Anion exchange properties of a mesoporous aluminophosphate

A mesoporous aluminophosphate support, meso-AlPO, was synthesized by phosph ate treatment of an AlO4Al12(OH)(24)(H2O)(7+) cluster/dodecyl sulfate salt, followed by extraction of the surfactant with an acetate/methanol solution . The meso-AlPO product was shown to be an effective anion exchange materia l. Anion exchange capacities for chromate and several monoanionic and diani onic organic dyes fell in the range from approximately 1.3-1.6 meq/g. Contr ol experiments with the neutral support MCM-41 and a nonionic dye indicated that anion adsorption in meso-AlPO was caused predominantly by electrostat ic interactions rather than pure physisorption. Multiple exchanges were pos sible if the support was regenerated by acid treatment at pH 4.3. While the material exhibited size-selectivity for anionic dyes, the average pore siz es increased during anion exchanges in aqueous solutions. The mesopore stru cture of meso-AlPO was thermally stable up to 200 degrees C, and anion exch anges at 100 degrees C under aqueous reflux resulted in similar exchange ca pacities as room-temperature exchanges.