Preparation and Chemical Properties of a Novel Layered Cerium(IV) Phosphate

Abstract

Abstract A synthetic method of a novel cerium(IV) bis(hydrogenphosphate) dihydrate, Ce(HPO4)2·2H2O, hereafter referred to as CeP·2H2O, has been established by the hydrothermal reaction of cerium(IV) oxide with phosphoric acid in an autoclave. The preparation of CeP·2H2O was significantly affected by the reaction conditions: the mixing ratio (P2O5/CeO2) of CeO2 and phosphoric acid, heating temperature and time, and water vapor pressure. The optimum condition for the preparation of CeP·2H2O was the mixing ratio of 1.5—2.0, heating temperature 175—200 °C, heating time 5 h, and water vapor pressure 5.0—7.0 atm. The results of X-ray powder diffraction, fluorescent X-ray analysis, differential thermal analysis and thermogravimetry (DTA-TG), IR spectrum, and phase transition showed that CeP·2H2O is a novel crystalline layered cerium(IV) phosphate having a interlayer distance d = 18.0 Å, longer than any layered phosphates (zirconium(IV), titanium(IV), and tin(IV) phosphates) so far reported. The reversible phase transition of CeP·2H2O occurred as follows, when exposed to various relative humidities: CeP·2H2O dissolved slightly in distilled water and hydrochloric acid, and much more in aqueous sodium hydroxide and aqueous ammonia. CeP·2H2O effectively adsorbed ammonia in an aqueous solution and ammonia gas.