The phase analysis and nanostructural properties of the precipitates formed by forced hydrolysis of FeCl
3
solutions at 160 °C in the presence of Cr
3+
ions and hexamethylenetetramine (HMTA) were ...investigated. The phase analyses of the precipitates showed the presence of ferrihydrite (amorphous-like), α-FeOOH, β-FeOOH, and α-Fe
2
O
3
. The exact phase composition was strongly dependent on the starting chemical composition in the solution and the precipitation time. Ferrihydrite, α-FeOOH, and β-FeOOH were the precursors of α-Fe
2
O
3
as the end-product. Upon 2 h of autoclaving at 160 °C, the precipitates consisted of nanoparticles ~ 35 to ~ 50 nm in size, whereas after 24 h their size increased to ~ 100 nm. New shapes of these nanoparticles were found. In these precipitation systems crystalline chromium (hydrous)oxide phase was not detected. However, the formation of solid solutions between Cr
3+
ions and iron oxides could not be excluded taking into account Energy-dispersive X-ray spectroscopy (EDS) measurements.
Graphical abstract
Electrospun Ti-doped haematite fibres and their properties Robić, Marko; Ristić, Mira; Marciuš, Marijan ...
Journal of nanoparticle research : an interdisciplinary forum for nanoscale science and technology,
12/2020, Volume:
22, Issue:
12
Journal Article
Electrospun Ti-doped α-Fe
2
O
3
fibres were synthesized and their properties compared with electrospun α-Fe
2
O
3
and TiO
2
fibres as reference samples. All samples were characterized with FE SEM ...(field emission scanning electron microscopy), XRD (X-ray diffraction),
57
Fe Mössbauer, FT-IR (Fourier transform infrared) and UV/Vis/NIR (ultraviolet/visible/near infrared) techniques. Ti-doped α-Fe
2
O
3
fibres consisted of the interconnected nanoparticles. These fibres showed a hollow substructure. XRD and
57
Fe Mӧssbauer spectroscopy showed the titanium cations to be incorporated up to 10 mol% into the α-Fe
2
O
3
crystal structure. The incorporation of titanium cations into the α-Fe
2
O
3
crystal structure caused changes in the corresponding FT-IR spectra. The band gap values of the electrospun fibres were determined and the photocatalytic degradation of rhodamine B (RhB) with the same fibres was investigated.
The development of an efficient and stable photo(electrochemical) catalyst is a very challenging task because its catalytic activity depends directly on the electronic structure and the charge ...carrier transfer through the catalyst/electrolyte interface. Therefore, the main objective of this study was to optimize the semiconducting properties of the electrospun α-Fe
2
O
3
fibres by Ru
3+
and Pt
4+
doping, to determine the effect of these cations on magnetic and optical properties, as well as on the photocatalytic and photoelectrochemical activity of α-Fe
2
O
3
fibres. Increased temperature of the Morin transition, enhanced remanent magnetization, lower coercivity and narrower optical bandgap in hematite fibres by Pt
4+
and Ru
3+
doping was observed. Electrochemical measurements revealed
n
-type conductivity of all fibres, while increased donor density and anodic shift of the flatband potential were registered for the doped fibres. The photoactivity of fibres, which was tested for the degradation of rhodamine B, depended on the dopant used.
Graphical abstract
Cr-doped α-Fe
2
O
3
fibres were synthesized by combining electrospinning and the thermal treatment of electrospun composite fibres at 500 °C. XRD analysis showed the formation of solid solutions with ...a corresponding small decrease in the unit-cell volume due to a difference between the ionic radii of Fe
3+
and Cr
3+
cations. Mössbauer spectroscopy showed that the incorporation of Cr
3+
into the α-Fe
2
O
3
crystal structure induced a decrease in the hyperfine magnetic field. Doping of α-Fe
2
O
3
with Cr
3+
also influenced the shape and position of IR bands in relation to reference α-Fe
2
O
3
fibres in the corresponding FT-IR spectra. The FE-SEM images of Cr-doped α-Fe
2
O
3
fibres showed that they consisted of interconnected nanoparticles and possessed a hollow substructure. The photocatalytic degradation of rhodamine B using electrospun fibres was also investigated.
Phase composition, microstructural and magnetic properties of electrospun hematite/cuprospinel composites were investigated. Samples were synthesized starting with 0 to 10 mol% of copper relative to ...iron. The round shape of reference electrospun fibres was preserved upon their heating up to 600 °C in air, whereas at 700 °C hollow substructure was additionally formed. In these reference samples the presence of hematite phase was detected by XRPD. A small amount (traces) of Fe
3
O
4
/γ-Fe
2
O
3
was also found, due to the reduction conditions created during the burning of the polyvinylpyrrolidone matrix. Rietveld analysis of samples containing 10 mol% copper and produced at 500 °C and 700 °C did not show the tendency to form solid solutions between hematite and Cu cations. Electrospun fibres containing 10 mol% copper after heating at 500 °C consisted of magnetite and cubic cuprospinel as the dominant phases and hematite as the associated phase. Upon heating at 700 °C the phase composition showed the presence of hematite as the dominant phase and tetragonal cuprospinel as the associated phase. For this tetragonal cuprospinel the formula Cu
0.6
Fe
2.4
O
4
was calculated. Mössbauer spectra recorded at 20 °C and at liquid helium temperature also showed the presence of hematite and spinel structures. Measured hyperfine magnetic splitting reflected the distributions of Fe
2+
, Fe
3+
and Cu
2+
cations in the spinel structures. The magnetic measurements also confirmed that there is no Cu incorporation into the electrospun hematite.
Pure and Sn-doped goethite (α-FeOOH) nanoparticles with good uniformity were synthesized by a facile precipitation method. The effects of Sn doping on the particle size and shape, structural, ...thermal, vibrational, optical and photocatalytic properties of prepared goethite nanoparticles were investigated. The Sn
4+
-for-Fe
3+
substitution in the crystal structure of goethite was proved by determination of a significant unit cell expansion (the effect of larger Sn
4+
ions) and a substantial reduction of the hyperfine magnetic field (the effect of magnetic dilution by non-magnetic Sn
4+
ions). Sn doping induced a decrease in length and an increase in thickness of goethite nanocrystallites and nanoparticles, i.e., the change in particle shape from thin goethite nanorods to shorter and thicker Sn-doped goethite nanoellipsoids and nanocuboids. Thermal dehydroxylation of goethite was shifted to significantly higher temperatures by the Sn
4+
-for-Fe
3+
substitution. The optical band gap of goethite nanoparticles narrowed with the increased Sn
4+
-for-Fe
3+
substitution. The visible light photocatalytic efficiency for rhodamine B (RhB) degradation by a heterogeneous photo-Fenton process was gradually enhanced by Sn doping from 38% for pure goethite nanorods to 55% for Sn-doped nanoellipsoids and 70% for Sn-doped goethite nanocuboids.
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.
Grimaldiite (α-CrOOH) was precipitated hydrothermally from the CrCl
3
aqueous solution in the presence of hexamethylenetetramine (HMTA). The crystallite size of grimaldiite samples was estimated to ...be ~ 2 nm. Eskolaite (α-Cr
2
O
3
) was produced by the calcination of grimaldiite at 500 and 700 °C. FE-SEM images showed amorphous-like aggregates of grimaldiite due to very fine particles (crystallites), whereas eskolaite was in the form of sphere-like nanoparticles. Synthesized grimaldiite and eskolaite were used in the investigation of rhodamine B (RhB) degradation. The significant degradation percentage of RhB obtained by grimaldiite was explained as catalytic effect (in dark) and photocatalytic contribution (with illumination).
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.
A simple one-pot synthesis was utilized to prepare Mn-doped maghemite nanoparticles. A homogenized mixture of Mn- and Fe-acetylacetonates was heated in air atmosphere at 300 °C to produce Mn-doped ...maghemite. XRD showed only the presence of a spinel crystal structure with a linear increase of the unit-cell volume up to 20 mol% of the Mn dopant. Possible structural changes with increased Mn doping are briefly discussed.
57
Fe Mössbauer spectra recorded at 77 K were fitted with two sextets of lines corresponding to Fe
3+
ions at A-tetrahedral and B-octahedral sites in maghemite. FE SEM images showed that Mn-doped maghemite nanoparticles were of good uniformity, with the crystallite size varying from 24 to 35 nm, as determined by XRD.
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