Mohamed A. Ghanem

Electrochemical syntheses of highly ordered macroporous conducting polymers grown around self-assembled colloidal templates

Three-dimensional highly ordered macroporous conducting polymer films were prepared using a self-assembled colloidal template based on poly(styrene) latex spheres. Poly(pyrrole), poly(aniline) and poly(bithiophene) were polymerised electrochemically and the polymer grown through the interstitial spaces between poly(styrene) latex spheres (0.5xa0µm or 0.75xa0µm in diameter) self-assembled in a close-packed array on gold substrates. The latex sphere template was subsequently removed by dissolution in toluene. Regular pore sizes and interconnected channels within the conducting polymer films were evident from scanning electron microscopy studies. The pore sizes for the conducting polymers studied were related to the dimensions of poly(styrene) spheres used as the template. Evidence for shrinkage of the structure was found for some polymers studied.

Electrochemical deposition of macroporous magnetic networks using colloidal templates

Nanostructuring of magnetic materials, on a scale comparable to the dimensions of the magnetic domain boundaries, is known to have a significant effect on the magnetic properties of a material. Here we demonstrate a simple and versatile technique for the preparation of two- or three-dimensional highly ordered macroporous cobalt, iron, nickel, and nickel iron alloy films containing close packed arrays of spherical holes of uniform size (an inverse opal structure). The films were prepared by electrochemical deposition from aqueous solution within the interstitial spaces of pre-assembled templates. The templates were assembled from colloidal polystyrene latex spheres (0.20, 0.50, 0.75 or 1.00 µm in diameter) assembled onto gold electrode surfaces from aqueous solution by slow evaporation. Following the electrochemical deposition of the metal or alloy films the polystyrene templates were removed by dissolution in toluene. Scanning electron microscopy of the resulting films show well-formed two- or three-dimensional porous structures consisting of interconnected close packed arrays of spherical voids. X-Ray diffraction analysis confirms that the nickel iron alloy in the walls of the structure is polycrystalline fcc in structure with a grain size which is significantly smaller than the thickness of the walls. The diameter of the spherical voids within the structures can be varied by changing the diameter of the polystyrene latex spheres used to form the template. Studies of the magnetic properties of the macroporous films show a large coercivity enhancement in comparison to the corresponding plain films and we find that the coercive field gradually increases as the diameter of the spherical voids decreases for films of a constant thickness.

Electrochemical deposition of macroporous platinum,palladium and cobalt films using polystyrene latex sphere templates

Highly ordered macroporous films of platinum, palladium and ncobalt with regular arrays of spherical pores with diameters of 0.40, 0.70 nor 1 μm are prepared by electrochemical deposition into the interstitial nspaces of a template formed by polystyrene latex spheres self-assembled on ngold electrodes; after deposition of platinum, palladium or cobalt, the npolystyrene spheres are fully removed by washing in toluene to leave a nhighly periodic, hexagonal close packed, interconnected network of nmonodisperse spherical pores within the metal film, the size of which is ndetermined by the diameter of the polystyrene latex particles used to nprepare the template.

Templated electrochemical deposition of nanostructured macroporous PbO2

We report a simple method for the preparation of novel nanostructured macroporous α- and β-PbO2 films with arrays of spherical pores arranged in a highly ordered close-packed structure. The nanostructured macroporous α- and β-PbO2 films were prepared by electrochemical deposition through the interstitial spaces between polystyrene spheres (500 or 750 nm in diameter) assembled on gold or indium tin oxide substrates. After deposition, the template was removed by dissolving in toluene to leave PbO2 films that have the inverse structure of the original template. Scanning electron microscopy and X-ray characterisation of the films shows a well-formed regular three-dimensional, porous α- or β-PbO2 framework, with the spherical pores arranged in a highly ordered close-packed three-dimensional structure. The spherical pores have the same diameter as the latex spheres used to form the templates and are interconnected through a series of smaller pores. The oxide frameworks are highly polycrystalline, self-supporting and free from defects. The confinement of α-PbO2 and β-PbO2 in the interstitial spaces between the polystyrene spheres that make up the template does not affect the mechanism of nucleation and deposition or the crystal structure of the oxide, as confirmed by scanning electron microscopy and X-ray characterisation. The electrochemical activity of the resulting macroporous β-PbO2 is greater than that of the corresponding plain film, as determined by the charge passed to convert the β-PbO2 to PbSO4 on electrochemical cycling in H2SO4. Due to the increase in volume accompanying the electrochemical conversion of β-PbO2 to PbSO4, the macroporosity of the film is significantly degraded and the electrochemical activity decreased after a few cycles in sulfuric acid.

Covalent modification of glassy carbon surface with organic redox probes through diamine linkers using electrochemical and solid-phase synthesis methodologies

Various mono-Boc-protected diamines have been covalently grafted to glassy carbon electrodes by electrochemical oxidation of the free amine. After deprotection of the Boc group, anthraquinone and nitrobenzene probes were coupled to the linkers using solid-phase coupling reactions. X-Ray photoelectron spectroscopy and cyclic voltammetry were used to monitor the coupling efficiency, effect of linker length on the surface coverage and electron transfer between the attached redox probes and electrode. The anthraquinone surface coverage was found to decrease as the chain length of alkyl diamine linker increased and the electron transfer kinetics were found to be faster for the lower coverages and the longer, more flexible linkers. In the case of nitrobenzene, there was only a slightly change in coverage with increasing linker length. This electrochemical attachment of protected diamine linkers followed by solid-phase coupling provides a very versatile methodology for attaching a wide range of molecular architectures onto glassy carbon surfaces.

Covalent Tethering of Organic Functionality to the Surface of Glassy Carbon Electrodes by Using Electrochemical and Solid-Phase Synthesis Methodologies

Organic linkers such as (N-Boc-aminomethyl)phenyl (BocNHCH2C6H4) and N-Boc-ethylenediamine (Boc-EDA) have been covalently tethered onto a glassy carbon surface by employing electrochemical reduction of BocNHCH2C6H4 diazonium salt or oxidation of Boc-EDA. After removal of the Boc group, anthraquinone as a redox model was attached to the linker by a solid-phase coupling reaction. Grafting of anthraquinone to electrodes bearing a second spacer such as 4-(N-Boc-aminomethyl)benzoic acid or N-Boc-beta-alanine was also performed by following this methodology. The surface coverage, stability and electron transfer to/from the tethered anthraquinone redox group through the linkers were investigated by cyclic voltammetry. The effects of pH and scan rate were studied, and the electron-transfer coefficient and rate constant were determined by using Lavirons equation for the different types of linker. The combination of electrochemical attachment of protected linkers and subsequent modifications under the conditions of solid-phase synthesis provides a very versatile methodology for tailoring a wide range of organic functional arrangements on a glassy carbon surface.

Magnetic antidot arrays from self-assembly template methods

Using self assembly from lyotropic liquid crystalline phases and from colloidal suspensions of polystyrene spheres templates, we have prepared well-ordered, nanostructured magnetic materials. We present the results of electrochemical deposition of magnetic metals and alloys in the interstitial space between these templates. This technique has enabled us to create magnetic nanostructures with three-dimensional achitectures on length scales of 4 nm–1 μm. We find changes in coercive field, by more than 1 order of magnitude, dominated by the effects of the nanoscale shapes. Varying the parameters in the preparation allows us to produce materials with predetermined magnetic parameters. The templated electrodeposition technique offers the potential of a low-cost preparation method for submicron patterned magnetic media.

Electrochemical and solid-phase synthetic modification of glassy carbon electrodes with dihydroxybenzene compounds and the electrocatalytic oxidation of NADH

We report the preparation, using electrochemical and solid-phase synthesis, and characterisation of a 26 member library of 13 dihydroxybenzene derivatives covalently attached to glassy carbon through ethylenediamine (EDA) and C(6)H(4)CH(2)NH linkers. First, Boc-protected EDA or Boc-NHCH(2)C(6)H(4) were electrochemically attached to the GC surface. After Boc-deprotection, dimethoxybenzoyl chlorides were coupled to the EDA and C(6)H(4)CH(2)NH linkers using solid-phase synthesis followed by deprotection of the methoxy groups to give the corresponding dihydroxybenzene compounds. Surface coverage and electrochemical parameters of the dihydroxybenzene modified electrodes were evaluated in parallel using cyclic voltammetry. The mid-peak potentials, E(mp), and surface coverages for the 13 dihydroxybenzene derivatives were found to be independent of the choice of linker. The mid-peak potentials of the immobilised dihydroxybenzene derivatives varied between 0.0 and 260 mV vs. SCE and their surface coverages varied between 0.07 and 1.1 nmol cm(-2), depending on the pattern of substitution of the dihydroxybenzene ring. The electrocatalytic activities of the library were evaluated for mediation of NADH oxidation, and the ortho-dihydroxybenzene derivatives were found to have higher catalytic activity.

The oxidation of ascorbate at copolymeric sulfonated poly(aniline) coated on glassy carbon electrodes

Self-doped poly(aniline)s as electrode coatings to catalyze ascorbate oxidation are revisited in this article. Sulfonated poly(aniline) (SPAN) was deposited on glassy carbon electrodes as a copolymer of aniline and its sulfonated derivative, 2-aminobenzenesulfonic acid (2-ABSA). The resulting deposits are reproducible and show good stability and electroactivity at pH>7, enabling studies at typical physiological pH values. Calibration curves were obtained using a rotating disc electrode at a sampling potential of 0.2V, displaying linear dependence in the region 0-20mM ascorbate. A kinetic model based on the Michaelis-Menten reaction mechanism, previously validated for poly(aniline) composites, was used to analyse the form of the calibration curve leading to values of the effective reaction constants K(ME) and k(ME). New calibration curves constructed for different sampling potentials were used to elucidate the rate limiting step at saturated kinetics. Rotating disc voltammetry performed at increasing pH (from pH 2 to 9) showed a dramatic decrease in the limiting current, without any evidence for a change in the reaction mechanism.

Oscillatory thickness dependence of the coercive field in magnetic three-dimensional antidot arrays

Recent developments in magnetic applications, such as data storage, sensors, and transducers, are stimulating intense research into magnetism on submicrometer-length scales. Emerging self-assembly fabrication techniques have been proposed as viable, low-cost methods to prepare such submicron structures. In this letter we present studies on magnetic nanostructures with 3D architectures, fabricated using a self-assembly template method. We find that the patterning transverse to the film plane, which is a unique feature of this method, governs the magnetic behavior. In particular, the coercive field, a key parameter for magnetic materials, was found to demonstrate an oscillatory dependence on film thickness.