Ammonium Ion Exchange and Ammonia Gas Uptake on Crystalline α-Hafnium Phosphate

Abstract

Crystalline α-hafnium phosphate was prepared by the direct precipitation method and NH₄⁺ ion exchange behavior was investigated both in forward and backward directions. The forward ion exchange was a single-step reaction without formation of an intermediate mono-ammonium salt form, whereas the backward ion exchange proceeded in two steps. On the other hand, ammonia gas was contacted with the exchanger, and ammonium salt of α-hafnium phosphate was obtained, which gave the identical X-ray powder patterns to that of the product of the forward exchange experiment. Intercalation of ammonia molecules was suggested for the mechanism of the forward ion exchange.