- Fullerenes (A. Popov)
- Spectroelectrochemistry (E. Dmitrieva)
- Functional crystals on the nanoscale (S. Hampel)
The morphology of nanoscale materials such as the size and the shape of the nanoparticles and nanocrystals can dramatically affect their properties. Research on nanoscale materials is motivated by the observation that materials, previously only known in their bulk phase, show a significant change in physical and chemical properties or even exhibit novel phenomena at the nanoscale due to a high surface-to-volume ratio and finite size effects. The thorough characterization and understanding of these properties in interplay with nanoscopic length scales will ultimately guide the way to the exploitation of these effects in applications, including high density storage media and biomedical materials. The group of nanoscale chemistry is focusing on the synthesis of inorganic, organic, and hybrid nanomaterials. For instance, we develop new methods to synthesize single-crystalline inorganic nanowires and nanocrystals directly inside the carbon nanotubes. On even a smaller scale, single metal ions and small clusters are encapsulated inside fullerenes during their formation in arc-discharge synthesis forming endohedral fullerenes. Carbon nanostructures in such hybrid materials act not only as templating matrices but also as protecting shields stabilizing the nanosized forms of inorganic materials. Unique electronic, transport, and magnetic properties of these hybrid heterostructures are achieved due to nanosize of encapsulated structures and the interface effects at the boundary with the carbon π-system are then studied in close cooperation with other groups of IFW. Reducing only one dimension to nanoscopic length scale we have to consider ultrathin layers of the materials. The charge carrier densities of ultrathin layers which are part of an electric double layer can be influenced strongly by applying an electrochemical potential. Our aim is to investigate how huge charge carrier densities will influence the electric and magnetic properties of appropriate materials.
4th Summer School Spectroelectrochemistry at Center of Spectroelectrochemistry
(18 – 25 August 2017, Dresden, Germany)
The empty space inside the fullerene cage can be filled with atom, ions, clusters, or even small molecules. The fullerenes with encapsulated species are called endohedral fullerenes. Particular focus of our work is the synthesis of endohedral metallofullerenes (EMFs) with different clusters. The group in IFW Dresden pioneered in the development of the reactive atmosphere method, in which NH3 or CH4 gases are used as a source of nitrogen or hydrogen in the arc-discharge synthesis of EMF. More recent developments include the use of solid nitrogen-containing organic compounds as the sources of nitrogen. Reaction atmosphere method results in the dramatic suppression of the empty fullerene formation, leading to EMFs as the main fullerene products. We are also looking for new types of EMFs, which led to the discovery of such clusterfullerenes as Sc3CH@C80, Sc2S@C82, or TiLu2C@C80. Encapsulation of metal atoms within the carbon-based π-system results in a variety of unprecedented chemical and physical properties of EMFs. In IFW Dresden we are specifically focused on the electron-transfer mechanism in EMFs as studied by electrochemistry and spectroelectrochemistry, and on the magnetic properties of lanthanide-based EMFs (e.g., single molecule magnetism was discovered in Dy-containing nitride clusterfullerenes). Experimental studies are accompanied by quantum-chemical calculations of molecular structure, spectroscopic properties, and fullerene formation mechanism.
Spectroelectrochemistry as the combination of electrochemistry and different spectroscopic methods delivers detailed structural information on the intermediates and products in electrochemical reactions. By using different spectroelectrochemical methods formation and stabilization of charged species, follow-up processes, and mechanism of the electron transfer reaction can be investigated. To consolidate the spectroelectrochemical facilities of IFW and increase their visibility to other research groups and industrial partners, the Center of Spectroelectrochemistry was founded at the IFW Dresden in 2009 inspired by Prof. Dr. Lothar Dunsch.
The aims of the Center of Spectroelectrochemistry:
- Basic research in spectroelectrochemistry
- Development of spectroelectrochemical techniques
- Application of spectroelectrochemical studies for applied research
- International exchange of scientists for spectroelectrochemical research
- International training courses in spectroelectrochemistry
The center has expertise in various electrochemical and spectroscopic techniques and their combinations for in situ measurements, including in situ ESR, NMR, UV-vis-NIR, luminescence, IR, and Raman spectroelectrochemistry. These methods are applied to study the electrochemical electron transfer processes and intermediates of π-conjugated organic structures (small organic molecules, oligomers, conducting polymers etc.), carbon nanostructures (nanotubes, empty and endohedral fullerenes, and their functional derivatives etc.), hybrid molecular structures (organometallic compounds, coordination complexes, endohedral metallofullerenes etc.).
Offers of the Center of Spectroelectrochemistry
- Spectroscopic and spectroelectrochemical study on π-conjugated organic structures
- Pre-Screening of semiconductor organic materials for organic devices
- Spectroscopic determination of reactive oxygen species in solution (singlet oxygen, hydroxyl radical, peroxide, superoxide anion radical)
- Study of doping processes in conducting polymers and oligomers
- Study of electrode reaction mechanism
- Matrix-assisted laser desorption ionization mass spectrometry on organic compounds
Functional crystals on the nanoscale
Scaling a material down to nanometer-size reveals several opportunities to increase physical properties compared to bulk material or even create new ones. When quantum effects come into play electrical conductivity, magnetic permeability and chemical reactivity change as a function of particle size. Our approach uses carbon nanotubes (CNT) as a reaction container for the synthesis of intermetallic nanoparticles. With the given diameter of the tube particle size becomes adjustable. Furthermore the presence of the CNT-surrounding eases the reduction to metallic particle and protects nanoparticles from chemical influences (e.g. oxidation). Depending on the used material one obtains single particles or nano wires inside the inner cavity of the CNT. CNT have been filled for example with elements of main group IV in their metallic state. 3 different procedures to post synthetically fill the inner cavity of the CNT were used and by variation of the reaction parameters the appearance of filling particles, degree of filling and the purity of the samples in terms of coating to filling particle ratio can be tailored. These filled CNT with high rates of filling are promising for sensoric and energy storage applications.
Beside industrial applications carbon nanostructures are also interesting materials for biomedical applications. In our group we develop new strategies for the design and in-depth characterization of multifunctional carbon-based nanohybrid systems with the advantages of well-established cancer therapies. The starting material, CNT or/and NGO, will be functionalized with magnetic nanoparticles and with biocompatible polymer. By loading with chemotherapeutic or radiosensitiser or a combined loading these innovative nanohybrid materials will be able to improve the efficacy and reduce toxicity associated with current cancer therapy. One example, a new hybrid material made of gelatin (Gel), catechin (CT) and carbon nanotubes was tested. The anticancer activity on different cancer cells was evaluated and a considerable increase in the therapeutic activity was recorded moving from the free to the conjugated form in the presence of CNT, while in absence of CNT a reduction of the efficiency was observed. Furthermore the catechin-loaded and gelatin-conjugated CNT (Gel_CT_CNT) demonstrate their potential for the eradication of prostate cancer stem cells in combination with X-ray irradiation. Catechin-gelatin-conjugated CNT showed a significant enhancement of in vitro anticancer activity as compared to catechin alone.
The interest on 2D materials is rapidly growing and chemical approaches offer absolute control over the structure of 2D materials at the molecular-level. The chemical approach will serve as strategy to develop new multifunctional systems, featuring exceptional physical or chemical properties with optimal control over the correlation between structure and function. Our research currently focusses on the chemical vapor transport (CVT) in sealed ampules. One example is the CVT of bismuth chalcogenides nanostructures (Bi2Ch3; Ch = S, Se, Te) which can be synthesized by catalyst-free decomposition sublimation. The nanostructures directly grow on Si/SiO2 substrates by a vapor−solid growth mechanism and show high degree of crystallinity with dimensions of >10 μm in length and simultaneously <10 nm in height (nanoribbons). In order to optimize the growth process in a reproducible way we realize parallel thermodynamic calculations. The electrical transport data are evidence that this approach offers the chance to synthesize and investigate crystals with high quality and to measure surface state properties.