Sulfur isotope analysis of aerosol particles by NanoSIMS

A new method to measure the sulfur isotopic composition of individual aerosol particles by NanoSIMS has been developed and tested on several standards such as barite (BaSO4), anhydrite (CaSO4), gypsum (CaSO4·2H2O), mascagnite ((NH4)2SO4), epsomite (MgSO4·7H2O), magnesium sulfate (MgSO4·xH2O), thenardite (Na2SO4), boetite (K2SO4) and cysteine (an amino acid). This ion microprobe technique employs a Cs+ primary ion beam and measures negative secondary ions permitting the analysis of sulfur isotope ratios in individual aerosol particles down to 500 nm in size (0.001-0.5 ng of sample material). The grain-to-grain reproducibility of measurements is typically 5‰ (1σ) for micron-sized grains, <5‰ for submicron-sized grains, and <2‰ for polished thin sections and ultra microtome sections which were studied for comparison. The role of chemical omposition (matrix effect) and sample preparation techniques on the instrumental mass fractionation (IMF) of the 34S/32S ratio in the NanoSIMS has been investigated. The IMF varies by ~15‰ between the standards studied here. A good correlation between IMF and ionic radius of the cations in sulfates was observed. This permits to infer IMF corrections even for sulfates for which no isotope standards are available. The new technique allows to identify different types of primary and secondary sulfates based on their chemical composition and to measure their isotopic signature separately. It was applied to marine aerosol samples collected in Mace Head and urban aerosol samples collected in Mainz. It was shown that primary sulfate particles such as sulfate in NaCl or gypsum particles precipitated from ocean water retain the original isotopic signature of their source. The isotopic composition of secondary sulfate depends on the isotopic composition of precursor SO2 and the oxidation pathway. The 34S/32S fractionation with respect to the precursor SO2 is -9‰ for homogeneous oxidation and +16.5‰ for heterogeneous oxidation. This large difference between the isotopic fractionation of both pathways allows identifying the oxidation pathway from which the SO42- in a secondary sulfate particle is derived, by means of its sulfur isotope ratio, provided that the isotopic signature of the precursor SO2 is known. The isotopic composition of the precursor SO2 of secondary sulfates was calculated based on the isotopic composition of particles with known oxidation pathway such as fine mode ammonium sulfate.

Role of the crystallite phase of TiO2 in heterogeneous photocatalysis for phenol oxidation in water

A series of TiO2 samples with different anatase-to-rutile ratios was prepared by calcination, and the roles of the two crystallite phases of titanium(IV) oxide (TiO2) on the photocatalytic activity in oxidation of phenol in aqueous solution were studied. High dispersion of nanometer-sized anatase in the silica matrix and the possible bonding of Si-O-Ti in SiO2/TiO2 interface were found to stabilize the crystallite transformation from anatase to rutile. The temperature for this transformation was 1200 degrees C for the silica-titania (ST) sample, much higher than 700 degrees C for Degussa P25, a benchmarking photocatalyst. It is shown that samples with higher anatase-to-rutile ratios have higher activities for phenol degradation. However, the activity did not totally disappear after a complete crystallite transformation for P25 samples, indicating some activity of the rutile phase. Furthermore, the activity for the ST samples after calcination decreased significantly, even though the amount of anatase did not change much. The activity of the same samples with different anatase-to-rutile ratios is more related to the amount of the surface-adsorbed water and hydroxyl groups and surface area. The formation of rutile by calcination would reduce the surface-adsorbed water and hydroxyl groups and surface area, leading to the decrease in activity.

A new oxovanadium(IV)-cucurbit[6]uril complex: Properties and potential for confined heterogeneous catalytic oxidation reactions

This work presents a new oxovanadium(IV)-cucurbit[6]uril complex, which combines the catalytic properties of the metal ion with the size-excluding properties of the macrocycle cavity. In this coordination compound, the VO(2-) ions are coordinated to the oxygen atoms located at the rim of the macrocycle in slightly distorted square-pyramidal configurations, which are in fact C(2v) symmetries. This combination results in a size-selective heterogeneous catalyst, which is able to oxidize linear alkanes like n-pentane at room temperature, but not styrene, cyclohexane or z-cyclooctene, which are too big to enter the cucurbit[6]uril cavity. The results presented here contribute to understanding the mechanism of alkane catalytic oxidation by oxovanadium(IV) complexes. (C) 2010 Elsevier Ltd. All rights reserved.

Mn-II and Cu-II complexes with arylhydrazones of active methylene compounds as effective heterogeneous catalysts for solvent- and additive-free microwave-assisted peroxidative oxidation of alcohols

A one-pot template reaction of sodium 2-(2-(dicyanomethylene) hydrazinyl) benzenesulfonate (NaHL1) with water and manganese(II) acetate tetrahydrate led to the mononuclear complex [Mn(H2O)(6)](HL1a)(2)center dot 4H(2)O (1), where (HL1a) -= 2-(SO3-)C6H4(NH)=N=C(C N) (CONH2) is the carboxamide species derived from nucleophilic attack of water on a cyano group of (HL1) . The copper tetramer [Cu-4(H2O)(10)(-) (1 kappa N: kappa O-2: kappa O, 2 kappa N: k(O)-L-2)(2)]center dot 2H(2)O (2) was obtained from reaction of Cu(NO3)(2)center dot 2.5H(2)O with sodium 5-(2( 4,4-dimethyl-2,6-dioxocyclohexylidene) hydrazinyl)-4-hydroxybenzene-1,3-disulfonate (Na2H2L2). Both complexes were characterized by elemental analysis, IR spectroscopy, ESI-MS and single crystal X-ray diffraction. They exhibit a high catalytic activity for the solvent-and additive-free microwave (MW) assisted oxidation of primary and secondary alcohols with tert-butylhydroperoxide, leading to yields of the oxidized products up to 85.5% and TOFs up to 1.90 x 103 h(-1) after 1 h under low power (5-10 W) MW irradiation. Moreover, the heterogeneous catalysts are easily recovered and reused, at least for three consecutive cycles, maintaining 89% of the initial activity and a high selectivity.

A new oxovanadium(IV)-cucurbit[6]uril complex: Properties and potential for confined heterogeneous catalytic oxidation reactions

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Wireless Rotating Disk Electrode (wRDE) for assessing Heterogeneous Water Oxidation Catalysts (WOCs)

A novel method for assessing the activity of a powdered water oxidation catalyst (WOC) is described, utilising an easily-prepared wireless rotating disc electrode of the WOC, thereby allowing its activity to be probed, via the observed kinetics of water oxidation by Ce(IV) ions, and so provide invaluable electrochemical information.

Gold is not a Faradaic-Efficient Borohydride Oxidation Electrocatalyst: An Online Electrochemical Mass Spectrometry Study

Direct borohydride fuel cells are promising high energy density portable generators. However, their development remains limited by the complexity of the anodic reaction: The borohydride oxidation reaction (BOR) kinetics is slow and occurs at high overvoltages, while it may compete with the heterogeneous hydrolysis of BH(4)(-). Nevertheless, one usually admits that gold is rather inactive toward the heterogeneous hydrolysis of BH(4)(-) and presents some activity regarding the BOR, therefore yielding to the complete eight-electron BOR. In the present paper, by coupling online mass spectrometry to electrochemistry, we in situ monitored the H(2) yield during BOR experiments on sputtered gold electrodes. Our results show non-negligible H(2) generation on Au on the whole BOR potential range (0-0.8 V vs reversible hydrogen electrode), thus revealing that gold cannot be considered as a faradaic-efficient BOR electrocatalyst. We further propose a relevant reaction pathway for the BOR on gold that accounts for these findings.

In situ infrared (FTIR) study of the mechanism of the borohydride oxidation reaction

Early reports stated that Au was a catalyst of choice for the BOR because it would yield a near complete faradaic efficiency. However, it has recently been suggested that gold could yield to some extent the heterogeneous hydrolysis of BH(4)(-),therefore lowering the electron count per BH(4)(-), especially at low potential. Actually, the blur will exist regarding the BOR mechanism on Au as long as no physical proof regarding the reaction intermediates is not put forward. In that frame, in situ physical techniques like FTIR exhibit some interest to study the BOR. Consequently, in situ infrared reflectance spectroscopy measurements (SPAIRS technique) have been performed in 1 M NaOH/1 M NaBH(4) on a gold electrode with the aim to detect the intermediate species. We monitored several bands in B-H ((nu) over bar similar to 1180,1080 and 972 cm(-1)) and B-O bond regions ((nu) over bar =1325 and similar to 1425cm(-1)), which appear sequentially as a function of the electrode polarization. These absorption bands are assigned to BH(3), BH(2) and BO(2)(-) species. At the light of the experimental results, possible initial elementary steps of the BOR on gold electrode have been proposed and discussed according to the relevant literature data.

Copper/MCM-41 as catalyst for the wet oxidation of phenol

A heterogeneous copper catalyst supported on mesoporous MCM-41 was developed. The parent MCM-41 has a large pore area of over 1400 m(2)/g. Copper was chosen as the active element of catalyst and loaded into MCM-41 by adsorption at ambient temperature. The prepared catalysts were evaluated in the catalytic wet oxidation of phenol solution with an initial concentration of 1,300 ppm at 150 and 200 degreesC. The catalyst was found to be of high catalytic activity. It is also shown that the catalyst with a higher copper loading exhibits higher ability of accelerating the catalytic reaction to certain extent but reaches its constant level afterwards. (C) 2001 Elsevier Science B.V. All rights reserved.

Copper/MCM-41 as catalyst for photochemically enhanced oxidation of phenol by hydrogen peroxide

Heterogeneous copper catalyst was developed using the mesoporous molecular sieve MCM-41 as the catalyst support. Copper was impregnated onto the support. Catalysts with different copper loadings were obtained. The performance of the developed catalysts was evaluated in photochemically enhanced oxidation of phenol using hydrogen peroxide as the oxidant. The catalyst was found to significantly increase the oxidation rate and enhance the removal level of phenol with UV light present. The effects of copper loading on the catalyst, photo (UV), H2O2 concentration, and catalyst dosage on the photo-oxidation of phenol were studied. (C) 2001 Elsevier Science B.V. All rights reserved.

Ironporphyrin immobilized onto montmorillonite as a bimimetical model for azo dye oxidation

In this work, we studied the oxidation of the azo dye Disperse orange 3 (DO3) by hydrogen peroxide, catalyzed by 5,10,15, 20-tetrakis(4-N-methylpyridyl)porphyrin iron(III) chloride immobilized onto montmorillonite K10, FeP-K10. Results showed that the FeP-K10/H2O2 system is efficient for discoloration of the DO3 dye, especially at pH 3.0. The catalyst was shown to be relatively stable and could be recycled many times, leading to good yields. DO3 oxidation products were analyzed by gas chromatography and mass spectrometry, being 4-nitroaniline the main product. Tert-butylhydroperoxide and iodosylbenzene were also used as oxidants, giving rise to 4-nitroaniline as product too. The studied system is a good biomimetic model of oxidative enzymes, being a promising discoloring agent for azo dyes. (C) 2007 Elsevier Ltd. All rights reserved.

Heterogeneous kinetics of the reduction of chromium (VI) by elemental iron

Zero valent iron (ZVI) has been extensively used as a reactive medium for the reduction of Cr(VI) to Cr(III) in reactive permeable barriers. The kinetic rate depends strongly on the superficial oxidation of the iron particles used and the preliminary washing of ZVI increases the rate. The reaction has been primarily modelled using a pseudo-first-order kinetics which is inappropriate for a heterogeneous reaction. We assumed a shrinking particle type model where the kinetic rate is proportional to the available iron surface area, to the initial volume of solution and to the chromium concentration raised to a power ˛ which is the order of the chemical reaction occurring at surface. We assumed α= 2/3 based on the likeness to the shrinking particle models with spherical symmetry. Kinetics studies were performed in order to evaluate the suitability of this approach. The influence of the following parameters was experimentally studied: initial available surface area, chromium concentration, temperature and pH. The assumed order for the reaction was confirmed. In addition, the rate constant was calculated from data obtained in different operating conditions. Digital pictures of iron balls were periodically taken and the image treatment allowed for establishing the time evolution of their size distribution.

Solvent-free microwave-assisted peroxidative oxidation of alcohols catalyzed by Iron(III)-TEMPO catalytic systems

The iron(III) complexes [H(EtOH)][FeCl2(L)(2)] (1), [H(2)bipy](1/2)[FeCl2(L)(2)].DMF (2) and [FeCl2(L)(2,2'-bipy)] (3) (L = 3-amino-2-pyrazinecarboxylate; H(2)bipy = doubly protonated 4,4'-bipyridine; 2,2'-bipy = 2,2'-bipyridine, DMF = dimethylformamide) have been synthesized and fully characterized by IR, elemental and single-crystal X-ray diffraction analyses, as well as by electrochemical methods. Complexes 1 and 2 have similar mononuclear structures containing different guest molecules (protonated ethanol for 1 and doubly protonated 4,4'-bipyridine for 2) in their lattices, whereas the complex 3 has one 3-amino-2-pyrazinecarboxylate and a 2,2'-bipyridine ligand. They show a high catalytic activity for the low power (10 W) solvent-free microwave assisted peroxidative oxidation of 1-phenylethanol, leading, in the presence of TEMPO, to quantitative yields of acetophenone [TOFs up to 8.1 x 10(3) h(-1), (3)] after 1 h. Moreover, the catalysts are of easy recovery and reused, at least for four consecutive cycles, maintaining 83 % of the initial activity and concomitant rather high selectivity. 3-Amino-2-pyrazinecarboxylic acid is used to synthesize three new iron(III) complexes which act as heterogeneous catalysts for the solvent-free microwave-assisted peroxidative oxidation of 1-phenylethanol.

Degradación de efluentes de las industrias del cuero y textil mediante procesos fotocatalíticos heterogéneos empleando la luz solar. Degradation of effluents from the leather and textile industries through heterogeneous photocatalytic processes using sunlight.

El creciente desarrollo de la industria del cuero y textil en nuestro país, y específicamente en la provincia de Córdoba, ha hecho resurgir en los ultimos años una problemática aún no resuelta que es la elevada contaminación de los recursos hídricos. En ambas industrias, la operación de teñido involucra principalmente colorantes de tipo azoico los cuales son "no biodegradables" y se fragmentan liberando aminas aromáticas cancerígenas. Para abordar esta problemática, la fotocatálisis heterogénea aparece como una nueva tecnología que permitiría la completa mineralización de estos colorantes. A través de radiación y un fotocatalizador sólido adecuado se pueden generan radicales libres eficientes para la oxidación de materia orgánica (colorantes) en medio acuoso. En este sentido, se proponen tamices moleculares mesoporosos modificados con metales de transición (MT) como fotocatalizadores potencialmente aptos para la degradación de estos contaminantes. El propósito principal de este proyecto es el diseño, síntesis, caracterización y evaluación de materiales mesoporosos que presenten actividad fotocatalítica ya sea mediante la modificación de su estructura con diversos metales fotosensibles y/o empleándolos como soporte de óxido de titanio. Se pretende evaluar estos materiales en la degradación de colorantes intentando desplazar su fotosensibilidad hacia la radiación visible para desarrollar nuevas tecnologías con menor impacto ambiental y mayor aprovechamiento de la energía solar. Para ello se sintetizarán materiales del tipo MCM-41 modificados con distintos MT tales como Fe, Cr, Co, Ni y Zn mediante incorporación directa del ión metálico o impregnación. Al mismo tiempo, tanto estos últimos materiales como el MCM-41 silíceo serán empleados como soporte de TiO2. Sus propiedades fisicoquímicas se caracterizarán mediante distintas técnicas instrumentales y su actividad fotocatalítica se evaluará en la degradación de colorantes azoicos bajo radiación visible. Se seleccionará el catalizador más eficiente y se estudiarán los diversos factores que afectan el proceso de fotodegradación. Así mismo, el análisis de la concentración del colorante y los productos presentes en el medio en función del tiempo de reacción permitirá inferir sobre la cinética de la decoloración y postular posibles mecanismos de fotodegradación. Con esta propuesta se espera contribuír al desarrollo de un sector industrial importante en nuestra provincia como es el de las industrias del cuero y textil, mediante la generación de nuevas tecnologías que empleen la energía solar para la degradación de sus efluentes (colorantes). En este sentido, se espera desarrollar nuevos materiales optimizados para lograr la mayor eficiencia fotocatalítica. Esto conduciría entonces hacia la remediación de un problema ambiental de alto impacto tanto para nuestra provincia y nuestro país como para la población mundial, como es la contaminación de los recursos hídricos. Finalmente, con este proyecto se contribuirá a la formación de dos doctorandos y un maestrando, cuyos temas de tesis están vinculados con nuestro objeto de estudio. The increasing development of the textile and leather industries in our country, and specifically in Córdoba, has revived an unresolved problem that is the high contamination of water resources. In both industries, the dyeing involves mainly type azoic dyes which are not biodegradable and break releasing carcinogenic aromatic amines. Heterogeneous photocatalysis appears as a new technology that would allow the complete mineralization of these pollutants. Through radiation and a suitable solid it is possible to generate free radicals for efficient oxidation of organic matter (dyes) in aqueous medium. In this respect, mesoporous molecular sieves modified with transition metals are proposed as potential photocatalysts. The main purpose of this project is the synthesis of mesoporous materials having photocatalytic activity for the degradation of dyes. We will try to move their photosensitivity to visible radiation to develop new technologies with lower environmental impact and greater use of solar energy. Materials MCM-41 modified with metals (Fe, Cr, Co, Ni and Zn) will be synthesized by direct incorporation or impregnation. These materials and the siliceous MCM-41 will be then employed as support of TiO2. The materials will be evaluated in the photocatalytic degradation of azoic dyes under visible radiation. The influence of different factors on the photodegradation proccess will be studied. Kinetic studies will be carried out and a possible reaction way will be proposed. Thus, this work will contribute to the advancement of an important industrial sector and the remediation of an environmental problem with high impact for our province and our country. Moreover, this proyect will contribute to the development of two doctoral tesis and one magister tesis which are vinculated with our study subject.