Clay films

Clay films cast from a pure aqueous colloid appear to form a regular array of microplatelets, thin films of which show selective cation exchange, e.g. segregation of Ru(bipy)i from Na" and methylviologen dication and even partial separation of the enantiomers of Co bipy)3 Thicker films (approx. 3 pm) can be supported by the addition of polyvinyl alcohol additive also aids swelling of the... 

Thin self-supporting clay films (appropriate for IR measurement) readily take up organic amines such as cyclohexylamine with displacement of the major fraction of the intercalated water. For the Ua -exchanged sample the majority of the amine is present in the unprotonated form - there being insufficient Bronsted acidity generated by the interlayer cation. When Al + is the exchangeable cation, however, a major fraction of the intercalated amine becomes protonated (see Figure 2). 

Layered materials are of special interest for bio-immobilization due to the accessibility of large internal and external surface areas, potential to confine biomolecules within regularly organized interlayer spaces, and processing of colloidal dispersions for the fabrication of protein-clay films for electrochemical catalysis [83-90], These studies indicate that layered materials can serve as efficient support matrices to maintain the native structure and function of the immobilized biomolecules. Current trends in the synthesis of functional biopolymer nano composites based on layered materials (specifically layered double hydroxides) have been discussed in excellent reviews by Ruiz-Hitzky [5] and Duan [6] herein we focus specifically on the fabrication of bio-inorganic lamellar nanocomposites based on the exfoliation and ordered restacking of aminopropyl-functionalized magnesium phyllosilicate (AMP) in the presence of various biomolecules [91]. 

Zhou, Y., Hu, N., Zeng, Y. and Rusling, J.F. (2002) Heme protein-clay films Direct electrochemistry and electrochemical catalysis. Langmuir, 18, 211-219. 

Clays are usually cation-exchangeable aluminosilicates, and exfoliated clay particles have a platelet shape with nanoscopic size. Cast protein-clay films on electrodes have been used to immobilize proteins. The Clay/Mb electrode has good electrocatalytic properties for the reduction of oxygen and hydrogen peroxide [236] and the biosensors can also be made based on these properties. 

Powder x-ray diffraction patterns of oriented clay films on glass slides were obtained for both the air-dry and fully wet Na+- and Ca +-smectites using a Philips Norelco diffractometer. 

Table III. Hyperfine splitting (A) values of TEMPAMINE+ adsorbed on fully wetted oriented clay films.

If we select the z axis to be normal to the plane of the clay film, the angle 0 can be imagined to fluctuate rapidly as the probe tumbles in the interlayer. This time-averaged system is symmetric about the z axis because of the random orientation of the a and b axes of the clay platelets in the x y plane. 

Figure 6. Plot of TEMPAMINE hyperfine splitting as a function of orientation of the clay film (angle between plane of film and the applied magnetic field) for hectorite (O), montmorilIonite ( ) and beidellite (n).

Table IV. ESR parameters of Cu + in air-dry oriented layer silicate clay films.

Several general observations can be made from the spectra and the calculated ESR parameters. First, the Na+- smectites possess narrower resonance line widths than the Ca +-smectites, with the exception of the saponite. Since Ca +-smectites, unlike Na+ -smectites, do not disperse into individual platelets in aqueous suspension, the Na+-smectite films formed by drying suspensions onto a smooth flat surface have the silicate surfaces more perfectly oriented in the plane of the film. As a result, less angular variation of the z-axis of Cu + relative to the plane of the film would narrow the spectra. One can see evidence of hyperfine splitting in the gj component of the Na+-smectite spectra, but not in the Ca +-smectite spectra. Saponite, unlike the other smectites, has very similar spectral linewidths for the Na+ and Ca + form (Figure 16). Since this Na+-saponite sample does not disperse completely in water (Table II), the alignment of Na+-saponite platelets in the clay film may be no better than that of the Ca +-saponite. 

In addition, with respect to the frequency of t ie main absorption band of safranine in water (495 nm, 5 10 M), the spectrum observed for the Na clay suspension,0.1% solid/water, is blue shifted (468 nm), whereas it is red shifted (510 nm) for the Ni and Fe clays suspensions. X ray data suggested that bimolecular layers of safranine are formed within the interlayer space of the Na clay. The blue shift was suggested to result from dimerization of S because of lower acidity due to higher clay dilution. Upon drying clay films, the Na-safranine clay spectrum is red shifted (at 504 nm, whereas the Fe and Ni-safranine clay spectra are further red shifted (at 540 nm) suggesting higher protonation. 

Quenching mechanism. Steady state measurements of the luminescence quantum yield of Ru(byp)3 intercalated in clay films brings about more detailed information with respect to the possible role of electron transfer in luminescence quenching. The quantum yield is dependent upon the amount of co-adsorbed water and s strongly depleted by transition metal impurities, such as Fe5 or Cr in the lattice (28). 

Kyotani, T., Mori, T., and Tomita, A. Formation of a flexible graphite films from poly(acrylonitrile) using a layered clay film as template. Chem. Mater. 6, 1994 2138-2142. 

Thus Geus et al. studied oriented silicalite-1 crystals in an expoxy matrix on perforated metal with each crystal fully covering one hole of the metal support [12], Geus also investigated [13] monolayers of silicalite-1 crystals on macroporous alumina covered with a thin clay film. Zeolite surface coverages of 75% were achieved (Figure 4). 

To summarize, in order to obtain XANES spectra that may be meaningfully compared, we recommend orienting the sample, when a single crystal, always at the same angle of rotation a = 54.7°. This is essentially the same conclusion reached by Manceau et al. (1998) for the self-supporting clay films they experimentally investigated by... 

Within each stratigraphic entity studied samples of fine-grained sandstones and those containing well-developed illitic clay films plot in the lower right of the respective diagram whereas those of coarser grain size and with few illitic films or none at all plot in the upper left. 

Quantitative petrophysical and petrographic analyses with the aid of cathodolumines-cence and SEM studies have shown that in the Saharan sandstones pressure solution has been influenced by a number of geological variables. In the complexes studied there is a linear correlation between median grain size and pressure solution by which finer-grained sandstones suffer more pressure solution. The presence of stronger clay films on the quartz grains also favours pressure solution. Sorting and variations in the compaction of the matrix of the sandstones exert little influence on the process of pressure solution. The presence of early cement dominates pressure solution and con-... 

Peel transfer Once the slurry has been filtered, carefully separate the vacuum apparatus, take off the filter, and transfer the clay film from the filter to a standard glass petrographic slide. This is usually the most difficult task of the preparation procedure and requires considerable practice. Refer to Reynolds Moore (1997) and Drever (1973) for hints and guidelines on making successful peel transfers. 

Schryver, F.C. Multilayered clay films Atomic force microscopy study and modeling. Langmuir 1999, 15, 7520-7529. 

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