Reusable water oxidation catalyst with dual active center for enhanced water oxidation: Iridium oxide nanoparticles immobilized on monodisperse-porous Mn5O8 microspheres

A reusable catalyst with dual active center for chemical water oxidation is synthesized for the first time by immobilization of iridium oxide nanoparticles (IrO₂ NPs) on monodisperse-porous manganese oxide microspheres acting both catalytic active center and support. Individual catalytic activity of manganese oxide microspheres is explained by multiple oxidation states of manganese which are capable of forming oxidative oxygen species. Monodisperse-porous microspheres in the form of Mn₅O₈, MnO₂ and Mn₂O₃ are used for synthesis of different catalysts and the highest activity in water oxidation is observed with the catalyst synthesized using Mn₅O₈ microspheres. The catalytic activity is correlated with the total Mn(II) and Mn(III) percentage of manganese oxide type selected for composite catalyst. The oxygen evolution up to 244 μmol is achieved in 30 min with the catalyst synthesized using Mn₅O₈ microspheres. Maximum TON and TOF numbers are obtained as 298 and 557 h^?1 with excellent reusability.     

Photoluminescence and decay characteristics of cerium,gallium and vanadium - containing borate-based bioactive glass powders for bioimaging applications

Biomaterials having photoluminescent properties play a crucial role in real-time bioimaging after in vivo implantation. In this study, photoluminescence properties and decay characteristics of the borate-based 13–93B3 glasses containing different concentrations of cerium, gallium, and vanadium oxides were investigated for biomedical applications. The borate-based bioactive glass powders were prepared using melt-quench technique and size reduction was performed through planetary ball milling. Bioactivity of the prepared powders was investigated in simulated body fluid at 37 °C under static conditions. The photoluminescent properties and decay kinetics of the as-prepared and the SBF-treated bioactive glass powders were analyzed by steady-state and time-resolved photoluminescence measurements. Results revealed that the cerium activated glasses exhibited an intense luminescence centered at 538 nm. Broad-band emission of the gallium and vanadium doped samples was centered at 440 and 572 nm, respectively. All of the SBF-treated glasses exhibited enhanced lifetimes and bi-exponential decays both in nanosecond and microsecond regime measurements. It was concluded that depending on the dopant concentration, bioactive glass particles prepared in the study showed remarkable photoluminescence and have potential to be used in bioimaging applications.     

Enzymatic degradation behavior and cytocompatibility of silk fibroin–starch–chitosan conjugate membranes

The objective of this study was to investigate the influence of silk fibroin and oxidized starch conjugation on the enzymatic degradation behavior and the cytocompatability of chitosan based biomaterials. The tensile stress of conjugate membranes, which was at 50 Megapascal (MPa) for the lowest fibroin and starch composition (10 weight percent (wt.%)), was decreased significantly with the increased content of fibroin and starch. The weight loss of conjugates in α-amylase was more notable when the starch concentration was the highest at 30 wt.%. The conjugates were resistant to the degradation by protease and lysozyme except for the conjugates with the lowest starch concentration. After 10 days of cell culture, the proliferation of osteoblast-like cells (SaOS-2) was stimulated significantly by higher fibroin compositions and the DNA synthesis on the conjugate with the highest fibroin (30 wt.%) was about two times more compared to the native chitosan. The light microscopy and the image analysis results showed that the cell area and the lengths were decreased significantly with higher fibroin/chitosan ratio. The study proved that the conjugation of fibroin and starch with the chitosan based biomaterials by the use of non-toxic reductive alkylation crosslinking significantly improved the cytocompatibility and modulated the biodegradation, respectively.     

Improved magnetic properties of bismuth ferrite ceramics by La and Gd co-substitution

Increased magnetic properties of La and Gd substituted bismuth ferrite (Bi_0.9La_0.1Fe_1-xGd_xO₃) (BLFGO) ceramics are reported. Considering perovskite structure of bismuth ferrite (BiFeO₃), Bi and Fe sites were partially substituted by La and Gd, respectively. These materials were synthesized by conventional solid state reaction method. Crystal structure and phase purity were confirmed by X-ray diffraction and Raman scattering spectroscopy at room temperature. A considerable improved ferromagnetic properties with double remnant magnetization of 0.184 emu/g was observed by increasing Gd ratio up to 5%. With different ionic sizes and due to magnetic moment of Gd, an induced deformation of spin cycloid structure had thereby resulted in net magnetization. Also, we monitor some decrease in dielectric loss upon La and Gd substitutions. Additionally, these ceramics showed significant magnetoelectric coupling. Such improvements on magnetic, insulation, and magnetoelectric properties demonstrated the potential of BLFGO for possible multiferroic device applications.     

Determination of trace element contents of baby foods from Turkey

The levels of trace elements in different types of baby foods consumed in Turkey were determined by flame and graphite furnace atomic absorption spectrometry. Dry, wet and microwave digestion procedures were compared and the microwave digestion method was found to be the best. The accuracy of the method was ensured by using a standard reference material (NIST-SRM 8418 Wheat Gluten). The levels of elements in analyzed samples were found to be under legal limits. The range of the investigated elements were 0.52–4.38 μg/g, 0.22–7.20 μg/g, 1.02–67.5 μg/g, 0.92–37.2 μg/g, 0.12–0.32 μg/g, 2.02–68.8 μg/kg, 10.7–66.8 μg/kg, 0.05–10.3 μg/g, 2.67–25.4 μg/kg for Cu, Mn, Fe, Zn, Se, Cr, Al, Ni and Co, respectively.     

Electrical and memory window properties of Sr0.8-xBaxBi2.2Ta2-yZryO9 ferroelectric gate in metal-ferroelectric-insulator-semiconductor structure

Electrical characteristics of Sr_0.8-xBa_xBi_2.2Ta_2-yZr_yO₉ ferroelectric films grown on HfO₂/Si wafers by sol–gel spin coating technique were investigated from the viewpoint of application as ferroelectric gates in metal-ferroelectric-insulator-semiconductor (MFIS) stacks. It was observed that the leakage current density level was 10^-8 A/cm² under 14?V for moderate doping ratio. Determined memory windows from C-V characteristics of Sr_0.8Bi_2.2Ta₂O₉ (SBT) and Sr_0.8-xBa_xBi_2.2Ta_2-yZr_yO₉ (x?=?0.04, 0.08, 0.12 and y?=?0.1, 0.2, 0.3) are 0.59, 0.65, 0.75, and 0.86?V at gate sweeping bias of 5?V, respectively. Some part of electronic properties of Sr_0.8-xBa_xBi_2.2Ta_2-yZr_yO₉ with the objective to enhance memory window up to 45?% were discussed. It was interpreted that defects which are formed in Ba and Zr modified SBT affected the electronic processes like leakage current, memory window and charge trapping.     

Sub-nanomolar sensing of ionic mercury with polymeric electrospun nanofibers

Ethyl cellulose (EC) based electrospun nanofibers were exploited for sub-nanomolar level optical chemical sensing of ionic mercury. An azomethine ionophore was used as Hg (I) and Hg (II) sensing material. Ethyl cellulose nanofibers with varying amounts of the ionic liquid; 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄) were prepared and characterized. The nanofibers were fabricated by electrospinning technique. The offered chemosensor allow determination of mercury ions in a large linear working range between 1.0 × 10⁻¹⁰ and 1.0 × 10⁻⁴ mol L⁻¹. Limit of detection was found to be 0.07 nM which makes this technique alternative to cold-vapor atomic absorption spectrometry (CV-AAS), flame emission methods and to inductively coupled plasma-mass spectrometry (ICP-MS).     

Total Antioxidant Capacity Assay Using Optimized Ferricyanide/Prussian Blue Method

The existing ferricyanide/Prussian blue assay of reducing capacity measurement was optimized so as to obtain a more reproducible, linear and additive response from antioxidants. The modification involved the simultaneous use of ferricyanide and iron(III) to regulate more favorable redox conditions for a greater variety of antioxidants. Prussian blue precipitation was hindered with the addition of sodium dodecyl sulfate, and the optimal pH was adjusted to 1.7 to maintain the redox activity of ferric ion while preventing its hydrolysis. Incubation of the reaction mixture at room temperature for 30 min enabled more complete oxidations than observed in the conventional ferricyanide method. The order of trolox equivalent antioxidant capacities was quercetin > rosmarinic acid > gallic acid > ferulic acid ≥ catechin > caffeic acid ≥ rutin ≥ ascorbic acid ≈ trolox. Synthetic antioxidant mixtures gave the theoretically expected total antioxidant capacities conforming to Beer’s law. The assay was nonresponsive to simple sugars and citric acid (which are not true antioxidants) but responsive to biologically important thiols which are not oxidized by other Fe(III)-based assays. The assay was used in real sample solutions by using the method of standard additions to green tea, nettle, and sage, and validated against other similar antioxidant assays.     

Novel solid phase extraction procedure for gold(III) on Dowex M 4195 prior to its flame atomic absorption spectrometric determination

A method for solid phase extraction (SPE) of gold(III) using Dowex M 4195 chelating resin has been developed. The optimum experimental conditions for the quantitative sorption of gold(III), pH, effect of flow rates, eluent types, sorption capacity and the effect of diverse ions on the sorption of gold(III) have been investigated. The chelating resin can be reused for more than 100 cycles of sorption-desorption without any significant change in sorption of gold(III) ions. The recovery values for gold(III) and detection limit (LOD) of gold were greater than 95% and 1.61 microg L(-1), respectively. The preconcentration factor was 31. The relative standard deviation of the method was <5%. The adsorption capacity of the resin was 8.1 mg g(-1). The proposed method has been applied for the determination of gold(III) in some real samples including water, soil and sediment samples.