Preparation of Original and Calcined Layered Double Hydroxide as Low-Cost Adsorbents: The Role of the Trivalent Cation on Methylene Blue Adsorption

Layered double hydroxides with the hydrotalcite-like structure, containing Mg(2+), Al(3+), and Fe(3+) (with different Al/Fe ratios) in the layers, have been synthesized and fully characterized, as have the mixed oxides formed upon their calcination at 500 °C. Both series of solids (original and calcined ones) have been tested for methylene blue adsorption. In the case of the Fe-containing sample, oxidation of methylene blue takes place simultaneously with adsorption. For the calcined samples, their reconstruction to the hydrotalcite-like structure plays an important role in their adsorption ability.