Efficient low-temperature oxidation of carbon-cluster anions by SO2

Carbon-cluster anions, CN-, are very reactive toward SO2 (sticking probability of 0.012 +/- 0.005 for C27- at 25 degrees C), in contrast to their inertness toward other common atmospheric gases and pollutants. In flow reactor experiments at ambient temperature and near atmospheric pressure, primary adsorption of SO2 by the carbon cluster anions, N = 4-60, yields CNSO2- or CN-1S-. The inferred elimination of neutral CO2 is also detected as meta-stable decay in collision-induced dissociation. At higher temperatures, the reaction of SO2 with nascent carbon clusters yields CN-1SO- as well as undetected CO. The size-dependent initial reactivity reflects the previously established structural transitions (i.e., from chain to cyclic to cage structures). Such carbon clusters are formed in sooting flames and may act as nuclei for the formation of primary soot particles and serve as models for the local structural features of active soot particle sites for black-carbon soot. The facile generation of reactive carbon-sulfide and -sulfinate units may therefore have implications for understanding the health and environmental effects attributed to the coincidence of soot and SO2.     

Evolution and potential of the BiAS procedure for the determination of non-ionic surfactants

The evolution of the BiAS procedure is reviewed and its standard recommended version was compared with the modified version combined with the indirect tensammetric method (BiAS-ITM). New applications of the use of BiAS-ITM for the determination of nonionic surfactants (in the presence of hydrocarbons or adsorbed on particles) and polyethylene glycols were discussed.     

Oxygen adsorption on hydrated gold cluster anions: experiment and theory

The discovery that supported gold clusters act as highly efficient catalysts for low-temperature oxidation reactions has led to a great deal of work aimed at understanding the origins of the catalytic activity. Several studies have shown that the presence of trace moisture is required for the catalysts to function. Using near-atmospheric pressure flow reactor techniques, we have studied humidity and temperature effects on the reactivity of gas-phase gold cluster anions with O2. Near room temperature, the humid source produces abundant gold-hydroxy cluster anions, Au(N)OH(-), and these have a reversed O2 adsorption activity: Nonreactive bare gold clusters become active when in the form Au(N)OH(-), while active bare clusters are inactive when -OH is bound. The binding energies for the stable structures obtained from density functional calculations confirm fully these findings. Moreover, the theory provides evidence that electron-transfer induced by the binding of a OH group enhances the reactivity toward molecular oxygen for odd anionic gold clusters and suppresses the reactivity for the even ones. The temperature dependence of O2 addition to Au(3)OH(-) and Au(4)(-) indicates deviations from equilibrium control at temperatures below room temperature. The effects of humidity on gold cluster adsorption activity support the conclusion drawn for the mechanism of O2 adsorption on "dry" gold cluster anions and provides insight into the possible role of water in the enhanced activity of supported gold cluster catalysts.     

Tensammetric determination of non-ionic surfactants combined with BiAS separation procedure (wickbold)-I. precipitation of different ethoxylates with modified Dragendorff reagent in the proposed and classical BiAS procedures

The proposed procedure (BiAS-ITM) combines BiAS separation scheme of non-ionic surfactants with their determination by indirect tensammetric method (ITM). The method is based on (i) gas stripping separation of ethoxylates, (ii) their precipitation with modified Dragendorff reagent and (iii) determination of their concentration in the dissolved precipitate using ITM. Washing of the precipitate with glacial acetic acid, necessary in classical BiAS procedure which is a source of serious error, is omitted in the proposed separation scheme. The presented method determines the non-ionic surfactants instead of bismuth in the classical BiAS. The precipitation of 12 oxyethylated alcohols, four oxyethylated alkylphenols and four other ethoxylates were investigated according to the proposed procedure. Adsorptive stripping tensammery (AdST) was applied for additional control of investigated surfactants in the precipitate and in the filtrate. Simultaneously 13 ethoxylates were precipitated and determined according to classical BiAS procedure. The BiAS-ITM procedure shows significantly better recoveries and lower sensitivities vs. the chemical structure of the determined surfactants and thus BiAS-ITM is less sensitive to the composition of determined mixture than classical BiAS procedure. It enables the determination of ethoxylates having three or more oxyethylene subunits, while classical BiAS determines only those having five or more.     

Fractional nonlinear systems with sequential operators

In the paper possible approximation of solutions to initial value problems stated for fractional nonlinear equations with sequential derivatives of Caputo type is presented. We proved that values of Caputo derivatives in continuous case can be approximated by corresponding values of h-difference operators with h being small enough. Numerical examples are presented.     

Reactivity of small Mo(x)Oy- clusters toward methane and ethane

The reactions of Mo2Oy- suboxide clusters with both methane and ethane have been studied with a combination of mass spectrometry, anion photoelectron spectroscopy, and density functional theory calculations. Reactions were carried out under "gentle" and "violent" conditions. For methane, a number of products appeared under the gentler source conditions that were more logically attributed to dissociation of Mo2Oy- clusters upon reacting with methane to form MoCH2-, Mo(O)CH2-, and HMo(O2)CH3-. With ethane, products observed under the same gentle conditions were Mo(O)C2H2-, Mo(O)C2H4-, Mo(O2)C2H4-, and Mo(O2)(C2H5)2-. As expected, more products were observed when the reactions were carried out under violent conditions. The photoelectron spectra obtained for these species were compared to calculated adiabatic and vertical electron affinities and vibrational frequencies, leading to definitive structural assignments for several of the products.