Raman spectroscopy of hydrotalcites with phosphate in the interlayer: implications for the removal of phosphate from water

Hydrotalcites with phosphate in the interlayer were prepared at different pH values. At pH >11.0 (PO4)(3-) was the intercalated ionic species, whereas at pH < 11.0 a mixture of (PO4)(3-) and (HPO4)(2-) ions was intercalated. Powder X-ray diffraction shows that the hydrotalcite formed at pH 9.5 is poorly diffracting with a d-spacing of 11.9 angstrom; whereas the d(003) spacing for the phosphate interlayered hydrotalcite formed at pH 11.9 and 12.5 was 8.0 and 7.9 angstrom respectively. The addition of a thermally activated ZnAl-HT to a phosphate solution resulted in the uptake of the phosphate and the reformation of the hydrotalcite. Raman spectroscopy of the phosphate interlayered hydrotalcites shows that the interlayered anion is pH dependent and only above pH 11.9 is the orthophosphate anion intercalated. At lower pH, the monohydrogen phosphate anion is intercalated. Raman spectroscopy shows that upon addition of the thermally activated hydrotalcite to an aqueous phosphate solution, results in the uptake of phosphate anion from the solution. Copyright (C) 2006 John Wiley & Sons, Ltd