The empty space in different crystalline and clathrate phases of syndiotactic polystyrene (s-PS) is evaluated by a numerical procedure. It is shown that the δ form is nanoporous and includes two identical cavities per unit cell, whose shape and volume are characterized. As a consequence of clathration, the unit cell of the δ form is enlarged and the cavity is able to include molecules definitely larger than its starting size. Sorption experiments of nitrogen at 77 K for s-PS powders in different crystalline forms are also presented. These can be interpreted by inclusion of three nitrogen molecules per cavity of the δ crystalline phase and hence give an independent estimate of its volume.

Sorption experiments have been conducted for syndiotactic polystyrene (s-PS) aerogels with different crystalline forms and of different porosities. Nitrogen uptake experiments at 77 K have confirmed that δ-form aerogels present crystalline nanocavities as well as amorphous porosity. The equilibrium uptake of organic molecules, from dilute aqueous solutions, for δ-form aerogels is high (e.g., more than 5 wt % of 1,2-dichloroethane, DCE, from 1 ppm solutions) and independent of aerogel porosity. Gravimetric experiments, as well as FTIR conformational studies on absorbed DCE, clearly indicate that guest absorption from diluted solutions occurs only in the crystalline nanocavities. High-porosity δ-form aerogels (P > 98%) can also exhibit substantial water adsorption from the amorphous porosity, which is favorable to the pollutant absorption kinetics. In fact, apparent guest diffusivity increases of several orders of magnitude, with respect to the corresponding films, have been observed.

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High energy ball milling (HEBM) was utilized, as an innovative process, to incorporate carbon nanotubes (CNTs) into a polyethylene (PE) matrix avoiding: high temperatures, solvents, ultrasonication, chemical modification of carbon nanotubes. Composites with 1, 2, 3, 5, and 10 wt % of carbon nanotubes were prepared. Films were obtained melting the powders in a hot press. Morphology and physical properties (thermal, mechanical, electrical properties) were evaluated. The used processing conditions allowed to obtain a satisfactory level of dispersion of CNTs into the PE matrix with a consequent improvement of the physical properties of the samples. The thermal degradation was significantly delayed already with 1–2% wt of CNTs. The mechanical properties resulted greatly improved for low filler content (up to 3% wt). The electrical measurements showed a percolation threshold in the range 1–3 wt % of CNTs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 597–606, 2007

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This study was focused on the application of white and blue light emitting diodes (LEDs) as sources for the photocatalytic degradation of organic dyes in liquid phase with visible light. The photocatalytic activity of N-doped titanium dioxide, synthesized by direct hydrolysis of titanium tetraisopropoxide with ammonia, was evaluated by means of a batch photoreactor. The bandgap energy of titanium dioxide was moved in the visible range from 3.3 eV to 2.5 eV. The visible light responsive photocatalysts showed remarkably effective activity in decolorization process and in the removal of total organic carbon. Methylene blue was also used as a model dye to study the influence of several parameters such as catalyst weight and initial concentration. The effect of dye on the photocatalytic performance was verified with methyl orange (MO). The results demonstrated that the right selection of operating conditions allows to effectively degrade different dyes with the N-doped TiO2photocatalysts irradiated with visible light emitted by LEDs.

We present the fabrication of thick and dense carbon nanotube networks in the form of freestanding films (CNTFs) and the study of their electric resistance as a function of the temperature, from 4 to 420 K. A nonmetallic behavior with a monotonic R(T)R(T) and a temperature coefficient of resistance around −7×10−4 K−1−7×10−4 K−1 is generally observed. A behavioral accordance of the CNTF conductance with the temperature measured by a solid-state thermistor (ZnNO, Si, or Pt) is demonstrated, suggesting the possibility of using CNTFs as temperature small-sized (freely scalable) sensors, besides being confirmed by a wide range of sensitivity, fast response, and good stability and durability. Concerning electric behavior, we also underline that a transition from nonmetal to metal slightly below 273 K has been rarely observed. A model involving regions of highly anisotropic metallic conduction separated by tunneling barrier regions can explain the nonmetallic to metallic crossover based on the competing mechanisms of the metallic resistance rise and the barrier resistance lowering

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