An in-situ x-ray diffraction and infrared spectroscopic study of the dehydration of AlPO4-54

Marco Fabbiani (1, 2) , Michelangelo Polisi (1) , Bernard Fraisse (1) , Rossella Arletti (3) , Mario Santoro (4) , Frederico Alabarse , Julien Haines (1)

1 ICGM - Institut Charles Gerhardt Montpellier - Institut de Chimie Moléculaire et des Matériaux de Montpellier
2 Dipartimento di chimica (IFM) - Dipartimento di chimica (IFM)
3 UNIMORE - Università degli Studi di Modena e Reggio Emilia = University of Modena and Reggio Emilia
4 INO - Istituto Nazionale di Ottica

The dehydration of the large pore aluminophosphate AlPO4-54•xH2O was studied in situ as a function of vacuum pressure at room temperature by infrared spectroscopy and x-ray diffraction. On polycrystalline samples, under primary vacuum, the adsorbed water is removed very rapidly. The structural water in the AlO6 octahedra is then removed slowly with the quantity of the fully dehydrated form gradually increasing from 43 to 65% of the total material. This results in a two-phase mixture of fully dehydrated and a distinct partially dehydrated AlPO4-54•1/2H2O phase containing structural water. These phases have almost identical a cell parameters and very close c parameters. Secondary vacuum increases the amount of fully dehydrated material to more than 76%. Prolonged heating under vacuum increases the amount of fully dehydrated material to 90%. On single crystal samples, removal of adsorbed water is slower and results in a reduction in crystal quality, however prolonged exposure to primary vacuum yielded fully dehydrated material without the need for heating. The monoclinic structure of anhydrous AlPO4-54, space group Cm, with a doubled unit cell was confirmed using single crystal synchrotron x-ray diffraction data.

Mots clés: Aluminophosphate; dehydration; x-ray diffraction; infrared spectroscopy

Domaines: Chimie inorganique

Marco Fabbiani, Michelangelo Polisi, Bernard Fraisse, Rossella Arletti, Mario Santoro, et al.. An in-situ x-ray diffraction and infrared spectroscopic study of the dehydration of AlPO4-54. Solid State Sciences, 2020, 108, pp.106378. ⟨10.1016/j.solidstatesciences.2020.106378⟩. ⟨hal-02943271⟩