An alkaline precipitation method was introduced to produce hydrous cerium oxides. The prepared powder was characterized by Brunauer-Emmett-Teller (BET) nitrogen adsorption-desorption, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry, and thermal gravimetry (TG) approaches. The adsorbent has a chemical formula of CeO 2 ⋅nH 2 O (n < 2) and a cubic fluorite-type structure after high temperature treatment. Adsorption capacity of different temperature treated hydrous cerium oxides does not directly correlate with BET specific surface area. Phosphate adsorption isotherms follow the Langmuir equation below the treatment temperature of 800°C. Phosphate adsorption causes no change on the structure of a hydrous cerium oxides, and no signs of CePO 4 precipitates are found. The ion-exchanging structure of hydrous cerium oxide plays a fundamental role in phosphate adsorption. The structure is highly temperature resistant and forms adsorption sites which adsorb both water and some anions. Complete loss of adsorption ability cannot be achieved unless the treatment temperature is higher than 1200°C. Mechanism study shows that the adsorption of phosphates is mainly an anion-exchange process.
The adsorption isotherms of chloro-1,1,2,2,2-pentafluoroethane) and HFC-125 (1,1,1,2,2pentafluoroethane) on Vruf activated carbon (Calgon Carbon Corp.; brand code, VRU-F) and silicalite-1 have been accurately measured at pressures up to 120 kPa and temperatures ranging from 273 to 348 K. The To ´th or dual-site Langmuir (DSL) model appropriately describes the equilibrium data for the adsorptives CFC-115 and HFC-125 on Vruf carbon or silicalite-1, respectively. Because HFC-125 molecule has a higher packing efficiency in the pores of Vruf carbon, its saturation capacity extracted by the To ´th model is higher than that for CFC-115. For CFC-115, a "kink" in the isotherm on silicalite-1 is observed at about 4 molecules (unit cell of silicalite-1) -1 , and the measured isotherms of CFC-115 for the first time show a second-step adsorption at loadings over 4 molecules (unit cell) -1 . This is ascribed to a large difference in the adsorption entropy between the molecular locations in the intersections and in the channels. The DSL model with fixed saturation capacities describes this behavior well. The mixture adsorption isotherms predicted by the ideal adsorbed solution theory show that both adsorbents could be industrially applicable in the separation of
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