Ga 13–polyethyleneoxide-modified smectites: relationship between physico-chemical properties and local pillar structure

Abstract

Clay-based microporous materials were synthesized by replacing the interlayer cations of a natural montmorillonite and of two synthetic saponites with Ga 13 polycations. The resulting materials were further modified by adding various amounts of polyethyleneoxide (PEO) in the pillaring solutions. X-ray diffraction, chemical analyses and nitrogen adsorption measurements show that the pillared products are structurally analogous to materials synthesized using Al 13 polycations and present similar physicochemical properties. Furthermore, the properties of Ga 13–PEO-modified montmorillonites evolve in the same way as those of Al 13–PEO-modified samples. X-ray absorption spectroscopy at the Ga-K edge was used for investigating the local environment of gallium atoms constituting the interlayer pillars. Such results can then be transferred to aluminum pillars. For each synthesis, involving PEO or not, with montmorillonite or with saponite, gallium pillars exhibit the same local environment on samples synthesized without PEO, which could be related to the collapse of the initial pillar structure. On the other hand, when PEO is used as a pillaring co-agent, the local pillar structure is conserved. After calcination, gallium-pillared montmorillonite exhibits a significant decrease of Ga–O distances and of the number of oxygen and gallium backscatters, which suggests that the Ga 13 structure is not conserved upon heating. Gallium neighbors are even less numerous for calcined samples synthesized with PEO in the pillaring solution. Pillared saponites are less highly affected by calcination, that shows that, when layer charge is tetrahedrally located, the destruction of pillars upon heating is reduced.