of its heat of formation, (2) a decrease in the Ca accommodation coefficient to silicon less than unity and the formation of a mixture close to CaSi, (3) a better matching between the parameters of the CaSi(010) plane lattice and the Si(001) plane lattice, and (4) lower CaSi (010)/Si (001) interface energy compared with the CaSi2(001)/Si(001) system. It is assumed that the formation of CaSi2 occurs in the subsurface region of the growing film at 500 °C due to increased diffusion of Ca atoms into the Si substrate and increased intergranular diffusion of Si atoms, which leads to the formation of a mixture with the CaSi2 composition. Both factors create conditions for the crystallization of CaSi2 on the surface of the CaSi layer at Т = 500 оС. The epitaxial ordering of CaSi2 on the CaSi surface and the decrease in the energy of hR3-CaSi2(001)/CaSi(010) interface is associated with small distortions of their lattices during superstructural matching, which is proved by modeling their matching.

Enhanced performance of a novel superparamagnetic g-C3N4/NiO/ZnO/Fe3O4 nanohybrid photocatalyst for removal of esomeprazole: Effects of reaction parameters, co-existing substances and water matrices

In this work, a hydrothermal route was adopted for the construction of a nanohybrid of g-C3N4/NiO/ZnO/Fe3O4. For determination of the structure, morphology and composition, the nanohybrid photocatalyst was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray (EDX). UV–visible (UV–vis) spectrophotometry and photoluminescence spectroscopy were performed on the nanohybrid sample for proper assessment of its optical properties. The superparamagnetic nature of the nanocomposite was evaluated with vibrating sample magnetometer (VSM) techniques. XRD, TEM, HRTEM, XPS and EDX data revealed the formation of the intended nanocomposite. The band gap of the nanohybrid using Tauc plot was determined to be ~ 2.8 eV. This confirmed a modification of the band edges of the individual moieties- ZnO, NiO and g-C3N4. A remarkable reduction in the rate of electron-hole recombination was thus induced via enhanced charge separation as evident from photoluminescence studies of the nanocomposite. An efficient photocatalytic activity of the heterojunction that had originated from the synergistic effects of the individual moieties was therefore observed. The hybrid photocatalyst was found to cause ~ 95.05% degradation of esomeprazole, an emerging organic water pollutant, under visible light irradiation within 70 min. The photodegradation followed pseudo-first order kinetics with a specific reaction rate of 0.06616 min−1. Additionally, the effects of various reaction parameters, other species and water matrices were studied. The current work fulfills its objective of designing a hybrid nano-photocatalyst that is active in the visible region of electromagnetic spectrum, demonstrates the ability to cause disintegration of emerging, non-biodegradable organic water pollutant, has superior photostability, and is magnetically retrievable.

Strain Effects on the Band Gap and Diameter of CdSe Core and CdSe/ZnS Core/Shell Quantum Dots at Any Temperature

We present the results of an experimental study about strain effects on the core band gap and diameter of spherical bare CdSe core and CdSe/ZnS core/shell quantum dots (QDs) synthesized by using a colloidal technique at varying temperatures. Structural characterizations were made by using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) techniques. Optical characterizations were made by using UV-Vis absorption and fluorescence emission spectroscopies. The XRD analysis suggests that the synthesized bare CdSe core and CdSe/ZnS core/shell QDs have zinc blende crystal structure. HRTEM results indicate that the CdSe core and CdSe/ZnS QDs have average particle sizes about 3.50 nm and 4.84 nm, respectively. Furthermore, compressive strain causes an increase (decrease) in the core band gap (diameter) of spherical CdSe/ZnS core/shell QDs at any temperature. An elastic strain-modified effective mass approximation (EMA) predicts that there is a parabolic decrease (increase) in the core band gap (diameter) of QDs with temperature. The diameter of spherical bare CdSe core and CdSe/ZnS core/shell QDs calculated by using the strain-modified EMA, with core band gap extracted from absorption spectra, are in excellent agreement with the HRTEM data.

Orientation Relationships upon the Structural Transformation of Monoclinic and Cubic Phases in Silver Sulfide

The orientation relationships between the low-temperature monoclinic semiconductor acanthite α-Ag2S and the high-temperature body-centered argentite β-Ag2S are determined based on high-temperature X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) data on silver sulfide. It is found that, in contrast to acanthite, the possible distances between silver atoms in cubic argentite are too small to allow Ag atoms to occupy metal sublattice sites with a probability of 1. It is shown that the (010) and (001) atomic planes of acanthite are parallel to the (1 $$\bar {1}$$ 0) and (221) planes of argentite, respectively. The found orientation relationships between acanthite and argentite are important for understanding the physical operation of the Ag2S/Ag heteronanostructure, which is considered as a potential basis for designing resistive switches and nonvolatile memory devices.