Study of pillar precursors [Ga(III)-Al(III), Ln(III)-Al(III), Zr(IV)] for hydrothermally stable pillared clays

The hydrolysis of mixed solutions of AI(III), Ga(III), Al(III), Ln(III) and Zr(IV) was studied by potenbometric, spectrophotometric and Al-27- and Ga-71-NMR techniques. For the AI-Ga system formation of GaAl12(OH)(28)(11+) species seems more probable into the pH range 4 less than or equal to pH less than or equal to 5. Afterwards, the Al-13(OH)(32)(7+) species predominate in agreement with thermodynamic data obtained by SUPERQUAD program. Both tetrahedral Ga-IV and Al-IV may coexist in solution, the interval being defined by potentiometric methods. For the Ln(III)-Al(III) systems Al-27-and La-139-NMR does not confirm the chemical interaction between the two species in solution, but the physicochemical properties of the La-Al/PILCS were different than Al/PILCS, suggesting a strong interaction in the solid state. Ce(III) and Ce(IV) ions do interact with AI(III) in solution, into the pH range 2.78<pH<3.99, according with the spectrophotometric behavior. Finally, the Zr(IV) hydrolysis was followed by UV in the pH range greater than 2.0, showing the formation of Zr-4(OH)(8)(8+) species, which was verified by calculations using SQUAD program, but the precipitation occurs at pH>3.0. (C) 1998 Elsevier Science B.V. All rights reserved.