Nanocrystalline EuCrO3 particles (∼25 nm) have been prepared by pre-milling a 1 : 1 molar mixture of Eu2O3 and Cr2O3 for 60 h followed by sintering at 700 °C (12 h). This temperature is ∼500–600 °C lower than those at which the material, in bulk form, is conventionally prepared. Rietveld analysis of the x-ray powder diffraction pattern of the EuCrO3 nanoparticles favours a structural model involving a slight degree of cationic exchange where ∼11% of the Eu3+ and Cr3+ ions exchange their normal dodecahedral A- and octahedral B-sites, respectively, in the perovskite-related structure. This cationic site exchange, which is unusual in a perovskite structure, has been well supported by the corresponding room-temperature 151Eu Mössbauer spectrum of the nanoparticles that in addition to displaying a distribution in the principal component of the EFG tensor (V
zz
) at the usual A-sites of the 151Eu nuclei, also revealed the presence of a subcomponent with ∼11% area fraction and a considerably increased |V
zz
| value that was associated with Eu3+ ions at octahedral B-sites. X-ray photoelectron and Auger electron spectroscopic techniques reveal a complex surface structure where extremely thin layers of un-reacted Eu2O3 and Cr2O3 cover most of the EuCrO3 nanoparticles' surfaces together with some traces of elemental Cr. The binding energies associated with Eu3+ 3d5/2, Eu3+ 4d3/2, Cr3+ 2p3/2 and O2− 1s core-level electrons in EuCrO3 are estimated from the x-ray photoelectron data for the first time.
Prevention of iron chlorosis with Fe synthetic chelates is a widespread agronomical practice but implies high costs and environmental risks. Blood meal is one of the main fertilizers allowed to be used in organic farming. Through this work a novel blood meal fertilizer was audited. Measurements such as FTIR, Raman, electron paramagnetic resonance, and Mössbauer spectroscopy, UV-visible properties, stability against pH, and batch experiments were performed to characterize and assess the reactivity on soil constituents and agronomic soils. The spectroscopy findings give clear indications that Fe is in the ferric oxidation state, is hexacoordinated, and has a low-spin form suggesting a similar structure to hemin and hematin. A spectrophotometric method at 400 nm was validated to quantify blood meal concentration at low electrolyte concentrations. Batch experiments demonstrated high reactivity of blood meal fertilizer with soil constituents, mainly in the presence of calcium, where aggregation processes are predominant, and its ability to take Fe from synthetic Fe (hydr)oxides. The beneficial profile of blood meal by a providing nitrogen source together with the capability to keep the Fe bound to porphyrin organic compounds makes it a good candidate to be used as Fe fertilizer in organic farming.
Abstract:In meeting the need for environmental remediation in wastewater treatment and the development of popular sulfate-radical-based advanced oxidation processes (SR-AOPs), a series of Co/Fe-based catalysts with confirmed phase structure were prepared through extended soft chemical solution processes followed by atmosphere-dependent calcination. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and 57 Fe Mössbauer spectroscopy were employed to characterize the composition, morphology, crystal structure and chemical state of the prepared catalysts. It was shown that calcination in air, nitrogen and ammonia atmospheres generated Co-Fe catalysts with cobalt ferrite (CoFe 2 O 4 ), Co-Fe alloy and Co-Fe nitride as dominant phases, respectively. The prepared Co/Fe-based catalysts were demonstrated to be highly efficient in activating peroxymonosulfate (PMS) for organic Orange II degradation. The activation efficiency of the different catalysts was found to increase in the order CoFe 2 O 4 < Co-Fe nitride < Co-Fe alloy. Sulfate radical was found to be the primary active intermediate species contributing to the dye degradation for all the participating catalysts. Furthermore, a possible reaction mechanism was proposed for each of the studied catalysts. This study achieves progress in efficient cobalt-iron catalysts using in the field of SR-AOPs, with potential applications in environment remediation.
Tin oxide intercalated montmorillonite nanocomposites were prepared by an in situ preadsorption method in aqueous solution in the absence of surfactants and organic solvents. The tin oxide particle size was controlled by adjusting the relative supersaturation ratio, S (S ) (Q -L)/L), where Q is the amount of the dissolved material, the Sn(OH)4 precipitate, and L is its solubility). Increasing the relative supersaturation results in a progressive increase of the size of the SnO2 nanoparticles up to a maximum, after which a further increase of S results in a decrease of the size of the nanoparticles, since their growth is inhibited. Calcination of the 2-3 nm diameter SnO2/Sn(OH)4 nanoparticles at 400 °C for 3 h resulted in the formation of an oxide lattice structure from a tin oxide/hydroxide structure. XRD measurements indicated the sizes of tin oxide nanocrystals to be in the 1-2 nm diameter range between the layers of montmorillonite. The specific surface area of montmorillonite significantly changed from 30 to 112.5 m 2 /g upon SnO2 intercalation, as evidenced by BET. The thermoanalytical investigations revealed the optimal calcination temperature of the nanocomposites (400 °C) and proved the presence of the SnO 2 nanoparticles by the heat effect of their crystallization process. The Mo ¨ssbauer studies of the samples indicated the particle size dependence on the effective vibrating mass (Meff) and the Debye temperature (ΘM) of the tin oxide nanocrystals. It was confirmed by all of the measurement methods that smaller particle size can be attained by increasing the relative supersaturation ratio of the Sn(OH) 4 precipitate.
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