Formation Of Secondary Oxides Research Articles

Simulated solar photocatalytic ozonation of contaminants of emerging concern and effluent organic matter in secondary effluents by a reusable magnetic catalyst

A magnetic TiO2/Fe3O4/activated carbon composite was used as a photocatalyst for the removal of contaminants of emerging concern (CECs) and effluent organic matter (EfOM) of real and simulated effluents from municipal wastewater treatment plants (MWWTPs). While the catalyst showed limited activity under simulated solar irradiation in the absence of ozone, the CECs were completely eliminated and dissolved organic carbon (DOC) removal efficiencies reached up to more than 75% by simulated solar photocatalytic ozonation. The effects of EfOM (0–30 mg·L−1 DOC), carbonate/bicarbonate (0–60 mg·L−1 IC) and PO4-P (0–3.5 mg·L−1) concentrations of the secondary effluent on the photocatalytic activity was studied. Both EfOM and carbonate/bicarbonate concentration accelerated the DOC removal in single ozonation experiments (i.e., absence of catalyst and radiation) due to the presence of initiators of the hydroxyl radical chain, the formation of secondary oxidants (i.e., hydrogen peroxide and carbonate radical) and the buffering capacity of the effluent. However, the interaction of EfOM and carbonate/bicarbonate with the catalyst brought about a decrease of its photocatalytic activity. Phosphates, in the concentration range studied, did not influence appreciably the catalytic activity. The reusability of the catalyst was evaluated through eight consecutive simulated solar phototacalytic ozonation runs. Samples of fresh and reused catalysts were examined by bulk composition analysis, N2 adsorption-desorption isotherms, XRD, XPS, SQUID magnetometry and the pHPZC. Despite some changes in the porous structure and the fixation of some oxygen groups on the carbon surface as a result of ozonation, the catalyst showed good stability and the oxidation efficiency was maintained through runs.

Structure and phase composition of oxide dispersion strengthened fcc alloys prepared via strong deformation in the Fe2O3-Fe-Ni-M (M = Ti, Zr) systems

Deformation-induced Fe 2 dissolution in fcc Fe-Ni-M (M = Ti, Zr) alloys has been studied by Mossbauer spectroscopy, X-ray diffraction, and transmission electron microscopy. The results indicate that high-pressure shear deformation in Bridgman anvil cells and ball milling lead to dissolution of the low-stability oxide Fe2O3 in the fcc matrix and the formation of metallic solid solutions and secondary oxides of the alloying elements. This enables preparation of oxide dispersion strengthened Fe-Ni alloys and grain size reduction of the fcc matrix. The formation of secondary oxides occurs more actively during ball milling than during high-pressure shear deformation because of the more significant local heating of the mixture and the larger specific surface area and higher reactivity of the powder.

Esterification affects phytosterol oxidation

The effect of esterification with rapeseed oil fatty acids on the oxidation reactions of sitosterol, campesterol and sitostanol was investigated, as well as the interactions between phytosterol/stanol compounds and the saturated lipid matrix at 100 °C and 180 °C. Free and esterified phytosterols differed in their reactivity in terms of the formation and profile of secondary oxidation products. Phytosteryl esters were more reactive than free phytosterols during prolonged heating at 100 °C. In contrast, free phytosterols were slightly more reactive than phytosteryl esters at 180 °C. The oxidation reactions of phytostanol compounds were low under all conditions studied. Changes in the phytosterol compounds during heating were also studied via the losses in the original phytosterol contents. This study revealed that the formation of secondary oxides did not account for all the phytosterol losses; this indicates the presence of other oxidation products, especially at 180 °C, and during the heating of free sitosterol. Thus, in order to understand the overall deterioration of phytosterol and phytostanol compounds, both the secondary oxide formation and the sterol loss need to be studied. The deterioration of the saturated lipid matrix used in this study was rather low and was mainly associated with the heating temperature and time.

Mechanical synthesis in the iron oxide–metal system

The specific features of dynamic dissolution of iron oxides in metals (Fe, Ni, Cr, Zr, Ti and Al) under high-pressure compression shear at 300 K and their subsequent precipitation during thermal annealing were analyzed using Mössbauer spectroscopy, X-ray diffraction analysis, and transmission electron microscopy. Dissolution of iron oxides and formation of secondary oxides with matrix metals during deformation and subsequent annealing depended on the ability of metals to form solid solutions and chemical compounds with iron and oxygen. Formation of secondary oxides was accompanied by evolution of the surface of boundaries, providing conditions for formation of a nanocrystalline structure. It is shown that deformation-induced transport of oxygen atoms from iron oxides of low stability to the metal matrix is possible, and the formation of special oxides suitable for oxide dispersion-strengthening is demonstrated.

Formation of interbasaltic laterite horizons in NE Ireland by early Tertiary weathering processes

Geochemical and quantitative mineralogical analyses have been carried out on laterites that formed during the early Tertiary (Palaeocene) in Northern Ireland. Enrichment/depletion patterns have been identified for major, minor and trace (including rare earth) elements related to breakdown of the primary minerals plagioclase, augite and olivine and formation of secondary oxides and clay minerals. Maximum concentrations of Si, Mn, Mg, Ca, Na, K and Sr were found to occur in the parent basalt whereas concentrations of Ti, Fe, Pb, Th, U, Cr, Nb, Rb, Ba, V and Zr are at a maximum in the highly weathered iron crust. Redistribution of Al, Cu and Ni occurred during lateritization with these elements leached from the uppermost iron crust horizon and reprecipitated further down the weathering profile. Weathering caused mobilization and fractionation of the rare earth elements with the light rare earth elements leached preferentially to the heavy rare earth elements.