The behavior of hydroxyl groups of sepiolite and Ti(OH)(4) has been investigated by in situ diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) during heat treatment, in order to understand the generation of new properties due to the mutual interaction between Ti(OH)(4) and sepiolite. The higher intensity ratio of SiOH/(Mg)(3)OH in the mechanical mixture than that in pure sepiolite shows the dissociation of Si-O-Si bond in sepiolite crystalline structure. The new acid property generated in the physical mixing between sepiolite and Ti(OH)(4) can be explained by the formation of Ti-O-Si bonds due to the interaction of Si-OH and Si-O-Si in sepiolite with Ti(OH)(4). (C) 2003 Elsevier B.V. All rights reserved.