Single-phase multicomponent
perovskite-type cobalt oxide containing
five cations in equiatomic amounts on the A-site, namely, (Gd0.2Nd0.2La0.2Sm0.2Y0.2)CoO3, has been synthesized via the modified coprecipitation
hydrothermal method. Using an original approach for heat treatment,
which comprises quenching utilizing liquid nitrogen as a cooling medium,
a single-phase ceramic with high configuration entropy, crystallizing
in an orthorhombic distorted structure was obtained. It reveals the
anomalous temperature dependence of the lattice expansion with two
weak transitions at approx. 80 and 240 K that are assigned to gradual
crossover from the low- via intermediate- to high-spin state of Co3+. The compound exhibits weak ferromagnetism at T ≤ 10 K and signatures of antiferromagnetic correlations in
the paramagnetic phase. Ab initio calculations predict a band gap
Δ = 1.18 eV in the ground-state electronic structure with the
dominant contribution of O_p and Co_d orbitals in the valence and
conduction bands, respectively. Electronic transport measurements
confirm the negative temperature coefficient of resistivity characteristic
to a semiconducting material and reveal a sudden drop in activation
energy at T ∼ 240 K from E
a ∼ 1 eV in the low-temperature phase to E
a ∼ 0.3 eV at room temperature. The possibility
of fine tuning of the semiconducting band gap via a subtle change
in A-site stoichiometry is discussed.
Metformin (MET) is an antidiabetic drug most commonly used in treatment of diabetes mellitus type 2 (T2D). Adsorptive stripping voltammetric method using carbon black – hydrated ruthenium dioxide – Nafion modified glassy carbon electrode (CB‐RuO2‐Nafion GC electrode) have been developed for metformin determination in pharmaceutical formulations. By using ruthenium dioxide, electrode's lifespan was extended to at least 3 weeks (change of metrological parameters estimated as 3–4 %) what is an excellent result concerning other solutions previously described in the literature. Moreover the fabrication of the sensor is simple and fast. Deposition step was carried out at the potential 0 mV for 15 s. The best results were obtained in 0.05 M acetate buffer (pH 4.6). Important aspect was fixed MET : Cu(II) ratio equal to 1 : 8, otherwise linear dependence between register current and MET concentration could not be obtained. In addition, a significant improvement in the parameters of the calibration curve was obtained. Limit of detection was equal to 0.7 μM. Developed method was successfully applied in analysis of 2 pharmaceuticals products and in wastewater and river water. Accuracy of the method was estimated using recoveries, which were in the range 101–110 %. In order to adapt developed system into hydrodynamic conditions, amperometry in hydrodynamic transport conditions and flow injection analysis (FIA) measurements have been conducted. Conducted FIA measurements prove that developed method has potential for application in automized flow systems without frequent calibration.
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