Konstantinos Dimos

Nanoscale zero-valent iron supported on mesoporous silica: Characterization and reactivity for Cr(VI) removal from aqueous solution

MCM-41-supported nanoscale zero-valent iron (nZVI) was sytnhesized by impregnating the mesoporous silica martix with ferric chloride, followed by chemical reduction with NaHB4. The samples were studied with a combination of characterization techniques such as powder X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) and Mössbauer spectroscopy, N2 adsorption measurements, transmission electron microscopy (TEM), magnetization measurements, and thermal analysis methods. The experimental data revealed development of nanoscale zero-valent iron particles with an elliptical shape and a maximum size of ∼80 nm, which were randomly distributed and immobilized on the mesoporous silica surface. Surface area measurements showed that the porous MCM-41 host matrix maintains its hexagonal mesoporous order structure and exhibits a considerable high surface area (609 m(2)/g). Mössbauer and magnetization measurements confirmed the presence of core-shell iron nanoparticles composed of a ferromagnetic metallic core and an oxide/hydroxide shell. The kinetic studies demonstrated a rapid removal of Cr(VI) ions from the aqueous solutions in the presence of these stabilized nZVI particles on MCM-41, and a considerably increased reduction capacity per unit mass of material in comparison to that of unsupported nZVI. The results also indicate a highly pH-dependent reduction efficiency of the material, whereas their kinetics was described by a pseudo-first order kinetic model.

Revealing the ultrafast process behind the photoreduction of graphene oxide

Effective techniques to reduce graphene oxide are in demand owing to the multitude of potential applications of this two-dimensional material. A very promising green method to do so is by exposure to ultraviolet irradiation. Unfortunately, the dynamics behind this reduction remain unclear. Here we perform a series of transient absorption experiments in an effort to develop and understand this process on a fundamental level. An ultrafast photoinduced chain reaction is observed to be responsible for the graphene oxide reduction. The reaction is initiated using a femtosecond ultraviolet pulse that photoionizes the solvent, liberating solvated electrons, which trigger the reduction. The present study reaches the fundamental time scale of the ultraviolet photoreduction in solution, which is revealed to be in the picosecond regime.

Graphene oxide derivatives with variable alkyl chain length and terminal functional groups as supports for stabilization of cytochrome c

In this study we report the ability of reduced and non-reduced graphene oxide-based nanomaterials (GONs), modified with variable alkyl chain length and terminal functional groups, to act as effective scaffolds for the immobilization of cytochrome c (cyt c) using different immobilization procedures. The GONs/cyt c conjugates are characterized by a combination of techniques, namely atomic force microscopy, X-ray photoelectron and FT-IR spectroscopies as well as thermo-gravimetric and differential thermal analysis. The effect of the structure of functional groups and the surface chemistry of GONs on the immobilization efficiency, the peroxidase activity and the stability of the cyt c was investigated and correlated with conformational changes on the protein molecule upon immobilization. The enhanced thermal stability (up to 2-fold) and increased tolerance (up to 25-fold) against denaturing agents observed for immobilized cyt c, indicates that these functionalized GONs are suitable as nanoscaffolds for the development of robust nanobiocatalysts.

Cationic and anionic azo-dye removal from water by sulfonated graphene oxide nanosheets in Nafion membranes

Graphene oxide flakes functionalized with 3-amino-1-propanesulfonic acid (denoted as GOSULF) as a powder or incorporated into an ionomer membrane such as Nafion (DuPont) were studied for water purification applications. The adsorption and the photocatalytic activity of the GOSULF powder itself or confined as a nano-additive in the membrane (Nafion–GOSULF) were investigated by measuring the degradation of a cationic dye, methylene blue (MB), in the dark and under UV/Visible light illumination. The results were compared with the ability of these systems to degrade an anionic dye, methyl orange (MO), in order to evaluate the role of the polymer–dye interaction. The degradation of the azo dyes depends on the mutual interaction between GOSULF flakes, the polymeric matrix and the dye: Nafion–GOSULF strongly reduces MB both under dark and illumination conditions in the same way as the GOSULF powder, while, for MO degradation, the composite membrane is more efficient than GOSULF alone. Finally, the possibility of reusing the same photocatalytic material several times, which is the main advantage of embedding active nanomaterials in a polymer matrix, is demonstrated by the effective regeneration of the nanocomposite membranes.

Formation of carbon nanotubes on iron/cobalt-modified zeolites: Effect of zeolite framework/pore structure and method of modification

The present study focuses on the effect of the metal-modification method (ion-exchange or impregnation) and of the type of dealumination procedure (steaming, AHFS) of zeolite-Y on the quantity, quality and properties of the carbon nanotubes that are formed on the supported iron or cobalt oxides. Severe dealumination of zeolite-Y by steaming, which induced secondary meso/macropores, resulted in significant decrease in the carbon nanotube formation activity of the metal-impregnated zeolite-Y catalysts, while moderate dealumination by ammonium hexafluorosilicate had a less pronounced effect. The micro-Raman spectra revealed the presence of high quality as-grown CNTs with low degree of disordered.

A bottom-up approach for the synthesis of highly ordered fullerene-intercalated graphene hybrids

Much of the research effort on graphene focuses on its use as a building block for the development of new hybrid nanostructures with well-defined dimensions and properties suitable for applications such as gas storage, heterogeneous catalysis, gas/liquid separations, nanosensing and biomedicine. Towards this aim, here we describe a new bottom-up approach, which combines self-assembly with the Langmuir Schaefer deposition technique to synthesize graphene-based layered hybrid materials hosting fullerene molecules within the interlayer space. Our film preparation consists in a bottom-up layer-by-layer process that proceeds via the formation of a hybrid organo-graphene oxide Langmuir film. The structure and composition of these hybrid fullerene-containing thin multilayers deposited on hydrophobic substrates were characterized by a combination of X-ray diffraction, Raman and X-ray photoelectron spectroscopies, atomic force microscopy and conductivity measurements. The latter revealed that the presence of C60 within the interlayer spacing leads to an increase in electrical conductivity of the hybrid material as compared to the organo-graphene matrix alone.

Catalytic production of carbon nanotubes over first row transition metal oxides supported on montmorillonite

Clay-carbon nanotube composites were prepared by employing the catalytic chemical vapor deposition method (CCVD) over different transition metal oxides supported on montmorillonite. Various analytical techniques including SEM, TEM, XRD and DTA/TGA were used for the characterization of the final composite materials. The morphology, quality and structure of the produced nanotubes is shown to be dependent on the type of transition metals.

Production of hierarchical all graphitic structures: A systematic study.

We report the production of hierarchical all graphitic structures through a systematic study involving the use of wet chemical treatments for dip coating of carbon fibers (CFs) for surface grafting with multiwalled carbon nanotubes (CNTs). Realization of a thin homogeneous veil of CNTs onto the CF surface was achieved through an extensive parametric survey. Optimization of aqueous dispersions of CNTs eliminated the need for oxidation of the CF surface. The effects of chemical processes onto the surface and structural characteristics of the involved graphitic species were evaluated via thermogravimetric analysis, and X-ray photoelectron, infrared and Raman spectroscopies. The dielectric properties of the produced CNT aqueous dispersions were monitored via electrochemical impedance spectroscopy. A final assessment of the produced hierarchical CFs was performed through scanning electron microscopy.

Tissue Engineering for Post-Myocardial Infarction Ventricular Remodeling

Myocardial tissue engineering involves the design of biomaterial scaffolds, aiming at regenerating necrotic myocardium after myocardial infarction. Biomaterials provide mechanical support to the infarct area and they can be used as vehicles for sustained and controlled local administration of cells and growth factors. Although promising results have been reported in experimental studies, many issues need to be addressed before human use.

The non-innocent nature of graphene oxide as a theranostic platform for biomedical applications and its reactivity towards metal-based anticancer drugs

The self-assembly process in a solution of a mononuclear iron(II) complex based on the bispyrazolylpyridine scaffold with graphene oxide (GO) micrometer-sheets allows not only the devising of a new hybrid-architecture for GO-based materials suitable for nanomedicine, but also the unveiling of the reactive nature of GO as a drug-carrier. The neat iron complex is found to be highly active in disrupting the cell cycle through DNA binding, with behaviour and efficiency similar to that expressed by ruthenium-complexes as well as antibiotic-drugs such as doxorubicin. On the contrary, in the hybrid material the proclivity of neat GO to produce reactive oxygen species (ROS) became down-regulated by the electron-buffering properties of the loaded iron complex, evidencing the presence of an active electron transfer from the drug to GO. These findings question the use of the neat GO platform as a suitable carrier for metal-based anticancer drugs and highlight the importance of addressing the chemical/physical integrity of the drug being loaded into GO before drawing conclusions on the potential effectiveness of the hybrid material for medical applications.