Krzysztof Winkler

Two-Component Polymeric Materials of Fullerenes and the Transition Metal Complexes: A Bridge between Metal–Organic Frameworks and Conducting Polymers

In this review, we examined the interactions of metal complexes and metal surfaces with fullerenes. That information has been related to the formation of redox-active materials produced by electrochemical reduction of solutions of various transition metal complexes and fullerene or fullerene adducts. These redox-active polymers are strongly bound to electrode surfaces and display electrochemical activity in solutions containing only supporting electrolyte. Extensive studies of the electrochemical behavior of these films have been used to characterize their properties and structure. The process that produces these poly-Pd(n)C60 and poly-Pt(n)C60 films can also produce composite materials that consist of metal nanoparticles interspersed with the poly-Pd(n)C60 and poly-Pt(n)C60 materials. The relationship between these redox-active films and conducting metal organic framework materials has been examined. These insoluble, redox-active polymers have potential utility for the adsorption of various gases, for the construction of capacitors, for sensing, for the preparation of metal-containing heterofullerenes, and for catalysis.

Electrochemical Properties of Small Carbon Nano-Onion Films

The electrochemical properties of small carbon nano-onions (CNOs) in the solid phase, nonmodified carbon nano-onions (n-CNOs), and CNOs functionalized with carboxylic acid groups [oxidized carbon nano-onions (ox-CNOs)] were investigated by cyclic voltammetry. The redox properties of CNO films depend on the functionalization of the carbon surface. In aqueous solutions, the n-CNO/tetra(n-octyl)ammonium bromide (TOABr) films show a behavior typical of an ideal double-layer capacitor with a specific capacitance close to 9.68 F g -1 . The ox-CNOs are electrochemically active at negative potentials due to carboxylic group reduction. Modification of the nano-onion surface with carboxylic groups results in a decrease in the specific capacitance of ox-CNO/TOABr films to 6.57 F g -1 .

Small noncytotoxic carbon nano-onions: First covalent functionalization with biomolecules

Small carbon nano-onions (CNOs, 6-8 shells) were prepared in high yield and functionalized with carboxylic groups by chemical oxidation. After functionalization these nanostructures were soluble in aqueous solutions. 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2 tetrazolium (MTS) tests showed excellent cytocompatibility of all CNOs analyzed at 30 and 300 microg mL(-1), so these carbon nanostructures can be safely used for biological applications. The first covalent functionalization of oxidized CNOs (ox-CNOs) with biomolecules, by using biotin-avidin interactions is reported here. Multilayers were prepared on a gold surface by layer-by-layer assembly and the process was monitored by surface plasmon resonance (SPR) spectroscopy and atomic force microscopy (AFM). Covalent binding of molecules to the short amine-terminated organosulfur monolayers was assessed by Fourier transform infrared spectroscopy using total attenuated reflactance mode (FT-IR/HATR).

Study of Redox Active C 60 / Pd Films by Simultaneous Cyclic Voltammetry and Piezoelectric Microgravimetry at an Electrochemical Quartz Crystal Microbalance

The formation and properties of redox active C 60 /Pd films on gold electrodes of quartz oscillators were investigated by simultaneous cyclic voltammetry and piezoelectric microgravimetry at a quartz crystal microbalance. The films were prepared by electroreduction of solutions of C 60 and [Pd II (CH 3 COO) 2 ] 3 in 0.1 mol dm -3 tetra(n-butyl)ammonium perchlorate in acetonitrile-toluene (1:4, v:v). The composition of the solution from which the films were prepared significantly influenced the pattern of the film growth. The present results confirm that palladium clusters are codeposited with the C 60 /Pd film if the palladium complex to C 60 ratio was high. The reduced polymer film becomes partially electrochemically inactive at a sufficiently negative potential range. However, this electrically inactive film can be oxidized at very positive potentials. For charge compensation, the tetra(n-butyl)ammonium countercations enter the film during its electroreduction and are expelled from the film during electro-oxidation. At relatively high potential scan rates, only the outermost layers of the film that are in direct contact with the bathing solution are electrochemically active. At low scan rates, however, the bulk film material is also active. At very negative potentials, the film is removed from the electrode. The size of the tetra(n-alkyl)ammonium countercation is a major factor that determines both the electrochemical properties of the C 60 /Pd films and their stability with respect to dissolution.

Mechanistic studies of the electrochemical polymerization of C60 in the presence of dioxygen or C60O

Electropolymerization of C60 in the presence of dioxygen, in a mixture of acetonitrile and toluene (1 : 4, v : v) containing tetra(alkyl)ammonium perchlorate, was investigated by multi-scan cyclic voltammetry and piezoelectric microgravimetry with the use of an electrochemical quartz crystal microbalance. The fullerene was readily electropolymerized if the O2 to C60 concentration ratio in solution exceeded 1 : 10 and the applied potential reached values where electro-reduction of dioxygen to superoxide, O2˙−, and C60 to C602− occurred. The redox activity of the polymer was determined by cyclic voltammetry for solutions with different tetra-(alkyl)ammonium perchlorates used as supporting electrolytes. The film conductivity was higher the smaller the size of the cation in the supporting electrolyte. The C60 electropolymerization in the presence of dioxygen was suppressed when a spin trapping agent, N-tert-butyl-α-(4-nitrophenyl)nitrone that could intercept superoxide, was present. The fullerene was also electropolymerized in the presence of small amounts of the epoxide, C60O, in the absence of dioxygen. We postulate that the C60 electropolymerization in the presence of O2 proceeds via the initial nucleophilic attack of superoxide on C60 to form a C60O2˙− radical anion, which then interacts with another molecule of C60 to produce C60O and C60O˙−. Under further electro-reduction, these intermediates serve to initiate polymerization of C60 through the formation of C60O2−, as determined earlier in studies of the electropolymerization of C60O itself.

Structure and properties of C60–Pd films formed by electroreduction of C60 and palladium(II) acetate trimer: evidence for the presence of palladium nanoparticles

The composition, surface morphology, structure, and electrochemical properties of thin solid films of the polymer, C60–Pd, were studied by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and energy dispersive X-ray fluorescence (EDXRF) as well as being examined by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) with selective area diffraction (SAD) and by cyclic voltammetry (CV), respectively. The C60–Pd films were deposited onto Au or Pt electrodes by electroreductive co-polymerization of C60 and the palladium(II) acetate trimer, [Pd(ac)2]3, in a mixed acetonitrile–toluene (4∶1, v/v) solution of 0.1 M tetra(n-butyl)ammonium perchlorate under multicyclic voltammetry or potentiostatic conditions. The structure and composition of the C60–Pd films were dependent on the relative concentration of the polymer precursors, i.e., C60 and [Pd(ac)2]3, in the solution for electropolymerization. That is, in films grown in solutions with a high [Pd(ac)2]3∶C60 ratio, (–C60–Pd–)n polymeric chains were separated by the Pd nanoclusters. These films were relatively smooth and uniform. In contrast, films electropolymerized in solutions with a low [Pd(ac)2]3∶C60 ratio were rough, porous and much less uniform. The presence of the Pd nanoclusters in the C60–Pd film influenced the electrode processes of probing redox species dissolved in solution. That is, electro-oxidation of an N,N,N′,N′-tetramethyl-1,4-phenylenediamine (TMPDA) electrochemical redox probe was partially inhibited at the electrode coated by the C60–Pd film with a relatively low Pd nanocluster content. In contrast, electro-oxidation of TMPDA was effectively mediated by the C60–Pd film containing appreciable amounts of dispersed Pd nanoclusters.

Electrochemical properties of composites containing small carbon nano-onions and solid polyelectrolytes

The preparation and electrochemical properties of a novel type of composite made of small carbon nano-onions (CNOs) with poly(diallyldimethylammonium chloride) (PDDA) or chitosan (Chit) were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Composite films on glassy carbon electrode surfaces were deposited by a coating method, applying a drop of solution containing the suspended CNOs and filler, PDDA or Chit. Composites form relatively porous structures on the electrode surface and exhibit typical capacitive behavior, as well as excellent mechanical and electrochemical stability over a wide potential window, from +600 to −600 mV. The capacitance of the films is primarily related to the amount of CNOs incorporated into the layer of the filler. The capacitance ranges between 20 and 30 F g−1 of incorporated CNOs. The composites also show a low relaxation time from resistive to capacitive behavior, therefore indicating that they can operate as capacitors in short time windows.

Two-Component Films of Fullerene and Palladium as Materials for Electrochemical Capacitors

The redox-active films, C 60 /Pd, formed by electrochemical reduction of solutions containing palladium(II) acetate and C 60 fullerene have been studied as active components for electrochemical capacitors. The capacitance properties of these materials have been investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The structure and electrochemical properties of films deposited on an electrode surface depend on the composition of the solution from which they are grown. Films formed in a solution with a low concentration of palladium(II) acetate exhibit conductivity in the potential range of the film reduction. The faradaic process of C 60 reduction gives rise to pseudocapacitance. The capacitance of this polymer depends on the solvent and the size of the cations in the supporting electrolyte. For an acetonitrile solution containing only tetra(methyl)ammonium perchlorate, the film displays a high specific capacitance, close to 300 F/g. Films formed in a solution with a high concentration of palladium(II) acetate also contain metallic palladium nanoparticles. Such systems exhibit conductivity at potentials less negative than the potentials for film reduction, and these films can be considered as double-layer capacitors. The specific capacitance of these films is much smaller (about 20 F/g) but a large potential window (from +800 to-2000 mV) is available for the performance of these capacitors.

Conductive, capacitive, and viscoelastic properties of a new composite of the C60-pd conducting polymer and single-wall carbon nanotubes.

Thin films of a new composite of an electroactive fullerene-based (C60-Pd) polymer and HiPCO single-wall carbon nanotubes, which were noncovalently modified by 1-pyrenebutiric acid (pyr-SWCNTs), were electrochemically prepared under multiscan cyclic voltammetry conditions. With respect to blank polymer, superior conductive, capacitive, and viscoelasitic properties of the composite were demonstrated. Composition of pyr-SWCNTs was determined by thermogravimetric analyses, which showed one molecule of 1-pyrenebutiric acid per approximately 20 carbon atoms of SWCNT. Atomic force microscopy imaging revealed that pyr-SWCNTs form tangles of pyr-SWCNTs bundles surrounded by globular clusters of the C60-Pd polymer. Peaks characteristic of both pyr-SWCNTs (radial breathing modes at approximately 200 to 300 cm(-1)) and C60-Pd polymer in the Raman spectra recorded for the composite confirmed the presence of pyr-SWCNTs in the composite film. The mass of the deposited film was in situ measured by piezoelectric microgravimetry with the use of an electrochemical quartz crystal microbalance (EQCM). Then, curves of the current, resonant frequency change, and dynamic resistance change versus the potential in different potential ranges were simultaneously recorded in a blank acetonitrile solution of tetrabutylammonium perchlorate. Specific capacitance, determined at -1.20 V for the composite as 90 F g(-1), was twice as high as that for the polymer. Electrochemical impedance spectroscopy was used to determine impedance parameters of both the C60-Pd polymer and C60-Pd/pyr-SWCNTs composite film. This data analysis indicated increased capacitance and decreased resistance for the new composite film.

Redox-active films formed by electrochemical reduction of solutions of C60 and platinum complexes

Electroreduction of a toluene–acetonitrile (4∶1 v/v) solution of C60 and cis-Pt(py)2Cl2 in the presence of 0.10 M tetra(n-butyl)ammonium perchlorate as supporting electrolyte produces a black, redox active film that coats the electrode surface. This film retains its redox activity when transferred to an acetonitrile solution that contains only the supporting electrolyte, 0.10 M tetra(n-butyl)ammonium perchlorate. The film has been characterized by infrared spectroscopy, laser desorption mass spectrometry, and XPS spectroscopy. The formation of this film is dependent on the platinum complex used as precursor and on the potential range utilized during film growth. No film growth is observed when Pt(bipy)Cl2, Pt(py)2I2, cis-Pt(PPh3)2Cl2 or trans-Pt(py)2Cl2 are used as precursors, but {Pt(μ-Cl)Cl(C2H4)}2 is a useful precursor which allows film growth at less negative potentials. Chemically prepared C60Pt1 is also electrochemically active when precipitated on a platinum electrode. The formation of an electroactive film from the electroreduction of C70 and cis-Pt(py)2Cl2 is also reported.