Anion exchange properties of a mesoporous aluminophosphate

A mesoporous aluminophosphate support, meso-AlPO, was synthesized by phosphate 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 material. Anion exchange capacities for chromate and several monoanionic and dianionic organic dyes fell in the range from approximately 1.3-1.6 meq/g. Control experiments with the neutral support MCM-41 and a nonionic dye indicated that anion adsorption in meso-AlPO was caused predominantly by electrostatic interactions rather than pure physisorption. Multiple exchanges were possible if the support was regenerated by acid treatment at pH 4.3. While the material exhibited size-selectivity for anionic dyes, the average pore sizes increased during anion exchanges in aqueous solutions. The mesopore structure of meso-AlPO was thermally stable up to 200°C, and anion exchanges at 100°C under aqueous reflux resulted in similar exchange capacities as room-temperature exchanges.