Electron Spectroscopic Imaging Research Articles

Magnetic properties and identification of Griffiths-like phase in Mn2FeSi Heusler antiferromagnet

Materials having low magnetic moments with high spin polarization are promising for spintronic applications. Among these materials, Mn-based Heusler alloys are attractive candidates due to the antiferromagnetic alignment of Mn atoms. Theoretical calculations predict Mn2FeSi to have an inverse Heusler (XA) structure with a magnetic moment of 2 μB/f.u. However, no experimental reports exist on a phase-pure composition of this material. In this study, our first principle calculations demonstrate the effect of various types of disorder on the electronic and magnetic properties of Mn2FeSi. The B2-type disorder seems responsible for forming secondary phases in stoichiometric Mn2FeSi. We verify this by conducting theoretical calculations for different configurations of the atomic disorders permissible in a Heusler phase. We substantiate our theoretical investigation with an experimental study wherein we first stabilize the phase-pure Mn2FeSi in an inverse Heusler structure by substituting Al at the Si site. Amongst the prepared Mn2FeSi1−xAlx (x = 0, 0.1, 0.15), the compositions with x = 0 and 0.15 show a clear presence of a secondary phase, identified as the β − Mn phase with a lattice constant of 6.24 Å. Analysis of the back-scattered electron spectroscopy images and X-ray diffraction patterns confirm the formation of a pure Heusler phase in x = 0.1 composition. Magnetization measurements reveal an antiferromagnetic behavior in all compositions, with a N é el temperature of ∼ 50 K. However, deviation from Curie-Weiss law was observed for x = 0.1, suggesting competing magnetic interactions. Further investigation into the magnetic properties of this composition displays signatures of Griffiths phase, possibly caused by antisite disorder in the compound.

True-to-scale DNA-density maps correlate with major accessibility differences between active and inactive chromatin

Chromatin compaction differences may have a strong impact on accessibility of individual macromolecules and macromolecular assemblies to their DNA target sites. Estimates based on fluorescence microscopy with conventional resolution, however, suggest only modest compaction differences (∼2-10×) between the active nuclear compartment (ANC) and inactive nuclear compartment (INC). Here, we present maps of nuclear landscapes with true-to-scale DNA densities, ranging from <5 to >300 Mbp/μm3. Maps are generated from individual human and mouse cell nuclei with single-molecule localization microscopy at ∼20nm lateral and ∼100nm axial optical resolution and are supplemented by electron spectroscopic imaging. Microinjection of fluorescent nanobeads with sizes corresponding to macromolecular assemblies for transcription into nuclei of living cells demonstrates their localization and movements within the ANC and exclusion from theINC.

Using elemental staining and mapping techniques for simultaneous visualization of biological structures in the nucleus by multichannel electron microscopy.

Transmission electron microscopy (TEM) has been essential in defining the structural organization of the cell due to its ability to image cell structures at molecular resolution. However, the absence of colour has made it very difficult to compare the distributions and relationships of two or more types of biomolecules simultaneously if they lack clear morphological distinctions. Furthermore, single-channel information limits functional analysis, particularly in the nucleoplasm, where fibrillar material could be chromatin, ribonucleic acid or protein. Where specific stains exist to discriminate among these molecules, they cannot be combined because conventional TEM is a single-channel technology. A potential path around this barrier is through electron spectroscopic imaging (ESI). ESI can map the distributions of chemical elements within an ultrathin section. Here, we present methods to stain specific molecules with elements that ESI can visualize to enable multichannel electron microscopy.

Direct Visualization of Homogeneous Chemical Distribution in Functional Polyradical Microspheres.

It is demonstrated that the postfunctionalization of solid polymeric microspheres can generate fully and throughout functionalized materials, contrary to the expectation that core-shell structures are generated. The full functionalization is illustrated on the example of photochemically generated microspheres, which are subsequently transformed into polyradical systems. Given the all-organic nature of the functionalized microspheres, characterization methods with high analytical sensitivity and spatial resolution are pioneered by directly visualizing the inner chemical distribution of the postfunctionalized microspheres based on characteristic electron energy loss signals in transmission electron microscopy (TEM). Specifically, ultrasonic ultramicrotomy is combined successfully with electron energy loss spectroscopy (EELS) and electron spectroscopicimaging (ESI) during TEM. These findings open a key avenue for analyzing all-organic low-contrast soft-matter material structures, while the specifically investigated system concomitantly holds promise as an all-radical solid-state functional material.

Ultrastructure of pathologic deposits and cellular inclusions

Intra- and extracellular depositions and inclusions occur in awide range of diseases with exogenous (e.g. infectious, environmental and toxic) or endogenous (e.g. genetic, inflammatory, neoplastic and degenerative) aetiology. The noxious agent and the pathogenesis influence the organ of manifestation, the subcellular localisation and the ultrastructural appearance of the depositions. Whereas some of the inclusions like pathogens, foreign material (e.g. asbestos) or microvilli have an almost pathognomonic morphology, other inclusions are present in lower amounts also under normal conditions (e.g. lipid vacuoles and glycogen). Therefore, the interpretation of ultrastructural findings makes acorrelation with the histological features and clinical constellation necessary. Auxiliary investigations by electron energy loss spectroscopy (EELS) or electron spectroscopic imaging (ESI) provide additional information about the chemical composition of the material and are therefore especially helpful for the identification of foreign substances. This review focuses on aselection of deposits and inclusions relevant to diagnostic pathology.

A light and electron microscopical study on the resting cyst of the tintinnid Schmidingerella (Alveolata, Ciliophora) including a phylogeny-aware comparison

Resting cysts protect ciliates against adverse environmental conditions. The morphology and ultrastructure of resting cysts has been described in very few Oligotrichea, a group of mainly marine planktonic ciliates. The present study provides the first ultrastructural data for loricate choreotrichids, applying light and electron microscopy on the cysts of the tintinnid Schmidingerella meunieri (Kofoid and Campbell, 1929) Agatha and Strüder-Kypke, 2012. The morphology of live cysts and the wall ultrastructure of cryofixed cysts were morphometrically analysed. The resting cyst is roughly flask-shaped, broadening to a slightly concave, laterally protruding anterior plate. An emergence pore closed by a skull cap-shaped papula is directed to the bottom of the lorica on the opposite side of the cyst. The cyst wall consists of an ectocyst, mesocyst, and endocyst differing in thickness, structure, and nitrogen concentration as revealed by conventional transmission electron microscopy, electron energy loss spectroscopy, and electron spectroscopic imaging. The cysts of S. meunieri belong to the kinetosome-resorbing type, which also occurs in the majority of hypotrich ciliates. Two main features (flask-shape and presence of an emergence pore) are shared with the closely related aloricate choreotrichids and oligotrichids, distinguishing the Oligotrichea from the hypotrich and the more distantly related euplotid ciliates.

Ag nanoparticles anchored on NiO octahedrons (Ag/NiO composite): An efficient catalyst for reduction of nitro substituted phenols and colouring dyes

The development of an efficient sustainable catalyst for effective removal of hazardous chemicals, viz. nitrophenols and organic dyes, from wastewater is a challenging task. Herein, facile synthesis of Ag/NiO composites by anchoring Ag nanoparticles (NPs) on NiO octahedrons with different amounts of Ag NPs (AN-5% (5% Ag), AN-10% (10% Ag) and AN-15% (15% Ag)) has been demonstrated. SEM (scanning electron microscopic) and TEM (transmission electron spectroscopic) images ensured the proper anchoring of spherical Ag NPs (particle size = 16.54 ± 1.88 nm) on octahedron particles of NiO, which was also ensured by XPS (X-ray photoelectron spectroscopy) analysis. Moreover, the resulting composites have an average surface area (49–52 m2g‒1) and pore size (2.39–2.26 nm). All three synthesized Ag/NiO composites (100 μL) catalyzed the complete reduction of para-np (4-nitrophenol: 0.1587 mM) within 2–3 min in the presence of 0.04 M NaBH4. Among them, AN-5% has been chosen because of the lowest anchored Ag (5%) to obtain the optimized catalyst's amount (50 μL) and concentration of para-np (0.1587 mM). AN-5% also exhibited excellent catalytic activity towards different nitro substituted phenols, viz. ortho-np (2-nitrophenol), meta-np (3-nitrophenol), para-np (4-nitrophenol) and tri-np (2,4,6-trinitrophenol). AN-5% displayed ∼100% catalytic efficiency for reducing meta-np in 2 min with the apparent first order rate constant (kapp) and normalized rate constant (Knor) as 1.99 s−1 and 398.14 s−1 g−1, respectively. Additionally, AN-5% (29.41 μg mL−1) reduced >95% of the colouring dyes (10 ppm) such as CONG-R (congo red: 95% in 6 min), METH-O (methyl orange: 97.5% in 7 min), METH-B (methylene blue: 98.3% in 10 min) and RHOD-B (rhodamine B: 99.2% in 5 min). AN-5% not only demonstrated catalytic reduction towards individual pollutants, but also showed excellent activity for reduction of the mixtures of nitrophenols/dyes and for treatment of simulated industrial effluent samples (EFF1, EFF2) and a real industrial sample (textile dye-bath effluent). AN-5% can also be reused up to several cycles with almost same efficiency and followed the Langmuir-Hinshelwood apparent first order kinetics model.

Synthesis, characterization and functional evaluation of gold nanoparticles prepared using Dovyalis abyssinica leaf extracts as reducing and surface capping agent

Green synthesis of nanoparticles using plants and microorganisms is biologically safe, cost effective, and environmentally friendly technology. Gold nanoparticles (Au NPs) were synthesized using aqueous extracts of leaves of Dovyalis abyssinica as reducing and surface capping agent and the catalytic activity, antibacterial action and antioxidant potential of the synthesized AU NPs were evaluated. Firstly, HAuCl4 was synthesized in the laboratory from metallic gold and hydrochloric acid using a predesigned method. Secondly, Au NPs was synthesized by mixing HAuCl4 and the plant extract at 45 oC with a digestion time of 1 h. The size of the nanoparticles was modulated by varying the ratio of the plant extract and HAuCl4 with known concentrations. The synthesized Au NPs showed strong absorption around 540 nm which lies in the characteristic absorption region of Au metal nanoparticles (520–580 nm). The X-ray diffraction spectrum of the synthesized Au NPs showed characteristic crystalline structures of gold. The scanning electron spectroscopy images of the synthesized Au NPS revealed the presence of mixed shapes predominantly of irregular shapes and a particle size analyzer displayed an average size of 63.13 nm. The fourier-transform infrared spectrum of Au NPS confirmed the presence of amine, carbonyl and hydroxyl functional groups as surface capping molecules. Although the synthesized Au NPs showed poor bacterial growth inhibition activity on two selected bacteria, it demonstrated excellent free radical scavenging activity against 2, 2-Diphenyl-2-picrylhydrazyl (DPPH) radical and good catalytic activity for degrading bromothymol blue and methyl red compounds. In contrast to the hexane and ethyl acetate extracts, the aqueous fraction was identified as powerful reducing fraction for the synthesis of Au NPs in this experiment.

Heme Detoxification in the Malaria Parasite: A Target for Antimalarial Drug Development.

Over the last century, malaria deaths have decreased by more than 85%. Nonetheless, there were 405 000 deaths in 2018, mostly resulting from Plasmodium falciparum infection. In the 21st century, much of the advance has arisen from the deployment of insecticide-treated bed nets and artemisinin combination therapy. However, over the past few decades parasites with a delayed artemisinin clearance phenotype have appeared in Southeast Asia, threatening further gains. The effort to find new drugs is thus urgent. A prominent process in blood stage malaria parasites, which we contend remains a viable drug target, is hemozoin formation. This crystalline material consisting of heme can be readily seen when parasites are viewed microscopically. The process of its formation in the parasite, however, is still not fully understood.In early work, we recognized hemozoin formation as a biomineralization process. We have subsequently investigated the kinetics of synthetic hemozoin (β-hematin) crystallization catalyzed at lipid-aqueous interfaces under biomimetic conditions. This led us to the use of neutral detergent-based high-throughput screening (HTS) for inhibitors of β-hematin formation. A good hit rate against malaria parasites was obtained. Simultaneously, we developed a pyridine-based assay which proved successful in measuring the concentrations of hematin not converted to β-hematin.The pyridine assay was adapted to determine the effects of chloroquine and other clinical antimalarials on hemozoin formation in the cell. This permitted the determination of the dose-dependent amounts of exchangeable heme and hemozoin in P. falciparum for the first time. These studies have shown that hemozoin inhibitors cause a dose-dependent increase in exchangeable heme, correlated with decreased parasite survival. Electron spectroscopic imaging (ESI) showed a relocation of heme iron into the parasite cytoplasm, while electron microscopy provided evidence of the disruption of hemozoin crystals. This cellular assay was subsequently extended to top-ranked hits from a wide range of scaffolds found by HTS. Intriguingly, the amounts of exchangeable heme at the parasite growth IC50 values of these scaffolds showed substantial variation. The amount of exchangeable heme was found to be correlated with the amount of inhibitor accumulated in the parasitized red blood cell. This suggests that heme-inhibitor complexes, rather than free heme, lead to parasite death. This was supported by ESI using a Br-containing compound which showed the colocalization of Fe and Br as well as by confocal Raman microscopy which confirmed the presence of a complex in the parasite. Current evidence indicates that inhibitors block hemozoin formation by surface adsorption. Indeed, we have successfully introduced molecular docking with hemozoin to find new inhibitors. It follows that the resulting increase in free heme leads to the formation of the parasiticidal heme-inhibitor complex. We have reported crystal structures of heme-drug complexes for several aryl methanol antimalarials in nonaqueous media. These form coordination complexes but most other inhibitors interact noncovalently, and the determination of their structures remains a major challenge.It is our view that key future developments will include improved assays to measure cellular heme levels, better in silico approaches for predicting β-hematin inhibition, and a concerted effort to determine the structure and properties of heme-inhibitor complexes.

A Long-Term Stable Sensor Based on Fe@PCN-224 for Rapid and Quantitative Detection of H2O2 in Fishery Products.

Hydrogen peroxide (H2O2) has been reported to be used for the illegal treatment of fishery products in order to obtain “fake” freshness. Residues of H2O2 in food may be of toxicology concern. In this study, a nonenzymatic sensor was developed based on Fe@PCN-224 metal–organic frameworks wrapped by Nafion to detect H2O2 concentration. The hybrid structure of Fe@PCN-224 was fabricated by incorporated free FeIII ions into the center of PCN-224, which was ultra-stable due to the strong interactions between Zr6 and the carboxyl group. Scanning electron spectroscopy images exhibited that Nafion sheets crossed together on the surface of Fe@PCN-224 nanoparticles to form a hierarchical and coherent structure for efficient electron transfer. Electrochemical investigations showed that the Fe@PCN-224/Nafion/GCE possessed good linearity from 2 to 13,000 μM (including four orders of magnitude), low detection limits (0.7 μM), high stability in continuous monitoring (current remained nearly stable over 2300 s) and in long-term measurement (current decreased 3.4% for 30 days). The prepared nanohybrid modified electrode was effectively applied to H2O2 detection in three different fishery products. The results were comparable to those measured using photometrical methods. The developed electrochemical method has a great potential in detecting the illegal management of fishery products with H2O2.

A Diverse Range of Hemozoin Inhibiting Scaffolds Act on Plasmodium falciparum as Heme Complexes.

A diverse series of hemozoin-inhibiting quinolines, benzamides, triarylimidazoles, quinazolines, benzimidazoles, benzoxazoles, and benzothiazoles have been found to lead to exchangeable heme levels in cultured Plasmodium falciparum (NF54) that ranged over an order of magnitude at the IC50. Surprisingly, less active compounds often exhibited higher levels of exchangeable heme than more active ones. Quantities of intracellular inhibitor measured using the inoculum effect exhibited a linear correlation with exchangeable heme, suggesting formation of heme-inhibitor complexes in the parasite. In an effort to confirm this, the presence of a Br atom in one of the benzimidazole derivatives was exploited to image its distribution in the parasite using electron spectroscopic imaging of Br, an element not naturally abundant in cells. This showed that the compound colocalized with iron, consistent with its presence as a heme complex. Direct evidence for this complex was then obtained using confocal Raman microscopy. Exchangeable heme and inhibitor were found to increase with decreased rate of killing, suggesting that slow-acting compounds have more time to build up exchangeable heme complexes. Lastly, some but not all compounds evidently cause pro-oxidant effects because their activity could be attenuated with N-acetylcysteine and potentiated with t-butyl hydroperoxide. Collectively, these findings suggest that hemozoin inhibitors act as complexes with free heme, each with its own unique activity.

Test and Characterization of a New Post-column Imaging Energy Filter

Abstract Spectrometers and energy filters for electron energy-loss spectroscopy and electron spectroscopic imaging in transmission electron microscopy have a long history. The first commercial post-column imaging energy filter became available already in the early 1990s. Since then this technique has become an important tool for analytic electron microscopy. Nevertheless, the imaging performance of post-column energy-filters is undoubtedly inferior compared to in-column energy filters and their principal design is clearly restricted by practical constraints we found that significant improvements with respect to optical performance and alignment flexibility are still possible compared to the presently available instrumentation. By applying calculation methods originally developed for the design of aberration correctors and spending much care on the precise design of the optical elements and the alignment strategies we could develop a new post-column imaging energy filter with a minimalistic and robust optical design but remarkable optical properties. Compared to other state-of-the-art devices in our design the aberrations determining the energy resolution are reduced by one order of magnitude for the same entrance aperture. Therefore, if desirable, the field of view can be enlarged by more than a factor of two in area while the optical aberrations stay comparable or even better. We describe the principal optical design of the CEOS Energy-Filtering and Imaging Device (CEFID), explain methods for aberration measurement and optical characterization, and finally demonstrate its optical performance by measured imaging and spectroscopy data from two prototype systems.

One-pot synthesized citric acid-modified bimetallic PtNi hollow nanospheres as peroxidase mimics for colorimetric detection of human serum albumin.

The combination of Pt with low-cost transition metal is an effective way to diminish the bulk utilization of costly Pt and to design new nanostructured materials with improved enzyme-like activity. In the present work, citric acid-functionalized platinum-nickel hollow nanospheres (CA@PtNi hNS) were synthesized through a simple one-pot wet chemical method, which involves the galvanic replacement reaction between the Ni nanoparticles and the Pt precursor that leads to the formation of hollow nanostructures. Transmission electron spectroscopic images revealed the uniformity of the CA@PtNi hNS, with an average diameter of 10.3±2nm. Moreover, zeta potential, FTIR, and XPS measurements confirmed the existence of citric acid in the CA@PtNi hNS. During synthesis, the use of citric acid not only facilitates monodispersity but also provides a negative surface charge (-11mV) to the CA@PtNi hNS that electrostatically attracts the 3,3',5,5'-Tetramethylbenzidine (TMB) substrate. As-prepared CA@PtNi hNS possessed excellent peroxidase-like activity due to rich Pt surfaces, large surface area, and heterogeneous interaction between Pt and Ni atoms. Furthermore, a nanozyme-linked immunosorbent assay (NLISA) for human serum albumin (HSA) detection was developed by replacing the enzyme in a standard enzyme-linked immunosorbent assay with CA@PtNi hNS. The CA@PtNi hNS based-NLISA showed sensitive detection of HSA concentrations ranging from 0 to 400ngmL-1 with a LOD of 0.19ngmL-1 and an average of 112% recovery of HSA from the spiked human plasma samples. The outcomes of the present study confirm the applicability of CA@PtNi hNS as substitutes for natural enzymes.

Nano-characterization of silicon-based multilayers using the technique of STEM-EELS spectrum-imaging

Silicon (Si) and its compounds are still actively being used by electronic and solar-energy industries. In this work, we focus on one-stop-instrument (OSI) for the characterization of silicon (Si)-based thin-films namely Si, silicon nitride (SiNx), and silicon oxide (SiO2). The goal of performing the characterization of Si-based compounds with OSI has been achieved by carrying out their nanoscale-characterization (Nano-Characterization) with a modern transmission electron microscope (TEM). The presented results demonstrate that TEM is proven to be a powerful OSI for carrying out the Nano-Characterization of Si-based multilayer stacks. It does that via electron microscopy imaging (EMI), and electron spectroscopic imaging (ESI) routes. The presented results show that while EMI allows imaging the structure and morphology of thin-films at nanoscale, the ESI, by combining imaging and spectroscopy techniques, enables distinguishing the pure Si regions from its oxide and nitride regions. Moreover, for the first time, we show that the ESI is sensitive enough to differentiate the crystalline Si regions from that of amorphous Si ones.

Preparation of natural rubber-OMMT nanocomposites using mechanical mixing and acid free co-coagulation methods: effect of processing method on mechanical properties

The masterbatches were prepared by acid free co-coagulation (AFCC) method in which OMMT was incorporated into natural rubber latex (NRL) or conventional mechanical mixing. Inherent slow coagulation, and drying, stages of the AFCC method were overcome by introducing a novel gelling agent; a combination of two surfactants, namely, Cetyl tri methyl ammonium bromide (CTAB) and Sodium dodecyl sulphate (SDS). Six nanocomposites (A-nanocomposite, C-nanocomposite and M-nanocomposite) were prepared at the OMMT loadings of 2 and 5 phr; of them, two with gelling agent (A-2, A-5) and two without gelling agent (C-2, C-5) using AFCC method and two using mechanical mixing (M-2 &amp; M-5). Controls of them (A-0, C-0 and M-0) were prepared without using OMMT. X-ray diffractograms and scanning electron spectroscopic images showed that a higher amount of aggregated clay structures was present in the M-nanocomposites, and less aggregated clay structures were present in C-nanocomposites. However randomly distributed ordered structures along with exfoliated clay structures were in the A-nanocomposites. Crosslink density and the bound rubber content of the A-nanocomposites were significantly higher than M-nanocomposites but lower than C-nanocomposites. The mechanical properties of the A- nanocomposites and C-nanocomposites were greater than those of the M-nanocomposites at each OMMT loading. The cure time of the A-nanocomposites and C-nanocomposites were also remarkably lowered compared to the M-nanocomposites. It was observed that the effect of the combined gelling agent had no adverse effect on mechanical properties.

Defect Passivation via the Incorporation of Tetrapropylammonium Cation Leading to Stability Enhancement in Lead Halide Perovskite

AbstractImproving the performances of photovoltaic (PV) devices by suppressing nonradiative energy losses through surface defect passivation and enhancing the stability to the level of standard PV represents one critical challenge for perovskite solar cells. Here, reported are the advantages of introducing a tetrapropylammonium (TPA+) cation that combines two key functionalities, namely surface passivation of CH3NH3PbI3 nanocrystals through strong ionic interaction with the surface and bulk passivation via formation of a type I heterostructure that acts as a recombination barrier. As a result, nonencapsulated perovskite devices with only 2 mol% of TPA+ achieve power conversion efficiencies over 18.5% with higher VOC under air mass 1.5G conditions. The devices fabricated retain more than 85% of their initial performances for over 1500 h under ambient conditions (55% RH ± 5%). Furthermore, devices with TPA+ also exhibit excellent operational stability by retaining over 85% of the initial performance after 250 h at maximum power point under 1 sun illumination. The effect of incorporation of TPA+ on the structural and optoelectronic properties is studied by X‐ray diffraction, ultraviolet–visible absorption spectroscopy, ultraviolet photon–electron spectroscopy, time‐resolved photoluminescence, and scanning electron microscopy imaging. Atomic‐level passivation upon addition of TPA+ is elucidated employing 2D solid‐state NMR spectroscopy.

Impact of mineral composition and distribution on the mechanical properties of porous media

Geological sequestration of CO2 in deep saline formations is a promising means of reducing atmospheric CO2 emissions. Once injected, CO2 dissolves into formation brine, lowering pH and creating conditions favorable for mineral dissolution. Cations released from dissolving minerals may create conditions favorable for secondary mineral precipitation, which can result in the long-term mineralogical trapping of injected CO2. These reactions may alter the natural rock mechanical properties, which can affect the safety and efficiency of geological sequestration. This work aims to investigate the impact of mineral composition and distribution on the mechanical properties of porous media. In this study, the mineralogy, mineral distribution, and mechanical properties of samples from Escambia County, AL, are evaluated. The mechanical properties of the rock samples are evaluated using the unconfined compression and indirect tensile tests in the combination with digital image correlation. The mineral composition and distribution are determined through the analysis of scanning electron microscopy backscattered electron and energy dispersive X-ray spectroscopy images of thin sections. These analyses showed that the mechanical properties vary with composition, which may have significant practical consequences for geological sequestration of CO2.

Catalytic activity of surface‐functionalized nanoscale nickel zinc multiferrites: potential vector for water purification

AbstractBACKGROUNDDecontamination of water by means of photocatalysis is seen as a sustainable solution. However, catalysts with low recovery from liquid suspension remain the main predicament that obstructs their industrial applications. To overcome this shortcoming, a methodology is reported here for the functionalization of nanospinel nickel zinc ferrite by cystamine ligand to develop Ni0.5Zn0.5Fe2O4@cystamine magnetic recyclable catalyst for water decontamination applications.RESULTSThe diffraction patterns of bare and functionalized nanoferrites indicated that the cubic inverse spinel structure of the particles was not changed after cystamine functionalization. X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy analyses confirmed the chemical bonding between cystamine and spinel ferrites. The spherical morphology and elemental composition were studied through high‐resolution transmission electron spectroscopy (HRTEM) images and energy‐dispersive X‐ray (EDX) analysis respectively. Deeper understanding of the catalyst's optical behavior and calculation of the energy band gap were achieved by means of photoluminescence spectroscopy. Magnetic saturation values were calculated from vibrating sample magnetometer (VSM) analysis, and almost negligible change was found. A possible photocatalytic mechanism for the removal of organic dye is proposed.CONCLUSIONThe present findings imply that the presence of amine groups on the catalyst surface, good dispersibility stability and outstanding catalytic activity make functionalized nanoferrite a suitable candidate for industrial wastewater treatment. Easy synthesis, easy work‐up and short reaction times are some of the advantages of the methodology. © 2019 Society of Chemical Industry

Photoluminescence studies of a YOF phosphor synthesized by the pyrolysis method

Photoluminescence (PL) studies of praseodymium (Pr3+) doped yttrium oxyfluoride (YOF) samples were investigated for solar cell applications. The PL emission results showed green Pr3+ emission during excitation of a broad band at 250 nm at room temperature. YOF:Pr3+ samples were synthesized by the pyrolysis method with trifluoroacetate as precursor. The X-ray diffraction patterns exhibited a crystalline phase of stoichiometric rhombohedral YOF (space group: R3‾mm (166)) after annealing at 900 °C. The crystallite sizes decreased with an increase in Pr3+ doping concentration. During thermal decomposition from trifluoroacetate to YOF (600 °C to 900 °C), the scanning electron spectroscopy images showed an agglomeration of small particles (<100 nm) that started to melt and agglomerate to form bigger particles with sizes > 500 nm. X-ray photoemission spectroscopy high resolution peak fits for the high Pr3+ doped sample (YOF:0.5% Pr3+) revealed two Pr oxidation states, Pr3+ and Pr4+. Annealing in air caused the formation of a small amount of Pr4+. The PL excitation spectra showed an intense band at 250 nm with weaker bands at 456, 470 and 483 nm. The weaker bands were ascribed to the 4f-4f 3H4–3P2, 3H4–1I6, 3P1 and 3H4–3P0 transition bands of the Pr3+ ion, respectively. The green Pr3+ PL emission was ascribed to the 4f-4f [3P0–3H4] and [3P0–3F2] transitions at 498 nm and 659 nm, respectively. A YOF:Ce3+ sample was synthesized in order to predict the value of the Pr3+ 4f-5d level in the YOF host. The PL excitation and emission results obtained showed that the lowest 4f-5d excitation of Pr3+ in this host has to peak around 250 nm. The 250 nm band was therefore ascribed to the 4f-5d band of Pr3+ in the YOF host. The optimum Pr3+ concentration for the PL emission was recorded for the sample doped with 0.3% of Pr3+. Concentration quenching occurred through a cross relaxation process due to dipole-quadrupole interactions. Near infra-red emission for the 0.3% Pr3+ doped sample during excitation of 250 nm showed multi narrow peaks in the range between 885 nm and 1120 nm that corresponded to the 3P0 → 1G4 and the 1D2 → 3F3, 3F4 transitions. The decay lifetimes were calculated to be in the μs range.

Making Sense of Complex Carbon and Metal/Carbon Systems by Secondary Electron Hyperspectral Imaging.

Carbon and carbon/metal systems with a multitude of functionalities are ubiquitous in new technologies but understanding on the nanoscale remains elusive due to their affinity for interaction with their environment and limitations in available characterization techniques. This paper introduces a spectroscopic technique and demonstrates its capacity to reveal chemical variations of carbon. The effectiveness of this approach is validated experimentally through spatially averaging spectroscopic techniques and using Monte Carlo modeling. Characteristic spectra shapes and peak positions for varying contributions of sp2‐like or sp3‐like bond types and amorphous hydrogenated carbon are reported under circumstances which might be observed on highly oriented pyrolytic graphite (HOPG) surfaces as a result of air or electron beam exposure. The spectral features identified above are then used to identify the different forms of carbon present within the metallic films deposited from reactive organometallic inks. While spectra for metals is obtained in dedicated surface science instrumentation, the complex relations between carbon and metal species is only revealed by secondary electron (SE) spectroscopy and SE hyperspectral imaging obtained in a state‐of‐the‐art scanning electron microscope (SEM). This work reveals the inhomogeneous incorporation of carbon on the nanoscale but also uncovers a link between local orientation of metallic components and carbon form.