Forced hydrolyses in the precipitation systems (a) Fe(NO
3
)
3
/Fe
2
(SO
4
)
3
and FeCl
3
/Fe
2
(SO
4
)
3
and (b) FeCl
3
/N-guanylurea sulphate were investigated using
57
Fe Mössbauer and FT-IR ...spectroscopies and scanning electron microscopy (FE SEM). Forced hydrolyses of Fe(NO
3
)
3
/Fe
2
(SO
4
)
3
solutions at 90 °C yielded superparamagnetic goethite nanorods, whereas in the case of FeCl
3
/Fe
2
(SO
4
)
3
solutions the clusters of akaganéite nanoneedles were formed. With a prolonged heating time at 90 °C the conversion of these akaganéite nanoneedles into goethite nanorods was observed. Forced hydrolysis in the system FeCl
3
/N-guanylurea sulphate at 160 °C generated only hematite and goethite phases and their fractions depended on the concentration of FeCl
3
and the amount of N-guanylurea sulphate in the solution. Different shapes of iron(III) oxyhydroxides and hematite in dependence on the experimental conditions were monitored with FE SEM. Specifically adsorbed sulphates on these particles, as shown by FT-IR spectroscopy, served as directing agents in the particle/crystal growth.
This study aims to find a suitable method to transform the amorphous iron oxides obtained from the incineration of combustible waste slag into hematite. The resulting samples were utilized as ...heterogeneous photocatalysts for the photo-Fenton degradation of methylene blue (MB) aqueous solution. A good correlation was found between the MB degradation and the amount of hematite phase as confirmed by XRD and Mössbauer measurements. The largest rate constant (
k
) was (4.1 ± 0.08) × 10
−2
min
−1
for MB decomposition under visible-light for the sample N5-50-800. The results are promising for both low-cost photocatalysts and recycling of combustible waste slags.
Debye temperatures of α-SnxFe1−xOOH nanoparticles (x = 0, 0.05, 0.10, 0.15 and 0.20, abbreviated as Sn100x NPs) prepared by hydrothermal reaction were estimated with 57Fe- and 119Sn-Mössbauer spectra ...measured by varying the temperature from 20 to 300 K. Electrical properties were studied by solid-state impedance spectroscopy (SS-IS). Together, the charge–discharge capacity of Li- and Na-ion batteries containing Sn100x NPs as a cathode were evaluated. 57Fe-Mössbauer spectra of Sn10, Sn15, and Sn20 measured at 300 K showed only one doublet due to the superparamagnetic doublet, while the doublet decomposed into a sextet due to goethite at the temperature below 50 K for Sn 10, 200 K for Sn15, and 100 K for Sn20. These results suggest that Sn10, Sn15 and Sn20 had smaller particles than Sn0. On the other hand, 20 K 119Sn-Mössbauer spectra of Sn15 were composed of a paramagnetic doublet with an isomer shift (δ) of 0.24 mm s−1 and quadrupole splitting (∆) of 3.52 mm s−1. These values were larger than those of Sn10 (δ: 0.08 mm s−1, ∆: 0.00 mm s−1) and Sn20 (δ: 0.10 mm s−1, ∆: 0.00 mm s−1), suggesting that the SnIV-O chemical bond is shorter and the distortion of octahedral SnO6 is larger in Sn15 than in Sn10 and Sn20 due to the increase in the covalency and polarization of the SnIV-O chemical bond. Debye temperatures determined from 57Fe-Mössbauer spectra measured at the low temperature were 210 K, 228 K, and 250 K for Sn10, Sn15, and Sn20, while that of α-Fe2O3 was 324 K. Similarly, the Debye temperature of 199, 251, and 269 K for Sn10, Sn15, and Sn20 were estimated from the temperature-dependent 119Sn-Mössbauer spectra, which were significantly smaller than that of BaSnO3 (=658 K) and SnO2 (=382 K). These results suggest that Fe and Sn are a weakly bound lattice in goethite NPs with low crystallinity. Modification of NPs and addition of Sn has a positive effect, resulting in an increase in DC conductivity of almost 5 orders of magnitude, from a σDC value of 9.37 × 10−7 (Ω cm)−1 for pure goethite Sn (Sn0) up to DC plateau for samples containing 0.15 and 0.20 Sn (Sn15 and Sn20) with a DC value of ~4 × 10−7 (Ω cm)−1 @423 K. This non-linear conductivity pattern and levelling at a higher Sn content suggests that structural modifications have a notable impact on electron transport, which is primarily governed by the thermally activated via three-dimensional hopping of small polarons (SPH). Measurements of SIB performance, including the Sn100x cathode under a current density of 50 mA g−1, showed initial capacities of 81 and 85 mAh g−1 for Sn0 and Sn15, which were larger than the others. The large initial capacities were measured at a current density of 5 mA g−1 found at 170 and 182 mAh g−1 for Sn15 and Sn20, respectively. It is concluded that tin-goethite NPs are an excellent material for a secondary battery cathode and that Sn15 is the best cathode among the studied Sn100x NPs.
•Nanoparticles of ε-Fe2O3 in an amorphous silica matrix were prepared by the sol–gel method and it is proposed that the formation of ε-Fe2O3 phase follows γ → ε → α Pathway.•The occurrence of ε-Fe2O3 ...particles depends on several factors like annealing temperature, particle size and iron concentration in initial chemicals.•The optimized conditions for preparation of ε-Fe2O3 rich sample were confirmed and ~ 90% of the ε-phase was obtained with the particle size of 15 ± 0.6 nm.•The high coercivity of ~ 1.18 T at room temperature was confirmed for our nanoparticle system.
Nanoparticles of ε-Fe2O3 in an amorphous silica matrix were prepared by the sol–gel method without using a precursor. X-ray diffraction patterns reflect a completely amorphous state for the samples even after heat-treated up to 600 °C, while at higher temperatures the formation of crystalline iron oxide phases was observed. Transmission electron microscopy analysis showed a wide size distribution of nanoparticles from 3±0.5 to 46±0.8 nm. The occurrence of ε-Fe2O3 particles depends on several factors like annealing temperature, particle size and iron concentration in initial chemicals. Based on the 57Fe Mössbauer spectra, three octahedral and one tetrahedral iron site were identified for ε-phase. The optimized conditions for the preparation of ε-Fe2O3 rich sample were confirmed and ~ 90% of the ε-Fe2O3 phase was obtained with the particle size of 15±0.6 nm. The high coercivity of ~ 1.18 T at room temperature was confirmed for our nanoparticle system.
Nanoscroll formation by casacade intercalation–exfoliation method was investigated for a high iron-content kaolin and after the removal of its iron-bearing mineral constituents (goethite, hematite) ...by 11 M HCl treatment. Hindered kaolinite nanoscroll formation was observed by TEM in both cases, where the 11 M HCl treatment only slightly improved the occurrence of nanoscrolled shapes. The presence of minor amounts of well-dispersed, resilient Fe was observed after the exfoliation of 11 M HCl-treated sample, which was identified as structural Fe
3+
/Fe
2+
in the octahedral sheet of kaolinite by Mössbauer and X-ray absorption spectroscopy. Iron substitution in the nanokaolinite TO layers was probed by computational chemistry. The computational results indicate inner coordination changes and elongation of bonds in the iron-substituted TO structure, and the increased curvature values offer an explanation for the observed experimental results for hindered nanoscroll formation.
Graphical abstract
In this paper, tin-phosphate amorphous glass and nano-crystallized ceramic materials were synthesized by sol-gel methods and heat treated at 400 °C with the composition of xSnO2− (100-x)P2O5 (xSnP: ...‘x’ from 40 to 90 mol%). The electrical and thermal properties of tin-phosphate materials were investigated by electrical impedance spectroscopy (EIS) and thermogravimetry – differential thermal analysis – mass spectroscopy (TG–DTA–MS). Moreover, the local structure of xSnP was characterized by 119Sn-Mössbauer and magic angle spinning (MAS) 31P NMR spectroscopies. Homogeneous glasses were obtained for xSnP with ‘x’ from 50 to 80, while Sn(HPO4), SnO2, and Sn3(PO4)2 nanoparticles formed in 40SnP and 90SnP compositions, respectively. The nano-crystallized 40SnP and 90SnP samples showed large electrical conductivity (σ) of 2.02×10−5 and 1.04×10−4S cm−1 due to the conductive crystalline phases of SnP2O7 and defective SnO2, respectively. The lower σ of about 10−8S cm−1 were recorded for xSnP with ‘x’ from 50 to 80 owing to the decomposition of the 3D network built by phosphate tetrahedrons. 119Sn-Mössbauer spectra proved the growing number of SnIVO6 units, which do not contribute to the rise of electrical conductivity. On the other hand, larger σ values of 1.79×10−4 and 6.4×10−3S cm−1 were confirmed for 40SnP and 90SnP samples after heat treatment, resulting in partial reduction of SnIV to SnII and growing of the 3D network structure by PO43−. It is concluded that highly electrically conductive xSnP samples can be synthesized by the sol-gel method followed by slow heat treatment. In addition, the battery evaluation was performed of xSnP samples as cathode and anode in a sodium-ion battery. The highest initial capacity recorded for 90SnP nano-crystallized ceramic at 37.97 mAh g−1 under a current rate of 20 mA g−1 with capacity retention (%) of 48.15% after 100 cycles as a cathode material. The anode test showed that the 40SnP nano-crystallized ceramic has the largest initial capacity of 375 mAh g−1 and after heat treatment 50SnP glass significantly increased to 425 mAh g−1 compared with 186 mAh g−1 before heat treatment. Also, the heat treatment effect on the initial capacity of 90SnP nano-crystallized ceramic with observation largest value of 470 mAh g−1. These results open the way to maybe applying these glass and nano-crystallized ceramic materials in all-solid-state batteries.
•The xSnO2−(90−x)P2O5 glass was successfully prepared with a wider chemical composition of SnO2 concentration from 50 to 80 mol% by the sol-gel method.•The 40SnP and 90SnP samples exhibited notably high σ’s of 1.79×10−4 and 6.40×10−3 Scm−1 attributed to their elevated levels of proton conductivity.•90SnP as cathode demonstrated the highest initial capacity, achieving 37.97 mAh g−1 and maintaining a capacity retention of 48.15% after 100 cycles.•40SnP and 90SnP exhibited a large initial capacity of 375 mAh g−1 and 470 mAh g−1, as anode materials in SIBs.
•Sol-gel synthesized and heat-treated 40FexAlSi samples with ‘x’ of 10, 15, and 20 resulted in the precipitation of fayalite, hematite and maghemite NPs with photocatalytic properties.•The ...corresponding degradation rate constant k, following the first-order reaction kinetics, was 14.89 × 10−2 min−1 for 40Fe2O3-15Al2O3-45SiO2 sample.•The presence of various crystalline phases that contain iron ions in mixed-valence states favors the formation of continuous pathways for uninterrupted polaronic transport which enhances an increase in DC conductivity.•Electrical conductivity and photocatalytic activity of the composites increase with the alumina content.
The glass samples with the composition of 40Fe2O3-xAl2O3-(60−x)SiO2 were prepared by sol-gel method. The samples were characterized by XRD, 80 K 57Fe Mössbauer spectroscopy, TEM, FTIR and impedance spectroscopy. In the glass samples with less than 10% alumina, fayalite and hematite were crystallized by addition of hercynite. Whereas nanoparticles of hematite (α-Fe2O3) and maghemite (γ-Fe2O3) doped with Al were confirmed with the increase of alumina contents (15% and 20%). The glass samples exhibit the electronic conduction which is explained by the polaronic conduction mechanism. It is noticed that the catalysts containing a mixture of hematite and maghemite nanoparticles showed higher photocatalytic degradation of Rhodamine B dye than those containing hematite alone. It is suggested from the characterizations of newly developed iron-containing aluminosilicate glass samples that the materials with several bandgaps and without dissolving itself should be developed in the future for water purification under visible light irradiation.
Two fresh commercial pharmaceutical products containing ferrous sulfate such as Tardyferon® and Fenules® were studied by X-ray diffraction and Mössbauer spectroscopy. The obtained results ...demonstrated that each product contains iron compounds assigned to (i) FeSO
4
× H
2
O and FeSO
4
× 4H
2
O in Tardyferon® and probably two FeSO
4
× H
2
O compounds with some tiny variations in the iron local microenvironments in Fenules®, and (ii) one ferric compound which was unidentified for Tardyferon® but identified as ferric acidic iron sulfate for Fenules®. A water free ferrous sulfate declared by the manufacturer was not found in Fenules®.
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