Heterogeneous microchemistry between CdSO4 and CaCO3 particles under humidity and liquid water.

Laboratory experiments using in situ Raman imaging combined with ex situ TOF-S-SIMS demonstrate the behavior of CdSO4·8/3H2O microparticles in contact with 101¯4 CaCO3 (calcite) surface under three different experimental conditions representative of unpolluted atmosphere. The contact of CdSO4·8/3H2O particles with CaCO3 surface in humid air (RH∼40-80%) does not induce any chemical reaction. In contrast, the condensation of a water drop on CdSO4·8/3H2O/CaCO3 interface causes the free dissolution of CdSO4·8/3H2O particle in the drop. A CdSO4·8/3H2O microcrystal is reformed after gentle drying with a CdSO4·H2O coating of the CaCO3 surface. The TOF-S-SIMS image of the CaCO3 surface provides evidence of a thin layer corresponding probably to insoluble coating of CdCO3 (otavite) or CdxCa1-xCO3 solid solution at the liquid-solid interface. This layer armours the CaCO3 from further dissolution and stops the reaction. The deposition of CdSO4·8/3H2O particle in water drop previously in contact with CaCO3 for a long time generates CdCO3 small rhombohedral crystals while gentle drying provokes the crystallization of bar shape crystals of CaSO4·2H2O (gypsum). These laboratory results provide valuable chemical prediction for a possible fate of cadmium rich particles emitted in the atmosphere and thus, can contribute to realistic assessment of human exposure to Cd hazard.

Photoinduced electron transfers in zeolites: impact of the aluminum content on the activation energies.

We report the activation energy determination corresponding to the recombination of the radical cation electron moiety created through photoionization of the 1,6-diphenyl-1,3,5-hexatriene molecule incorporated in ZSM-5 zeolite channels. We demonstrate that the charge separated state stabilization in zeolite does not depend only on the Al content but also on the Al repartition.

Effects of spatial constraints and Brønsted acid site locations on para-terphenyl ionization and charge transfer in zeolites.

The locations of Brønsted acid sites (BAS) in the channels of medium-pore zeolites have a significant effect on the spontaneous ionization of para-terphenyl (PP(3)) insofar as spatial constraints determine the stability of transition states and charge-transfer complexes relevant to charge separation. The ionization rates and ionization yield values demonstrate that a strong synergy exists between the H(+) polarization energy and spatial constraints imposed by the channel topology. Spectroscopic and modeling results show that PP(3) incorporation, charge separation, charge transfer and charge recombination differ dramatically among zeolites with respect to channel structure (H-FER, H-MFI, H-MOR) and BAS density in the channel. Compartmentalization of ejected electrons away from the initial site of ionization decreases dramatically the propensity for charge recombination. The main mode of PP(3)(.+) decay is hole transfer to form AlO(4)H(.+) ⋅⋅⋅PP(3) charge-transfer complexes characterized by intense absorption in the visible range. According to the nonadiabatic electron-transfer theory, the small reorganization energy in constrained channels explains the slow hole-transfer rate.

Kinetics and characterization of photoinduced long-lived electron-hole pair of p-terphenyl occluded in ZSM-5 zeolites. Effects of aluminium content and extraframework cation.

Diffuse reflectance UV-visible in combination with FT-Raman spectroscopies demonstrate the total incorporation without any solvent of p-terphenyl (p-TP) as an intact molecule in the medium size channel of non-acidic M(n)ZSM-5 (M = Li(+), Na(+), K(+), Rb(+), Cs(+) and n = 0, 3.4, 6.6) zeolites. The combined effects of confinement and electrostatic field induced by alkaline ions in the M(n)ZSM-5 zeolites lead only to weak conformational changes in the occluded p-TP after very long organization periods. The interaction between the counterbalancing cation and p-TP occurs through one phenyl group facially coordinated to the cation near the O atoms binding Al atoms. The laser UV photolysis of p-terphenyl occluded as intact molecules in non-acidic M(n)ZSM-5 zeolites generates long-lived charge separated states. The photoionization induces a p-TP*(+)-electron pair as a primary phenomenon. The recombination of the p-TP*(+)@M(n)ZSM-5*(-) radical cation moiety occurs mainly through unusual electron abstraction from the zeolite framework and p-TP@M(n)ZSM-5*(-)*(+) electron-hole pair formation which exceeds several days at room temperature in Li(6.6)ZSM-5. The very long-lived radical pairs are characterized by conventional DRUVv, FT-Raman and CW-EPR spectroscopy. Two-dimensional hyperfine sublevel correlation (2D-HYSCORE) experiments reveal the structural surroundings of the unpaired electrons through the proper assignment of unpaired electron couplings. The subsequent hole transfer from the radical cation of the channels as well as the final electron-hole pair recombination appear to be largely controlled by the aluminium content, the size of the extra framework cation and the associated local electrostatic field. The effects of the counterbalancing cations have been investigated and because the zeolite electron affinity increases on going from Li(+) to Cs(+), the electron transfer rates increase according to the following order Li(+) < Na(+) < K(+) < Rb(+) < Cs(+).

Incorporation and electron transfer of anthracene in pores of ZSM-5 zeolites. Effect of Brønsted acid site density.

The sorption course of anthracene (ACENE-3) into Brønsted-acidic medium pore MFI zeolites was monitored by in situ EPR and diffuse reflectance UV-visible absorption over one year. Weighed amounts of solid ACENE-3 were merely exposed to H(n)ZSM-5 (H(n)(AlO(2))(n)(SiO(2))(96-n)), with the following Brønsted acid site (BAS) densities, n = 0.0, 0.17, 0.57, 0.95, 2.0, 3.4, 6.6, dehydrated at 623 K under argon. The weighed amounts correspond to 1 ACENE-3 per zeolite unit cell. ACENE-3 is found to be incorporated as intact molecules in purely siliceous MFI (silicalite-1). Monte Carlo simulations indicate that ACENE-3 lies in the intersection of straight and zigzag channels. In contrast, the presence of BASs on the inner surface of channels induces spontaneous ionization of ACENE-3 (ionization potential = 7.44 eV). The charge separation as ACENE-3*(+)@H(n)ZSM-5*(-) is caused by the strong Coulombic field gradient of Si-O(-)(H(+))-Al BAS in the absence of any Lewis acid site. The rate and yield of ionization are found to increase dramatically with BAS density increase. The stabilization of ACENE-3*(+)@H(n)ZSM-5*(-) is explained by the tight fit between the rod-shape ACENE-3 and the channel dimensions and especially by the compartmentalization of ejected electrons as AlO(4)H*(-) centers away from the initial site of ionization. The final charge recombination occurs after more than one year and leads to ACENE-3 occluded in the straight channel in close proximity to BAS without any protonation of ACENE-3 (pK(a) = -13.5).

Incorporation of anthracene into zeolites: confinement effect on the recombination rate of photoinduced radical cation-electron pair.

FT-Raman spectrometry in combination with diffuse reflectance UV/Vis absorption (DRUVv) and fluorescence emission indicate that complete anthracene (ANT) sorption as intact molecules takes place over 6 months in the medium pores of non-Brønsted acidic M(n)ZSM-5 zeolites (n=0.0, 3.4, 6.6; M=Na+, K+, Rb+, Cs+) with 1 ANT per unit cell loading. The combined effect of confinement and electrostatic field induced by bulky cations (Rb+, Cs+) leads to specific changes in the occluded ANT Raman spectra after very long organization periods (one year). The laser photolysis (266 nm, 355 nm) of ANT@M(n)ZSM-5 equilibrated samples generates long-lived charge separated species in aluminum rich zeolites (n=3.4, 6.6). The very long-lived radical pairs are characterized by conventional DRUVv and CW-EPR spectroscopy. The direct charge recombination rates of ANT.+-electron pairs are dispersive, extending over a broad range of timescales. The kinetic constant values are found to increase dramatically with the aluminum content and increase markedly with M+ according to the following order Na+ < K+ < Rb+ < Cs+. The small reorganization energy (lambda) of ZSM-5 zeolite pores coupled with large negative free energy changes (-DeltaG degrees ) between the ground state ANT oxidation potential and Fermi level of aluminum rich M(n)ZSM-5 explain the observed trends of the ANT.+@M(n)ZSM-5.- charge recombination rates.

Confocal microprobe Raman imaging of urban tropospheric aerosol particles.

Particulate matter with aerodynamic diameters of < 1, 1-2.5, and 2.5-10 microm were collected during two seasons in two urban zones situated northeast and southwest, respectively, of a lead/zinc smelter located in a former mining region of northern France. We demonstrate the effectiveness of the combined use of computer-controlled Raman mapping and multivariate curve resolution (MCR) of the Raman images to determine heterogeneous chemistry at the level of aerosol particle. The resulting molecular images of major species were found to be in accurate agreement with elemental images obtained by WDS X-ray-mapping. Environmental SEM was very useful to localize spare metal-rich particles before Raman mapping. Some spare particles containing pyromorphite (Pb5(PO4)3OH) and franklinite (ZnxFe3-xO4) mixed with mineral dust were detected at the northeast (NE) sampling site, when the wind was blowing from the west (W) sector. These particles were probably suspended in the troposphere by the action of wind or by mechanical disturbance of polluted top soils. The most abundantly encountered particles in the 10-2.5 and 2.5-1 microm fractions were found to be aggregates of NaCl, CaCO3, CaSO4 x 2H2O, CaMg(CO3)2, SiO2, feldspar, clay minerals, alpha-Fe2O3, NaNO3, and Ca(NO3)2 x 4H20. Black carbon and (NH4)2SO4 particles were observed predominantly in the finest fraction. It was not rare to detect Pb and Zn-rich particles in the 10-2.5 and 2.5-1 microm fractions collected at the southwest (SW) sampling site, when the wind was blowing from the NE sector. Most of these mixed particles probably result from the aggregation between PbSO4, PbO x PbSO4, and ZnS particles emitted by the smelters and hydroscopic mineral dust during transport in the troposphere.

Heterogeneous chemistry between PbSO4 and calcite microparticles using Raman microimaging.

Currently, the smelting activities of lead and zinc are the loudest sources of local pollution by emission in the troposphere of dust of micrometer size containing PbSO(4). As the particles evolve in the troposphere, their chemical and physical properties - and hence their characteristics such as toxicity - change by accumulation of atmospheric heterogeneous reactions. Calcite (CaCO(3)) represents a large part of the mineral fraction in tropospheric aerosols with aerodynamic diameters less than 10 microm. The calcite particles are expected to react with PbSO(4) particles. In an effort to model the chemical behaviour of PbSO(4) individual particles in the troposphere, we present the in situ Raman imaging results during the course of the reactions in a water droplet of PbSO(4) particles with a calcite microcrystal surface. The computer-microcontrolled XY scanning and Z focusing of confocal Raman imaging combined with multivariate curve resolution (MCR) of Raman images have resolved the severe spectral overlaps of the Raman spectra which are not resolved by the spatial resolution of the instrument ( approximately 1 microm(3)). The results pointed out the identification and the mapping of Pb(3)(CO(3))(2)(OH)(2), PbCO(3) and CaSO(4).2H(2)O (gypsum) on the calcite surface.

Chemistry at level of individual aerosol particle using multivariate curve resolution of confocal Raman image.

Airborne particles with aerodynamic diameter in the 10-1 microm range have been collected in an industrial/urban zone by impaction and have been investigated by automated confocal Raman microspectrometry. The computer-microcontrolled XY scanning and Z focusing of Raman images provided many pixel Raman spectra which are characteristics of complex mixture at level of individual particle. The large heterogeneity was not resolved by the spatial resolution of the instrument which is limited by the optical diffraction. The severe spectral overlaps generated by heterogeneity were resolved by multivariate curve resolution (MCR) methods. The purity based method (SIMPLISMAX) was used to resolve both luminescence spectra and pure Raman spectra without prior information. The MCR-alternating least square (ALS) was used as a refined method of both spectra and spectral concentrations. The reconstructing Raman images of the respective spectral contribution supply a versatile potential to characterize the chemistry of atmospheric aerosols at the level of the individual particles.

Long-lived spin-correlated pairs generated by photolysis of naphthalene occluded in non-Brønsted acidic ZSM-5 zeolites.

Long-lived spin-correlated pairs were generated by laser irradiation of naphthalene (NAP) occluded as intact molecule within non-Brønsted acidic MnZSM-5 zeolites with MnSiO(2))(96-n)(AlO(2)n formula per unit cell. The laser UV photoionization generates primary NAP.+-electron pair as a fast phenomenon. These charge carriers exhibit lifetimes that extend over less than 1 h at room temperature and disappear according to two parallel competitive ways: direct charge recombination and electron transfer. This subsequent electron transfer takes place between the electron-deficient radical cation (NAP.+) and the electron-donor oxygen atom of zeolite framework. The aluminum rich MnZSM-5 zeolites (n = 3.4, 6.6) hinder efficiently the charge recombination and promote the electron transfer to generate a very long electron-hole pair which exceeds several weeks at room temperature in NAP@Li(6.6)ZSM-5. The electron-hole pair exhibits broad visible absorption bands at 482 and 525 nm. The electron-hole distance, 1.3 nm, was deduced from the dipolar interaction term (D) value. The spin density of trapped electron appears spread over (27)Al, (29)Si, (7)Li, and (1)H nuclei as deduced by two-dimensional approach of hyperfine sublevel correlation (HYSCORE). The very low recombination rate by tunneling effect was found to be in agreement with the very low value (J approximately 0) of the magnetic exchange. The combined effects of tight fit between NAP size and straight-channel dimension, the high aluminum content of the framework, and the highly polarizing cation Li(+) trapped efficiently the ejected electron in the conduction band and the hole in the valence band of the porous materials.

Long-lived radical cation-electron pairs generated by anthracene sorption in non Brønsted acidic zeolites.

The sorption of anthracene (ANT) in non Brønsted acidic ZSM-5 zeolite through the mere exposure at room temperature of solid ANT and dehydrated zeolite crystals with Li(3.4)(AlO2)n(SiO2)(96-n) chemical formulas per unit cell generates spontaneous ionization of ANT (IP 7.44 eV in the gas phase). In contrast, ANT was found to be sorbed as an intact molecule in M(3.4)ZSM-5 with M = Na+, K+, Rb+, and Cs+. The radical cation (ANT*+) of the long-lived ANT*+@Li(3.4)ZSM-5*- pair was characterized by conventional diffuse reflectance UV-visible and resonance Raman spectrometry. In contrast, the X-band continuous wave (CW) EPR signal was found to be typical of a weakly coupled spin correlated ion pair. The two-dimension hyperfine sublevel correlation (2D-HYSCORE) spectra provide a detailed description of the microenvironment of the trapped electron of the ANT*+@Li(n)ZSM-5*- pair. The trapped electron appears localized in close proximity of occluded ANT*+, Li+, and the Si-O-Al nearest group of the zeolite framework.

Speciation of PM10 sources of airborne nonferrous metals within the 3-km zone of lead/zinc smelters.

The purpose of this study was to estimate the speciation of PM10 sources of airborne Pb, Zn, and Cd metals (PM10 is an aerosol standard of aerodynamic diameter less than 10 microm.) in the atmosphere of a 3 km zone surrounding lead/zinc facilities in operation for a century. Many powdered samples were collected in stacks of working units (grilling, furnace, and refinery), outdoor storages (ores, recycled materials), surrounding waste slag (4 Mt), and polluted topsoils (3 km). PM10 samples were generated from the raw powders by using artificial resuspension and collection devices. The bulk PM10 multielemental analyses were determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The proportions in mass of Pb (50%), Zn (40%), and Cd (1%) contents and associated metals (traces) reach the proportions of corresponding raw powdered samples of ores, recycled materials, and fumesize emissions of plants without specific enrichment. In contrast, Pb (8%) and Zn (15%) contents of PM10 of slag deposit were found to be markedly higher than those of raw dust, Pb (4%), and Zn (9%), respectively. In the same way, Pb (0.18%), Zn (0.20%), and Cd (0.004%) were enriched by 1.7, 2.1, and 2.3 times, respectively, in PM10 as compared with raw top-soil corresponding values. X-ray wavelength dispersive electron-microprobe (EM-WDS) microanalysis did not indicate well-defined phases or simple stoichiometries of all the PM10 samples atthe level of the spatial resolution (1 microm3). X-ray photoelectron spectroscopy (XPS) indicated that minor elements such as Cd, Hg, and C are more concentrated on the particle surface than in the bulk of PM10 generated by the smelting processes. (XPS) provided also the average speciation of the surface of PM10; Pb is mainly represented as PbSO4, Zn as ZnS, and Cd as CdS or CdSO4, and small amounts of coke were also detected. The speciation of bulk PM10 crystallized compounds was deduced from XRD diffractograms with a raw estimation of the relative quantities. PbS and ZnS were found to be the major phases in PM10 generated by the smelting facilities with PbSO4, PbSO4 x PbO, PbSO4 x 4PbO, Pb metal, and ZnO as minor phases. The slag waste PM10 was found to contain some amounts of PbCO3, PbSO4 x PbO, and ZnFe2O4 phases. The large heterogeneity at the level of the individual particle generates severe overlap of chemical information even at the microm scale using electron microprobe (WDS) and Raman microprobe techniques. Fortunately, scanning Raman microspectrometry combined with SIMPle-to-use Interactive Self-modeling Mixture Analysis (SIMPLISMA) performed the PM10 speciation at the level of individual particles. The speciation of major Pb, Zn, and Cd compounds of PM10 stack emissions and wind blown dust of ores and recycled materials were found to be PbSO4, PbSO4 x PbO, PbSO4 x 4PbO, PbO, metallic Pb, ZnS, ZnO, and CdS. The PM10 dust of slag waste was found to contain PbCO3, Pb(OH)2 x 2PbCO3, PbSO4 x PbO, and ZnS, while PM10-bound Pb, Zn of the top-soils contain Pb5(PO4)3Cl, ZnFe2O4 as well as Pb(II) and Zn(II) compounds adsorbed on Fe(III) oxides and in association with clays.

Combined use of conventional and second-derivative data in the SIMPLISMA self-modeling mixture analysis approach.

Simple-to-use interactive self-modeling mixture analysis (SIMPLISMA) is a successful pure variable approach to resolve spectral mixture data. A pure variable (e.g., wavenumber, frequency number, etc.) is defined as a variable that has significant contributions from only one of the pure components in the mixture data set. For spectral data with highly overlapping pure components or significant baselines, the pure variable approach has limitations; however, in this case, second-derivative spectra can be used. In some spectroscopies, very wide peaks of components of interest are overlapping with narrow peaks of interest. In these cases, the use of conventional data in SIMPLISMA will not result in proper pure variables. The use of second-derivative data will not be successful, since the wide peaks are lost. This paper describes a new SIMPLISMA approach in which both the conventional spectra (for pure variables of wide peaks) and second-derivative spectra (for pure variables of narrow peaks, overlapping with the wide peaks) are used. This new approach is able to properly resolve spectra with wide and narrow peaks and minimizes baseline problems by resolving them as separate components. Examples will be given of NMR spectra of surfactants and Raman imaging data of dust particle samples taken from a lead and zinc factory's ore stocks that were stored outdoors.

Photoionization and Electron Transfer of Biphenyl within the Channels of Al-ZSM-5 Zeolites.

Evidence of the photogenerated long-lived biphenyl radical and a trapped electron in the void space of aluminated nonacidic ZSM-5 zeolites has been obtained from the time-resolved UV/Vis absorption, Raman scattering, and EPR spectra. The restoration of the ground states implicates the existence of long-lived positive holes in the framework.