Basicity of the oxygen plane at the surface of the silicate
The surface basicity of the oxygen planes of four Na-smectites layer arises from the ability of O atoms to donate nonbonding and one Na-vermiculite was studied by visible spectroscopy of lone-pair electrons to acidic entities. The basic strength of the clay suspensions saturated with the metachromic cationic dye acrioxygen plane depends on whether there is an isomorphous tetradine orange. A metachromic band in the spectrum is an indication hedral substitution of Al for Si (5). The induction of tetrahedral of p interactions in which the cationic dye is involved. Curves Al on the nonbonding electrons of the O atoms is weaker than describing the wavelength of the metachromic band in the presence that of Si. Consequently, the basic strength of the oxygen plane of clay minerals as a function of the degree of saturation showed should increase with the tetrahedral substitution.
three regions. X-ray diffractions proved that in the first region
One would also expect that the basic strength of the oxygen monomeric acridine orange cations were located in the interlayer space with the aromatic rings lying parallel to the silicate layers. plane at the surface of the silicate layer will depend on whether Thus, metachromasy in the first region was due to p interactions the clay is di-or trioctahedral. In a trioctahedral clay, the oxygen in which atoms from the O-planes donate lone-pair electrons to p which bridges between the tetrahedral and octahedral sheets is antibonding orbitals of the organic cations. From the location of coordinated by four atoms (one Si and three Mg). It is involved the metachromic band it was concluded that the basic strength of in an sp 3 hybridization and has no contribution to a d p -p p bond the O-planes decreased in the order: beidellite ΓΊ vermiculite ΓΊ with the Si. On the other hand, in a dioctahedral clay, where montmorillonite ΓΊ saponite ΓΊ laponite.