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- Magnetic and transport properties of diluted granular multilayersPublication . Silva, Hugo G.; Gomes, Henrique L.; Pogorelov, Y. G.; Pereira, L. M. C.; Kakazei, G. N.; Sousa, J. B.; Araújo, J. P.; Mariano, José F. M. L.; Cardoso, S.; Freitas, P. P.The magnetic and transport properties of Co80Fe20t /Al2O34 nm multilayers with low nominal thicknesses t=0.7 and 0.9 nm of Co80Fe20 granular layers are studied. Magnetic studies find a superparamagnetic state above the blocking temperature Tb of field-cooled/zero-field-cooled splitting that grows with t and decreases with H. The low-voltage Ohmic tunnel transport passes to non-Ohmic IV3/2 law for applied fields above 500 V/cm. At fixed V, the temperature dependence of conductance reveals an anomalous dip around 220 K, which can be attributed to the effect of surface contamination by supercooled water. Current-in-plane tunnel magnetoresistance MR ratio tends, at lower t, to higher maximum values 8% at room temperature but to lower field sensitivity. This may indicate growing discorrelation effect e.g., between shrinking areas of correlated moments in this regime and corroborates the deficit of granule magnetization estimated from the Inoue–Maekawa MR fit, compared to that from direct magnetization measurements. MR displays a mean-field-like critical behavior when t approaches the point of superparamagnetic/ superferromagnetic transition tc1.3 nm at room temperature from below, different from the formerly reported percolationlike behavior at approaching it from above.With growing temperature, MR reveals, beyond the common decrease, an anomalous plateau from Tb30–50 K up to some higher value T150–200 K, not seen at higher t.
- A single drop histamine sensor based on AuNPs/MnO2 modified screen-printed electrodePublication . Knezevic, Sara; Ognjanovic, Milos; Nedic, Nemanja; Mariano, José; Milanovic, Zorana; Petkovic, Branka; Antic, Bratislav; Djuric, Sanja Vranjes; Stankovic, DaliborIn order to ensure high food quality, one of the prime importance is the detection and quantification of histamine, well known marine food poison. In this work, we constructed novel electrochemical biosensor for the detection of histamine based on gold nanoparticles decorated on manganese dioxide (Au/MnO2) and used for modification of screen-printed carbon electrode (Au/MnO2@SPCE). The constructed sensor was then used for the estimation of histamine content in a single drop. Materials used in this study were synthesized and characterized using HR-TEM, XRPD and electrochemical methods. The amperometric detection method was optimized and, under selected operating parameters (supporting electrolyte pH 6, working potential of 1 V), the proposed sensor possesses linear working range from 0.3 mu M to 5.1 mu M, with a detection limit of 0.08 mu M. The effect of selected interferences was investigated and it was found that the developed approach offers accurate, precise, selective, fast and reproducible quantification of histamine using only one drop of the sample. In the end, this work stands as a proof-of-concept of the modified electrodes and electrochemical detection as a promising and prospective approach for the applications in real-time monitoring of the food quality.
- Study of structural, magnetic, magnetocaloric properties and critical behavior of CoFeCuO4 spinel ferritePublication . Nasri, M.; Henchiri, C.; Dhahri, R.; Khelifi, J.; Dhahri, E.; Mariano, JoséOur research work centers on studying the structural, magnetic, magnetocaloric properties and the critical behavior of the Cu-substituted CoFe2O4. The XRD analysis revealed that this compound prepared via sol-gel method crystallized in the cubic spinel structure with the Fd3m space group and exhibited nanometric size. In addition, the positive slope in Arrott plots and the universal master curve confirmed the second order ferromagnetic-paramagnetic (FM-PM) phase transition exhibited by our material at a Curie temperature TC = 688 K. Furthermore, it is demonstrated that substituting iron by copper in CoFe2O4 decreases the Curie-temperature and increases the maximum magnetic entropy change. Indeed, for CoFeCuO4, the magnetic entropy change (-Delta SM) rose upon increasing the applied magnetic field and presented a peak around the Curie temperature, its maximum value (-Delta SmaxM ) of 0.6 J.kg- 1.K-1 is reached at mu 0H = 5 T, it corresponds to a relative cooling power (RCP) value of 62.55 J.kg- 1. Moreover, the heat capacity Delta CP was evaluated in order to explore further the performance of our compound with respect to the magnetocaloric effect (MCE). As a final point, the critical exponents were estimated through different experimental and theoretical techniques, they are found reliable obeying to the mean-field model, symptomatic of short-range ferromagnetic interactions.
- Investigation of Cr substitution effect on the evolution of La0.67Ca0.2Ba0.13Fe1−xCrxO3 (x = 0 and 0.03) electrical properties under frequency and temperature variationPublication . Dhahri, Ah.; Bougoffa, Amira; Zaouali, A.; Benali, A.; Graça, M. P. F.; Valente, M. A.; Costa, B. F. O.; Abdelmoula, N.; Mariano, José F. M. L.In this study, La0.67Ca0.2Ba0.13Fe1-xCrxO3 (x = 0 and 0.03) powders were prepared by auto-combustion method. The examination of the purity and crystalline structure of the samples by X-ray diffraction showed a cubic structure formed with the Pm (3) over barm space group. Scanning electron microscopy was used to study the morphology and grains size, indicating an agglomeration of nanometric particles. Impedance spectroscopy in the temperature range from 200 to 360 K was used in order to understand the evolution of the electrical behavior of the substituted perovskites. The real and imaginary parts of the impedance were adjusted with two different equivalent circuits. The activation energies extracted from the imaginary part of the impedance, and the electrical conductivity was very closed indicating a transformation of the electrical behavior. This was confirmed by a decrease in the resistance after substitution of Fe cations by Cr ones. AC conductivity studies showed a Jonscher's behavior and a change of conduction process from a succession of NSPT and CBH model to the existence of only CBH one after the substitution.
- Construction of sensor for submicromolar detection of riboflavin by surface modification of SPCE with thermal degradation products of nickel acetate tetrahydratePublication . Ognjanović, Miloš; Stanković, Dalibor M.; Jaćimović, Željko K.; Kosović‐Perutović, Milica; Mariano, José F. M. L.; Krehula, Stjepko; Musić, Svetozar; Antić, BratislavNickel acetate tetrahydrate (NAT) sample series were used to modify screen-printed carbon electrodes (SPCE). The samples were hybrid Ni/NiO nanocomposites, where the NiO phase increased with an applied treatment temperature. Results of electrochemical measurements pointed that the Ni/NiO550/SPCE-modified electrode had the best analytical performance toward the detection of riboflavin (RF). The Ni/NiO550/SPCE-based sensor showed linear response with RF in the concentration range of 0.5-75 mu M and 0.15 mu M LOD in BRBS. Sensor offered fast response time, good repeatability, and selectivity with an RSD of 1.4 %. Our results show that the Ni:NiO nanocomposite ratio strongly influenced the electroanalytical performance of SPCE.
- Design of titanium nitride- and wolfram carbide-doped RGO/GC electrodes for determination of gallic acidPublication . Stankovic, Dalibor M.; Ognjanovic, Milos; Martin, Fabian; Svorc, L'ubomir; Mariano, José; Antic, BratislavIn the present paper, the electrochemical behavior and the properties of two modified glassy carbon (GC) electrodes used for quantification of gallic acid in sweet wines were compared. A comparative study was conducted between titanium nitride- or wolfram carbide-doped reduced graphene oxide, labeled as TNrGO and WCrGO, respectively, modified GC electrodes, which are promising composite nanomaterials for electroanalytical applications. For the first time, WCrGO was synthesized and its electroanalytical properties compared with those of TNrGO. Results showed that the proposed materials exhibited enhanced characteristics, e.g., low limits of detection (1.1 mu M and 3.1 mu M for TNrGO and WCrGO, respectively), wide linear ranges (for TNrGO 4.5-76 mu M and for WCrGO 10-100 mu M), low adsorption, and low background current, which make them promising candidates for electrochemical sensing applications.
- TiO2:(Fe, S) Thin Films Prepared from Complex Precursors by CVD, Physical Chemical Properties, and PhotocatalysisPublication . Bessergenev, V.; Mateus, Maria da Conceição; Vasconcelos, D. A.; Mariano, José; do Rego, A. M. Botelho; Lange, R.; Burkel, E.The TiO2 thin films were prepared using Ti(dpm)(2)(OPri)(2) and Ti(OPri)(4) (dpm = 2,2,6,6-tetramethylheptane-3,5-dione, Pr-i = isopropyl) as the precursors. The volatile compounds Fe[(C2H5)(2)NCS2](3) and [(CH3)C](2)S-2 were used to prepare doped TiO2 films. The synthesis was done in vacuum or in the presence of Ar and O-2. The pressure in the CVD chamber was varied between 1.2 x 10(-4) mbar and 0.1 mbar, with the system working either in the molecular beam or gas flow regime. Physical, chemical, and photocatalytic properties of the (Fe, S)-doped TiO2 films were studied. Those TiO2:(Fe, S) films prepared from the Ti(OPri)(4) precursor show increased photocatalytic activities, very close to those of Degussa P25 powder in UV region.
- Magnetic hysteresis loops revisited: step closer to understand the role of exterior anglesPublication . Nikolić, Violeta N.; Rajnak, Michal; Morais Lopes, Fernando; Lazarov, Nenad Dj.The characterization of nanocomposite samples which contain Cu, Fe-species, prepared by the sol-gel method, was established by Nikolic et al., in a previous article (Nikolic et al. in Journal of Solid State Physics 513:1, 2021). In this study, the magnetic behavior of nanocomposite samples was examined The basic parameters of the room- and low-temperature magnetic hysteresis loops are discussed. To better describe the shape of magnetic hysteresis loop, the authors proposed to consider additional parameters - measures of the exterior angles of the hysteresis curve. Behavior of hysteresis parameters and exterior angles, caused by annealing treatment, was investigated by measuring hysteresis loops at two measured temperatures: 298K, and 5K. Correlation between changes in the behavior of hysteresis parameters and exterior angles was discussed. An attempt has been made to attribute physical meaning to chosen measured angles, which would allow a better understanding of the magnetic hysteresis curve.
- Saturation effect for dependence of the electrical conductivity of planar oriented nematic liquid crystal 6CB on the concentration of Cu7PS6 nanoparticlesPublication . Kovalchuk, O. V.; Studenyak, I. P.; Izai, V. Yu; Rybak, S. O.; Pogodin, A. I.; Kopčanský, P.; Timko, M.; Gdovinova, V.; Mariano, José; Kovalchuk, T. M.The influence of Cu7PS6 nanoparticles with the average size 117 nm on the dielectric properties of planar oriented nematic liquid crystal 6CB has been investigated within the frequency range 10(1) ...10(6) Hz and at the temperature 293 K. It has been shown that when changing the concentration of nanoparticles within the range 0 to 1 wt.%, the conductivity of the liquid crystal changes stronger than its dielectric permittivity. It has been shown that the electrical conductivity increases monotonously with increasing the concentration of nanoparticles. However, for this dependence a saturation effect is observed. The mechanism of this effect was proposed.
- Isolation and purification treatments change the metal-binding properties of humic acids: effect of HF/HCl treatmentPublication . Botero, Wander G.; Pineau, Michael; Janot, Noemie; Domingos, Rute F.; Mariano, José; Rocha, Luciana S.; Groenenberg, Jan E.; Benedetti, Marc F.; Pinheiro, Jose P.Environmental contextStudying the mechanism of binding between metals and natural organic matter is fundamental to understanding the transport and availability of these contaminants in the environment. The influence of sample treatment on the purification of organic matter showed significant differences in the interaction with metals. The results will contribute to improved modelling of metal binding to organic matter in soils, thereby providing a basis for a more realistic risk assessment. AbstractWe studied the changes in metal binding characteristics of extracted humic acids induced by HF/HCl treatment followed by dialysis, i.e. the last step of the International Humic Substances Society (IHSS) extraction protocol. We performed metal binding experiments with both the alkaline-extracted material (AE) and the fully purified (FP) humic acid using the electrochemical stripping technique (AGNES) and modelled the results using the NICA-Donnan model. The results showed an increase of free Zn, Cd and Pb concentrations of similar to 1 order of magnitude for the AE compared with the FP. These differences may be mostly explained by the different carbon content (51.3% FP and 36.5% AE) associated with an AE/FP carboxyl ratio of 0.5. Simulations using the NICA-Donnan model showed that halving the amount of carboxylic groups (Q(max,1)) for the FP reduced this difference to 0.25 log units for Cd and Zn and to 0.15 log unit for Pb. There is a clear need for further research on the differences between purified v. less-disturbed natural organic material, which will contribute to improved modelling of metal binding to organic matter in soils, hence providing a basis for a more realistic risk assessment.