D. Gournis

Effects of acetate on cation exchange capacity of a Zn-containing montmorillonite: physicochemical significance and metal uptake.

Fundamental properties such as cation exchange capacity (CEC), permanent charge, pH(PZC), and metal uptake of a Zn-containing montmorillonite are modified, in a predictable manner, by a mild chemical treatment using acetate. Acetate treatment allows a controllable increase of the CEC of montmorillonite up to 180 mequiv/100 g. The CEC of the clay is increasing for decreasing Zn content, with a slope of Delta[Zn]/Delta[CEC] approximately -2. X-ray powder diffraction analysis shows that the lamellar structure of the clay remains unaltered by the acetate treatment, while XPS substantiates the removal of Zn. H(+) uptake data show that the intrinsic protonation pK values and concentration of the variable charge sites ( identical with SOH) are not modified by the acetate treatment. In contrast, the concentration of the permanent charge sites ( identical with X(-)) increased linearly with Zn removal by acetate, leading to a significant H(+) and Cd(2+) uptake enhancement. A physical model is suggested where acetate removes Zn ions strongly bound in the clay, and this in turn modulates the permanent charge and the CEC of the clay.

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.

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.

Solubilisation of Multiwalled Carbon Nanotubes by Synthetic Humic Acids Studied by ATR-FTIR Spectroscopy

A well-characterised humic acid-like polycondensate (HALP) produced with no use of a catalyst (Giannakopoulos et al. J Colloids Interface Sci 336:59–66, 2009) shows remarkable capability for solubilisation of (otherwise water insoluble) multiwall carbon nanotubes. Attenuated total reflection (ATR) FTIR was used to study the molecular interactions between the HALP (as well as IHSS Leonardite HA as a reference) with MWCNTs at various pH values.