Chemical speciation and mobilization of copper and zinc in naturally contaminated mine soils with citric and tartaric acids

A one-step extraction procedure and a leaching column experiment were performed to assess the effects of citric and tartaric acids on Cu and Zn mobilization in naturally contaminated mine soils to facilitate assisted phytoextraction. A speciation modeling of the soil solution and the metal fractionation of soils were performed to elucidate the chemical processes that affected metal desorption by organic acids. Different extracting solutions were prepared, all of which contained 0.01 M KNO3 and different concentrations of organic acids: control without organic acids, 0.5 mM citric, 0.5 mM tartaric, 10 mM citric, 10 mM tartaric, and 5 mM citric +5 mM tartaric. The results of the extraction procedure showed that higher concentrations of organic acids increased metal desorption, and citric acid was more effective at facilitating metal desorption than tartaric acid. Metal desorption was mainly influenced by the decreasing pH and the dissolution of Fe and Mn oxides, not by the formation of soluble metal–organic complexes as was predicted by the speciation modeling. The results of the column study reported that low concentrations of organic acids did not significantly increase metal mobilization and that higher doses were also not able to mobilize Zn. However, 5–10 mM citric acid significantly promoted Cu mobilization (from 1 mg kg−1 in the control to 42 mg kg−1 with 10 mM citric acid) and reduced the exchangeable (from 21 to 3 mg kg−1) and the Fe and Mn oxides (from 443 to 277 mg kg−1) fractions. Citric acid could efficiently facilitate assisted phytoextraction techniques.

Analysis of single and binary phases in cerium doped sodium bismuth titanate -Na0.5Bi0.5TiO3 materials

The pure and cerium doped sodium bismuth titanate inorganic powders were synthesized by solid state reaction method. The presence of rhombohedral phase was observed in cerium doped NBT compounds. At 1200 ºC, the 5% of cerium doped NBT compound forms single perovskite phase. The samples of x = 0.10 and 0.15 were heat treated to 1350 ºC, the binary phases with cerium and bismuth oxides were observed. The X-ray diffraction, fourier transform infrared spectroscopy, reflectance spectra, differential thermal analysis and thermo gravimetric analysis were used to analyze the various properties of samples. Moreover, the effects of cerium doping and calcining temperature on NBT samples were investigated. In this work we present our recent results on the synthesis and characterization of Ce doped sodium bismuth titanate materials.

Improving the photoactivity of bismuth vanadate thin film photoanodes through doping and surface modification strategies

Currently, one of the most attractive and desirable ways to solve the energy challenge is harvesting energy directly from the sunlight through the so-called artificial photosynthesis. Among the ternary oxides based on earth–abundant metals, bismuth vanadate has recently emerged as a promising photoanode. Herein, BiVO4 thin film photoanodes have been successfully synthesized by a modified metal-organic precursor decomposition method, followed by an annealing treatment. In an attempt to improve the photocatalytic properties of this semiconductor material for photoelectrochemical water oxidation, the electrodes have been modified (i) by doping with La and Ce (by modifying the composition of the BiVO4 precursor solution with the desired concentration of the doping element), and (ii) by surface modification with Au nanoparticles potentiostatically electrodeposited. La and Ce doping at concentrations of 1 and 2 at% in the BiVO4 precursor solution, respectively, enhances significantly the photoelectrocatalytic performance of BiVO4 without introducing important changes in either the material structure or the electrode morphology, according to XRD and SEM characterization. In addition, surface modification of the electrodes with Au nanoparticles further enhances the photocurrent as such metallic nanoparticles act as co-catalysts, promoting charge transfer at the semiconductor/solution interface. The combination of these two complementary ways of modifying the electrodes has resulted in a significant increase in the photoresponse, facilitating their potential application in artificial photosynthesis devices.

Cu and Fe oxides dispersed on SBA-15:a Fenton type bimetallic catalyst for N,N-diethyl-p-phenyl diamine degradation

A bimetallic oxidation catalyst has been synthesized via wet impregnation of copper and iron over a mesoporous SBA-15 silica support. Physicochemical properties of the resulting material were characterized by XRD, N2 physisorption, DRUVS, FTIR, Raman, SEM and HRTEM, revealing the structural integrity of the parent SBA-15, and presence of highly dispersed Cu and Fe species present as CuO and Fe2O3. The CuFe/SBA-15 bimetallic catalyst was subsequently utilized for the oxidative degradation of N,N-diethyl-p-phenyl diamine (DPD) employing a H2O2 oxidant in aqueous solution.

Characterization of oxide layers grown on D9 austenitic stainless steel in lead bismuth eutectic

Lead bismuth eutectic (LBE) is a possible coolant for fast reactors and targets in spallation neutron sources. Its low melting point, high evaporation point, good thermal conductivity, low reactivity, and good neutron yield make it a safe and high performance coolant in radiation environments. The disadvantage is that it is a corrosive medium for most steels and container materials. This study was performed to evaluate the corrosion behavior of the austenitic stainless steel D9 in oxygen controlled LBE. In order to predict the corrosion behavior of steel in this environment detailed analyses have to be performed on the oxide layers formed on these materials and various other relevant materials upon exposure to LBE. In this study the corrosion/oxidation of D9 stainless steel in LBE was investigated in great detail. The oxide layers formed were characterized using atomic force microscopy, magnetic force microscopy, nanoindentation, and scanning electron microscopy with wavelength-dispersive spectroscopy (WDS) to understand the corrosion and oxidation mechanisms of D9 stainless steel in contact with the LBE. What was previously believed to be a simple double oxide layer was identified here to consist of at least 4 different oxide layers. It was found that the inner most oxide layer takes over the grain structure of what used to be the bulk steel material while the outer oxide layer consists of freshly grown oxides with a columnar structure. These results lead to a descriptive model of how these oxide layers grow on this steel under the harsh environments encountered in these applications.

(Table 8, page 38) Spectrographic analyses of deep sea manganese nodules from the Pacific and Indian Oceans

In an earlier paper by two of the authors the conclusion was reached that the 33 recognized species of oxides of Mn could be separated into 3 groups: 1) those which appeared to be persistently supergene in origin, 2) those which appeared to be persistently hypogene, and 3) those which were supergene in some localities and hypogene in other localities. When that paper was written, there were available about 250 X-ray diffraction analyses of mineral specimens, also 35 complete and about 150 partial chemical analyses. The conclusions of that paper were based upon the interpretation of the geologic conditions under which these specimens occurred. Late in the preparation of that paper, it seemed worthwhile to make numerous semiquantitative analyses of specimens, largely from 9 western [U.S.A] states, selected carefully from 5 groups of geologic environments, in the hope that the frequency and percentages of some elements might be distinctive of the several geologic groups. For this purpose, 95 specimens were selected from the 5 groups, as follows: 19 specimens interpreted as supergene oxides by the geologists who collected them, 35 specimens of hypogene vein oxides, 22 specimens of Mn-bearing hot spring aprons, 9 specimens of stratified oxides, and 10 specimens of deep-sea nodules. The spectrographic analyses here recorded indicate that a group of elements - W, Ba, Sr, Be, As, Sb, Tl, and Ge - are present more commonly, and largely in higher percentages, in the hypogene oxide than in the supergene oxides and thus serve to indicate different sources of the Mn. Also, the frequency and percentages of some of these elements indicate a genetic relation of the manganese oxides in hypogene veins, hot spring aprons, and stratified deposits. The analyses indicate a declining percentage of some elements from depth to the surface in these 3 related groups and increasing percentages of some other elements. It is concluded that some of the elements in deep-sea nodules indicate that sources other than rocks decomposed on the continents, probably vulcanism on the floors of the seas, have contributed to their formation.

Opportunities for ceria-based mixed oxides versus commercial platinum-based catalysts in the soot combustion reaction. Mechanistic implications

The aim of this paper is to study the activities of ceria–zirconia and copper/ceria–zirconia catalysts, comparing with a commercial platinum/alumina catalyst, for soot combustion reaction under different gas atmospheres and loose contact mode (simulating diesel exhaust conditions), in order to analyse the kinetics and to deduce mechanistic implications. Activity tests were performed under isothermal and TPR conditions. The NO oxidation to NO2 was studied as well. It was checked that mass transfer limitations were not influencing the rate measurements. Global activation energies for the catalysed and non-catalysed soot combustion were calculated and properly discussed. The results reveal that ceria-based catalysts greatly enhance their activities under NOx/O2 between 425 °C and 450 °C, due to the “active oxygen”-assisted soot combustion. Remarkably, copper/ceria–zirconia shows a slightly higher soot combustion rate than the Pt-based catalyst (under NOx/O2, at 450 °C).