No abstract

The crystallization of synthetic layered magnesium silicate hectorite clays from both silica sol and organosilane sources is compared. For the silica sol-derived clays, a templating method is employed wherein organic or polymeric molecules are included during clay crystallization that are then removed from the composites via calcination. The mechanism of silane-derived hectorite formation is followed by XRD, TGA, 29 Si MAS NMR, and small angle X-ray scattering (SAXS), and results are compared to those obtained for the sol-derived hectorite. The mechanism appears to be similar but the rate is approximately doubled when the silane is used rather than silica sol. Analytical transmission electron microscopy (TEM) is exploited to glean structural morphology information towards resolving the nature of the resulting pore network structures. Results are compared with nitrogen adsorption-desorption isotherm behavior; dominant hysteresis loops are present in the type IV isotherms. Pore size distributions based on both the adsorption and desorption isotherms are compared. Small angle neutron scattering (SANS) experiments reveal that the average particle size increases as synthetic laponite v sol-derived hectorite v silane-derived hectorite v natural hectorite. Contrast matching SANS studies in aqueous and organic solvents are carried out to extract information about pore accessibility.

The utility of various synthetic hectorites for the preparation of active enzyme complexes by simple adsorption processes was examined. The smectites compared include commercially available Laponite RD, mesostructured hectorites (both with and without organic template), and silane-modified mesostructured hectorite. The complexes were evaluated by the amount of cytochrome c that was incorporated and the fraction of enzyme available for redox reaction. The quantity of adsorbed cyt c was determined by optical absorption spectroscopy of the supernatant solution, yielding enzyme densities that ranged from 20 to 50 wt %. There was no correlation between weight percent loading and either the surface area or the pore volume of the clay mineral. Rather, other characteristics such as surface compatibility appear to play the major role in this regard. Immobilized enzyme conformation was examined by EPR. Qualitative information regarding protein stability and redox activity was also obtained by chemical reduction experiments. These studies revealed the effects of organo-tailoring of the inorganic surface in terms of steric hindrance of enzyme in active conformation and denaturation within a clay pore microenvironment.

No abstract

No abstract

A homologous series of ferrocenyl surfactants, normalFcfalse(CH2)normalnNfalse(CH3)3+ where n=1, 6, or 11, have been intercalated into thin clay films in an effort to design novel electroactive nanocomposites. Cyclic voltammetry of clay-modified electrodes has been used to investigate the electrochemical properties of the surfactants. The rate of intercalation into the clay and steady-state currents were found to be highly dependent on chain length. Of the three, the compound containing one carbon in the chain is the only molecule to be effectively modeled by an ion-exchange mechanism, implying that the ferrocene resides close to the surface of the clay. The electrochemistry of the two longer chain compounds is markedly different from the one with a single carbon in the chain. The six- and eleven-carbon chain compounds have been shown to generate a larger capacitive current in the clay and represent possible charge-storage devices. © 2002 The Electrochemical Society. All rights reserved.

No abstract

No abstract