Mg–Zn ferrites with porous cavity structure were produced by sol-gel auto-combustion method utilizing a new mixture of dl-alanine and urea as an organic fuel-reductant. The influence of non-magnetic ...Zn ions content on the structural, morphological and adsorption characteristics of Mg–Zn NPs has been investigated. It was found that Zn effects the porosity of Mg–Zn ferrospinels. X-ray diffraction analysis confirmed the formation of cubic spinel phase and the crystallite size was calculated by the SSP method, W-H method and modified Scherrer formula. SEM observations revealed mesh-like microstructure with the presence of 1–2 μm macropores and agglomerated nanoparticles. The EDS spectra confirmed the desired chemical composition of ferrites powders. Mössbauer spectroscopy confirmed the valence state of cations and their distribution over the spinel sublattices. The adsorption characteristics of spinel compounds were studied on Congo Red dye removal. The appropriateness of Langmuir, Freundlich, and Dubinin-Radushkevich adsorption models were investigated and the parameters of all models were determined. The observed data fitted well by Langmuir model, indicating that the Congo Red adsorption occurred on a homogeneous surface and that the active surface centers possessed similar energy values. The Dubinin-Radushkevich isotherm model was utilized to calculate the free energy of Congo Red adsorption, i.e. setting in the range 7.81–22.4 kJ/mol and indicating that the Zn content affects the mechanism of Congo Red adsorption onto ferrite surfaces and the removal efficiency is enhanced with the rise in Zn content.
Display omitted
•Mg–Zn ferrites with porous cavity microstructure have been synthesized.•Cationic distribution of Mg–Zn ferrites confirmed by both XRD and Mossbauer spectroscopy.•Presence of Zn ions in Mg ferrite enhance its surface morphology.•Mg–Zn ferrites exhibit enhanced adsorption efficiency for the Congo Red dye.
The magnesium-zinc ferrites Mg1-xZnxFe2O4 (x = 0…1) were studied as magnetic sorbents for environmental applications. Low-temperature Mössbauer spectroscopy was used to determine the distribution of ...magnesium and ferric ions in the spinel crystal lattice. The influence of Zn content on magnetic parameters was investigated on the basis of VSM data. As the molar ratio of zinc to magnesium increases from 0 to 1, the pHPZC value decreases from 10.5 to 8.9. Langmuir and Freundlich models were used to check whether single-layer or multi-layer adsorption occurs. The adsorption of Cr(VI) and Ni(II) ions is well fitted by the Langmuir equation. To check the physical or chemical nature of the sorption process, the Dubinin-Radushkevich equation was used. It was found that the processes of adsorption of Cr(VI) and Ni(II) ions are of a chemical nature. The best Cr(VI) ion adsorption capacity was found for the Mg0·2Zn0·8Fe2O4 sample (qe = 30.49 mg/g). The percentage of heavy metal removal by the mixed ferrite samples increases with increasing zinc content. The most effective sorbent for Ni(II) removal is the Mg0·4Zn0·6Fe2O4 sample (93.2%). Modeling the antistructure provides deeper insight into the mechanism of heavy metal adsorption. The obtained magnesium-zinc ferrites are promising magnetic adsorbents for removing chromate and nickel ions from the environment.
Display omitted
•Magnesium-zinc ferrites were investigated as adsorbents for the Cr(VI) and Ni(II) removal.•Mg0·2Zn0·8Fe2O4 sample showed the best adsorption capacity (qe = 30.49 mg/g).•Mg0·4Zn0·6Fe2O4 sample is the most effective sorbent for Ni(II) removal (93.2%).•Adsorption capacity is influenced by the surface active centers.•The higher the content of octahedral Mg cations, the lower the adsorption capacity.
Nanostructured Zn-doped cobalt ferrites (Co
1−
x
Zn
x
Fe
2
O
4
, where
x
ranges from 0.0 to 1.0 with a step of 0.1) were studied in order to elucidate the relation between their cationic distribution ...within the spinel sublattices and catalytic properties. The thermal transformation of the precursors (metal hydroxides) obtained through the hydroxide co-precipitation method was studied by DTA, TGA and FTIR. The thermal behavior of the precursors showed that cobalt ferrite was formed at a lower temperature (376 °C) in comparison to zinc ferrite (478 °C). FTIR analysis revealed vibrational bands around 400 cm
−1
and 600 cm
−1
related to (MO
4
)
6−
and (MO
6
)
9−
groups, respectively. The cationic distribution was determined from Mössbauer spectra analysis and the results showed that Zn ions occupy the A-sites, while Co and Fe ions are located in the A- and B-sites. The spectra indicate spinel magnetic ordering in samples with
x
= 0.0...0.5. The increase in Zn content influences the difference in the Pauling electronegativities, distances between magnetic ions (hopping length) and polaron radius of Co
1−
x
Zn
x
Fe
2
O
4
ferrites, inducing changes in the ionic bond strength for the A- and B-sites. Photoelectrochemical measurements demonstrated that the introduction of Zn
2+
into the spinel structure modifies the ability of the materials to reduce O
2
. Whereas photoinduced reduction of dioxygen at CoFe
2
O
4
competes successfully with anodic photocurrent generation (observed as a decrease of photocurrent), for ZnFe
2
O
4
this process is negligible. The relation between the cationic distribution (analyzed in terms of antistructure modeling) and the catalytic activity of spinel ferrites was demonstrated for the example of the soot combustion process. It was shown that the octahedral cobalt centers exhibit a higher catalytic activity than the tetrahedral ones.
The strong relation between the cationic distribution and catalytic properties of Co-Zn ferrite nanoparticles was studied and the new antistructure modeling approach has been proposed for identification of the active centers in the redox reaction.
Cobalt (II) ferrite-chromites CoCr2-xFexO4 (x = 0.0 ÷ 2.0, step is 0.2) with spinel structure have been synthesized using sol-gel method with citrate metal-polymer precursor. The relations between ...structural, morphological and catalytic properties of the mixed spinels have been studied. The CoCr2-xFexO4 powders were analyzed using X-ray diffraction analysis, Mössbauer spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, energy-dispersive analysis and Brunauer–Emmett–Teller (BET) methods. The average crystallite size was calculated using the Williamson-Hall and size-strain plot methods. Increase of Fe content resulted in increase of the crystallite size from 10 nm (CoCr2O4) to 35 nm (CoFe2O4). Chromium ions were located mainly in octahedral sites, whereas the cobalt and ferric ions were distributed between the octahedral and tetrahedral sites. The lattice parameter was dependent mostly on the octahedral site radius. Superparamagnetic properties of the nanoparticles were described by two-level relaxation model. The samples with a high content of chromium (III) have highly porous structure. Porosity of the samples was decreased with increasing the Fe content. IR spectra contain two peaks corresponding to two characteristic sites in the cubic spinel structure. The mixed ferrite-chromite spinels have catalytic activity in decomposition of hydrogen peroxide. Rate of H2O2 decomposition in the presence of cobalt (II) ferrite-chromite NPs corresponds to the first-order kinetic model. Within 25 min, the decomposition degree is 76.6% with the most active CoFe2O4 sample. Catalytic activity of the samples depends on two factors: the specific surface area and the surface active sites. Antistructure modeling revealed that the tetrahedral Fe(III) sites have electron acceptor properties. The formed Fe(II) ions are active centers in the Fenton-like processes. Probably, the red-ox pairs Co2+/Co3+ in the spinel lattice promote catalytic activity due to acceleration of electron transfer. The spinel cobalt (II) ferrite-chromites are promising catalysts for oxidation of toxic organic impurities in wastewaters with using H2O2.
CD4 Th cells producing the proinflammatory cytokine IL-17 (Th17) have been implicated in a number of inflammatory arthritides including the spondyloarthritides. Th17 development is promoted by IL-23. ...Ankylosing spondylitis, the most common spondyloarthritis (SpA), is genetically associated with both HLA-B27 (B27) and IL-23R polymorphisms; however, the link remains unexplained. We have previously shown that B27 can form H chain dimers (termed B27(2)), which, unlike classical HLA-B27, bind the killer-cell Ig-like receptor KIR3DL2. In this article, we show that B27(2)-expressing APCs stimulate the survival, proliferation, and IL-17 production of KIR3DL2(+) CD4 T cells. KIR3DL2(+) CD4 T cells are expanded and enriched for IL-17 production in the blood and synovial fluid of patients with SpA. Despite KIR3DL2(+) cells comprising a mean of just 15% of CD4 T in the peripheral blood of SpA patients, this subset accounted for 70% of the observed increase in Th17 numbers in SpA patients compared with control subjects. TCR-stimulated peripheral blood KIR3DL2(+) CD4 T cell lines from SpA patients secreted 4-fold more IL-17 than KIR3DL2(+) lines from controls or KIR3DL2(-) CD4 T cells. Strikingly, KIR3DL2(+) CD4 T cells account for the majority of peripheral blood CD4 T cell IL-23R expression and produce more IL-17 in the presence of IL-23. Our findings link HLA-B27 with IL-17 production and suggest new therapeutic strategies in ankylosing spondylitis/SpA.
The series of Er2-xHoxFe14B (x = 0.5, 1.0, 1.5, 2.0) intermetallic compounds was studied in order to investigate different types of spin arrangements expected in this series. The variety of processes ...connected with spin reorientation, especially transition through conical spin arrangements was of special interest. The compounds have been measured with 57Fe Mössbauer spectroscopy over the temperature range 5.2–320 K. Each compound was studied with precise Mössbauer scanning in the vicinity of the transition. A special fitting procedure of Mössbauer spectra, enabling to analyze up to ten spectra simultaneously, was developed to determine the arrangement of spins. The path of spin rotation was proposed. The results were verified and compared by applying computer simulations based on the Yamada-Kato model. The spin arrangement diagram was constructed. Obtained results are convincing enough to conclude that Mössbauer spectroscopy can be very helpful in studies of tilt angle in conical spin arrangements in the studied type compounds.
•Spin reorientation process has been studied in a new series of Er2-xHoxFe14B.•Unique method of simultaneous spectra analysis is presented.•Computer simulation of spin reorientation process is performed.•Temperature dependence of tilt angle is presented.•Spin arrangement diagram is constructed.
We report on an extended cavity quantum cascade laser based on a cavity resonator integrated grating filter (CRIGF) that acts as both cavity end-reflector and spectral selector. Stable, mode-hop ...free, single-mode emission around 2150 cm
is obtained over large injection current ranges (more than 50 mA) with a typical threshold around 290 mA. A digital frequency tuning over more than 65 cm
is obtained by changing the periodicity of the CRIGF ending the extended cavity.
Cavity Resonator Grating Filters (CRIGFs) working in the Mid-Infrared are reported, with narrow-band resonant reflectivity peaks around 2200 cm
(4.6 µm). They are fabricated in the GaAs/AlGaAs ...material system that can potentially cover the whole 1-12 µm spectral range. TE-polarized peak reflectivity is 30% with a 4 cm
full width at half maximum.
The data set of the Warta discharges in Poznań (Poland) is one of the largest in the world as the daily observations of river stages have been conducted without interruptions since January, 1
, 1822. ...The Poznań measurement profile is situated in the 243.6 km and closes the catchment area of approximately 25 thousand square kilometers. The data used as the input in the paper were daily values of the Warta discharges in Poznań in the years 1822-2012. The climate in Poznań, a city situated in the centre of the Wielkopolska (Greater Poland) region, is relatively stable (Miler et al. 2005). Also the Warta River runoff shows considerable stability, especially in terms of mean annual values. Short-term trends are random in character. It was found that the Jeziorsko reservoir (total storage volume of 203 000 000 m
, officially put to use on September, 9
, 1987) significantly reduced daily variability of the flows and reduced peak discharge of the flood wave in the summer of 1997 on the Warta River at Poznań. The calculated periodogram for mean annual discharges of the Warta River in Poznań shows that there are main periodicities of ca. 10 year lengths. The research of the Provincial Inspectorate for Environmental Protection (WIOŚ) in Poznań shows a gradual improvement of water quality in the Warta River in Poznań.
Zbiór danych o przepływach Warty w Poznaniu (Polska) jest jednym z największych na świecie zbiorów codziennych obserwacji stanów wody w rzece. Obserwacje te prowadzone są nieprzerwanie od 1 stycznia 1822 roku. Profil pomiarowy w Poznaniu znajduje się na 243,6 km i zamyka zlewnię o powierzchni około 25 tys. km
. Dane użyte jako wejście w tej pracy stanowiły przepływy dobowe Warty w Poznaniu w latach 1822-2012. Klimat Poznania, położonego w centrum Wielkopolski, jest stosunkowo stały (Miler i in. 2005). Także odpływy Warty wykazują znaczną stabilność, szczególnie w odniesieniu średnich rocznych wartości. Krótkookresowe trendy mają charakter przypadkowy. Wykazano, że zbiornik Jeziorsko (pojemności całkowitej 203 mln m
, oficjalnie oddany do użytkowania 9 września 1987 roku) znacząco zmniejsza dobową zmienność przepływu oraz zredukował maksymalny przepływ fali powodziowej w lecie 1997 Warty w Poznaniu. Obliczony periodogram dla wartości średnich rocznych przepływów Warty w Poznaniu wskazuje, że główne są okresowości około 10-letnie. Badania Wojewódzkiej Inspekcji Ochrony Środowiska (WIOŚ) w Poznaniu wskazują na stopniową poprawę jakości wody w Warcie w Poznaniu.
PDF
