Marta E. Plonska-Brzezinska

Metal Nitride Cluster Fullerene M3N@C80 (M=Y, Sc) Based Dyads: Synthesis, and Electrochemical, Theoretical and Photophysical Studies

The first pyrrolidine and cyclopropane derivatives of the trimetallic nitride templated (TNT) endohedral metallofullerenes I(h)-Sc(3)N@C(80) and I(h)-Y(3)N@C(80) connected to an electron-donor unit (i.e., tetrathiafulvalene, phthalocyanine or ferrocene) were successfully prepared by 1,3-dipolar cycloaddition reactions of azomethine ylides and Bingel-Hirsch-type reactions. Electrochemical studies confirmed the formation of the [6,6] regioisomers for the Y(3)N@C(80)-based dyads and the [5,6] regioisomers in the case of Sc(3)N@C(80)-based dyads. Similar to other TNT endohedral metallofullerene systems previously synthesized, irreversible reductive behavior was observed for the [6,6]-Y(3)N@C(80)-based dyads, whereas the [5,6]-Sc(3)N@C(80)-based dyads exhibited reversible reductive electrochemistry. Density functional calculations were also carried out on these dyads confirming the importance of these structures as electron transfer model systems. Furthermore, photophysical investigations on a ferrocenyl-Sc(3)N@C(80)-fulleropyrrolidine dyad demonstrated the existence of a photoinduced electron-transfer process that yields a radical ion pair with a lifetime three times longer than that obtained for the analogous C(60) dyad.

Synthesis, Characterization, and Photoinduced Electron Transfer Processes of Orthogonal Ruthenium Phthalocyanine-Fullerene Assemblies

The convergent synthesis, electrochemical characterization, and photophysical studies of phthalocyanine-fullerene hybrids 3-5 bearing an orthogonal geometry (Chart ) are reported. These donor-acceptor arrays have been assembled through metal coordination of linear fullerene mono- and bispyridyl ligands to ruthenium(II) phthalocyanines. The hybrid [Ru(CO)(C(60)Py)Pc] (3) and the triad [Ru(2)(CO)(2)(C(60)Py(2))Pc(2)] (5) were prepared by treatment of the phthalocyanine 6 with the mono- and hexakis-substituted C(60)-pyridyl ligands 1 and 2, respectively. The triad [Ru(C(60)Py)(2)Pc] (4) was prepared in a similar manner from the monosubstituted C(60)-pyridyl ligand 1 and the phthalocyanine precursor 7. The simplicity of this versatile synthetic approach allows to determine the influence of the donor and acceptor ratio in the radical ion pair state lifetime. The chemical, electrochemical, and photophysical characterization of the phthalocyanine-fullerene hybrids 3-5 was conducted using (1)H and (13)C NMR, UV/vis, and IR spectroscopies, as well as mass spectrometry, cyclic voltammetry, femtosecond transient absorption studies, and nanosecond laser flash photolysis experiments. Arrays 3-5 exhibit electronic coupling between the two electroactive components in the ground state, which is modulated by the axial CO and 4-pyridylfulleropyrrolidine ligands. With respect to the excited state, we have demonstrated that RuPc/C(60) electron donor-acceptor hybrids are a versatile platform to fine-tune the outcome and dynamics of charge transfer processes. The use of ruthenium(II) phthalocyanines instead of the corresponding zinc(II) complexes allows the suppression of energy wasting and unwanted charge recombination, affording radical ion pair state lifetimes on the order of hundreds of nanoseconds for the C(60)-monoadduct-based complexes 3 and 4. For the hexakis-substituted C(60) unit 2, the reduction potential is shifted cathodically, thus raising the radical ion pair state energy. However, the location of the RuPc triplet excited state is not high enough, and still offers a rapid deactivation of the radical ion pair state.

Carbon nano-onions for supercapacitor electrodes: recent developments and applications

This critical review covers the use of carbon nano-onion (CNO) based materials for electrochemical capacitor (EC) electrodes. The performance of CNO capacitors is reviewed in detail and compared to the results obtained using different carbon nanostructures. The physico-chemical vs. electrochemical properties of CNOs are discussed. Their advantages, challenges and applications, especially in EC electrodes, are discussed in detail through an extensive analysis of the literature. Exohedral carbon nano-onions are much less limited by mass transfer kinetics; they show low resistance and can operate over a wide voltage and temperature window, at very high charge–discharge rates with almost unlimited cyclabilities. Although carbon nano-onions make excellent supercapacitor electrode materials, many challenges still remain, particularly to characterize and understand the physical, chemical, and electrochemical interactions within multicomponent systems that contain CNOs. The full potential of carbon nano-onions as electrochemical power sources has not been realized yet, but as outlined in this review, the future looks very promising.

Preparation and characterization of composites that contain small carbon nano-onions and conducting polyaniline

Small multilayer fullerenes, also known as carbon nano-onions (CNOs; 5-6 nm in diameter, 6-8 shells), show higher reactivity than other larger carbon nanostructures. Here we report the first example of an in situ polymerization of aniline on phenyleneamine-terminated CNO surfaces. The green, protonated, conducting emeraldine polyaniline (PANI) was directly synthesized on the surface of the CNO. The functionalized and soluble CNO/PANI composites were characterized by TEM, SEM, DSC, Raman, and infrared spectroscopy. The electrochemical properties of the conducting CNO/PANI films were also investigated. In comparison with pristine CNOs, functionalized carbon nanostructures show dramatically improved solubility in protic solvents, thus enabling their easy processing for coatings, nanocomposites, and biomedical applications.

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).

Preparation and Characterization of Carbon Nano-Onion/ PEDOT:PSS Composites

Composites of unmodified or oxidized carbon nano-onions (CNOs/ox-CNOs) with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) are prepared with different compositions. By varying the ratio of PEDOT:PSS relative to CNOs, CNO/PEDOT:PSS composites with various PEDOT:PSS loadings are obtained and the corresponding film properties are studied as a function of the polymer. X-ray photoelectron spectroscopy characterization is performed for pristine and ox-CNO samples. The composites are characterized by scanning and transmission electron microscopy and differential scanning calorimetry studies. The electrochemical properties of the nanocomposites are determined and compared. Doping the composites with carbon nanostructures significantly increases their mechanical and electrochemical stabilities. A comparison of the results shows that CNOs dispersed in the polymer matrices increase the capacitance of the CNO/PEDOT:PSS and ox-CNO/PEDOT:PSS composites.

Synthesis of carbon nano-onion and nickel hydroxide/oxide composites as supercapacitor electrodes

“Small” carbon nano-onions (CNOs) are spherical, ca. 5 nm in diameter, concentric shells of graphitic carbon that can be also described as multi-shelled fullerenes. Given the easy functionalization and high thermal stability of the CNOs produced from nanodiamond, they are the most obvious choice for studying the potential applications of these multi-shelled fullerenes in electrochemical supercapacitors (ES). Since limited accessibility of the carbon surface to electrolyte penetration is observed for carbon nano-onions, performance enhancement was accomplished by modifying the CNO surfaces with pseudocapacitive redox materials: Ni(OH)2 and NiO. These composites were characterized by TEM, SEM, XRD, TGA-DTG-DTA and Raman spectroscopy. The electrochemical properties of these composites were also investigated. Compared with pristine CNOs (30.6 F g−1 at 5 mV s−1), modified CNOs (1225.2 F g−1 for CNOs/Ni(OH)2 and 290.6 F g−1 for CNOs/NiO, both at 5 mV s−1) show improved electrochemical performance, promising for the development of supercapacitors.

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.

Chemical versus Electrochemical Synthesis of Carbon Nano‐onion/Polypyrrole Composites for Supercapacitor Electrodes

The development of high-surface-area carbon electrodes with a defined pore size distribution and the incorporation of pseudo-active materials to optimize the overall capacitance and conductivity without destroying the stability are at present important research areas. Composite electrodes of carbon nano-onions (CNOs) and polypyrrole (Ppy) were fabricated to improve the specific capacitance of a supercapacitor. The carbon nanostructures were uniformly coated with Ppy by chemical polymerization or by electrochemical potentiostatic deposition to form homogenous composites or bilayers. The materials were characterized by transmission- and scanning electron microscopy, differential thermogravimetric analyses, FTIR spectroscopy, piezoelectric microgravimetry, and cyclic voltammetry. The composites show higher mechanical and electrochemical stabilities, with high specific capacitances of up to about 800 F g(-1) for the CNOs/SDS/Ppy composites (chemical synthesis) and about 1300 F g(-1) for the CNOs/Ppy bilayer (electrochemical deposition).