The effect of varying synthesis conditions on zinc chromium hydrotalcite: a spectroscopic study

Zn/Cr hydrotalcites were synthesised by coprecipitation, with varying pH values and divalent/trivalent metal ion ratio. Depending on the pH conditions, two 3R rhombohedral varieties were synthesised with different layer spacings of 7.8 and 8.9 Å, at room temperature. More carbonate was incorporated in the interlayer of samples prepared at low pH values, increasing the interlayer distance and the unit cell. Preparation under acidic conditions lead to a more crystalline, pure and thermally stable compound. Spectroscopy was used to determine the effect of varying the ratio of divalent/trivalent metal ion ratio. It was shown that although ratios >2 yield crystalline compounds a ratio of 3 was preferred for both phases.