Surfactant templating effects on the encapsulation of iron oxide nanoparticles within silica microspheres

Hollow silica microspheres encapsulating ferromagnetic iron oxide nanoparticles were synthesized by a surfactant-aided aerosol process and subsequent treatment. The cationic surfactant cetyltrimethyl ammonium bromide (CTAB) played an essential role in directing the structure of the composite. Translation from mesoporous silica particles to hollow particles was a consequence of increased loading of ferric species in the precursor solution and the competitive partitioning of CTAB between silicate and ferric colloids. The hypothesis was that CTAB preferentially adsorbed onto more positively charged ferric colloids under acidic conditions. At a critical Fe/Si ratio, most of the CTAB was adsorbed onto ferric colloids and coagulated the colloids to form larger clusters. During the aerosol process, a silica shell was first formed due to the preferred silicate condensation on the gas-liquid interface of the aerosol droplet. Subsequent drying concentrated the ferric clusters inside the silica shell and resulted in a silica shell/ferric core particle. Thermal treatment of the core shell particle led to encapsulation of a single iron oxide nanoparticle inside each silica hollow microsphere.     

Plasma Chemical Reactor with Exploding Water Jet

Exploding water jet discharge simultaneously generating powerful UV radiation, non-thermal plasma, and aerosol of fine water droplets has potential applications for removal of chemical and biological pollutants from air and water streams. A model plasma chemical reactor based on the exploding water jet discharge is considered. The radiation properties of the discharge, reactions of nitrogen oxide and hydrogen peroxide formation, and reactions of carbon dioxide and hydrogen sulfide decomposition are studied experimentally.     

RAMAN STUDIES OF AEROSOL CHEMICAL REACTIONS

Since Professor Matijevité and his colleagues published pioneering work on aerosol chemical reactions, based on experiments with monodisperse aerosol generators and laminar flow reactors, there has been considerable progress in the chemical characterization of aerosol particles and the study of their chemical reactions. This paper surveys recent developments and new research on the application of Raman spectroscopy to gas/liquid and gas/solid aerosol reactions. Of particular interest are applications of the vibrating orifice aerosol generator and electrodynamic and optical levitators coupled to Raman spectrometers to explore aerosol chemistry. The systems examined include the production of polymeric microsphcrcs, the generation of metal oxide particles from alkoxide droplets, SQ2/sorbent particle reactions used for demilitarization of stick gases, chemical characterization of particle arrays, and reactions following collisions of dissimilar particles. The complications associated with the interpretation of Raman data introduced by morphology-dependent resonances in the elastically scattered light are also examined.     

The effect of multi-component aerosol particles on quantitative laser-induced breakdown spectroscopy: Consideration of localized matrix effects

Spectral measurements were performed in a laser-induced plasma to assess the changes in sodium or magnesium analyte emission response from particle-derived sources with the addition of concomitant mass to the aerosol particles. Temporally resolved measurements revealed up to a 50% enhancement in analyte emission with the addition of the elements copper, zinc or tungsten at mass ratios from 1:9 to 1:19, although the enhancement generally diminished by delay times of 60 μs. Additional measurements in magnesium–cadmium aerosol particles were performed to assess the temporal profile of plasma temperature in the spatial vicinity of the aerosol particles using the ion-to-neutral emission ratios. These measurements revealed a general increase in localized plasma temperature with increasing delay time, which is attributed with an initial suppression of plasma temperature about the aerosol particles as plasma energy is required to vaporize and ionize the aerosol particle mass. These measurements provide direct evidence of a matrix effect for aerosol particles, which is attributed primarily to perturbations in the localized plasma properties. These perturbations are minimized at longer plasma delay times; hence quantitative LIBS analysis of aerosol particles should be performed with careful attention given to the temporal plasma evolution. The data further elucidate the complex interactions between the plasma gas and the aerosol particles, during which the finite time-scales of particle dissociation, and heat and mass transfer are equally important.     

Aerobic Oxidations Catalyzed by Colloidal Nanogold

Recently, dispersions of gold nanoclusters in liquid media (colloidal nanogold) have been extensively used as quasi‐homogeneous catalysts for various aerobic oxidation reactions. This review describes recent progress in such reactions, with a focus on our comprehensive studies on gold clusters (<2 nm) stabilized by poly(N‐vinyl‐2‐pyrrolidone) and their participation in oxidation reactions of alcohols, α‐hydroxylation reactions of benzylic ketones, and homocoupling reactions of organoboronates, as well as formal Lewis acidic reactions, such as intramolecular hydroalkoxylation and hydroamination reactions of nonactivated alkenes. Mechanistic studies have shown that a partial electron transfer from the gold clusters to O₂ generates superoxide‐ or peroxide‐like species and Lewis acidic centers, both of which play essential roles in the catalytic reactions.     

Cluster phase chemistry: gas-phase reactions of anionic sodium salts of dicarboxylic acid clusters with water molecules

A homologous series of anionic gas-phase clusters of dicarboxylic acids (oxalic acid, malonic acid, succinic acid, glutaric acid, and adipic acid) generated via electrospray ionization (ESI) are investigated using collision-induced dissociation (CID). Sodiated clusters with the composition (Na(+))(2)(n+1)(dicarboxylate(2-)(n+1) for singly charged anionic clusters, where n = 1-4, are observed as major gas-phase species. Isolation of the clusters followed by CID results mainly in sequential loss of disodium dicarboxylate moieties for the clusters of succinic acid, glutaric acid, and adipic acid (C4-C6). However, all oxalate (C2) and malonate (C3) clusters and dimers (n = 1) of succinate (C4) and glutarate (C5) exhibit more complex chemistry initiated by collision of the activated cluster with water molecules. For example, with water addition, malonate clusters dissociate to yield sodium acetate, carbon dioxide, and sodium hydroxide. More generally, water molecules serve as proton donors for reacting dicarboxylate anions in the cluster and introduce energetically favorable dissociation pathways not otherwise available. Density functional theory (DFT) calculations of the binding energy of the cluster correlate well with the cluster phase reactions of oxalate and malonate clusters. Clusters of larger dicarboxylate ions (C4-C6) are more weakly bound, facilitating the sequential loss of disodium dicarboxylate moieties. The more strongly bound small dicarboxylate anions (oxalate and malonate) preferentially react with water molecules rather than dissociate to lose disodium dicarboxylate monomers when collisionally activated. Implications of these results for the atmospheric aerosol chemistry of dicarboxylic acids are discussed.     

Direct on-strip analysis of size- and time-resolved aerosol impactor samples using laser induced fluorescence spectra excited at 263 and 351 nm

We report a novel atmospheric aerosol characterization technique, in which dual wavelength UV laser induced fluorescence (LIF) spectrometry marries an eight-stage rotating drum impactor (RDI), namely UV-LIF-RDI, to achieve size- and time-resolved analysis of aerosol particles on-strip. The UV-LIF-RDI technique measured LIF spectra via direct laser beam illumination onto the particles that were impacted on a RDI strip with a spatial resolution of 1.2 mm, equivalent to an averaged time resolution in the aerosol sampling of 3.6 h. Excited by a 263 nm or 351 nm laser, more than 2000 LIF spectra within a 3-week aerosol collection time period were obtained from the eight individual RDI strips that collected particles in eight different sizes ranging from 0.09 to 10 μm in Djibouti. Based on the known fluorescence database from atmospheric aerosols in the US, the LIF spectra obtained from the Djibouti aerosol samples were found to be dominated by fluorescence clusters 2, 5, and 8 (peaked at 330, 370, and 475 nm) when excited at 263 nm and by fluorescence clusters 1, 2, 5, and 6 (peaked at 390 and 460 nm) when excited at 351 nm. Size- and time-dependent variations of the fluorescence spectra revealed some size and time evolution behavior of organic and biological aerosols from the atmosphere in Djibouti. Moreover, this analytical technique could locate the possible sources and chemical compositions contributing to these fluorescence clusters. Advantages, limitations, and future developments of this new aerosol analysis technique are also discussed.     

The heterogeneous kinetics of HOBr and HOCl on acidified sea salt and model aerosol at 40-90% relative humidity and ambient temperature

The HOBr and HOCl uptake coefficient gamma on H(2)SO(4)-acidified submicron salt aerosol of known size distribution was measured in an atmospheric pressure laminar flow reactor. The interaction time of the trace gas with the aerosol was in the range 15 to 90 s and led to gamma values in the range 10(-4) to 10(-2). The acidity of the aerosol is essential in order to enable heterogeneous reactions of HOBr on NaCl, recrystallized sea salt (RSS) and natural sea salt (NSS) aerosols. Specifically, HOCl only reacts on acidified NSS aerosol with a gamma ranging from 0.4 x 10(-3) to 1.8 x 10(-3) at a relative humidity (rh) at 40 and 85%, respectively. Uptake experiments of HOBr on aqueous H(2)SO(4) as well as on H(2)SO(4)-acidified NaCl, RSS or NSS aerosol were performed for rh ranging from 40 to 93%. The gamma value of HOBr on acidified NSS reaches a maximum gamma = 1.9 x 10(-2) at rh = 76 +/- 1% and significantly decreases with increasing rh in contrast to acidified NaCl and RSS aerosols whose gamma values remain high at gamma = (1.0 +/- 0.2) x 10(-2) at rh >/= 80%. An explanation based on the formation of an organic coating on NSS aerosol with increasing rh is proposed.     

Clustering of catalytic nanocompartments for enhancing an extracellular non-native cascade reaction

Compartmentalization is fundamental in nature, where the spatial segregation of biochemical reactions within and between cells ensures optimal conditions for the regulation of cascade reactions. While the distance between compartments or their interaction are essential parameters supporting the efficiency of bio-reactions, so far they have not been exploited to regulate cascade reactions between bioinspired catalytic nanocompartments. Here, we generate individual catalytic nanocompartments (CNCs) by encapsulating within polymersomes or attaching to their surface enzymes involved in a cascade reaction and then, tether the polymersomes together into clusters. By conjugating complementary DNA strands to the polymersomes'' surface, DNA hybridization drove the clusterization process of enzyme-loaded polymersomes and controlled the distance between the respective catalytic nanocompartments. Owing to the close proximity of CNCs within clusters and the overall stability of the cluster architecture, the cascade reaction between spatially segregated enzymes was significantly more efficient than when the catalytic nanocompartments were not linked together by DNA duplexes. Additionally, residual DNA single strands that were not engaged in clustering, allowed for an interaction of the clusters with the cell surface as evidenced by A549 cells, where clusters decorating the surface endowed the cells with a non-native enzymatic cascade. The self-organization into clusters of catalytic nanocompartments confining different enzymes of a cascade reaction allows for a distance control of the reaction spaces which opens new avenues for highly efficient applications in domains such as catalysis or nanomedicine.

Compartmentalization is fundamental in nature, where the spatial segregation of biochemical reactions within and between cells ensures optimal conditions for the regulation of cascade reactions.     

氰化钾团簇的结构和形成机理研究

利用激光气化铁氰化钾或亚铁氰化钾并利用飞行时间质谱检测方法对氰化钾团簇的形成机理进行了研究，结果发现：团簇正离子可归属为［Ｋ（ＫＣＮ）＿ｎ］￣＋，ｎ＝０～３７，它们的幻数为ｎ＝４、１３、２２、３７；团族负离子可归属为［（ＫＣＮ）＿ｎＣＮ］￣－＝，ｎ＝０～１３，它们的幻数为ｎ＝４、１３。这些幻数与氯化钠等碱金属卤化物团簇体系完全一致。这表明：它们的团簇结构应该是相同的，即１×３×３（ｎ＝４）、３×３×３（ｎ＝１３）、３×３×５（ｎ＝２２）、３×５×５（ｎ＝３７）结构。因此氰化钾晶体的初期形成过程也应采取ＮａＣｌ型结构的增长途径。在激光气化产生的等离子体中，正、负离子与中性团簇的碰撞增长反应、正离子与负离子的复合反应以及团簇的亚稳态解离反应造成了团簇离子的不同丰度分布。氰化钾团簇中稳定立方体结构的产生决定了幻数的出现。     

Plasma enhanced aerosol–gel method: a new way of preparing ceramic coatings

The sol–gel process is widely used for the production of powders, coatings and bulk materials. However, being a wet-chemical technique, it has certain limitations related to properties of aqueous colloidal solution, especially when applied as a coating. The most frequently used methods, such as dip- and spin-coating, are difficult to apply onto more complex substrates. In these cases, the aerosol–gel deposition method can be regarded as the solution of this problem. In the present article, a novel plasma enhanced aerosol–gel method of coatings production is presented. A novelty of this method is based on an integration of the aerosol–gel deposition of thin films and their low temperature plasma treatment. Owing to the above, all stages of the coatings production process—substrate preparation, film deposition, and its plasma treatment, can be carried out in a single reactor. The design and operational scheme of such device is presented in this work. Using this device, thin coatings were first deposited on substrates and then plasma treated. The effect of deposition and plasma discharge conditions on morphology and chemical structure of the films has been studied. It was found that plasma treatment had a substantial influence on all the examined properties of the aerosol–gel deposited coatings.     

Heterogeneous atmospheric aerosol chemistry: laboratory studies of chemistry on water droplets

Heterogeneous chemical reactions on aerosol particles play a pivotal role in atmospheric chemistry. In this review, the fundamental concepts underlying the chemical dynamics of liquid aerosol droplets are discussed, with particular emphasis on the properties of the aqueous-air interface and the reaction mechanisms of key chemical processes. Recent laboratory studies of heterogeneous chemistry on aqueous aerosol particles are reviewed, with techniques that probe the gas phase, liquid phase and the interface directly, discussed in turn.     

The effect of humidity on the ozonolysis of unsaturated compounds in aerosol particles

Atmospheric aerosol particles are important in many atmospheric processes such as: light scattering, light absorption, and cloud formation. Oxidation reactions continuously change the chemical composition of aerosol particles, especially the organic mass component, which is often the dominant fraction. These ageing processes are poorly understood but are known to significantly affect the cloud formation potential of aerosol particles. In this study we investigate the effect of humidity and ozone on the chemical composition of two model organic aerosol systems: oleic acid and arachidonic acid. These two acids are also compared to maleic acid an aerosol system we have previously studied using the same techniques. The role of relative humidity in the oxidation scheme of the three carboxylic acids is very compound specific. Relative humidity was observed to have a major influence on the oxidation scheme of maleic acid and arachidonic acid, whereas no dependence was observed for the oxidation of oleic acid. In both, maleic acid and arachidonic acid, an evaporation of volatile oxidation products could only be observed when the particle was exposed to high relative humidities. The particle phase has a strong effect on the particle processing and the effect of water on the oxidation processes. Oleic acid is liquid under all conditions at room temperature (dry or elevated humidity, pure or oxidized particle). Thus ozone can easily diffuse into the bulk of the particle irrespective of the oxidation conditions. In addition, water does not influence the oxidation reactions of oleic acid particles, which is partly explained by the structure of oxidation intermediates. The low water solubility of oleic acid and its ozonolysis products limits the effect of water. This is very different for maleic and arachidonic acid, which change their phase from liquid to solid upon oxidation or upon changes in humidity. In a solid particle the reactions of ozone and water with the organic particle are restricted to the particle surface and hence different regimes of reactivity are dictated by particle phase. The potential relevance of these three model systems to mimic ambient atmospheric processes is discussed.     

气相过渡金属钽和钇-碳链团簇的质谱研究

Nd:YAG产生的二倍频532nm激光消融金属靶表面,同时含有3%乙炔的氦载气喷向旋转的金属靶,通过等离子体反应形成中性的气相过度金属-碳链团簇分子。经过超声膨胀,由Skimmer形成准直的分子束,进入飞行时间质谱仪的电离区,被193nm的准分子激光电离。实验发现,钽奇数碳链的过渡金属钽团簇离子信号较小,而偶数碳链的团簇离子信号较大。钇碳链观察到了YCm+(m=1～4,6)、Y2Cn+(n=2,4,6)和YCnH2+(n=2～6)的离子信号。     

Numerical simulation of laser-induced breakdown spectroscopy: Modeling of aerosol analysis with finite diffusion and vaporization effects

The application of laser-induced breakdown spectroscopy (LIBS) to aerosol systems has been shown to provide quantitative analysis of particle-derived species; however, the exact nature of the plasma/particle interactions remains to be fully understood. Although the plasma/particle interaction may be idealized within a framework of instantaneous vaporization and analyte diffusion throughout the plasma volume, experimental evidence suggests that these processes actually occur on finite time scales relative to the plasma decay times at which measurements are frequently taken. In the present work, a numerical simulation of the temperature and species concentration fields of a plasma containing a single particle, including dissociation and diffusion on semi-empirical finite time scales, is developed. Using these results, the intensity of analyte emission is calculated as a function of time, and the standard ion/neutral ratios typical of aerosol-derived LIBS signals are calculated. Furthermore, the ratio of ion/neutral ratios for two different species was used to assess the temperature homogeneity of the particle-derived analytes in comparison to the overall plasma temperature field. From this numerical study, it is shown that the finite time scale of evaporation and diffusion of aerosol material results in a non-uniform spatial distribution in concentration. This results, in turn, in temperature and free electron density gradients within the plasma, leading to variation between the local conditions surrounding aerosol mass and the bulk conditions of the plasma as a whole.     

Energetics of proton transfer in liquid water. I. Ab initio study for origin of many-body interaction and potential energy surfaces

The energetics of proton transfer in liquid water investigated by using ab initio calculation. The molecular electronic interaction of hydrated proton clusters in classified into many-body interaction elements by a new energy decomposition method. It is found that up to three-body molecular interaction is essential to describe the potential energy surface. The three-body effect mainly arises from the (non-classical) charge transfer and strongly depends on their configuration. Higher than three-body effects are small enough to be neglected. To simulate the liquid state reactions, two cluster models including all water molecules up to the second shell in the proton transfer reactions are employed. It is shown that these proton transfer reactions only involve small potential energy barriers of a few kcal/mol or less when structural rearrangement of the solvent is induced along the proton movement.     

Influence of water on conditions in the inductively coupled argon plasma

Aqueous media are used almost universally for sample introduction in both inductively coupled plasma atomic emission spectrometry (ICPAES) and in inductively coupled plasma/mass spectrometry (ICP/MS). In the process of aqueous sample introduction a substantial mass of water is introduced into the plasma as a combined aerosol/vapor mixture. In the present studies, the masses of water present as aerosol and vapor were controlled, in order to examine their separate influence on the key plasma properties of electron density n_e and ionization temperature T_ion. Water loading in the plasma was indeed found to have a major influence on n_e and T_ion, and plots of these parameters as a function of water loading are presented. Plasma viewing height and operating power were also found to be important variables in influencing the way in which water interacts with the plasma. The implications of water loading on background emission and noise level are also considered.     

Thermal benzene activation by 3d transition metal (Sc-Cu) oxide cations

Considering the importance and complexity of benzene oxidation on mineral oxide aerosol surfaces in the atmosphere,gas-phase 3 d-transition metal oxide cations were used as models of active sites on mineral oxide aerosols to mimic the corresponding reactions.The various cations have been prepared by laser ablation and reacted with benzene in a linear ion trap reactor.Of the 103 systematically investigated cations,39 clusters can oxidize benzene at room temperature.In addition to the adsorption channel,other five types of reaction channels were observed,including dehydrogenation of C6H6,charge exchange,hydrogen atom transfer,oxygen atom transfer,and the formation of C6H5O^+radical,among which the first two pathways are prevale nt and the formation of C6H6O^+cations has not been reported in literature.The insight into the benzene oxidation reactions derived from the gas-phase model systems is helpful to build a detailed picture of oxidative mechanisms of C6H6 and its derivatives over corresponding mineral oxide aerosols.     

Sampling statistics and considerations for single-shot analysis using laser-induced breakdown spectroscopy

A statistical analysis of single-shot spectral data is reported for laser-induced breakdown spectroscopy (LIBS). Fluctuations in both atomic emission and plasma continuum emission are investigated in concert for a homogenous gaseous flow, and fluctuations in plasma temperature are reported based on iron atomic emission in an aerosol-seeded flow. Threshold irradiance for plasma initiation and plasma absorption were investigated for pure gaseous and aerosol streams, with detailed statistical measurements performed as a function of pulse energy in the breakdown regime. The ratio of the analyte atomic emission intensity to the continuum emission intensity (peak/base) provided a robust signal for single-shot LIBS analysis. Moreover, at optimal temporal delay, the precision of the LIBS signal was maximized for pulse energies within the saturation regime with respect to plasma absorption of incident energy. Finally, single-shot temperature measurements were analyzed, leading to the conclusion that spatial variations in the plasma volume formation and subsequent plasma emission collection, play important roles in the overall shot-to-shot precision of the LIBS technique for gaseous and aerosol analysis.