Abstract
Degradation of pollutants in aqueous medium is of high interest due to the impact on environment and human health, therefore, design and study of the physico-chemical properties of ...photocatalysts for water remediation are of major significance. Among properties of photocatalyst, those related to the surface and electrical mechanism are crucial to the photocatalyst´s performance. Here we report the chemical and morphological characteristics of TiO
2
@zeolite photocatalyst by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) respectively, and a coherent electrical conduction mechanism was proposed based on data obtained from assisted laser impedance spectroscopy (ALIS), in which the zeolite was synthesized from recycled coal fly ash. The results obtained by SEM and XPS verified the presence of spherical particles of TiO
2
anatase with presence of Ti
3+
state. ALIS results showed that impedance of the entire system increases when the amount of TiO
2
increases and the samples with lower capacitive performance allowed a larger transfer of the charges between the solid–liquid interface. All results showed that higher photocatalytic performance of TiO
2
growth over hydroxysodalite with 8.7 wt% and 25 wt% of TiO
2
can be explained in terms of the morphology of TiO
2
and the interactions between substrate-TiO
2
mainly.
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•Hydrothermal treatment of Coal fly produce cancrinite and analcime zeolite.•Cancrinite zeolite exhibits ferrimagnetic signature.•Adsorption of blue methylene is described by ...Freundlich and Langmuir models.
Coal fly ash (CFA) was obtained from the Sochagota TermoPaipa IV power plant in Boyacá Colombia. CFA was subjected to a hydrothermal activation with NaOH. Morphology, elemental and mineralogical composition and magnetic properties of the obtained products were studied by means of SEM-EDX, XRD and VSM.
Activation with NaOH (4–5 M) between 80 and 150 °C for 24 h produced cancrinite zeolite; activation with NaOH at 2 and 3 M at 95 °C produced analcime zeolite. It was found out, that the synthesized zeolites exhibit a ferrimagnetic behavior due to iron coming from CFA. The magnetic response of the obtained products allows the use of these materials to environmental applications in aqueous medium. Adsorption test for methylene blue was performed for an analcime and cancrinite zeolite, the results show that equilibrium is reached after 60 min. The data of adsorption isotherms for analcime and cancrinite zeolite were fitted to Freundlich and Langmuir model, respectively. The synthesized zeolites from CFA were successfully used to remove methylene blue from aqueous solution.
Study of fly ash based zeolite by using slow positrons Supelano, G.I.; Palacio, C.A.; Weber, M. ...
Materials science & engineering. B, Solid-state materials for advanced technology,
January 2021, 2021-01-00, 20210101, Letnik:
263
Journal Article
Recenzirano
•Zeolites like materials were synthesized from fly ash by hydrothermal method.•Positron annihilation measurements show that increasing of NaOH increases porosity.•The increasing of synthesis ...temperature diminishes porosity.
After coal fly ash activation with alkaline NaOH solution by the hydrothermal method, it was possible to synthesize the zeolites type Cancrinite and Analcime. Slow positron beam experiments have been performed on two set of samples. One in which the NaOH concentration was varied and another one in which the synthesis temperature range was varied. The mineralogical composition was determined by X ray diffraction, the morphology of one of the zeolite samples as compared with the coal fly ash was observed by 3D X-ray imaging. Positron results suggest that increasing the NaOH concentration produces an increase in open volume and/or defects while increasing the temperature in the sample preparation diminishes it.
New Gd4-6-10 and Gd5-7-12 Cuprate Superconductors Supelano, G. I.; Buitrago, D. Martinez; Gómez, J. A. Mejía ...
Journal of low temperature physics,
11/2020, Letnik:
201, Številka:
3-4
Journal Article
Recenzirano
This paper describes the Gd
x
−2
Ba
x
Cu
2
x
−2
O
δ
(
x
= 6, 7) cuprate system synthesis using the conventional solid-state reaction method. Rietveld analysis of X-ray patterns evidences that ...samples crystallize in
Pmm
2 (#25) space group at room temperature with lattice parameter
a
= 3.8807 Å,
b
= 3.8735 Å,
c
= 38.7094 Å for Gd
4
Ba
6
Cu
10
O
δ
and
a
= 3.8680 Å,
b
= 3.8763 Å,
c
= 46.5065 for Gd
5
Ba
7
Cu
12
O
δ
. Resistivity measurements evidence zero-resistance state, which is a typical behavior of superconducting materials at bulk critical temperature of 15.5 K for Gd
4
Ba
6
Cu
10
O
δ
and 22.1 K for Gd
5
Ba
7
Cu
12
O
δ
.
In this paper, we report the production of cuprate-like superconductor RE3Ba5Cu8O18-δ (RE-358, RE = Dy, Gd, Sm, Eu and Ho) by using the solid reaction method. By means of vibrating sample ...magnetometry technique (VSM), magnetization curves as a function of temperature were acquired in a Zero Field Cooled/Field Cooled (ZFC/FC) mode. Critical temperature Tc and irreversibility temperature Tirr values were obtained from magnetization curves. The irreversibility line was constructed with Tirr data, it showed an Almeida-Thouless dominant trend for low magnetic fields and Gabay-Toulose behavior for high magnetic fields. Thermodynamic fluctuations were analyzed on magnetic measurements using Bulavskii, Ledvij y Kogan model (BKL) that analyze the vortex fluctuations on Lawrence-Doniach (LD) framework. With this model, penetration length parameters λab and ab-plane coherence length ξab band c-direction ξc was obtained. Crossing point coordinates of the excess magnetization vs. temperature curves for different applied magnetic field amplitudes T* and ΔMab* were determined. Weak magnetic fields were fitted at Δχ/T limit as a function of reduced temperature ε (≥10−2). This procedure allowed us to obtain the mid-field transition temperature value Tc0. Likewise, As (Schmidt diamagnetism) and BLD (LD parameter) constants were found for each of the RE-358 system samples. This showed that through thermodynamic fluctuations analysis, RE-358 system has an excellent bidimensional behavior (2D) and it is strongly anisotropic.
Cobaltites with the general formula ACoO
3
exhibit a wide variety of physical properties. Cobaltite Pr
0.5
Ca
0.5
CoO
3
exhibits a metal–insulator transition accompanied by a structural shift with a ...delocalized intermediate spin state (
t
2
g
5
e
g
1
) or
S
∗
at high temperature. In this work, Pr
0.5−
x
Sm
x
Ca
0.5
CoO
3−
δ
(
x
= 0.02, 0.04, 0.06, and 0.08) perovskites were synthesized by the standard solid-state method. Rietveld analysis for experimental X-ray diffraction (XRD) patterns showed that the samples crystallize in an orthorhombic structure with space group
Pnma
(62). Zero field cooling-field cooling (ZFC–FC) magnetization curves, at a temperature range from 50 to 300 K, show paramagnetic behaviors in each of the Sm doped samples. The analysis of magnetization curves suggests that the samples exhibit a short-range ferromagnetic phase at 50 K and a Co low spin (LS) state in the paramagnetic regime.
•Bi1-xYbxFeO3 system were obtained by the solid-state method.•The compounds crystallize in the rhombohedral phase with space group R3c (161).•For the sample with x = 0.02, the transition from ...paramagnetic to antiferromagnetic state is observed at a Néel temperature of ∼120 K.•The insulating nature of the samples was confirmed through DC resistivity measurements.•Unsaturated hysteresis loops in electric polarization were observed, with a notable impact from leakage currents.
This work reports the effect of Yb3+ substitution on the structural, magnetic, and electrical properties of the Bi1-xYbxFeO3 system (x = 0.00, 0.02, 0.04, 0.05 and 0.06) synthesized via the solid-state reaction method. Structural properties at room temperature were studied by means of XRD diffraction. The XRD pattern were analyzed using Rietveld refinement. The results showed that the Bi1-xYbxFeO3 samples mainly crystallize in rhombohedral phase with space group R3c (161). Magnetic measurements as a function of temperature showed two magnetic behaviors, the first for x < 0.05 and the second one for x < 0.06. From the DC resistivity measurements, the insulating nature of the samples was verified. The electrical behavior of the compounds was also investigated by means of complex impedance spectroscopy. Strong dependence of the electrical properties on the frequency and composition was observed. The electric polarization showed unsaturated hysteresis loops, strongly affected by leakage current.
The production and structural & magnetic characterization of new superconductor system TR:3811 (TR=Sm, Y, Yb) is presented in this work. The samples were produced by the solid state reaction method. ...The analysis of the measures of the diffraction X-ray, were made with the Rietveld refinement technique, that allowed to infer that the system presents a Pmm2 type structure with the following lattice parameters (a=3.88Å, b=3.82Å, c=42.82Å). The magnetization measurements were made by using the VSM-VERSALAB equipment with a magnetic field variation from a 100Oe to 7000Oe, and a temperature from 50K to 350K, showing the superconducting transition of the order of 90K.
In this work, we report the production of TR3Ba5Cu8Oδ (TR=Ho, Y and Yb) superconducting system using a usual solid state reaction method. The irreversibility line and the analysis of magnetization ...fluctuations for TR3Ba5Cu8Oδ (TR=Ho, Y and Yb) system were investigated. The curves of magnetization ZFC–FC were measured in magnetic fields of the 100–4000Oe to obtain the values for T⁎ and TC temperatures. The penetration depth and the coherence length parameters as a function of the applied magnetic field were obtained. The data of the magnetization excess ΔM(T, H) was analyzed from the curves of magnetization as a function of logarithm of applied field for different values of temperature in the corresponding range. The Bulavskii, Ledvij and Kogan theory was employed for this purpose which considers fluctuations effects in the free energy and into the equilibrium magnetization.
The production and the structural and magnetic characterization of the Bi1-xYxFeO3 (x= 0, 0.25 and 0.3) system is reported in this work. The system was produced through the solid-state reaction ...technique. The morphological characterization obtained by scanning electron microscopy technique evidences the granular behavior. The structural properties were studied by means of X-ray diffraction technique. Magnetization measurements in function of temperature of the Bi1-xYxFeO3 (x= 0, 0.25 and 0.3) system were performed with the magnetometer VSM by means of the Zero Field Cooled-Field Cooled method. The results obtained from all the techniques evidence the effect of yttrium on the physical properties of BiFeO3.
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