Eu-doped CdS quantum dots (QDs) with the Eu dopant concentration in the range of 0.5-10% and zinc blende (ZB) structure were successfully synthesized by a wet chemical method. The fabricated Eu-doped ...CdS QDs exhibited emissions in the visible window approximately at 465, 590, 618 and 696 nm, which correspond to the excitonic emission of CdS QDs and the electronic transitions of the intra 4f
6
configuration from the
5
D
0
level to
7
F
1
,
7
F
2
and
7
F
4
levels of Eu
3+
dopant ions, respectively. Judd-Ofelt theory was used to estimate the properties of ligand field and luminescence quantum efficiency of the material. The interaction mechanism and the efficiency of the energy transfer process from CdS QDs to Eu
3+
ions were found by using Reisfeld's approximation formulas. The luminescence quenching of Eu
3+
-doped CdS QDs was studied through analysis of emission spectra and decay curves. The dominant interaction mechanism between Eu
3+
ions and energy transfer parameters have been found by fitting the decay curves to the Inokuti-Hirayama model. The cross-relaxation channels leading to the luminescence quenching of Eu
3+
have also been predicted.
Eu-doped CdS quantum dots with the Eu dopant concentration in the range of 0.5-10% and zinc blende structure were successfully synthesized by a wet chemical method in the noncoordinating solvent.
This study presents the modification of cassava root husk-derived biochar (CRHB) with ZnO nanoparticles (ZnO-NPs) for the simultaneous adsorption of As(
iii
), Cd(
ii
), Pb(
ii
) and Cr(
vi
). By ...conducting batch-mode experiments, it was concluded that 3% w/w was the best impregnation ratio for the modification of CRHB using ZnO-NPs, and was denoted as CRHB-ZnO3 in this study. The optimal conditions for heavy metal adsorption were obtained at a pH of 6-7, contact time of 60 min, and initial metal concentration of 80 mg L
−1
. The heavy metal adsorption capacities onto CRHB-ZnO3 showed the following tendency: Pb(
ii
) > Cd(
ii
) > As(
iii
) > Cr(
vi
). The total optimal adsorption capacity achieved in the adsorption of the 4 abovementioned metals reached 115.11 and 154.21 mg g
−1
for CRHB and CRHB-ZnO3, respectively. For each Pb(
ii
), Cd(
ii
), As(
iii
), and Cr(
vi
) metal, the maximum adsorption capacities of CRHB-ZnO3 were 44.27, 42.05, 39.52, and 28.37 mg g
−1
, respectively, and those of CRHB were 34.47, 32.33, 26.42 and 21.89 mg g
−1
, respectively. In terms of kinetics, both the pseudo-first-order and the pseudo-second-order fit well with metal adsorption onto biochars with a high correlation coefficient of
R
2
, while the best isothermal description followed the Langmuir model. As a result, the adsorption process of heavy metals onto biochars was chemisorption on homogeneous monolayers, which was mainly controlled by cation exchange and surface precipitation mechanisms due to enriched oxygen-containing surface groups with ZnO-NP modification of biochar. The FTIR and EDS analysis data confirmed the important role of oxygen-containing surface groups, which significantly contributed to removal of heavy metals with extremely high adsorption capacities, comparable with other studies. In conclusion, due to very high adsorption capacities for metal cations, the cassava root husk-derived biochar modified with ZnO-NPs can be applied as the alternative, inexpensive, non-toxic and highly effective adsorbent in the removal of various toxic cations.
This study presents the modification of cassava root husk-derived biochar (CRHB) with ZnO nanoparticles (ZnO-NPs) for the simultaneous adsorption of As(
iii
), Cd(
ii
), Pb(
ii
) and Cr(
vi
).
In this work, we have carried out systematic studies on the critical role of polyvinyl pyrrolidone (PVP) and citrate in the well-known chemical reduction route to synthesize silver nanodecahedra ...(AgND). Silver nitrate (AgNO
3
) was used as silver source, which can be directly converted to metallic silver after being reduced by sodium borohydride (NaBH
4
) under blue light-emitting diode (LED) irradiation (
λ
max
= 465 nm), and polyvinyl pyrrolidone (PVP) as a capping agent to assist the growth of AgND. The obtained products were silver nanodecahedra of excellent uniformity and stability with high efficiency and yield. The results showed that PVP acted as a capping agent to stabilize the silver nanoparticles, prolonging the initiation time required for nanodecahedra nucleation, thus inducing anisotropic growth, allowing the size and morphology of the AgND to be controlled successfully. This improved understanding allows a consistent process for the synthesis of AgND with significantly enhanced reproducibility to be developed and the formation mechanism of these nanostructures to be elucidated. This is a simple, cost-effective and easily reproducible method for creating AgND. The typical absorption maxima in the UV-vis spectroscopy of Ag seeds was
λ
max
∼400 nm and that of AgND was
λ
max
∼480 nm. The size of the prepared AgND was in the range of 60-80 nm. SEM images confirmed the uniform and high density of AgND when the concentration of PVP was 0.5 mM. The XRD pattern showed that the final product of AgND was highly crystallized. In addition, the prepared AgND can be used to detect methylene blue (MB) in a sensitive manner with good reproducibility and stability using Surface-Enhanced Raman Scattering (SERS) phenomenon. Out of the obtained products, the AgND prepared with 50 min blue LED light irradiation (AgND-50) displayed the strongest SERS signal. Interestingly, MB in diluted solution can be detected with a concentration as low as 10
−7
M (the limit of detection, LOD) and the linear dependence between SERS intensity and the MB concentration occurred in the range from 10
−7
to 10
−6
M. The enhancement factor (EF) of the SERS effect was about 1.602 × 10
6
with a MB concentration of 10
−7
M using 532 nm laser excitation.
In this work, we have carried out systematic studies on the critical role of polyvinyl pyrrolidone (PVP) and citrate in the well-known chemical reduction route to synthesize silver nanodecahedra (AgND).
In this work, we have studied the crystal structure, microstructure, magnetic properties, and the effect of isothermal structural transition on the magnetic properties of Bi0.86Nd0.14Fe1-xCrxO3 ...(0.02 ≤ x ≤ 0.1) ceramic compounds. The analysis of X-ray diffraction patterns reveals a mixture of the R3c rhombohedral and PbZrO3-type orthorhombic phases. With increasing Cr concentration, the PbZrO3-type phase percentage is gradually increased from 33% for x = 0.02–63% for x = 0.1 at the expense of the R3c phase. The magnetic properties of compounds are mainly attributed to the destruction of the long-range incommensurate cycloidal spin structure in the orthorhombic symmetry. The isothermal structural transition (IST) is observed at room temperature when samples are stored in laboratory conditions. A remarkable change of magnetic properties is observed, which is believed originated from the IST and spin frustration at the phase boundary.
•Cr doped Bi0.86Nd0.14FeO3 samples were synthesized by solid-state reaction method.•The structural analysis reveals a coexistence of the polar R3c rhombohedral and antipolar PbZrO3-type structures.•Cr doping cannot suppress the cycloidal spin structure in the R3c phase.•The enhanced magnetization is attributed to an increase in PbZrO3-type phase percentage.•The isothermal structural transition greatly influences the magnetic properties.
•The magnetic aging is observed in Bi0.84La0.16Fe0.88Ti0.12O3 polycrystalline ceramic.•The magnetization and coercivity undergo a remarkable change over time.•The exchange bias and field ...step-dependent hysteresis loop are observed.•The spin frustration and magnetic interaction are explained for the abnormal magnetic behavior.
The magnetic aging is observed in Bi0.84La0.16Fe0.88Ti0.12O3 polycrystalline ceramic at the morphotropic phase boundary. The magnetic properties, including the magnetization and coercivity, undergo a drastic change over time. The magnetic aging is explained according to the spin frustration at the phase boundary (PB) induced by the competition in Gibbs free energy and lattice strain of the coexisting phase. The change in the spin state at the PB creates the ferromagnetic order, which in turn supports the magnetic interaction at the interface of antiferromagnetic (AFM)/ferromagnetic (FM)/AFM sandwich structure. The magnetic interaction is revealed in terms of the vertical hysteresis shift, exchange bias effect, and field step-dependent hysteresis loop.
In this work, critical behavior, and magnetocaloric effect, as well as the relationship between these characteristics in polycrystalline sample La
0.7
Ba
0.3
Mn
0.8
Ti
0.2
O
3
has been studied in ...detail. The positive value of the slope of Arrott plots exhibits that the magnetic phase transition of this sample is of a second order at Curie temperature of 96 K. The critical exponents
β
,
γ
, and
δ
have been determined using various ways including the modified Arrott plots, the Kouvel–Fisher plots, and the critical isotherm analysis. Interestingly, the experimental critical exponent values were
β
= 0.349 ± 0.002,
γ
= 1.350 ± 0.033, and
δ
= 4.868 ± 0.002, which are close to those deduced for the 3D-Heisenberg model below the Curie temperature and for the 3D-XY model above it. Additionally, the ferromagnetic interaction in La
0.7
Ba
0.3
Mn
0.8
Ti
0.2
O
3
was found to be at the borderline of the long-range and short-range magnetic coupling, which was confirmed through the exchange distance decaying of
J
r
∼
r
-
4.9
. Moreover, the magnetocaloric characteristics of La
0.7
Ba
0.3
Mn
0.8
Ti
0.2
O
3
were consistent with the analysis of critical behavior.
The structural, vibrational, electrical and magnetic properties of Bi0.9Sm0.1Fe1-xCrxO3 (0.02 ≤ x ≤ 0.1) ceramics have been investigated in the vicinity of the morphotropic phase boundary (MPB) ...between the rhombohedral and orthorhombic structures. X-ray diffraction (XRD) patterns reveal a gradual formation of the orthorhombic phase and Bi14CrO24 impurity with increasing chromium concentration. The Rietveld refinement and Raman scattering analysis confirm the structural transformation from the polar R3c to the anti-polar Pnam phases. The Cole-Cole plots show two relaxation regimes which are attributed to gain and grain boundary responses above room temperature. The slim magnetic hysteresis loops are observed in samples with x = 0.02–0.08, while a robust loop with the coercivity field of Hc ≈ 1200 Oe is observed for x = 0.1 sample where the canted antiferromagnetic phase is significantly contributed to the total magnetization. This result approves that the cycloidal spin structure cannot be suppressed by Cr doping.
•Cr doped Bi0.9Sm0.1FeO3 samples were synthesized by solid-state reaction method.•The structural analysis reveals a coexistence of the polar R3c rhombohedral and antipolar PbZrO3-type structures.•Cr doping cannot suppress the cycloidal spin structure in the R3c phase.•The enhanced magnetization is attributed to an increase in PbZrO3-type phase percentage.
Designing and fabricating microwave-absorbing materials (MAMs) with a widening effective absorption bandwidth, intense reflection loss, thin matching thickness, and lightweightness is an effective ...method to mitigate the drawbacks of electromagnetic (EM) radiation while enjoying its advantages for modern life. Among MAMs, composites of magnetic materials and dielectric materials could be the best candidates. CoFe2O4 (CFO), with its unique crystalline structure, excellent EM properties, and environmentally friendly and low-cost production, has been extensively used as MAM. Meanwhile, carbonaceous-based materials have also been used as MAMs due to their intriguing properties, including flexibility, lightweight, and suitable dielectric properties. Therefore, composites of CFO/carbonaceous-based materials could be among the best MAMs. This review will be systematically reviewed for MAMs of CFO/carbonaceous-based materials in the form of two, three, and four components. The principal microwave loss mechanism for attenuation mechanisms will be carefully examined. This review also summarized perspectives and challenges for the future of CFO/carbonaceous-based materials for human security, interference protection, and radar signal absorption.
Display omitted
•A systematic review of MAMs of CoFe2O4/carbonaceous-based materials was conducted.•The MAMs were in the form of binary, ternary, and quaternary components.•Biomass, plants, or seeds carbon-based materials improved the MAMs’ microwave absorption performance.•Ternary component composites would result in good microwave absorption performance.•Multiband MAMs of CFO/carbonaceous-based materials need further fabrication and investigation.
The weak ferromagnetism in BiFeO3 classically arises from the canting of the antiferromagnetically aligned Fe3+ spins by the Dzyaloshinskii–Moriya (DM) interaction. Here, we observed an abnormally ...weak ferromagnetism in morphotropic phase boundary (MPB) compounds of BiFeO3, which could not be fulfilled by sole DM interaction. The magnetic properties were studied for two different polymorphs of the rhombohedral/orthorhombic (R-O) and rhombohedral/tetragonal (R-T) structures. The R-T composition displays a superior weak ferromagnetism over the R-O one at a small applied magnetic field (10 kOe), while a comparable value is observed in a high magnetic field (70 kOe). The phase switching controlled by external stimuli revealed that magnetization is caused by both the weak ferromagnetism associated with DM interaction and the ferromagnetic component related to the phase boundary spins located at the superficial region of the coexisting structural phases.
•The weak ferromagnetism was studied for two polymophs of R-O and R-T structures.•The R-T composition displays a superior wFM over the R-O one at a small applied magnetic field.•The wFM is caused by both the DM interaction and the PB ferromagnetism.
•Bi0.83La0.17Fe1-xCrxO3 compounds were synthesized by solid-state reaction method.•The revival of polar R3c phase is observed with an increase in Cr concentration.•The compounds display some unique ...magnetic phenomena, such as the magnetic aging and field step-dependent hysteresis loop.•The electric-field-controlled magnetism shows a complex behavior due to the interplay of the phase boundary ferromagnetism and structural phase transition.
The polycrystalline ceramics of Bi0.83La0.17Fe1-xCrxO3 (BLFCO) have been synthesized by the solid-state reaction method to investigate the features of structural phase coexistence and complex magnetic response. The coexistence of the R3c rhombohedral and Pbam orthorhombic structures has been revealed by X-ray diffraction and Rietveld refinement. Selected-area Raman scattering spectra are used to further confirm a mixed phase state as both phonon vibrations of these phases are detectable. An unusual revival of the R3c phase is observed with increasing chromium concentration. The compound displays an intriguing weak magnetic response and some unique phenomena, such as the magnetic aging and field step-dependent hysteresis loop. The electric-field-controlled magnetism shows a complex behavior due to the interplay of the phase boundary ferromagnetism and structural phase transition.
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