Acid-base properties of pillared interlayered clays with single and mixed Zr-Al oxide pillars prepared from Tunisian-interstratified illite-smectite

Interstratified illite-smectite clay samples from Tunisia have been used in order to prepare Al, Zr and Zr-Al-pillared clays. Several Al/metal, OH/metal ratios were used in order to investigate the effect on the chemical and physical properties, specifically the point of zero charge (PZC) of the synthesized pillared clays. The structure of the pillared materials is studied by XRD and cationic exchange capacity. The textural property is investigated by the nitrogen adsorption/desorption method. The acid-base chemistry “surface acidity” of these products was analysed by using mass and potentiometric titration in order to determine the PZC and the equilibrium constants (pKa) of each sample. The resulting materials exhibited basal spacings in the range of 17.4-20.5 Å, with high surface areas (134-199 m2 g−1). Titration curves obtained by acid-base potentiometric titration for the starting material showed an indistinct cross-over point at about pH = 7.3, whereas in the case of pillared samples, points were observed at the acidic region between 4 and 6. In addition, the calculated pKas values of pillared clays show a shifting to the acidic values compared to the untreated sample.