Sepiolite as a deodorant material: an ESR study of its properties

Sepiolite, a Mg silicate, is used as a deodorant because of its strong adsorbing power. However, the principle by which sepiolite adsorbs gases is not known well. The present authors have tried to analyse this principle as a change of paramagnetic species in the crystal surfaces of sepiolite. After heat-processing sepiolite at the temperatures 150, 550 and 750C, the concentration change of paramagnetic species was observed using NH₃, air, or vacuum as atmospheric environment of sepiolite. The results indicate that, in the absence of zeolitic water, relatively high concentrations of Mn²⁺ and (Mg²⁺)_n^– (are observed, which are destroyed with NH₃ or water. A multi-line ESR spectrum has been found and is attributed to (Mg²⁺)_n^– ion which is an entire crystal lattice plane forming a big molecular orbital. The results and an analysis of it seem to indicate that a gas molecule is adsorbed to a crystal plane of sepiolite due to its free spin holding nature. This phenomenon may be called spin adsorption. There should be many more cases in which gas adsorption from the gas phase to the solid phase is controlled by the free-spin holding nature of the solid surface. For such cases the ESR method seems to be a quite powerful and proper technique.