Preparation and chemical properties of a novel layered cerium(IV) phosphate

A synthetic method of a novel cerium(IV) bis(hydrogenphosphate) dihydrate, Ce(HPO4)(2) . 2H(2)O, hereafter referred to as CeP . 2H(2)O, has been established by the hydrothermal reaction of cerium(IV) oxide with phosphoric acid in an autoclave. The preparation of CeP . 2H(2)O 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 . 2H(2)O was the mixing ratio of 1.5-2.0, heating temperature 175-200 degrees 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 . 2H(2)O is a novel crystalline layered cerium(IV) phosphate having a interlayer distance d = 18.0 Angstrom, longer than any layered phosphates (zirconium(IV), titanium(IV), and tin(IV) phosphates) so far reported. The reversible phase transition of CeP . 2H(2)O occurred as follows, when exposed to various relative humidities: [GRAPHICS] CeP . 2H(2)O dissolved slightly in distilled water and hydrochloric acid, and much more in aqueous sodium hydroxide and aqueous ammonia. CeP . 2H(2)O effectively adsorbed ammonia in an aqueous solution and ammonia gas.