Preparation and anion exchange propertie

Zirconia samples were obtained from zirconyl chloride or nitrate following two procedures. The gel precipitation is performed either at a non steady pH, starting at a value lower than 0.5 up to a final value between 4 and 12, or at constant pH. In the first procedure the specific area increases with the final pH. The water content of the amorphous gels maximizes at pH 10, reflecting an evolution of the textural properties. Precipitation at constant pH, using zirconyl chloride yields samples with specific areas higher than 300 m2 g−1. Upon calcination, structural and textural evolutions occur within the amorphous gel, with a progressive decrease of the specific area and crystallization into a tetragonal phase. The crystallization temperatures were determined in situ by XRD measurements using a high-temperature cell. The transformations of the amorphous gel into tetragonal and monoclinic phases are controlled by crystal size and excess energy. The exchange capacities of calcined samples were followed by a titration method, revealing anion exchange capacities of 0.25 meq g−1 for amorphous zirconia, which decrease by 65% upon conversion to tetragonal phase, while the monoclinic phase exhibits nearly no exchange capacity.