Synthesis and characterization of Al-pillared montmorillonite in presence of Mn(II)

Abstract The possibility of substituting aluminum in the Keggin tridecamer [Al 13 O 4 (OH) 24 (H 2 O) 12 ] 7+ by Mn(II) has been investigated and then the obtained polycation has been used as pillars for smectite. Pillaring solutions are prepared by a slow and partial hydrolysis of Al(III)–Mn(II) aqueous solutions with different Mn/(Al + Mn) molar ratio ( r = Mn/(Al + Mn) = 0, 1/13, 2/13 and 3/13) and examined by 27 Al NMR spectroscopy. Powder X-ray diffraction (XRD), physisorption of N 2 , chemical analysis and scanning electron microscope analyses (SEM) are used to study the precipitated sulfate salts and/or pillared clay minerals. This study reveals the absence of MnAl 12 species in the pillaring solution. The crystal system of the obtained Al 13 –SO 4 salt is cubic (tetrahedral particles) in absence of Mn(II) and monoclinic (plate particles) in presence of Mn(II). When r is equal to 3/13, in addition to the monoclinic phase, an amorphous phase takes place. The intercalation process of montmorillonite is only disturbed, when r is equal to 3/13, because of the presence of a high polymeric aluminum phase.