Free-standing carbon nanofibers are crucial electrode materials for supercapacitors. Herein, nanocube-embedded porous carbon nanofibers (P-CNFs) from manganese(II) chloride/cobalt(II) ...chloride/iron(III) nitrate-polyacrylonitrile (Mn/Co/Fe@PAN) were fabricated using electrospinning followed by a thermal treatment. The self-formation of uniformly distributed nanocubes over the carbon nanofiber was confirmed by scanning electron microscopy (SEM). P-CNF//P-CNF-based supercapacitors (SCs) using flexible and free-standing electrodes without any binder demonstrated a high mass specific capacitance of 107.4 F g
−1
at 1 A g
−1
and a good specific energy of 3.68 Wh kg
−1
in 1 M H
2
SO
4
electrolyte. Even at a high specific power, 2000 W kg
−1
, it retained a high specific energy of 3.18 Wh kg
−1
Moreover, the supercapacitor cell exhibited a remarkable rate capability with a retention of 85.5% from 1 to 8 A g
−1
and it possessed a prominent cycle stability of 97.9% after 50,000 cycles, which are really significant values reported in the literature for CNF-based electrodes to date. The high electrochemical cyclability and stability of P-CNFs originated from a combination of hierarchical porous structure of nanofibers with decoration of metallic nanoparticles. This unique nanocube structure provided more electrochemically active sites which are conductive towards electrochemical reactions. The reaction kinetics were also studied and the percentage of capacitive- and diffusion-controlled capacitance were found as 88% and 12%, respectively. As a result, addition of ternary metallic salts plays a significant role in improving ultrastable energy storage systems.
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•The reduction of azo dyes and nitro compounds were instantly completed with MnFe2O4@SiO2@Ag MRCs.•MnFe2O4@SiO2@Ag MRCs was used as heterogeneous catalyst.•MnFe2O4@SiO2@Ag MRCs with ...the room-temperature magnetism showed that it could be used as a recyclable catalyst.•MnFe2O4@SiO2@Ag MRCs showed high catalytic activity both for studied azo dyes and nitro compounds.
In this study, magnetically recycable MnFe2O4@SiO2@Ag nanocatalyst (MnFe2O4@SiO2@Ag MRCs) has been synthesized through co-precipition and chemical reduction method. XRD analysis confirmed the synthesis of single phase nanoproduct with crystallite size of 10nm. VSM measurements showed the superparamagnetic property of the product. Catalytic studies showed that MnFe2O4@SiO2@Ag MRC could catalyze the reduction of the various azo compounds like methyl orange (MO), methylene blue (MB), eosin Y (EY), and rhodamine B (RhB) and also aromatic nitro compounds such as 4-nitrophenol (4-NP), 4-nitroaniline (4-NA) and 2-nitroaniline (2-NA). Moreover, the magnetic nanocatalyst showed an excellent reusability properties that remained unchanged after several cycles. Therefore, MnFe2O4@SiO2@Ag is the potential candidate for the application of organic pollutants for wastewater treatment.
•Fe3O4@Nico@Ag magnetic recyclable nanocatalyst (MRC) is more effective for the reduction of azo dyes consisting of MB and MO.•It could be reused several times without significant loss in catalytic ...activity.•Fe3O4@Nico@Ag (MRCs) has been successively used for colour reduction of MO, MB, EY, RhB and their mixtures.
In this study, we report the successful synthesis of Fe3O4@Nico-Ag nanocomposite as magnetically recyclable nanocatalyst (MRCs) via reflux process at 80°C for 5h followed by reduction of Ag+. FeCl3·6H2O, FeCl2·4H2O, AgNO3 as starting reactants and nicotinic acid as linker. The structure, morphology, thermal behaviour and magnetic properties of the product were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectrometry (EDX), thermal gravimetry (TG) and vibrating sample magnetometry (VSM), respectively. The catalytic activity of product for various azo dyes such as methylene blue (MB), methyl orange (MO), Rhodamine B (RhB) and eosin Y (EY) and their double mixtures were studied. It was found that Fe3O4@Nico-Ag MRCs is an efficient catalyst and can also rapidly separated from the reaction medium using magnet without considerable loss in its catalytic activity and used several times. Fe3O4@Nico-Ag MRCs has potential for the treatment of industrial dye pollutants.
In this study, we reported the degradation of organic dyes (methyl orange, MO and methylene blue, MB) by Fe3O4@His@Ag MRC in which histidine was used as linker. The size of crystallite of MRC was ...calculated as 19nm. The M–H hysteresis loop of the product indicates that it exhibits superparamagnetic property at room temperature. Catalytic studies showed that this product could catalyze the degradation of MO and MB in a reasonable time. Moreover, the product can be recycled five times by magnetic separation without major loss of its activity. Thus, Fe3O4@His@Ag MRC can be served as an effective and convenient recyclable nanocatalyst for azo dye degradation and hence as an environmental protection application too.
A CoFe2O4/cetyl trimethylammonium bromide (CTAB) nanocomposite has been fabricated by a sol–gel auto-combustion method. Characterization of the material revealed the composition of the crystalline ...phase as CoFe2O4 while FT-IR confirmed the presence of CTAB on the nanoparticles. From X-ray line profile fitting, average crystallite size was estimated to be 22±6nm. SEM analysis showed a porous sheet-like morphology with internal nanosize grains of about 30nm. The room temperature coercive field (Hc) of the CoFe2O4/CTAB nanocomposite was found to be 1045Oe which is close to the previously reported room temperature values for bulk CoFe2O4. The Hc was observed to decrease almost linearly with the square root of the temperature (√T) according to Kneller's law. From the linear fit of Hc versus √T, the zero-temperature coercivity (Hc0) and superparamagnetic blocking temperature (TB) of the CoFe2O4/CTAB nanocomposite were found to be ∼9.1kOe and ∼425K, respectively. The remanence magnetization (Mr), the reduced remanent magnetization (Mr/Ms), and the effective magnetic anisotropy (Keff) decrease with increasing temperature. The Mr/Ms value of 0.6 at 10K higher than the theoretical value of 0.5 for non-interacting single domain particles with the easy axis randomly oriented suggests the CoFe2O4/CTAB nanocomposite to have cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model.
•Co0.7Zn0.3TmxFe2−xO4 (0.0 ≤ x ≤ 0.04) NPs were fabricated by sonochemical method.•IT exhibited superparamagnetic (SP) at RT and ferromagnetic property at 10 K.•An increasing trend in the Ms, Mr, Hc, ...and nB values was noticed for lower Tm3+ substitution content.
This study expressed the influence of Tm substitution on the structural, optical and magnetic properties of Co-Zn spinel ferrites (Co0.7Zn0.3TmxFe2−xO4 (0.0 ≤ x ≤ 0.04)). The different compositions were synthesized by sonochemical method using Qsonica ultrasonic homogenizer, frequency: 20 kHz and power: 70 W for 60 min. XRD patterns proved the presence of single-phase spinel ferrites with crystallites size in the 8–10 nm range. Cation distribution approved the occupancy of octahedral (B) site by Tm. The morphology and the elements stoichiometry are obtainable through FE-SEM, EDX and elemental mapping. Optical band gap (Eg) values were estimated via DR % (percent diffuse reflectance) investigations and Kubelka-Munk theory. Tauc plots revealed that direct Eg values are ranging between 1.49 and 1.68 eV. The analyses of magnetization versus magnetic field, M(H), were performed. The following magnetic parameters like saturation magnetization Ms, squareness ratio (SQR = Mr/Ms), magnetic moment nB, coercivity Hc and remanence Mr have been evaluated. M(H) curves revealed the superparamagnetic (SP) at RT and ferromagnetic property at 10 K. It was showed that the Tm3+ substitutions significantly affect the magnetic properties of host spinel ferrites. An increasing trend in the Ms, Mr, Hc, and nB values was noticed for lower Tm3+ substitution content.
Narrow size distribution nickel ferrite nanoparticles with average particle size of around 6nm has been synthesized via rapid thermo-decomposition method in the presence of oleylamine in solution ...which acted as neutralizing, stabilizing and reducing agent OAm coated NiFe2O4 NPs. X-ray powder diffraction (XRD), Fourier Transform Infrared Spectra (FT-IR), Thermal Gravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM), Vibrating Simple Magnetometer (VSM) and also Mössbauer Spectroscopy were used for structural, morphological, spectroscopic and magnetic characterization of the product. The XRD analysis revealed the formation of single phase nickel ferrite with Fd-3m space group. Both FT-IR and TGA analyses confirmed the formation of desired nanocomposite. FT-IR analysis also showed characteristic IR absorption bands of the spinel nickel ferrite phase and oleylamine. TEM and SEM analysis showed that product have almost spherical structural morphology. TEM images showed that NiFe2O4 nanoparticles have narrow size distribution and Energy Dispersive X-ray (EDX) analysis confirmed the presence of metal ions in the required stoichiometric ratio. Superparamagnetic property of the product was confirmed by VSM. From 57Fe Mössbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values have been determined. The Mössbauer spectra for OAm coated NiFe2O4 NPs. is consisting of one paramagnetic central doublets and one magnetic Zeeman sextet. Finally, the synthetic procedure can be extended to the preparation of high quality metal or alloy nanoparticles.
In this paper, we proposed the synthesis of CoFe nanoparticles (NPs) which have been deposited on carbon nanofibers (CNFs) with a facile electrospinning route followed by thermal reduction. The ...performance of obtained CNF supercapacitors are improved from 51 to 190 F/g (247 mF/cm
2
) at 0.5 A/g with the combination of CoFe NPs and graphitized carbon layers The device possessed an energy and power density of 6.6 Wh/kg and 125 W/kg, respectively. Furthermore, the capacitance retention can still maintain about 96.6% after 10,000 cycle test and it is worth noting that the cycling stability is ultrahigh. This research proves that bimetallic nanoparticles embedded in CNFs can elucidate new insights into the development new nanofiber electrode materials for the next generation of symmetric supercapacitors.
This study explored the microstructural and magnetic features of NiFe
2−
x
Dy
x
O
4
(
x
≤ 0.10) NPs (nanoparticles) that were synthesized by sol–gel auto-combustion method. The single phase of ...spinel ferrite has been verified for all samples without any impurity. The cubic morphology of the products was also showed by SEM. Room temperature (300 K) and 10 K magnetization curves were recorded applying a dc magnetic field up to ±50 kOe and it was observed that magnetic features of NiFe
2
O
4
NPs significantly changed by the substitution of Dy
3+
ion. Magnetization measurements showed low order of 300 and 10 K magnetic parameters (such as
K
eff
, coercivity and anisotropy field values), revealing soft ferrimagnetic behaviors of all pristine and doped NiDy
x
Fe
2−
x
O
4
(0.00 ≤
x
≤ 0.10) NPs at both 300 and 10 K. Pristine NiFe
2
O
4
has maximum magnetic moment and saturation magnetization values among all samples. Dy
3+
substitution showed a slight decrement in magnetization values compared with pristine sample. A slight increase in coercivity was noticed with Dy
3+
substitution. Squareness ratios (SQRs) have a range between 0.144 and 0.324. These values are smaller than the theoretical limit of 0.50, implying the multi-domain nature for NPs. Blocking temperature (
T
B
) was calculated as 28 K for NiFe
2
O
4
NPs.
Pure phase of NiDy
x
Fe
2−
x
O
4
(0.00 ≤
x
≤ 0.10) nanoparticles were prepared via sol–gel auto-combustion process. The structure, morphology, and magnetic properties were investigated.
Highlights
NiFe
2−
x
Dy
x
O
4
(
x
≤ 0.10) NPs were prepared via sol–gel auto-combustion method.
XRD analysis indicates the formation of pure single phase of spinel ferrites.
NiFe
2−
x
Dy
x
O
4
(
x
≤ 0.10
)
NPs exhibit soft ferrimagnetic nature.
All prepared NiFe
2−
x
Dy
x
O
4
(
x
≤ 0.10) NPs displayed a multi-domain nature.
Blocking temperature (
T
B
) was calculated as 28 K for NiFe
2
O
4
NPs.
We report the fabrication and characterization of a magnetically recyclable Fe3O4@Nico@Ag catalyst for reduction reactions in the liquid phase. Fe3O4 is a magnetic core and nicotinic acid was used as ...the linker for Ag. The characterization was done with X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, vibrating sample magnetometry （VSM）, and ultraviolet-visible spectroscopy. VSM measurements proved the super-paramagnetic property of the catalyst.
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