Current Physical Chemistry - Volume 2, Issue 3, 2012

A part of this special issue is devoted to conducting polymer-modified electrodes. Particular emphasis is laid on the problems of synthesis, structure, charge transport processes and practical applications of cross-linkable conjugated and ladder polymers. Different interpretations of the charge transport process at these polymer-modified electrodes on the basis of data extracted employing both traditional (Cyclic Voltammetry and Electrochemical Impedance Spectroscopy) and non-traditional (Surface Resistance) techniques, are presented. Concerning practical uses, the emphasis is placed on some applications of these materials as biosensors in analytical chemistry and optoelectronic devices. Other papers presented in this special issue refer to photomineralization of pharmaceutical pollutants, hydrate dissociation kinetics and applications of carbon nanotubes in catalysis.

This paper describes a potentiometric titration using a modified pencil graphite electrode with polyaniline (termed as PGE/PAniCl) for determination of halides at low concentrations (ppm). polyaniline (PAni) was first prepared by chemical polymerization of aniline in the presence of HCl. PGE/PAniCl was prepared using a pencil graphite electrode coated by a thin film of PAni/Cl via solution cast method. The PGE/PAniCl indicator electrode was successfully used for quantitative determination of halide ions by potentiometric titration. The titration curves were compared with those obtained by a commonly used silver indicator electrode and found to be more sensitive than commonly used silver indicator electrode. The electrode introduced in this article can be fabricated simply and can be used for determination of chloride ions in water samples via potentiometric titration with high accuracy.

This review article focuses on conducting polymers and their applications. Conducting polymers (CPs) are an exciting new class of electronic materials, which have attracted an increasing interest since their discovery in 1977. They have many advantages, as compared to the non-conducting polymers, which is primarily due to their electronic and optic properties. Also, they have been used in artificial muscles, fabrication of electronic device, solar energy conversion, rechargeable batteries, and sensors. This study comprises two main parts of investigation. The first focuses conducting polymers (polythiophene, polyparaphenylene vinylene, polycarbazole, polyaniline, and polypyrrole). The second regards their applications, such as Supercapacitors, Light emitting diodes (LEDs), Solar cells, Field effect transistor (FET), and Biosensors. Both parts have been concluded and summarized with recent reviewed 233 references.

π-Conjugated polymers have found applications as active materials in a range of optoelectronic devices due to being intrinsically semiconducting, exhibiting switchable properties in the course of redox processes, and the possibility of being processed from solution. Current developments in molecular design have been extended to include switchable solubility by means of chemical cross-linking via polymerization of photo-reactive groups attached to the polymer backbone. Exploiting the cross-linkable ability of conjugated polymers has allowed extending applications to multilayered devices fabrication, as the cross-linked structure does not re-dissolve upon further deposition of solutions, and also to patterning processes, at the sub-micrometric scale, based on photo-induced methods (photo-lithography) or on phaseseparation in spin cast polymer blends. Among the classes of cross-linkable conjugated polymers, those containing oxetane units as the cross-linking moiety have been the most explored in terms of applications in optoelectronic devices. In this article, we review the recent progress in the field of oxetane-functionalized conjugated polymers, focusing on their molecular design to control electronic and processing properties and their most relevant applications in organic electronics.

The use of surface resistance changes as an alternative method to study the metal|polymer interface is reviewed considering both experimental and theoretical aspects. The experimental arrangement in these investigations is, in general, one in which a polymer film is supported on a thin gold film, whose thickness is of the order of the mean free path of the conduction electrons (gold film thickness, φm ∼30 nm). Particular emphasis is laid on the effects of polymer thickness, electrolyte composition, degree of oxidation, and deactivation and reactivation processes of the polymer film on the metal film conductance. Relevant experiments, where the technique was employed to study the redox site distributions at the metal|polymer interface, during oxidation, deactivation and degradation of the polymer, were specially considered. The simple scattering model to explain surface resistance changes of a thin metal film coated with a poly(o-aminophenol) film is outlined on the basis of the specularity parameter, which represents the probability of an electron being reflected specularly or diffusely at the metal film surface. Information obtained by means of surface resistance is compared with that obtained by employing more traditional techniques such as cyclic voltammetry and rotating disc electrode voltammetry.

The effects of confinement in carbon nanotubes on the performance and lifetime of carbon nanotubes (CNT) supported cobalt Fischer–Tropsch (FT) catalysts are reported. A method was developed to control the position of the catalytic sites on either inner or outer surface of carbon nanotubes. TEM analyses revealed that about 80-85% of cobalt oxide particles can be controlled to be positioned at inner or outer surface of the nanotubes. Deposition of cobalt oxide inside the nanotube pores decreased the average size of the cobalt oxide particles from 16.6 to 7.2 nm and shifted the reduction peak temperature of cobalt oxide species to lower temperatures (from 330 to 318oC, and 446 to 428oC) and improved the reducibility of the catalyst by 7%. The catalysts were assessed in terms of their activity, selectivity and lifetime in a fixed-bed micro reactor. The catalyst with catalytic sites inside the pores showed 30.5% higher initial activity than the catalyst with catalytic sites outside the pores. Also, the catalyst with cobalt particles inside the pores exhibited higher selectivity to heavier hydrocarbons (79.5% vs. 76.2% C5 + selectivity). Deposition of cobalt particles on interior surface of the nanotubes resulted in a more stable catalyst, while its counterpart experienced 50.4% deactivation within a period of 20 days due to catalytic sites sintering. It is concluded that encapsulation of the catalytic metal nanoparticles inside the nanotubes prevents the catalytic site agglomeration.

The efficient photomineralization of ibuprofen and ketoprofen was achieved through the use of a novel combination of a conventional low-pressure mercury lamp (185/254 nm) and a xenon excimer flow-through photoreactor (λmax7equals; 172 nm) with an integrated ceramic gassing unit. During the vacuum-ultraviolet photolysis of water, hydrogen peroxide (H2O2) was produced both in the presence and in the absence of ibuprofen or ketoprofen (c0 = 1.0×10-4 mol L-1). Ibuprofen and ketoprofen enhanced the formation of H2O2 significantly. The influence of H2O2 on the photomineralization of these pharmaceutical pollutants was also investigated. The effects of the energy of the incident photons (the wavelength of the light) on the degradation of the contaminants and on H2O2 formation were compared.

Hydrate dissociation is involved in some practical processes, such as exploiting natural gas hydrates, resolving the plugging hazards, and developing industrial techniques. The decomposition mechanisms of gas hydrate above and below ice point are quite different. The presence of porous media may also result in the complication of hydrate dissociation compared with bulk water/hydrate system. In this work, the recent progresses achieved in the dissociation kinetics of gas hydrate from three aspects: dissociation kinetics of hydrate in bulk hydrate/water system above ice point, dissociation kinetics of hydrate in bulk hydrate/water system below ice point, and dissociation kinetics of hydrate in porous media, were reviewed. The influences of temperature, pressure, gas composition, and additive of aqueous phase such as inhibitors and promoters on the dissociation of hydrate have been examined. The corresponding mechanisms and models for hydrate dissociation under three aspects were also reviewed. A prospect to the future of research on gas hydrate dissociation is given.