Nanophase cobalt, nickel and zinc ferrites: synchrotron XAS study on the crystallite size dependence of metal distribution

Nanophase cobalt, nickel and zinc ferrites, in which the crystallites are in the size range 4-25 nm, were synthesised by coprecipitation and subsequent annealing. X-Ray absorption spectroscopy using synchrotron radiation (supported by X-ray powder diffraction) was used to study the effects of particle size on the distributions of the metal atoms over the tetrahedral and octahedral sites of the spinel structure. Deviations from the bulk structure were found which are attributed to the significant influence of the surface on very small particles. Like the bulk material, nickel ferrite is an inverse spinel in the nanoregime, although the population of metals on the octahedral sites increases with decreasing particle size. Cobalt ferrite and zinc ferrite take the inverse and normal forms of the spinel structure respectively, but within the nanoregime both systems show similar trends in being partially inverted. Further, in zinc ferrite, unlike the normal bulk structure, the nanophase system involves mixed coordinations of zinc(ii) and iron(iii) consistent with increasing partial inversion with size.     

Spectroscopic study on sorption of hydrogen sulfide by means of red soil

This paper reports the results of the characterization of red soils in relation to the sorption of H2S from coal gas at 500 degrees C by spectroscopic techniques in order to provide more information on red soils' structural change both before and after reaction. In addition, by-products analysis has also been studied using Fourier transform infrared (FTIR) spectroscopy. Before and after the experiments the red soils were characterized with X-ray powder diffraction (XRPD), energy dispersion spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and FTIR spectroscopy. XRPD results indicate that iron oxide species disappear from the original to reacted red soil. EDS analysis shows that a significant amount of sulfur is present in the reacted red soil, which is in agreement with the results of the elemental analysis and the calculated value based on breakthrough curve. XPS regression fitting results further indicate that sulfur retention may be associated with the iron oxides. S 2p XPS fittings point out that the major sulfur species present in the reacted red soil are composed of S(-2), elemental sulfur, polysulfide, sulfite and sulfate. Additionally, the binding energy of iron shifts to a lower position for the reacted red soil, which indicates that iron oxides in the original red soil have been converted into iron sulfide. Appreciable amounts of the by-products CO2, SO2 and COS are detected by on-line FTIR spectroscopy during the initial and later stages of the sorption process. The formation of CO2 is related to the water-shift reaction, and SO2 is probably attributable to the reaction of organic matters and H2S. The concentration of COS is quantified by GC/FPD and found it to be about 350 ppm, which is close to the equilibrium concentration of the reaction of inlet CO and H2S at a temperature of 500 degrees C.     

Characterization of southern Taiwan red soils as a regenerable sorbent for sorption of hydrogen sulfide from coal gas with spectroscopic techniques

The purpose of this research is to use red soils as a high-temperature regenerable sorbent for sorption of hydrogen sulfide from coal gas and collocates with a series of spectroscopic apparatuses in order to investigate the structure changes after multiple sorption/regeneration processes. Results indicate that red soils could be reused after 10 multiple sorption/regeneration cycles and maintain approximately 80% sorption efficiency. With EDS and EA analyses, residual sulfur species are detected in the 10th regenerated red soils and exist with values of 0.6 and 0.33%, respectively. Undesired sulfur species including sulfide, sulfate and elemental sulfur are further identified by XPS spectroscopy. With the best regression fitting results, sulfate species is the dominative sulfur species, which occupies approximately 71% of residual sulfur. It is believed that these residual sulfur species are the major cause to result in red soils' deterioration after regeneration and reduce the sorption efficiency. Appreciable amounts of regeneration gases CO, CO(2) and SO(2) are detected by on-line FTIR spectroscopy. Their formation mechanisms are attributed to the different gas-solid reaction, one is the reaction of carbon and oxygen, and the other is FeS and oxygen. From the analysis of solid-state nuclear magnetic resonance spectroscopy (SSNMR), a significant change for (27)Al and (29)Si and it is established that a portion of aluminum is reformed into pentacoordinated structure. Formation of aluminosilicate is maybe another reason to result in deterioration as a result of the loss of surface area.     

Determination of chemical form of antimony in contaminated soil around a smelter using X-ray absorption fine structure.

Only limited information is available about the behavior of antimony (Sb) in contaminated soils. However, understanding the behavior of Sb in contaminated soils is important, because the toxicity or solubility of this element depends on its chemical state. In this study, we investigated the levels of Sb and the chemical forms of Sb in the soil around a smelter using X-ray absorption fine structure (XAFS) spectra. The highest Sb concentration in the contaminated soil was 2900 mg/kg dry soil. According to Sb-K edge X-ray absorption near edge (XANE) spectra, the Sb in the soil was in the form of Sb(V) compounds. The similarity of extended XAFS (EXAFS) spectra suggests that Sb speciation was independent of the sampling site, which indicates that Sb or Sb2O3 emitted from the smelter was converted into Sb(V) compounds in the soil.     

Nickel ferrite spinel as catalyst precursor in the dry reforming of methane:Synthesis,characterization and catalytic properties

Dry reforming of methane by CO2 using nickel ferrite as precursor of catalysts was investigated.Nickel ferrite crystalline particles were prepared by coprecipitation of nitrates with NaOH or ammonia followed by calcination,or by hydrothermal synthesis without calcination step.The textural and structural properties were determined by a number of analysis methods,including X-ray diffraction (XRD),Raman spectroscopy and X-ray photoelectron spectroscopy (XPS),among which X-ray diffraction (XRD) was at room and variable temperatures.All synthesized oxides showed the presence of micro or nanoparticles of NiFe2O4 inverse spinel,but Fe2O3 (hematite) was also present when ammonia was used for coprecipitation.The reducibility by hydrogen was studied by temperature-programmed reduction (TPR) and in situ XRD,which showed the influence of the preparation method.The surface area (BET),particle size (Rietveld refinement),as well as surface Ni/Fe atomic ratio (XPS) and the behavior upon reduction varied according to the synthesis method.The catalytic reactivity was investigated using isopropanol decomposition to determine the acid/base properties.The catalytic performance of methane reforming with CO2 was measured with and without the pre-treatment of catalysts under H2 in 650-800 C range.The catalytic conversions of methane and CO2 were quite low but they increased when the catalysts were pre-reduced.A significant contribution of reverse water gas shift reaction accounted for the low values of H2 /CO ratio.No coking was observed as shown by the reoxidation step performed after the catalytic reactions.The possible formation of nickel-iron alloy observed during the study of reducibility by hydrogen was invoked to account for the catalytic behavior.     

Arsenic speciation in multiple metal environments II. Micro-spectroscopic investigation of a CCA contaminated soil

The speciation of arsenic (As) in a copper-chromated-arsenate (CCA) contaminated soil was investigated using micro-focused X-ray fluorescence (microXRF) and micro-focused X-ray absorption fine structure (microXAFS) spectroscopies to determine if and how the co-contaminating metal cations (Cu, Zn, Cr) influenced the speciation of As. 15 microXRF images were collected on 30-mum polished thin sections and powder-on-tape samples from which Pearson correlation coefficients (rho) between As and various metal species were determined based on the fluorescence intensity of each element in each image pixel. 29 microXAFS and two bulk-XAFS spectra were collected from depths of 0-20 cm (LM-A) and 20-40 cm (LM-B) to determine the chemical speciation of As in the soil by target analyses of principal components with circa 52 reference spectra and linear least-square combination fitting of individual experimental spectra with a refined reference phase list (32) of likely As species. Arsenic and metal cations (Cr, Mn, Fe, Cu, Zn) accumulated in distinct, isolated areas often not larger than 50 x 50 microm in which the Pearson correlation between the elements was strongly positive (rho>0.75). The correlation of As to Zn and Cr decreased from >0.9 to <0.8 and increased to Cu from approximately 0.6 to >0.8 with depth. Arsenic occurred predominantly in the +5 oxidation state. Abstract factor analysis and linear least square combination fit analysis suggested that As occurred as a continuum of fully and poorly-ordered copper-arsenate precipitates with additional components being characterized by surface adsorption complexes on goethite and gibbsite in the presence and absence of Zn. Precipitates other than copper-based ones, e.g., scorodite, adamite and ojuelaite were also identified. The significant co-localization and chemical speciation of As with Cu suggest that the speciation of As in a contaminated soils is not solely controlled by surface adsorption reactions, but significantly influenced by the co-contaminating metal cation fraction. Future studies into As contaminated soil therefore need to focus on identifying the speciation of As and the co-localizing metal cations.     

Thermal oxidation of 6 nm aerosolized silicon nanoparticles: size and surface chemistry changes

The earliest stages of thermal oxidation of 6 nm diameter silicon nanoparticles by molecular oxygen are examined using a tandem differential mobility analysis (TDMA) apparatus, Fourier-transform infrared (FTIR) spectroscopy, time-of-flight secondary ion mass spectroscopy (ToF-SIMS), and X-ray photoelectron spectroscopy (XPS). Particles are synthesized in and then extracted from a nonthermal RF plasma operating at approximately 20 Torr into the atmospheric pressure TDMA apparatus. The TDMA apparatus was used to measure oxidation-induced size changes over a broad range of temperature settings and N2-O2 carrier gas composition. Surface chemistry changes are evaluated in situ with an FTIR spectrometer and a hybrid flow-through cell, and ex situ with ToF-SIMS and XPS. Particle size measurements show that, at temperatures less than approximately 500 degrees C, particles shrink regardless of the carrier gas oxygen concentration, while FTIR and ToF-SIMS spectra demonstrate a loss of hydrogen from the particles and minimal oxide formation. At higher temperatures, FTIR and XPS spectra indicate that an oxide forms which tends toward, but does not fully reach, stoichiometric SiO2 with increasing temperature. Between 500 and 800 degrees C, size measurements show a small increase in particle diameter with increasing carrier gas oxygen content and temperature. Above 800 degrees C, particle growth rapidly reaches a plateau while FTIR and XPS spectra change little. ToF-SIMS signals associated with O-Si species also show an increase in intensity at 800 degrees C.     

Surfactants treatment of crude oil contaminated soils

This study reports experimental measurements investigating the ability of a biological (rhamnolipid) and a synthetic (sodium dodecyl sulfate, SDS) surfactant to remove the North Sea Ekofisk crude oil from various soils with different particle size fractions under varying washing conditions. The washing parameters and ranges tested were as follows: temperature (5 to 50 degrees C), time (5 to 20 min), shaking speed (80 to 200 strokes/min), volume (5 to 20 cm3), and surfactant concentration (0.004 to 5 mass%). The contaminated soils were prepared in the laboratory by mixing crude oil and soils using a rotating cylindrical mixer. Two contamination cases were considered: (1) weathered contamination was simulated by keeping freshly contaminated soils in a fan assisted oven at 50 degrees C for 14 days, mimicking the weathering effect in a natural hot environment, and (2) nonweathered contamination which was not subjected to the oven treatment. The surfactants were found to have considerable potential in removing crude oil from different contaminated soils and the results were comparable with those reported in literature for petroleum hydrocarbons. The removal of crude oil with either rhamnolipid or SDS was within the repeatability range of +/-6%. The most influential parameters on oil removal were surfactant concentration and washing temperature. The soil cation exchange capacity and pH also influenced the removal of crude oil from the individual soils. However, due to the binding of crude oil to soil during weathering, low crude oil removal was achieved with the weathered contaminated soil samples.     

Comparative study of methods for evaluating the mobility of element species in contaminated soil and technogenic sand under batch and dynamic extraction

A comparative study of the batch and dynamic extraction methods used to evaluate the physicochemical “mobility” of element species in environmental samples was carried out using samples of contaminated soils and technogenic sands of the Dzhida Tungsten–Molybdenum Factory. In determining the total concentration of mobile species of Cu, Zn, Pb, Cd, Mn, and Mo, they were extracted with an acetate–ammonium buffer solution (pH 4.8) in the batch mode. Fractionation of the most mobile and environmentally relevant element species, that is, exchange and acid-soluble, was carried out in a dynamic extraction mode in a rotating coil column using calcium nitrate and acetic acid. Element concentrations in the initial samples and extracts were determined by inductively coupled plasma atomic emission spectrometry and mass spectrometry. It is shown that the concentrations of mobile species of Cd, Mn, and Mo, isolated with an acetate–ammonium buffer solution, correspond to the sum of these elements in the exchange and acid-soluble fractions, while the concentration of lead in the acetate–ammonium extract is 2–4 times higher. The convergence of the results of dynamic and batch extraction of copper and zinc depends on the type of sample: for sand, the results are in satisfactory agreement, while for soil, the concentration of copper and zinc in the acetate–ammonium extract is 2–4 times lower than their concentration in the exchange and acid-soluble forms. Nevertheless, the data obtained confirm that the conventional method of batch extraction with an acetate–ammonium buffer solution (pH 4.8) can be considered acceptable for the rapid assessment of the physicochemical mobility and potential bioavailability of elements in soil and technogenic sand. For a more detailed study of highly contaminated samples and the assessment of their danger to the environment, it is advisable to separate exchange and acid-soluble fractions.     

Electrochemical screening procedure for arsenic contaminated soils

Voltammetry of immobilized microparticles was used to find arsenic and heavy metals in contaminated soils from areas with long history of industrial development. Traditional sample dissolution and extraction procedures are time consuming and might distort the chemical equilibrium of the sample causing a change in the original physicochemical forms of distribution. A minute amount of sample was physically attached to the carbon paste working electrode surface and an anodic differential pulse voltammogram was obtained without disturbing the original equilibria. The position of the peaks revealed the presence of Pb and Cu and As(V) and As(III) for the most contaminated soils. As(III) was detected when its percentage in soil was more than 0.001% (expressed as As₂O₃). The limit of detectability was strongly dependent on the presence of iron(III) which increased the signal 10 times.     

Speciation of As(III), As(V), MMA and DMA in contaminated soil extracts by HPLC-ICP/MS

A method to separate and quantify two inorganic arsenic species As(III) and As(V) and two organic arsenic species, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), by HPLC-ICP/MS has been developed. The separation of arsenic species was achieved on the anionic exchange column IonPac AS11 (Dionex) with NaOH as mobile phase. The technique was successfully applied to analyze extracts of two contaminated soils, sampled at a former tannery site (soil 1) and a former paint production site (soil 2). The soils were extracted at pH values similar to the natural environment. Extractions were performed at different pH values with 0.3 M ammonium oxalate (pH = 3), milli-Q water (pH = 5.8), 0.3 M sodium carbonate (pH = 8) and 0.3 M sodium bicarbonate (pH = 11). No organically bound arsenic was found in the extracts. As(V) was the major component. Only up to 0.04% of the total arsenic contained in soil 1 were mobilized. The highest amount of extracted arsenic was found at the highest pH. In the milli-Q water extract of soil 1 As(III) and As(V) were found. High amounts of As(V) were found in the extracts of soil 2. Up to 20% of the total arsenic bound to soil 2 constituents were released. The results show that the mobilization of arsenic depended on the pH value of the extraction solution and the kind of extracted soil. Dramatic consequences have to be expected for pH changes in the environment especially in cases where soils contain high amounts of mobile arsenic.     

The Analysis of Inorganic and Organic Pollutants in Soil with Special Regard to Their Bioavailability

Abstract

The most important inorganic pollutants in soil are the heavy metals. Problems related to the determination of the total and soluble content are discussed. Soluble contents are of interest in connection with studies about bioavailability. Because some of the heavy metals are essential for plant growth, most of the work about bioavailability has been done in the field of plant nutrition. Much less is known about the situation in polluted soils.

It was shown that neutral salt solutions which do not really change the pH of soil during the extraction procedure are best suited to define thresholds of excess. This is in contrast to much stronger extractants like EDTA or DTPA often proposed for the analysis of soils which are deficient in trace elements.

With three sets of experiments the correlation between the contents of cadmium, copper, nickel and zinc extracted by 0.1 M NaNO₃ (as an example of a neutral salt solution) and the plant response (phyto- or zootoxicity) are shown:

—pot experiments using soils which were contaminated by metal salt solutions

—pot experiments using soils from contaminated areas

—field studies in polluted areas. In these studies the aspect of heavy metal leaching was also considered.

The results were converted to indicative values in the Swiss Ordinance of Pollutants in the Soil. These indicative values derived from plant reactions were checked by the carbon mineralisation as an example of a soil microbiological process.

As it was found that organic pollutants are not easily taken up by plant roots the problem of bioavailability is much less important. However, the biodegradation and formation of metabolites has to be considered.     

表面修饰的二氧化锡纳米粒子的制备及微结构表征

采用胶体化学制得表面包覆有ＤＢＳ的二氧化锡纳米粒子，并运用一系列手段对其微结构进行了表征。     

钡铁氧体包覆碳纤维的制备及毫米波衰减性能

通过溶胶凝胶法,在碳纤维表面均匀包覆了一层厚度约为1 μm的钡铁氧体(BaFe₁₂O₁₉)。采用SEM、FTIR、XRD、XPS等技术对碳纤维/钡铁氧体复合材料的组成、结构、性能进行了表征和分析。利用8 mm波雷达装置测试了碳纤维、碳纤维/钡铁氧体复合材料的毫米波衰减性能。实验结果表明：由于碳纤维/钡铁氧体复合材料兼具电损耗和磁损耗吸收,其8 mm波衰减性能明显优于单纯的碳纤维。     

Speciation of As(III), As(V), MMA and DMA in contaminated soil extracts by HPLC-ICP/MS

A method to separate and quantify two inorganic arsenic species As(III) and As(V) and two organic arsenic species, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), by HPLC-ICP/MS has been developed. The separation of arsenic species was achieved on the anionic exchange column IonPac^®AS11 (Dionex) with NaOH as mobile phase. The technique was successfully applied to analyze extracts of two contaminated soils, sampled at a former tannery site (soil 1) and a former paint production site (soil 2). The soils were extracted at pH values similar to the natural environment. Extractions were performed at different pH values with 0.3 M ammonium oxalate (pH = 3), milli-Q water (pH = 5.8), 0.3 M sodium carbonate (pH = 8) and 0.3 M sodium bicarbonate (pH = 11). No organically bound arsenic was found in the extracts. As(V) was the major component. Only up to 0.04% of the total arsenic contained in soil 1 were mobilized. The highest amount of extracted arsenic was found at the highest pH. In the milli-Q water extract of soil 1 As(III) and As(V) were found. High amounts of As(V) were found in the extracts of soil 2. Up to 20% of the total arsenic bound to soil 2 constituents were released. The results show that the mobilization of arsenic depended on the pH value of the extraction solution and the kind of extracted soil. Dramatic consequences have to be expected for pH changes in the environment especially in cases where soils contain high amounts of mobile arsenic.     

Effects of RAMEB on Bioremediation of Different Soils Contaminated with Hydrocarbons

The limiting factor of soil remediation is often the low accessibility of the pollutants.Laboratory experiments have been carried out to investigate the effect of the randomlymethylated cyclodextrin (RAMEB) on bioremediation of various types of soils spikedwith Diesel and transformer oil and also on actual site soils contaminated with poorlydegradable mazout. The contaminated soil in the aerobic solid phase microcosm-experiments was amended with nutrients and supplemented with different amounts of RAMEB. An integrated chemical-biological-ecotoxicological methodology was applied to follow the bioremediation. The laboratory study proved the bioremediation enhancing effect of RAMEB both on artificially contaminated soils and on actual site mazout contaminated soils. RAMEB activated soil microbes by improving the bioavailability of the contaminants and accelerating biodegradation. Efficacy of RAMEB was influenced both by contaminantand environment related factors, such as the type and concentration of the pollutinghydrocarbons and characteristics of the soil.     

Rapid assessment of the impact of microwave heating coupled with UV-C radiation on the degradation of PAHs from contaminated soil using FTIR and multivariate analysis

The presence and fate of polyaromatic hydrocarbons (PAHs) in the environment are receiving a great concern. In this study, three oil-contaminated soils (industrial area, Dukhan city, and artificial soils) were utilized to examine the effect of microwave (MW) heating and UV-C irradiation on the PAHs degradation. A rapid assessment of the impact was evaluated using Fourier transform infrared (FTIR) and multivariate analysis. The total organic matter values for the maximum PAHs reduction were evaluated based on the FTIR spectra of the contaminated soils followed with the principal component analysis (PCA). The results showed that the highest total organic carbon reduction was achieved for the industrial soil sample that required a high MW power and long MW exposure time. On the other hand, the Dukhan city soil sample, which has the lowest total organic carbon, required a high MW power and short MW exposure time followed by UV-C treatment for 20 min to reach the maximal FTIR transmittance reduction. The cluster analysis was also used to evaluate the impact of MW heating, and MW heating followed by UV-C irradiation on the degradation of PAHs. The PCA results of the industrial city sample showed that neither MW treatment (100% MW, 15 min exposure time) followed by UV-C treatment for 20 min nor 10 min is significantly different from the MW treatment (100% MW, 15 min exposure time). However, for the Dukhan sample, the UV-C treatment at 10 min after high MW power and long exposure time (100% MW, 15 min exposure time) was the most efficient treatment.     

Effect of addition of ameliorative materials on the distribution of As,Cd, Pb,and Zn in extractable soil fractions

The effects of lime, limestone, and zeolite addition on the availability of As, Cd, Pb, and Zn in three contaminated soils were investigated in a pot experiment after four vegetation periods of spring wheat, spring barley, and oat. The results showed different responses of extractable element portions to soil amendment when 0.01 mol dm⁻³ aqueous CaCl₂ was applied as a soil extraction agent. Substantial differences were evident among the investigated elements as well as among the individual soil treatments. Except natural zeolite, the ability of ameliorative materials to redistribute cadmium and zinc from a soil solution into less mobile but labile soil fractions was observed. The lead availability was less affected and the extractability of arsenic even increased in some of the treated pots. Moreover, the availability of arsenic was more affected by different characteristics of experimental soils than by individual soil treatments. It was found that these treatments can be applied neither for multicontaminated nor for all the soil types. The soil treatments had a lower effect on the less mobile soil fractions. Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.     

Synthesis and characterization of ZnO and ZnO:Ga films and their application in dye-sensitized solar cells

Highly crystalline ZnO and Ga-modified zinc oxide (ZnO:Ga) nanoparticles containing 1, 3 and 5 atom% of Ga3+ were prepared by precipitation method at low temperature. The films were characterized by XRD, BET, XPS and SEM. No evidence of zinc gallate formation (ZnGa2O4), even in the samples containing 5 atom% of gallium, was detected by XRD. XPS data revealed that Ga is present into the ZnO matrix as Ga3+, according to the characteristic binding energies. The particle size decreased as the gallium level was increased as observed by SEM, which might be related to a faster hydrolysis reaction rate. The smaller particle size provided films with higher porosity and surface area, enabling a higher dye loading. When these films were applied to dye-sensitized solar cells (DSSCs) as photoelectrodes, the device based on ZnO:Ga 5 atom% presented an overall conversion efficiency of 6% (at 10 mW cm(-2)), a three-fold increase compared to the ZnO-based DSSCs under the same conditions. To our knowledge, this is one of the highest efficiencies reported so far for ZnO-based DSSCs. Transient absorption (TAS) study of the photoinduced dynamics of dye-sensitized ZnO:Ga films showed that the higher the gallium content, the higher the amount of dye cation formed, while no significant change on the recombination dynamics was observed. The study indicates that Ga-modification of nanocrystalline ZnO leads to an improvement of photocurrent and overall efficiency in the corresponding device.     

Vertical Mobility of Soil Contaminants: Preliminary Results of a Survey on the Herbicide Atrazine

Abstract

Atrazine is considered a potential contaminant of water bodies, where it has been repeatedly detected. Its use in Italy is almost limited to the Northern part of the country where corn monocultures are common. Northern Italy is characterized by the presence of an area with soil quite permeable and where ground waters are often present at not very deep levels. In this area well waters, which represent the main source of drinking water, have been frequently found contaminated by atrazine. A program has been started aimed at studying the role of soil nature and local factors in the process of groundwater contamination. Two atrazine application rates were used at two sites with loamy and loamy-sandy soils. Results clearly show a different mobility of atrazine in the two soil types. Since the two sites have similar organic carbon levels, the major proportion of clay to sand and the lower pH of loamy soil may explain the lower vertical mobility of atrazine in this soil. Work is in progress to study atrazine behaviour to a soil depth of 30cm and the effect of repeated atrazine applications on ground water pollution.