Degradation of polystyrene using montmorillonite clay catalysts

Summary The performance of acid-treated montmorillonite catalysts in the degradation of polystyrene (PS) was investigated in this study. The degradation was carried out in a semi-batch reactor with a mixture of PS and catalyst at 400-450^oC. The commercial Süd Chemie acid-treated montmorillonite clays (K-series) showed good catalytic activity for the degradation of PS. The styrene monomer and ethylbenzene were major liquid products. The increase of surface acidity enhanced further cracking of styrene dimer and trimer to produce styrene monomer. Higher production of ethylbenzene for K30 may be related to its bigger pore volume and surface area compared to those of K5. High degradation temperature favored styrene monomer production.     

Trivalent atom contribution on solid-solid transformation of Ga13 polycation intercalated clay into sodalite investigated by X-ray absorption spectroscopy

Solid-solid transformation mechanism of Ga Keggin-type ion intercalated clay into sodalite has been clarified by X-ray diffraction (XRD), FT-IR spectroscopy, and X-rayabsorption spectroscopy (XAS). To follow the structural evolution precisely by XANES and EXAFS, the XAS active element containing polycation [Ga13O4(OH)24(H2O)12]7+ was intercalated into montmorillonite (MMT). FT-IR and XAS spectra confirm that the formation of sodalite framework is initiated by the delocalized rearrangement between silicate networks and collapsed interlayered Ga species, and is followed by the incorporation of Al in the octahedral sheet of clay (MMT). According to the XAS studies, it is found that the formation of Ga(Al)-O-Si species is strongly influenced by the trivalent cations, which are rapidly changed in the environment, followed by reaction with the silicate network of clay during the solid-solid transformation.     

Langmuir monolayers of Co nanoparticles and their patterning by microcontact printing

In this paper, we describe an easy and reliable method for the production of patterned monolayers of Co nanoparticles. A two-dimensional monolayer of Co nanoparticles is fabricated by spreading a nanoparticle solution over an air-water interface and then transferring it to a hydrophobic substrate by using the Langmuir-Blodgett (LB) method. Transmission electron microscopy (TEM) was used to show that, with increasing surface pressure, the Co nanoparticles become well-organized into a Langmuir monolayer with a hexagonal close-packed structure. By controlling the pH of the subphase, it was found that a monolayer of Co nanoparticles with long-range order could be obtained. Further, by transferring the Langmuir monolayer onto a poly(dimethoxysilane) (PDMS) mold, the selective micropatterning of the Co nanoparticles could be achieved on a patterned electronic circuit. The electronic transport properties of the Co nanoparticles showed the ohmic I-V curve.     

Designed self-assembly of molecular necklaces

This paper reports an efficient strategy to synthesize molecular necklaces, in which a number of small rings are threaded onto a large ring, utilizing the principles of self-assembly and coordination chemistry. Our strategy involves (1) threading a molecular "bead" with a short "string" to make a pseudorotaxane and then (2) linking the pseudorotaxanes with a metal complex with two cis labile ligands acting as an "angle connector" to form a cyclic product (molecular necklace). A 4- or 3-pyridylmethyl group is attached to each end of 1,4-diaminobutane or 1,5-diaminopentane to produce the short "strings" (C4N4(2+), C4N3(2+), C5N4(2+), and C5N3(2+)), which then react with a cucurbituril (CB) "bead" to form stable pseudorotaxanes (PR44(2+), PR43(2+), PR54(2+), and PR53(2+), respectively). The reaction of the pseudorotaxanes with Pt(en)(NO(3))(2) (en = ethylenediamine) produces a molecular necklace [4]MN, in which three molecular "beads" are threaded on a triangular framework, and/or a molecular necklace [5]MN, in which four molecular "beads" are threaded on a square framework. Under refluxing conditions, the reaction with PR44(2+) or PR54(2+) yields exclusively [4]MN (MN44T or MN54T, respectively), whereas that with PR43(2+) or PR53(2+) produces exclusively [5]MN (MN43S or MN53S, respectively). The products have been characterized by various methods including X-ray crystallography. At lower temperatures, on the other hand, the reaction with PR44(2+) or PR54(2+) affords both [4]MN and [5]MN. The supermolecules reported here are the first series of molecular necklaces obtained as thermodynamic products. The overall structures of the molecular necklaces are strongly influenced by the structures of pseudorotaxane building blocks, which is discussed in detail on the basis of the X-ray crystal structures. The temperature dependence of the product distribution observed in this self-assembly process is also discussed.     

Chiral studies in amorphous solids: the effect of the polymeric glassy state on the racemization kinetics of bridged paddled binaphthyls

Optical activity, used here for the first time to gain information about the amorphous solid state, allows previously unavailable insight into the dynamic properties of polymer glasses and their effect on a chemical process. This is accomplished by dispersing in polymer glasses atropisomeric bridged binaphthyls with appended oligophenyl paddles of varying sizes and studying the racemization kinetics as a function of temperature. The racemization occurs by a simple one-dimensional twisting motion and, without effect on the intrinsic mechanism, sweeps out a variable volume of the matrix as the paddle length is increased. The racemization is limited by the polymer matrix only for probes with a minimum paddle size and only when the time scale for racemization is comparable to the time scale for segmental motion of the polymer matrix. The high barrier for this racemization is unique in probe studies of glasses and causes these overlapping time scales to occur significantly below the glass transition temperature. These measurements yield a clear quantitative view of the role of segmental dynamics on the racemization kinetics of the binaphthyls and allow the important demonstration, via the transition from first-order to stretched exponential kinetics, that heterogeneous dynamics persist deep within the glassy state.     

Airborne particulates (PM2.5/PM10) monitoring in Korea by instrumental neutron activation analysis

Instrumental neutron activation analysis was used for the analysis of 25 trace elements in airborne particulate matter (PM) for air pollution monitoring. For the collection of air samples, the Gent stacked filter unit low volume sampler and two types of Nuclepore polycarbonate filters were employed. Samples were collected at selected sampling dates in suburban and industrial regions of Daejon city in the Republic of Korea. Mass concentrations and black carbon of PM were measured, and enrichment factors were calculated. The results were used to describe the emission sources and their correlation patterns.     

Charge transfer and electron backdonation in metallofullerenes encapsulating NSc3

Orbital interaction analysis is employed to understand the complex charge transfer mechanism operative in endohedral metallofullerenes of composition NSc₃@C_n (n = 68, 78). This phenomenon combines substantial electron transfer from the core to the cage with electron backdonation, involving the interaction between the occupied orbitals of the negatively charged cage and the unoccupied d orbitals of the positively charged core. This electron backdonation differs fundamentally from conventional orbital hybridization, which takes place primarily between the HOMO of the metal core and the LUMO of the fullerene cage. These findings imply the pronounced stability of NSc₃@C_n (n = 68, 78), especially for NSc₃ encapsulated in the non-IPR C₆₈ enclosure, as experimentally established.     

The participation of the anion and alkyl substituent of diaryliodonium salts in photo‐initiated cationic polymerization reactions

The photo‐initiated cationic polymerization (PCP) of epoxides using diaryliodonium salt photoacid generators (PAGs) bearing alkyl groups and anions was investigated. The properties and reactivities of a series of iodonium salts containing various cations and anions were compared in the context of a PCP reaction. The products from the decomposition of the cations of these salts were analyzed using gas chromatography‐mass spectrometry (GC‐MS) spectra. The relationship between the molecular structure of the salts and their reaction mechanism in the PCP reaction was investigated. Based on the results of the investigation, it was concluded that the structures of the cations and anions of theiodonium salts affect the PCP reaction rate, which was controlled by the products from the diaryliodonium salts. As part of an additional investigation, the diaryliodonium salts‐epoxide materials were applied to 254 nm‐photo‐patterning. Copyright © 2006 John Wiley & Sons, Ltd.     

An expedient synthesis of (+)-quinolactacin A2

An expedient synthesis of quinolactacin A2 from N-methylisatoic anhydride and N-Boc-(2S,3S)-isoleucine has been achieved. The key step involves the Friedländer-type annulation of isatoic anhydride and β-ketoester derived from isoleucine.     

Reduction of Chemical Reactions in Nitrogen and Nitrogen–Hydrogen Plasma Jets Flowing into Atmospheric Air

The large number of possible chemical reactions represents a severe burdenfor modeling of even relatively simple plasma systems. Reduced sets ofchemical reactions have been obtained for numerical simulations of nitrogenand nitrogen-hydrogen plasma jets flowing into an atmospheric airenvironment. The important or active reactions are determined based on asimplified reduction method. A reaction is considered active if it leadsto higher sensitivities than a specified cutoff sensitivity of 1%. Theactive reactions exert a significant influence on main plasma parameters,such as velocity, temperature, and species concentrations. The sensitivityanalysis for the specified systems shows that two NO reactions, known asZel'dovich reactions (N₂+ONO+N andNO+OO₂+N),⁽¹⁾ are both active in a nitrogenplasma jet. On the other hand, the latter is not active and may be omittedin a nitrogen–hydrogen plasma jet. A nitrogen–hydrogen plasmajet requires contribution of two active charge exchange reactions:N₂+N⁺N⁺ ₂+N andN+H+N+ +H, while only the former is needed in a nitrogen plasmajet. The dissociation reactions are all active in both plasma jets, exceptthe dissociation of OH.