Structure and the point of zero charge of magnesium aluminium hydroxide

Abstract

Positively charged magnesium aluminium hydroxide sol has been prepared by coprecipitation. The structure and properties were studied using X-ray diffraction (XRD), thermogravimetry (TG), differential thermal analysis (DTA), transmission election microscopy (TEM), FTIR and potentiometric titration (PT). The structure was shown to be hydrotalcite-like; the lattice constants a and c both increased with decreasing mole fraction of Al, x=[Al]/([Al]+[Mg]); the highest value of x was 0.332. Three weight loss peaks were detected by TG–DTA of the sol particles. IR spectroscopy showed that the position of the OH-stretching vibration peak shifted to high frequency and the peaks broadened with decreasing x. PT showed that the sol particles bore positive charges; the point of zero charge (pzc) and the amount of permanent positive charge both increased with increasing x.