Influence of Cobalt and Nickel Sorption on the Texture of Crystalline α-Titanium Phosphate

Abstract

Crystalline titanium phosphate α-Ti(HPO₄)₂ · H₂O (α-TiP) has been prepared by reaction between phosphoric acid solution and titanium chloride in the temperature range 60–80 ⁰C. The solid obtained has been treated, in solid state with different concentrations of either cobalt or nickel. The pure and derivative materials are characterised using X-ray powder diffraction, Fourier transform IR, differential thermal analysis, and nitrogen adsorption. Due to their higher degree of hydration, the cobalt atoms are more sorbed by (α-TiP), where they enter into the cavities (containing the water molecules) between the layers of titanium phosphate. It is found that this process can induce small expanding of the interlayer spacing in the C direction and losing the crystallinity in the other directions. For the nickel, after sorption of more than 20%, an atomic layer may be formed preventing (α-TiP) from accommodating any more nickel ions in its framework, this is displayed by the appearance of diffraction peaks related to unsorbed nickel. The DTA curves indicate that more crystalline α-TiP materials have higher transition temperature. The nitrogen adsorption isotherms give an indication that when the cobalt atoms are sorbed by α-TiP, the latter is transformed from microporous to mesoporous material while it keeps its pore uniformity in the case of nickel.