L. Hussein

Synthesis, Stabilization, Functionalization and, DFT Calculations of Gold Nanoparticles in Fluorous Phases (PTFE and Ionic Liquids)

Gold nanoparticles (Au-NPs) were reproducibly obtained by thermal, photolytic, or microwave-assisted decomposition/reduction under argon from Au(CO)Cl or KAuCl(4) in the presence of n-butylimidazol dispersed in the ionic liquids (ILs) BMIm(+)BF(4)(-), BMIm(+)OTf(-), or BtMA(+)NTf(2)(-) (BMIm(+) = n-butylmethylimidazolium, BtMA(+) = n-butyltrimethylammonium, OTf(-) = (-)O(3)SCF(3), NTf(2)(-) = (-)N(O(2)SCF(3))(2)). The ultra small and uniform nanoparticles of about 1-2 nm diameter were produced in BMIm(+)BF(4)(-) and increased in size with the molecular volume of the ionic liquid anion used in BMIm(+)OTf(-) and BtMA(+)NTf(2)(-). Under argon the Au-NP/IL dispersion is stable without any additional stabilizers or capping molecules. From the ionic liquids, the gold nanoparticles can be functionalized with organic thiol ligands, transferred, and stabilized in different polar and nonpolar organic solvents. Au-NPs can also be brought onto and stabilized by interaction with a polytetrafluoroethylene (PTFE, Teflon) surface. Density functional theory (DFT) calculations favor interactions between IL anions instead of IL cations. This suggests a AuF interaction and anionic Au(n) stabilization in fluorine-containing ILs. The (19)F NMR signal in BMIm(+)BF(4)(-) shows a small Au-NP concentration-dependent shift. Characterization of the dispersed and deposited gold nanoparticles was done by transmission electron microscopy (TEM/HRTEM), transmission electron diffraction (TED), dynamic light scattering (DLS), UV/Vis absorbance spectroscopy, scanning electron microscopy (SEM), electron spin resonance (ESR), and electron probe micro analyses (EPM, SEM/EDX).

A highly efficient buckypaper-based electrode material for mediatorless laccase-catalyzed dioxygen reduction

The redox enzyme laccase from Trametes versicolor efficiently catalyzes the oxygen reduction reaction (ORR) in mediatorless biofuel cell cathodes when adsorbed onto multi-walled carbon nanotubes (MWCNTs). In this work we demonstrate that the fabrication of MWCNTs in form of buckypaper (BP) results in an excellent electrode material for laccase-catalyzed cathodes. BPs are mechanically stable, self-entangling mats with high dispersion of MWCNTs resulting in easy to handle homogeneous layers with highly mesoporous structures and excellent electrical conductivities. All biocathodes have been electrochemically investigated in oxygen-saturated buffer at pH 5 by galvanostatic polarization and potentiodynamic linear sweep voltammetry. Both methods confirm an efficient direct interaction of laccase with BP with a high open circuit potential of 0.882 V vs. normal hydrogen electrode (NHE). The high oxygen reduction performance leads to high current densities of 422±71 μA cm(-2) at a typical cathode potential of 0.744 V vs. NHE. When the current density is normalized to the mass of the electrode material (mass activity), the BP-based film electrodes exhibit a 68-fold higher current density at 0.744 V vs. NHE than electrodes fabricated from the same MWCNTs in a non-dispersed agglomerated form as packed electrodes. This clearly shows that MWCNTs can act more efficiently as cathode when prepared in form of BP. This can be attributed to reduced diffusional mass transfer limitations and enhanced electrical conductivity. BP is thus a very promising material for the construction of mediatorless laccase cathodes for ORR in biofuel cells. In addition we demonstrated that these electrodes exhibit a high tolerance towards glucose, the most common bioanode fuel.

Fabrication and characterization of buckypaper-based nanostructured electrodes as a novel material for biofuel cell applications

The fabrication process of buckypapers (BPs) made from stable suspensions of as-received or functionalized multi-walled carbon nanotubes (MWCNTs) with high purity (97.5 wt%, Baytubes), their characterization and their utilization towards novel biofuel cell electrode applications are reported. The BPs can vary in thickness between 1 μm and 200 μm, are mechanically robust, flexible, stable in solvents, possess high meso-porosities as well as high apparent electrical conductivities of up to 2500 S m(-1). Potentiodynamic measurements of biocathodes based on bilirubin oxidase (BOD)-decorated BPs for the oxygen reduction reaction (ORR) in neutral media (phosphate buffer solution) containing glucose indicate that BP electrodes based on functionalized MWCNTs (fBPs) perform better than BP electrodes of as-received MWCNTs and have high potential as an effective electrode material in biofuel cells and biosensors.

Decorated nanotube buckypaper as electrocatalyst for glucose fuel cells

We present novel metallic/bimetallic (Pt, Au-Pt) nanoparticle-decorated carbon nanotubes and bilirubin oxidase-decorated carbon nanotubes deposited on nano-tube buckypaper as promising supported electro-catalytic systems and as electrode material respectively for mixed-reactant biofuel cell applications at neutral pH. We found that the novel enzyme-decorated carbon nanotubes on nanotube buckypaper material is a promising cathode for glucose biofuel cells. It exhibited a high tolerance and catalytic activity resulting in higher current densities compared to carbon black based electrodes.