Relation between the infrared spectra and the lateral specific surface areas of gibbsite samples

The chemical behavior of crystalline Al(OH)(3) samples is governed by the l ateral-to-basal surface ratio. For well-crystallized gibbsite samples posse ssing the two types of surfaces clearly spatially separated, a vibrational component at similar to 3460 cm(-1) in the infrared absorption spectra, not displayed in the Raman spectra, increases linearly with the lateral specif ic area determined by a gas adsorption isotherm. This intense and broad lin e is related to hydroxyl stretching modes of AlOH21/2+ or AlOH1/2- species present on the edge faces. However, it is too simplistic to assign this ban d to a mode of one or the other of these species. More complex structures c ombining both species should also be considered. When an evacuated sample i s submitted during a short time to a D2O vapor injection, the OD spectral r egion displays essentially one broad component at 2563 cm(-1), correspondin g to the 3460 cm(-1) band in the OH region and not to the other modes of th e bulk hydroxyls. This experimental observation is also in agreement with t he assignment of this infrared band to reactive superficial species.