Pretreatment by recyclable Fe3O4@Mg/Al-CO3-LDH magnetic nano-adsorbent to dephosphorize for the determination of trace F− and Cl− in phosphorus-rich solutions

The magnetic nano-adsorbent Fe₃O₄@Mg/Al-CO₃-LDH (Mg/Al-type layered double hydroxide) with a CO₃²⁻ interlayer anion has been synthesized successfully on Fe₃O₄ nanoparticles via a urea hydrothermal method. It is confirmed that the nano-adsorbent can adsorb PO₄³⁻ rapidly and efficiently in multi-ion solutions; meanwhile, it did not adsorb any F⁻ and Cl⁻, even with a high amount of the nano-adsorbent or a longer adsorption time. This behaviour is beneficial for applications to remove PO₄³⁻ in phosphorus-rich solutions, and especially can be utilized to determine trace F⁻ and Cl⁻ anions in phosphorus-rich solutions by physical and chemical analysis methods including ion chromatography without serious interference from PO₄³⁻ for trace determinations. Herein, the hydrothermally synthesized Fe₃O₄@Mg/Al-CO₃-LDH was characterized via SEM, TEM, SAED, XRD, FTIR, magnetic hysteresis loop analysis and adsorption–desorption isotherm analysis. The structure and stability, adsorption mechanism, magnetic saturation value, specific surface area, total pore volume, phosphate adsorption capacity and recyclability are discussed. Using the optimized pretreatment conditions, Fe₃O₄@Mg/Al-CO₃-LDH was utilized successfully to adsorb PO₄³⁻ in real samples and determine trace F⁻ and Cl⁻ accurately by ion chromatography; this would be very beneficial for continuous analysis and on-line tests by physical and chemical analysis methods without interference from PO₄³⁻ in phosphorus-rich samples, leaving F⁻ and Cl⁻ even if in a trace content.

Synthesized recyclable Fe₃O₄@Mg/Al-CO₃-LDH magnetic nano-adsorbent is utilized to dephosphorize phosphorous-rich solutions but leave F⁻ and Cl⁻ to be detected chromatographically.     

Zinc(ii)-based coordination polymer encapsulated Tb3+ as a multi-responsive luminescent sensor for Ru3+, Fe3+, CrO42−, Cr2O72− and MnO4−

A zinc(ii)-based coordination polymer (CP), namely [Zn(modbc)₂]_n (Zn-CP) (modbc = 2-methyl-6-oxygen-1,6-dihydro-3,4′-bipyridine-5-carbonitrile), has been synthesized and characterized. Single-crystal structural determination reveals that Zn-CP is a two-dimensional framework structure with tetranuclear homometallic Zn₄(modbc)₄ units cross-linked by modbc. The excellent luminescence as well as good stability of Zn-CP do not enable it to have selective sensing capability for different ions. After encapsulation of Tb³⁺ in Zn-CP, the as-obtained fluorescent functionalized Tb³⁺@Zn-CP maintained excellent luminescence as well as stability, which made it a highly selective and sensitive multiresponsive luminescent sensor for Ru³⁺, Fe³⁺, CrO₄²⁻, Cr₂O₇²⁻, and MnO₄⁻ with high sensitivity, good anti-interference performance, and quick response time (∼10 s). The detection limits are 0.27 μM, 0.57 μM, 0.10 μM, 0.43 μM and 0.15 μM, respectively. A possible sensing mechanism was discussed in detail.

A composite, Tb³⁺@Zn-CP, for sensing Ru³⁺, Fe³⁺, CrO₄²⁻, Cr₂O₇²⁻ and MnO₄⁻ with fast response times was reported.     

Temperature switch of electrochemical Seebeck coefficient of Fe2+/Fe3+via formation of [FeCl4]2−/[FeCl4]−

The electrochemical Seebeck coefficient (α = dV/dT; V and T are the redox potential and temperature, respectively) is important parameter for thermoelectric conversion. Here, we found that α of Fe²⁺/Fe³⁺ in dimethyl sulfoxide (DMSO) with small amount of 19 M LiCl aqueous solution exhibits a crossover behavior from 1.4 mV K⁻¹ (20 °C ≤ T ≤ 40 °C) to ≈0 mV K⁻¹ (50 °C ≤ T ≤ 80 °C). The molar absorption (ε) spectra revealed that the crossover is ascribed to the transformation of the dominant Fe³⁺ complex from [FeL₆]³⁺ (L is solvent molecule) to [FeCl₄]⁻.

Temperature change switches the electrochemical Seebeck coefficient (α) of Fe²⁺/Fe³⁺via transformation of the electrochemically-active redox pair.     

First-principles study of coadsorption of Cu2+ and Cl− ions on the Cu (110) surface

Motivated by the importance of Cl⁻ in the industrial electrolytic Cu plating process, we study the coadsorption of Cl⁻ and Cu²⁺ on the Cu (110) surface using first-principles density functional theory (DFT) calculations. We treat the solvent implicitly by solving the linearized Poisson–Boltzmann equation and evaluate the electrochemical potential and energetics of ions with the computational hydrogen electrode approach. We find that Cl⁻ alone is hardly adsorbed at sufficiently negative electrochemical potentials μ_Cl but stable phases with half and full Cl⁻ coverage was observed as μ_Cl is made more positive. For Cl⁻ and Cu²⁺ coadsorption, we identified five stable phases for electrode biases between −2V < U_SHE < 2V, with two being Cl⁻ adsorption phases, two being Cl⁻ + Cu²⁺ coadsorption phases and one being a pure Cu²⁺ adsorption phase. In general, the free energy of adsorption for the most stable phases at larger |U_SHE| are dominated by the energy required to move electrons between the system and the Fermi level of the electrode, while that at smaller |U_SHE| are largely dictated by the binding strength between Cl⁻ and Cu²⁺ adsorbates on the Cu (110) substrate. In addition, by studying the free energy of adsorption of Cu²⁺ onto pristine and Cl⁻ covered Cu (110), we conclude that the introduction of Cl⁻ ion does not improve the energetics of Cu²⁺ adsorption onto Cu (110).

Free energy of adsorption for the most stable phases predicted by DFT calculations as a function of electrode potential.     

Highly selective fluorescent turn-on–off sensing of OH−, Al3+ and Fe3+ ions by tuning ESIPT in metal organic frameworks and mitochondria targeted bio-imaging

Herein we report a multifunctional high performance metal organic framework (Zn-DHNDC MOF) based chemosensor that displays an exceptional excited state intramolecular proton transfer (ESIPT) tuned fluorescence turn-on–off response for OH⁻, Al³⁺ and Fe³⁺ ions along with mitochondria targeted bio-imaging. Properly tuning ESIPT as well as the hydroxyl group (–OH) allows Zn-DHNDC MOF to optimize and establish chelation enhanced fluorescence (CHEF) and chelation enhanced quenching (CHEQ) based sensing mechanisms. The MOF benefits from acid-base interactions with the ions which generate a turn-on bluish green fluorescence (λ_Em 492 nm) for OH⁻, an intense turn-on green fluorescence (λ_Em 528 nm) for Al³⁺ and a turn-off fluorescence quenching response for Fe³⁺ ions. The aromatic –OH group indeed plays its part in triggering CHEF and CHEQ processes responsible for the turn-on-off events. Low limits of detection (48 nM of OH⁻, 95 nM for Al³⁺, 33 nM for Fe³⁺ ions), high recyclability and fast response time (8 seconds) further assist the MOF to implement an accurate quantitative sensing strategy for OH⁻, Al³⁺ and Fe³⁺ ions. The study further demonstrates the MOF''s behaviour in cellular medium by subjecting it to live cell confocal microscopy. Along with a bio-compatible nature the MOF exhibited successful accumulation inside the mitochondria of MCF7 cancer cells, which defines it as a significant bio-marker. Therefore the present work successfully represents the multidisciplinary nature of Zn-DHNDC MOFs, primarily in sensing and biomedical studies.

ESIPT tuned fluorescence sensing of OH⁻, Al³⁺ and Fe³⁺ ions and mitochondria targeted bio-imaging by a Zn-DHNDC MOF.     

Di-functional luminescent sensors based on Y3+ doped Eu3+ and Tb3+ coordination polymers: fast response and visible detection of Cr3+, Fe3+ ions in aqueous solutions and acetone

With the careful modulation of the relative ratio of Y³⁺/Eu³⁺and Y³⁺/Tb³⁺, two series of bimetallic RE-CPs (Eu_xY_1−x and Tb_xY_1−x) were successfully obtained through the isomorphous substitution method. Interestingly, the introduction of Y³⁺ ions does not change the fluorescence characteristic peak of 1-Eu and 1-Tb, but enhances its fluorescence lifetime and quantum yield. Experimental and theoretical simulation results show the co-doping process changes the intramolecular energy transfer process and reduces the non-radiative transition resulting from concentration quenching. Eu_0.1Y_0.9 and Tb_0.1Y_0.9 with the largest luminescence lifetime were selected as the representative research objects, their potential application for the detection of toxic metal ions and organic molecules was further investigated. Interestingly, Eu_0.1Y_0.9 and Tb_0.1Y_0.9 demonstrate high sensitivity and good selectivity towards Fe³⁺, Cr³⁺ and acetone. Besides, fine fluorescence visibility provides the necessary conditions for the preparation of simple and fast response fluorescent test papers in order to achieve real-time and convenient detection of these toxic materials.

Two series of doped coordination polymers (Eu_xY_1−x and Tb_xY_1−x) through isomorphous substitution method utilizing Y³⁺ in place of partial Eu³⁺/Tb³⁺ were obtained. The doped materials could detect Fe³⁺, Cr³⁺, and acetone selectively and sensitively.     

Exploring the pore charge dependence of K+ and Cl− permeation across a graphene monolayer: a molecular dynamics study

Selective permeation through graphene nanopores is attracting increasing interest as an efficient and cost-effective technique for water desalination and purification. In this work, using umbrella sampling and molecular dynamics simulations with constant electric field, we analyze the influence of pore charge on potassium and chloride ion permeation. As pore charge is increased, the barrier of the potential of mean force (PMF) gradually decreases until it turns into a well split in two subminima. While in the case of K⁺ this pattern can be explained as an increasing electrostatic compensation of the desolvation cost, in the case of Cl⁻ the pattern can be attributed to the accumulation of a concentration polarization layer of potassium ions screening pore charge. The analysis of potassium PMFs in terms of forces revealed a conflicting influence on permeation of van der Waals and electrostatic forces that both undergo an inversion of their direction as pore charge is increased. Even if the most important transition involves the interplay between the electrostatic forces exerted by graphene and water, the simulations also revealed an important role of the changing distribution of potassium and chloride ions. The influence of pore charge on the orientation of water molecules was also found to affect the van der Waals forces they exert on potassium.

Increase of graphene pore charge determines decrease of PMF barrier that turns into well: current increases, reaches plateau and declines.     

Additive effects of alkali metals on Cu-modified CH3NH3PbI3−δClδ photovoltaic devices

We investigated the addition of alkali metal elements (namely Na⁺, K⁺, Rb⁺, and Cs⁺) to Cu-modified CH₃NH₃PbI_3−δCl_δ photovoltaic devices and their effects on the photovoltaic properties and electronic structure. The open-circuit voltage was increased by CuBr₂ addition to the CH₃NH₃PbI_3−δCl_δ precursor solution. The series resistance was decreased by simultaneous addition of CuBr₂ and RbI, which increased the external quantum efficiencies in the range of 300–500 nm, and the short-circuit current density. The energy gap of the perovskite crystal increased through CuBr₂ addition, which we also confirmed by first-principles calculations. Charge carrier generation was observed in the range of 300–500 nm as an increase of the external quantum efficiency, owing to the partial density of states contributed by alkali metal elements. Calculations suggested that the Gibbs energies were decreased by incorporation of alkali metal elements into the perovskite crystals. The conversion efficiency was maintained for 7 weeks for devices with added CuBr₂ and RbI.

Addition of alkali metal elements (Na⁺, K⁺, Rb⁺, and Cs⁺) to Cu-modified CH₃NH₃PbI_3−δCl_δ devices improved the photovoltaic properties.     

Two-dimensional Cd(ii) coordination polymer encapsulated by Tb3+ as a reversible luminescent probe for Fe3+

A two-dimensional luminescent cadmium(ii) coordination polymer, [Cd(modbc)₂]_n (Cd-P); modbc = 2-methyl-6-oxygen-1,6-dihydro-3,4′-bipyridine-5-carbonitrile, was successfully synthesized by a solvothermal reaction and fully characterized. Cd-P exhibited excellent luminescence emission, and detected Cu²⁺, Co²⁺, Fe²⁺, Hg²⁺, Ni²⁺ and Fe³⁺ ions with high sensitivity and showed good anti-interference performance. After encapsulation of Tb³⁺ ions in Cd-P, the as-obtained fluorescent functionalized Tb³⁺@Cd-P maintained distinct chemical stabilities in different pHs and metal salt solutions. Subsequently, we explored the potential application of Tb³⁺@Cd-P as a probe for Fe³⁺ ions. A new and convenient method for individual identification of Fe³⁺ ions by the combination of Cd-P and Tb³⁺@Cd-P was successfully established. A possible sensing mechanism is discussed in detail.

A new and convenient method for individual identification of Fe³⁺ ions by the combination of Cd-P and Tb³⁺@Cd-P was successfully established.     

Solid base catalysts derived from Ca–Al–X (X = F−, Cl− and Br−) layered double hydroxides for methanolysis of propylene carbonate

The Ca–Al and Ca–Al–X (X = F⁻, Cl⁻ and Br⁻) catalysts were prepared via thermal decomposition of Ca–Al layered double hydroxides (LDHs), and tested for methanolysis of propylene carbonate (PC) to produce dimethyl carbonate (DMC). The catalytic performance of these catalysts increased in the order of Ca–Al–Br⁻ < Ca–Al < Ca–Al–Cl⁻ < Ca–Al–F⁻, which was consistent with the strong basicity of these materials. The recyclability test results showed that the addition of Al and halogens (F⁻, Cl⁻ and Br⁻) not only stabilized the CaO but also improved the recyclability of the catalysts. Particularly, the Ca–Al–F⁻ catalyst exerted the highest stability after 10 recycles. These catalysts have an important value for the exploitation of DMC synthesis by transesterification of PC with methanol.

The CA-F⁻ catalyst modified with Al³⁺ and F⁻ was highly active and recyclable for dimethyl carbonate synthesis.     

The aggression behavior study of Cl− on the defect structure of passive films on copper

The destructive role of chloride ions on the defect structure of barrier layers (bl) is vitally important for understanding the initial breakdown of passive films on metals. Here photo-electrochemical and density functional theory (DFT) were applied to investigate the influence of chloride on the defect structure of the bl in passive films. The results show a bl with a narrow band gap, in which the valence band maximum (VBM) increased upon introducing chloride into the electrolyte. DFT calculations indicate that an increase in the copper vacancy concentration, due to cation extraction at the bl/solution interface could increase the VBM while oxygen vacancy generation results in a decrease in the conduction band minimum (CBM). The combination of these results verifies the aggressive role of chloride as proposed by the Point Defect Model (PDM) where an enhancement of the cation vacancy concentration across the bl occurs in response to the absorption of Cl⁻ into oxygen vacancies on the bl.

The destructive role of chloride ions on the defect structure of barrier layers (bl) is vitally important for understanding the initial breakdown of passive films on metals.     

The aggregation of Fe3+ and their d–d radiative transitions in ZnSe:Fe3+ nanobelts by CVD growth

Transition metal (TM) doped II–VI semiconductors have attracted great attention due to their luminescence and diluted magnetism. In this study, the Fe³⁺-doped ZnSe nanobelts (NBs) were grown by a facile CVD method. The surface morphology observed via SEM is smooth and clean and the elemental composition measured via EDS confirms that the Fe³⁺ ions were incorporated into ZnSe NBs successfully. The micro-Raman scattering spectra demonstrate that the as-prepared NBs have the zinc blende structure. Furthermore, the Raman spectra of the Fe³⁺-doped NBs were compared with those of pure and Fe²⁺-doped reference samples. The former with a higher signal-to-noise ratio, an enhanced 2LO mode, a stronger LO mode redshift and a larger intensity ratio of LO/TO mode as well as the lower acoustic phonon modes confirms the better crystallization and the stronger electron–phonon coupling on Fe³⁺-incorporation. The emission of single Fe³⁺ ion, assigned to the ⁴T₁ → ⁶A₁ transition, was observed at about 570 nm. Moreover, increasing the doping concentration of Fe³⁺ ions caused the formation of different Fe–Fe coupled pairs in the lattice, which emitted light at about 530–555 nm for an antiferromagnetic-coupled pair, possibly due to the stacking faults and at about 620–670 nm for a ferromagnetic-coupled pair.

Transition metal (TM) doped II–VI semiconductors have attracted great attention due to their luminescence and diluted magnetism.     

Gd3+ and Bi3+ co-substituted cubic zirconia; (Zr1−x−yGdxBiyO2−δ): a novel high κ relaxor dielectric and superior oxide-ion conductor

Solid oxide fuel cells (SOFCs) offer several advantages over lower temperature polymeric membrane fuels cells (PMFCs) due to their multiple fuel flexibility and requirement of low purity hydrogen. In order to decrease the operating temperature of SOFCs and to overcome the high operating cost and materials degradation challenges, the Cubic phase of ZrO₂ was stabilized with simultaneous substitution of Bi and Gd and the effect of co-doping on the oxide-ion conductivity of Zr_1−x−yBi_xGd_yO_2−δ was studied to develop a superior electrolyte separator for SOFCs. Up to 30% Gd and 20% Bi were simultaneously substituted in the cubic ZrO₂ lattice (Zr_1−x−yGd_xBi_yO_2−δ, x + y ≤ 0.4, x ≤ 0.3 and y ≤ 0.2) by employing a solution combustion method followed by multiple calcinations at 900 °C. Phase purity and composition of the material is confirmed by powder XRD and EDX measurements. The formation of an oxygen vacant Gd/Bi co-doped cubic zirconia lattice was also confirmed by Raman spectroscopy study. With the incorporation of Bi³⁺ and Gd³⁺ ions, the cubic Zr_1−x−yBi_xGd_yO_2−δ phase showed relaxor type high κ dielectric behaviour (ε′ = 9725 at 600 °C at applied frequency 20 kHz for Zr_0.6Bi_0.2Gd_0.2O_1.8) with T_m approaching 600 °C. The high polarizability of the Bi³⁺ ion coupled with synergistic interaction of Bi and Gd in the host ZrO₂ lattice seems to create the more labile oxide ion vacancies that enable superior oxide-ion transport resulting in high oxide ion conductivity (σ_o > 10⁻² S cm⁻¹, T > 500 °C for Zr_0.6Bi_0.2Gd_0.2O_1.8) at relatively lower temperatures.

The high polarizability of the Bi³⁺ ion coupled with synergistic interaction of Bi and Gd in the host ZrO₂ lattice seems to create the more labile oxide ion vacancies that enable high oxide ion conductivity at lower temperatures.     

Color-tunable photoluminescence and energy transfer of (Tb1−xMnx)3Al2(Al1−xSix)3O12:Ce3+ solid solutions for white light emitting diodes

(Tb_1−xMn_x)₃Al₂(Al_1−xSi_x)₃O₁₂:Ce³⁺ solid solution phosphors were synthesized by introducing the isostructural Mn₃Al₂(SiO₄)₃ (MAS) into Tb₃Al₅O₁₂:Ce³⁺ (TbAG). Under 456 nm excitation, (Tb_1−xMn_x)₃Al₂(Al_1−xSi_x)₃O₁₂:Ce³⁺ shows energy transfers (ET) in the host, which can be obtained from the red emission components to enhance color rendering. Moreover, (Tb_1−xMn_x)₃Al₂(Al_1−xSi_x)₃O₁₂:Ce³⁺ (x = 0–0.2) exhibits substantial spectral broadening (68 → 86 nm) due to the 5d → 4f transition of Ce³⁺ and the ⁴T₁ → ⁶A₁ transition of Mn²⁺. The efficiency of energy transfer (η_T, Ce³⁺ → Mn²⁺) gradually increases with increasing Mn²⁺ content, and the value reach approximately 32% at x = 0.2. Namely, the different characteristics of luminescence evolution based on the effect of structural variation by substituting the (MnSi)⁶⁺ pair for the larger (TbAl)⁶⁺ pair. Therefore, with structural evolution, the luminescence of the solid solution phosphors could be tuned from yellow to orange-red, tunable by increasing the content of MAS for the applications of white light emitting diodes (wLED).

(Tb_1−xMn_x)₃Al₂(Al_1−xSi_x)₃O₁₂:Ce³⁺ solid solution phosphors were synthesized by introducing the isostructural Mn₃Al₂(SiO₄)₃ (MAS) into Tb₃Al₅O₁₂:Ce³⁺ (TbAG).     

A luminescent Cd(ii) coordination polymer as a multi-responsive fluorescent sensor for Zn2+, Fe3+ and Cr2O72− in water with fluorescence enhancement or quenching

A luminescent Cd(ii) coordination polymer, namely {[Cd(btic)(phen)]·0.5H₂O}_n (CP-1) (H₂btic = 5-(2-benzothiazolyl)isophthalic acid, phen = 1,10-phenanthroline), was constructed through the mixed-ligand method under solvothermal conditions. CP-1 manifests a chain structure decorated with uncoordinated Lewis basic N and S donors. CP-1 exhibits high sensing towards Zn²⁺, Fe³⁺ and Cr₂O₇²⁻ ions with fluorescence enhancement or quenching. CP-1 exhibited a fluorescence enhancement for Zn²⁺ ions through weak binding to S and N atoms, and a fluorescence quenching for Fe³⁺ and Cr₂O₇²⁻ ions by an energy transfer process. The binding constants were calculated as 1.812 × 10⁴ mol⁻¹ for Zn²⁺, 4.959 × 10⁴ mol⁻¹ for Fe³⁺ and 1.793 × 10⁴ mol⁻¹ for Cr₂O₇²⁻. This study shows CP-1 as a rare multi-responsive sensor material for the efficient detection of Zn²⁺, Fe³⁺ and Cr₂O₇²⁻ ions.

A luminescent Cd(ii) coordination polymer can act as a multi-responsive sensor for efficiently detecting Zn²⁺, Fe³⁺ and Cr₂O₇²⁻ ions.     

Fluorescence detection of malachite green and cations (Cr3+, Fe3+ and Cu2+) by a europium-based coordination polymer

Due to remarkable fluorescence characteristics, lanthanide coordination polymers (CP) have been widely employed in fluorescence detection, but it is rarely reported that they act as multifunctional luminescent probes dedicated to detecting malachite green (MG) and various metal ions. A europium-based CP fluorescent probe, Eu(PDCA)₂(H₂O)₆ (PDCA = 2,6-pyridinedicarboxylic acid), has been synthesized and exhibited excellent recognition ability for malachite green and metal cations (Cr³⁺, Fe³⁺ and Cu²⁺) among 11 metal cations, 13 anions and six other compounds. The recognition was achieved by fluorescence quenching when MG, Cr³⁺, Fe³⁺ and Cu²⁺ were added to a suspension of Eu(PDCA)₂(H₂O)₆ respectively. Eu(PDCA)₂(H₂O)₆ is a multifunctional luminescent probe, and displayed high quenching efficiencies K_sv (2.10 × 10⁶ M⁻¹ for MG; 1.46 × 10⁵ M⁻¹ for Cr³⁺; 7.26 × 10⁵ M⁻¹ for Fe³⁺; 3.64 × 10⁵ M⁻¹ for Cu²⁺), and low detection limits (MG: 0.039 μM; Cr³⁺: 0.539 μM; Fe³⁺: 0.490 μM; Cu²⁺: 0.654 μM), presenting excellent selectivity and sensitivity, especially for MG. In addition, Eu(PDCA)₂(H₂O)₆ was also made into fluorescent test strips, which can rapidly and effectively examine trace amounts of MG, Cr³⁺, Fe³⁺ and Cu²⁺ in aqueous solutions. This work provides a new perspective for detecting malachite green in fish ponds and heavy metal ions in waste water.

A europium-based CP fluorescent sensor was synthesized and exhibited excellent recognition ability for malachite green (MG) and metal cations (Cr³⁺, Fe³⁺ and Cu²⁺).     

Evaluation of BaCo0.4Fe0.4Zr0.2−xNixO3−δ perovskite cathode using nickel as a sintering aid for IT-SOFC

In this research work, BaCo₀.₄Fe₀.₄Zr_0.2−xNi_xO_3−δ (x = 0, 0.01, 0.02, 0.03, 0.04) perovskite cathode material for IT-SOFC is synthesized successfully using a combustion method and sintered at low temperature. The effects of nickel as a sintering aid on the properties of BaCo₀.₄Fe₀.₄Zr₀.₂O_3−δ are investigated through different characterization methods. The addition of nickel increased the densification and grain growth at a lower sintering temperature 1200 °C. XRD analysis confirms a single phase of BaCo₀.₄Fe₀.₄Zr₀.₂O_3−δ, and an increase in crystalline size is observed. SEM micrographs show formation of dense microstructure with increased nickel concentration. TGA analysis revealed that BaCo₀.₄Fe₀.₄Zr_0.2−xNi_x cathode materials are thermally stable within the SOFC temperature range, and negligible weight loss of 2.3% is observed. The bonds of hydroxyl groups and metal oxides are confirmed for all samples through FTIR analysis. The highest electrical properties are observed for BaCo₀.₄Fe₀.₄Zr_0.2−xNi_x (x = 0.04) due to increased densification and electronic defects compared to other compositions. The maximum power density of 0.47 W cm⁻² is obtained for a cell having cathode material BaCo₀.₄Fe₀.₄Zr_0.2−xNi_x (x = 0.02) owing to its permeable and well-connected structure compared to others.

Electrochemical performance of BaCo₀.₄Fe₀.₄Zr_0.2−xNi_xO_3−δ at 600 °C.     

Structure and transport properties of triple-conducting BaxSr1−xTi1−yFeyO3−δ oxides

In this work, Ba_xSr_1−xTi_1−yFe_yO_3−δ perovskite-based mixed conducting ceramics (for x = 0, 0.2, 0.5 and y = 0.1, 0.8) were synthesized and studied. The structural analysis based on the X-ray diffraction results showed significant changes in the unit cell volume and Fe(Ti)–O distance as a function of Ba content. The morphology of the synthesized samples studied by means of scanning electron microscopy has shown different microstructures for different contents of barium and iron. Electrochemical impedance spectroscopy studies of transport properties in a wide temperature range in the dry- and wet air confirmed the influence of barium cations on charge transport in the studied samples. The total conductivity values were in the range of 10⁻³ to 10⁰ S cm⁻¹ at 600 °C. Depending on the barium and iron content, the observed change of conductivity either increases or decreases in humidified air. Thermogravimetric measurements have shown the existence of proton defects in some of the analysed materials. The highest observed molar proton concentration, equal to 5.0 × 10⁻² mol mol⁻¹ at 300 °C, was obtained for Ba_0.2Sr_0.8Ti_0.9Fe_0.1O_2.95. The relations between the structure, morphology and electrical conductivity were discussed.

Ba_xSr_1−xTi_1−yFe_yO_3−δ-based perovskite materials with different barium and iron contents are reported as triple conducting oxides (TCOs), which may conduct three charge carriers: oxygen ions, protons and electrons/holes.     

Effects of in vitro glycation on Fe3+ binding and Fe3+ isoforms of transferrin

BACKGROUND: In diabetes, protein function is altered by glycation, but the impact on the Fe3+ binding and antioxidant functions of transferrin (Tf) is largely unknown. The aim of the present study was to investigate the effects of glycation on the distribution of Fe3+ on the two Fe3+ -binding sites of Tf. METHODS: In vitro glycation of Tf was accomplished by preincubation with glucose for 14 days. Tf was loaded with Fe3+ compounds to achieve theoretical Tf Fe3+ saturations of 32%, 64%, and 96% (monitored by spectrophotometry). Fe3+ -Tf isoforms were separated by isoelectric focusing. RESULTS: Fe3+ binding was highest when Tf was incubated with Fe:nitrilotriacetic acid and reached a steady state overnight. Increasing the Fe3+ load led to a shift of isoform profile toward the diferric form (Fe2-Tf): in freshly prepared Tf, Fe2-Tf represented 6%, 30%, and 66% of all isoforms at 32%, 64%, and 96% theoretical Fe3+ saturation, respectively. Fe3+ was equally distributed to the monoferric Tf forms with Fe3+ bound to the amino (Fe1N-Tf) and carboxy termini (Fe1C-Tf). Glycation decreased binding of Fe3+ to Tf (monitored at 450 nm). At low theoretical Fe3+ saturation (32%), glycation increased the mean (SD) proportion of Fe2-Tf: 18 (3)% in the presence of 33.3 mmol/L glucose vs 12 (4)% with 0 mmol/L glucose (P = 0.01). In contrast, at 96% theoretical Fe3+ saturation, Fe2-Tf decreased linearly with increasing glycation (r = 0.97; P = 0.008). Preincubation, independent of glycation, favored the Fe1N-Tf isoform at 64% theoretical Fe3+ saturation [27 (0.7)% vs 23 (1.1)% of the Fe1C-Tf isoform; P = 0.009]. CONCLUSIONS: Glycation impairs Fe3+ binding and affects Fe3+ -Tf isoform distribution depending on concentration. The diagnostic implications of these results need further elucidation in clinical studies.     

Transferrin binding of Al3+ and Fe3+

An understanding of Al3+-induced diseases requires identification of the blood carrier of Al3+ to the tissues where Al3+ exerts a toxic action. Quantitative studies demonstrate that the protein transferrin (iron-free) is the strongest Al3+ binder in blood plasma. Under plasma conditions of pH 7.4 and [HCO3-]27 mmol/L, the successive stability constant values for Al3+ binding to transferrin are log K1 = 12.9 and log K2 = 12.3. When the concentration of total Al3+ in plasma is 1 mumol/L, the free Al3+ concentration permitted by transferrin is 10(-14.6) mol/L, less than that allowed by insoluble Al(OH)3, by Al(OH)2H2PO4, or by complexing with citrate. Thus transferrin is the ultimate carrier of Al3+ in the blood. We also used intensity changes produced by metal ion binding to determine the stability constants for Fe3+ binding to transferrin: log K1 = 22.7 and log K2 = 22.1. These constants agree closely with a revision of the reported values obtained by equilibrium dialysis. By comparison with Fe3+ binding, the Al3+ stability constants are weaker than expected; this suggests that the significantly smaller Al3+ ions cannot coordinate to all the transferrin donor atoms available to Fe3+.