Taking advantage of the flexibility of the apatite structure, nano- and micro-particles of hydroxyapatite (HAp) were doped with different combinations of rare earth ions (RE
= Gd, Eu, Yb, Tm) to ...achieve a synergy among their magnetic and optical properties and to enable their application in preventive medicine, particularly diagnostics based on multimodal imaging. All powders were synthesized through hydrothermal processing at T ≤ 200 °C. An X-ray powder diffraction analysis showed that all powders crystallized in P6
/m space group of the hexagonal crystal structure. The refined unit-cell parameters reflected a decrease in the unit cell volume as a result of the partial substitution of Ca
with smaller RE
ions at both cation positions. The FTIR analysis additionally suggested that a synergy may exist solely in the triply doped system, where the lattice symmetry and vibration modes become more coherent than in the singly or doubly doped systems. HAp:RE
optical characterization revealed a change in the energy band gap and the appearance of a weak blue luminescence (λ
= 370 nm) due to an increased concentration of defects. The "up"- and the "down"-conversion spectra of HAp:Gd/Yb/Tm and HAp:Gd/Eu powders showed characteristic transitions of Tm
and Eu
, respectively. Furthermore, in contrast to diamagnetic HAp, all HAp:RE
powders exhibited paramagnetic behavior. Cell viability tests of HAp:Gd/Yb/Tm and HAp:Gd/Eu powders in human dental pulp stem cell cultures indicated their good biocompatibility.
Novel hybrid core-shell structures, in which up-converting (UC) NaYF4:Yb,Tm core converts near-infrared (NIR) to visible (Vis) light via multiphoton up-conversion processes, while anatase ...TiO2-acetylacetonate (TiO2-Acac) shell ensures absorption of the Vis light through direct injection of excited electrons from the highest-occupied-molecular-orbital (HOMO) of Acac into the TiO2 conduction band (CB), were successfully synthesized by a two-step wet chemical route. Synthesized NaYF4:Yb,Tm@TiO2-Acac powders were characterized by X-ray powder diffraction, thermogravimetric analysis, scanning and transmission electron microscopy, diffuse-reflectance spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence emission measurement. Tetracycline, as a model drug, was used to investigate the photocatalytic efficiencies of the core-shell structures under irradiation of reduced power Vis and NIR spectra. It was shown that the removal of tetracycline is accompanied by the formation of intermediates, which formed immediately after bringing the drug into contact with the novel hybrid core-shell structures. As a result, ~80% of tetracycline is removed from the solution after 6 h.
Nanopowders of up-conversion SrGd2O4 orthorhombic (Pnma) phase co-doped with different Yb3+ (1, 2.5 and 5 at%) and constant Er3+ (0.5 at%) ions were successfully prepared via sol-gel assisted ...combustion. Rietveld refinement indicated unit cell lattice parameters increase with Yb3+ and Er3+ ions doping. Scanning transmission electron microscopy with corresponding energy-dispersive X-ray spectroscopy revealed that obtained powders are composed of agglomerated nanoparticles that have a uniform distribution of all constituting elements. Photoluminescence measurements implied intensification of the up-conversion (UC) emission in the visible part of spectrum with the increase of Yb3+ content, which is followed by a significant change in the green to red ratio. Two-photon UC processes are established as a result of Er3+ f-f electronic transitions: green emission at 523 and 551 nm (2H11/2, 4S3/2 → 4I15/2) as well as a red emission at 661 nm (4F9/2 → 4I15/2). The highest value of absolute quantum yield of 0.055% is determined for SrGd2O4 nanoparticles doped with 0.5 at% of Er3+ and co-doped with 5 at% of Yb3+ (λexc = 976 nm, power density 200 W/cm2).
•Up-conversion SrGd2O4:Yb, Er nanoparticles are prepared via sol-gel combustion.•Random distribution of Yb over two Gd sites in Pnma structure is determined.•Two photon up-conversion (green and red) is affected by the Yb/Er ratio.•Quantum yield of 0.055 % is measured for radiation densities over 200 W/cm2.
This paper reports a detailed study of crystal structure and dielectric properties of ruthenium-substituted calcium-copper titanates (CaCu
Ti
Ru
O
, CCTRO). A series of three samples with different ...stoichiometry was prepared: CaCu
Ti
Ru
O
,
= 0, 1 and 4, abbreviated as CCTO, CCT3RO and CCRO, respectively. A detailed structural analysis of CCTRO samples was done by the Rietveld refinement of XRPD data. The results show that, regardless of whether Ti
or Ru
ions are placed in
crystallographic position in
'
O
(CaCu
Ti
Ru
O
) unit cell, the crystal structure remains cubic with Im3¯ symmetry. Slight increases in the unit cell parameters, cell volume and interatomic distances indicate that Ru
ions with larger ionic radii (0.62 Å) than Ti
(0.605 Å) are incorporated in the CaCu
Ti
Ru
O
crystal lattice. The structural investigations were confirmed using TEM, HRTEM and ADF/STEM analyses, including EDXS elemental mapping. The effect of Ru atoms share in CaCu
Ti
Ru
O
samples on their electrical properties was determined by impedance and dielectric measurements. Results of dielectric measurements indicate that one atom of ruthenium per CaCu
Ti
Ru
O
unit cell transforms dielectric CCTO into conductive CCT3RO while preserving cubic crystal structure. Our findings about CCTO and CCT3RO ceramics promote them as ideal tandem to overcome the problem of stress on dielectric-electrode interfaces in capacitors.
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.
Catalytic materials are the greatest challenge for the commercial application of water electrolysis (WEs) and fuel cells (FCs) as clean energy technologies. There is a need to find an alternative to ...expensive and unavailable platinum group metal (PGM) catalysts. This study aimed to reduce the cost of PGM materials by replacing Ru with RuO
2
and lowering the amount of RuO
2
by adding abundant and multifunctional ZnO. A ZnO@RuO
2
composite in a 10:1 molar ratio was synthesized by microwave processing of a precipitate as a green, low-cost, and fast method, and then annealed at 300°C and 600°C to improve the catalytic properties. The physicochemical properties of the ZnO@RuO
2
composites were investigated by X-ray powder diffraction (XRD), Raman and Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), UV-Vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. The electrochemical activity of the samples was investigated by linear sweep voltammetry in acidic and alkaline electrolytes. We observed good bifunctional catalytic activity of the ZnO@RuO
2
composites toward HER and OER in both electrolytes. The improved bifunctional catalytic activity of the ZnO@RuO
2
composite by annealing was discussed and attributed to the reduced number of bulk oxygen vacancies and the increased number of established heterojunctions.
The effect of Sn for Ti substitution on the crystal structure of a perovskite, barium titanate stannate (BTS), BaTi1−xSnxO3 for x = 0, 0.025, 0.05, 0.07, 0.10, 0.12, 0.15 and 0.20, was investigated. ...The powders were prepared by the conventional solid‐state reaction technique. The structural investigations of the BTS powders were done at room temperature by X‐ray powder diffraction (XRD), transmission electron microscopy (TEM), high‐resolution TEM (HRTEM), selected‐area electron diffraction (SAED) and Raman spectroscopy analyses. Rietveld refinement of XRD data indicates that gradual replacement of titanium by tin in BaTiO3 provokes a phase transition from tetragonal for 0 ≤x≤ 0.07 to cubic for x = 0.12, 0.15 and 0.20. The coexistence of tetragonal (P4mm) and cubic (Pmm) crystal phases was established in powder with nominal composition BaTi0.9Sn0.1O3. The crystal phases determined by Rietveld refinement were confirmed by HRTEM and SAED analyses. The crystal structures of the BTS powders at short‐range scale were studied by Raman spectroscopy, which shows tetragonal (P4mm) and a small fraction of orthorhombic (Pmm2) crystal phases for all the examined BTS powders, implying a lower local ordering when compared to the average symmetry.
•Titanate nanotubes (TTNT) were modified with 3-aminopropyltriethoxysilane (APTES).•Effects of TTNT sodium content and solvent on APTES grafting efficiency were studied.•Aqueous ethanol was a more ...efficient reaction medium for functionalization of TTNT.•Within aqueous ethanol TTNT with low sodium content were more efficiently grafted.•Grafting of APTES on TTNT surface occurs through Ti–O–Si primary chemical bonding.
One of the major challenges in the development of nanocomposites based on a polymer matrix and highly polar ceramic nanofillers is the lack of the compatibility between these two components. In order to improve the chemical interaction between titanate nanotubes (TTNT) and polymer matrix, such as nylon 11,3-aminopropyltriethoxysilane (APTES) was grafted onto TTNT. The effects of the TTNT chemical composition i.e. sodium content and solvent type on the grafting silane efficiency were thoroughly studied through CHN elemental analysis, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), surface area and zeta potential measurements. The present study brings evidences supporting aqueous ethanol as more efficient reaction medium for TTNT functionalization with APTES, independent of the sodium content of nanotubes, when compared with pure water. It is also worth noting that within aqueous ethanol medium, TTNT with low sodium content are more efficiently grafted than TTNT with high sodium content. Successful APTES grafting decreases concentration of the hydroxyl groups on TTNT surfaces and enables its future application for the fabrication of nylon 11 nanocomposites.
PDF
