This study refers to the application of in-situ electrochemical synthesis as an alternative method to improve the properties of porous materials against harmful external agents that deteriorate them. ...It is oriented to an understanding of the effects of crystallisation on the pore structure of different compounds commonly used in the restoration and conservation of porous materials (historical ceramics, building walls, sculptures, or biomedical applications). It analyses the microstructural, chemical details, and stability of the neo-formed phases that modify the pore network. The electrochemical synthesis was carried out at ambient temperature (20 °C), over high porous sandstone for crystallising Ca carbonate, Mg carbonate, Ca phosphate, and Ca oxalate compounds. Based on the neo-formed minerals, a comparison was made depending on their specific properties defining how they affected the pore structure. The characterisation included polarised light optical microscopy, environmental and field-emission scanning electron microscopy, digital image analysis, cathodoluminescence (CL-ESEM),energy-dispersive X-ray spectroscopy, and X-ray microdiffraction. Aragonite, hydromagnesite, hydroxyapatite, and whewellite were identified as the majority phases depending on the treatment. Phase transformation, dehydration, and dissolution-re-precipitation processes suggested different degrees of stability, including aragonite/calcite (CaCO3 treatment) and hydromagnesite/magnesite (MgCO3 treatment) transformations and simultaneous crystallisation of brushite/hydroxyapatite ((Ca3(PO4)2 treatment). Electrocrystallisation induced changes in inter-granular porosity, the development of secondary porosity inherent to the minerals, and differences in pore cementation depending on its mineralogy. Among the treatments, Mg carbonate reduced porosity most effectively, followed in descending order by calcium carbonate and calcium phosphate, being the calcium oxalate the less effective.
This paper reports on the synthesis of Ce-doped ZnO (CZO) nanoparticles (NPs) by an alternative polyol method at low temperature. The method, facile and rapid, uses acetate-based precursors, ethylene ...glycol as solvent, and polyvinylpyrrolidone as capping agent. The effects of the Ce-doping concentration (ranging from 0 to 8.24 atomic%) on the structural, morphological, compositional, optical, luminescence, and photocatalytic properties of the NPs were investigated by several techniques. The structural findings confirmed that the CZO NPs have a typical hexagonal wurtzite-type structure with a preferred orientation along the (101) plane. The results obtained by Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) revealed that the NPs size decreased (from ~30 to ~16 nm) with an increase in the Ce-doping concentration. Energy Dispersive X-Ray Spectroscopy (EDS) and High Resolution Transmission Microscopy (HRTEM) results confirmed the incorporation of Ce ions into the ZnO lattice. Ce-doping influences the photoluminescence (PL) emission compared to that of pure ZnO. The PL emission is related to the presence of different kinds of defects, which could take part in charge transfer and/or trapping mechanisms, hence playing an essential role in the photocatalytic activity (PCA). In fact, in this work we report an enhancement of PCA as a consequence of Ce-doping. In this sense, the best results were obtained for samples doped with 3.24 atomic%, that exhibited a photocatalytic degradation efficiency close to 99% after 60 min ultraviolet (UV) illumination, thus confirming the viability of Ce-doping for environmental applications.
In this work, we aim to highlight the increasing interest in semiconductors, particularly ZnO. A revision of the evolution of the scientific production on three selected topics has been conducted. As ...an indicator of scientific production, the number of publications indexed in the Web of Science Data Base has been used. The search terms selected range from the general to the particular: semiconductors, oxide semiconductors, and ZnO. The period considered is from 1 January 1900 to 6 June 2023. The importance of doping processes in tailoring the properties of these materials, and the relevance of the most recently derived applications are also revised. Since many of the most recent applications that have been developed or are under development refer to optoelecronic properties, doping with rare earth elements has a central role. This was the reason behind choosing the system ZnO doped with Rare Earth elements (Eu, Gd, and Ce) and codoped with Ru to illustrate the materials’ tuning potential of doping processes. Morphology, crystal structure, and luminescent properties have been investigated. Upon doping, both the Near Band Edge and the Deep Level emissions show a remarkable difference due to the change in the relative weight of the components constituting these bands. The spectra in all cases extend over the whole visible range, with a main emission in the violet-blue region corresponding to the Near Band Edge, and a broad band extending from the blue-green to orange-red region associated with the presence of different defects.
Y0.8−xGdxF3:Yb/Er mesocrystals with a biocompatible surface and diverse morphological characteristics were successfully synthesized using chitosan-assisted solvothermal processing. Their structural ...properties, studied using X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning and transmission electron microscopy and energy dispersive X-ray analysis, were further correlated with the up-conversion emission (λexc = 976 nm) recorded in function of temperature. Based on the change in the visible green emissions originating from the thermally coupled 2H11/2 and 4S3/2 levels of Er3+, the corresponding LIR was acquired in the physiologically relevant range of temperatures (25–50 °C). The detected absolute sensitivity of about 0.0042 °C−1, along with the low cytotoxicity toward both normal human lung fibroblasts (MRC-5) and cancerous lung epithelial (A549) cells, indicate a potential for use in temperature sensing in biomedicine. Additionally, their enhanced internalization in cells, without suppression of cell viability, enabled in vitro labeling of cancer and healthy cells upon 976 nm laser irradiation.
Preface of Special Issue: AMPT2015 Milosevic, Olivera; Naito, Makio; Rabanal, María Eugenia
Advanced powder technology : the international journal of the Society of Powder Technology, Japan,
01/2017, Letnik:
28, Številka:
1
Journal Article
Polycrystalline fine powders of yttrium aluminate doped with Ce3+ were synthesised by spray pyrolysis of a polymeric precursor, which was obtained by dissolving the corresponding nitrates in a ...solution of ethylenediaminetetraacetic acid (EDTA) in ethylene glycol (EG). Aerosol decomposition was performed at 550 °C followed by an additional thermal treatment (900–1100 °C). The yield of either a single yttrium aluminium perovskite (YAP) phase or a single yttrium aluminium garnet (YAG) phase was investigated as a function of the predefined yttrium/aluminium ratio, the cerium doping concentration, the processing temperature, and the thermal‐treatment regime, which included the variation of the heating and cooling rates (dT/dt), the residence time (τ), and the atmosphere. Changes in the composition and structure of the precursor during thermal decomposition were investigated by thermogravimetric and differential thermal analysis (TGA/DTA) and FTIR spectroscopy. The particle morphology and structure were analysed by a combination of scanning electron microscopy and energy‐dispersive X‐ray spectroscopy (SEM/EDS) and by high‐resolution transmission electron microscopy (HR‐TEM). The structural refinement was based on the phase identification performed by X‐ray powder diffraction (XRPD). The emission spectra were recorded within the range 325–800 nm by applying excitation wavelengths of 297 (YAP) and 450 nm (YAG). The employed synthesis conditions assured the formation of spherical, non‐agglomerated particles with well‐developed surfaces and diameters between 200 and 800 nm. For a predefined Y/Al ratio of 1:1, lower processing temperatures combined with longer heat treatments under stationary conditions resulted in a multiphase system, composed of YAP, YAG, and monoclinic yttrium aluminate (YAM) phases. However, a short heat treatment with a high heating rate (200 °C/min) at higher temperatures results in the formation of a kinetically favoured pure YAP hexagonal phase. On the other hand, for a predefined Y/Al ratio of 3:5, the generation of a thermodynamically favoured pure YAG phase has been confirmed, regardless of the applied heat‐treatment conditions. Although incomplete, Ce3+ introduction into the host matrix has been detected by XRPD and luminescence measurements.
Highly spherical, non‐agglomerated, polycrystalline yttrium aluminium perovskite (YAP) and yttrium aluminium garnet (YAG) particles were synthesised by spray pyrolysis of a polymeric precursor solution. Chelating agents enable the generation of pure phases under a strictly defined thermal regime. Ce3+ introduction into the host matrix was confirmed by X‐ray powder diffraction (XRPD) and luminescence studies.
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•NaYF4:Yb3+/Er3+ up-converting particles (UCPs) are processed via solvothermal route.•Either PEG or PVP are used as structure directing and coating agents.•There is α- and ...β-NaYF4:Yb3+/Er3+ phase coexistence in PEG assisted processing.•PVP leads to the prominent hexagonal β-NaYF4:Yb3+/Er3+ phase formation.•Yellow and green emissions are achieved in PEG and PVP coated NaYF4:Yb3+/Er3+ UCPs.
Owing to their unique optical properties, up-converting rare earth fluorides have attracted extensive attention in recent years. Varieties of synthesis procedures which generate nano- and micro-crystals with controllable compositions have been reported. In the vast majority, surfactants, complexing agents and solvents play essential role in controlling particles morphology and surface characteristics. Here we report on a rapid solvothermal synthesis (200°C, 2h) of either PEG or PVP capped NaYF4:Yb3+/Er3+ particles. Their structural, morphological and luminescence characteristics have been studied based on X-ray powder diffractometry (XRPD), Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), high resolution transmission electron microscopy (HRTEM) and photoluminescence measurements. Both polymers proved to be a good structure directing agents enabling generation of the well crystalline polymer coated up-converting particles with efficient emissions in visible spectrum. It was shown that generation of the hexagonal P63/m β-NaYF4:Yb3+/Er3+ phase with the most efficient green emission (CIE 0.31, 0.66) is enhanced when PVP is used during synthesis, while promotion of the cubic Fm-3m α-NaYF4:Yb3+/Er3+ phase that has a yellowish spectral output (CIE 0.41, 0.56) was observed in the particles produced in the presence of PEG. Beneficial effect on the luminescence intensity was observed with additional particles annealing in argon atmosphere.
Photocatalytic activity of electric-arc furnace flue dusts Alcaraz, Lorena; Urbieta, Ana; Rabanal, María Eugenia ...
Journal of materials research and technology,
March-April 2020, 2020-03-00, 2020-03-01, Letnik:
9, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Two electric-arc furnace flue dusts, a waste generated during the steel production process, were characterized and their photocatalytic activity was assessed. Chemical composition by X-ray ...fluorescence (XRF) analysis identified that both dusts were principally formed by iron, zinc and chromium oxides. Structural characterization carried out by X-ray diffraction patterns (XRD), and micro-Raman measurements demonstrated that ZnFe2O4 (zinc ferrite), FeCr2O4 (chromite) and ZnO (zincite) are present in both waste dusts as majority phases. Scanning electron microscopy (SEM) images showed that both dusts are formed by nanoparticles with a globular and octahedral morphology characteristic of the type of flue dusts formation and the obtained phases. Cathodoluminescence (CL) spectra show the characteristics bands of spinel structure (ZnFe2O4) and Fe3+ emission. X-ray photoelectron spectroscopy (XPS) measurements indicate that Fe ions could be present in 2+ and 3+ oxidation state in the spinel structure, while zinc and chromium ions are in 2+ and 3+, respectively. In addition, the photocatalytic experiments demonstrated that the analyzed samples could be useful as photocatalyzed showing a degradation percentage above 75 %.
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•Several types of Zn/Mn oxide were produced from the spent alkaline batteries.•Photocatalysis experiments are carried out.•Degradation of methylene blue and Rhodamine B is evaluated ...under UV radiation.•All the compounds studied show photocatalytic properties.
Several phases with variable stoichiometry ZnxMn3−xO4 (with x=0.25, 0.85 and 1) and ZnO have been obtained from the black mass, a widely generated residue of wasted alkaline batteries. The obtained samples have been characterized by X-ray diffraction (XRD) and Raman spectroscopy showing results consistent with the stoichiometry obtained from chemical analysis. The study of the degradation of methylene blue (MB) and rhodamine B (RhB) under UV radiation demonstrates the photocatalytic behavior in all samples obtained, reaching degradation percentages higher than 70% and 50%, respectively.
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•Yb3+/Er3+ doped YF3 and NaYF4 particles are processed via EDTA assisted hydrothermal route.•Particles exhibit compositional and morphological dependence on the nucleation rate.•With ...course of processing time transformation of α→β→α NaYF4:Yb3+/Er3+ is observed.•Up-conversion is phase dependent and can be tuned from green to yellowish-orange.
In this feature article, we highlight our works on compositional and structural dependence of up-converting rare earth (RE) fluorides obtained through ethylenediamine tetraacetic acid (EDTA) assisted hydrothermal synthesis. Various nanostructures were obtained by tuning of experimental conditions, such as precursor’s concentration, degree of doping, reaction time and solvent used during synthesis. We correlated in detail the structural, morphological and optical properties of YF3 and NaYF4 compounds co-doped with Yb3+ and Er3+ (introduced in total mol% of 8 and 20). For this purpose, X-ray powder diffraction, scanning and transmission electron microscopy, energy dispersive X-ray and Furrier transform infrared spectroscopy, as well as, the photoluminescence spectra and decay times were recorded and analyzed. The particle size and phase content were found to be dependent on the nucleation rate, which, in turn, was governed by the precursor concentration, degree of doping and solvent type. The transformation from cubic to hexagonal NaYF4:Yb3+/Er3+ phase was found to be sensitive to the reaction time and precursors concentration, while the crystallization of orthorhombic YF3:Yb3+/Er3+ phase is achieved through lowering of dopants concentration or by changing of solvent during hydrothermal treatment. The up-conversion photoluminescence demonstrated morphology and crystal phase dependence and is found to be superior in microcrystalline samples, independent on their phase composition.
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