Temperature Sensing Properties of Biocompatible Yb/Er-Doped GdF3 and YF3 Mesocrystals

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.

Tetracycline Removal through the Synergy of Catalysis and Photocatalysis by Novel NaYF4:Yb,Tm@TiO2-Acetylacetone Hybrid Core-Shell Structures

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.

Enhancement of ZnO@RuO2 bifunctional photo-electro catalytic activity toward water splitting

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 RuO₂ and lowering the amount of RuO₂ by adding abundant and multifunctional ZnO. A ZnO@RuO₂ 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@RuO₂ 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@RuO₂ composites toward HER and OER in both electrolytes. The improved bifunctional catalytic activity of the ZnO@RuO₂ composite by annealing was discussed and attributed to the reduced number of bulk oxygen vacancies and the increased number of established heterojunctions.

Crystal Structure and Electrical Properties of Ruthenium-Substituted Calcium Copper Titanate

This paper reports a detailed study of crystal structure and dielectric properties of ruthenium-substituted calcium-copper titanates (CaCu₃Ti_4-xRu_xO₁₂, CCTRO). A series of three samples with different stoichiometry was prepared: CaCu₃Ti_4-xRu_xO₁₂, x = 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 Ti⁴⁺ or Ru⁴⁺ ions are placed in B crystallographic position in AA'₃B₄O₁₂ (CaCu₃Ti_4-xRu_xO₁₂) unit cell, the crystal structure remains cubic with Im3¯ symmetry. Slight increases in the unit cell parameters, cell volume and interatomic distances indicate that Ru⁴⁺ ions with larger ionic radii (0.62 Å) than Ti⁴⁺ (0.605 Å) are incorporated in the CaCu₃Ti_4-xRu_xO₁₂ 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 CaCu₃Ti_4-xRu_xO₁₂ samples on their electrical properties was determined by impedance and dielectric measurements. Results of dielectric measurements indicate that one atom of ruthenium per CaCu₃Ti_4-xRu_xO₁₂ 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.

Simultaneous enhancement of natural sunlight- and artificial UV-driven photocatalytic activity of a mechanically activated ZnO/SnO2 composite

Mechanical milling of commercial ZnO and SnO₂ was used to produce a ZnO/SnO₂ composite with a high density of surface defects; in particular, zinc interstitials (Zn_i) and oxygen vacancies (V_O).

The effect of Sn for Ti substitution on the average and local crystal structure of BaTi1−xSnxO3(0 ≤x≤ 0.20)

The effect of Sn for Ti substitution on the crystal structure of a perovskite, barium titanate stannate (BTS), BaTi1−xSnxO3forx= 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 BaTiO3provokes a phase transition from tetragonal for 0 ≤x≤ 0.07 to cubic forx= 0.12, 0.15 and 0.20. The coexistence of tetragonal (P4mm) and cubic (Pm\overline 3m) 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.