Synthesis of anionic clays by hydrothermal crystallization of amorphous precursors

Synthesis of anionic clays ([M2+1−xM3+x(OH)2]x+xnXn− · yH2O; M2+ = Mg, Zn, Ni, etc.; M3+ = Al, Cr, Fe, etc.; x = 0.20–0.50; X = anion; n = anionic charge) by crystallization of amorphous precursors is described. The method involves the crystallization of amorphous gels of M203 in presence of suitable crystallization agents, generally MO oxides. In C02 free conditions, anionic clays characterized by negatively charged interlayers containing OH− anions are produced. nthesis of anionic clays is discussed in terms of the following parameters: nature and properties of both amorphous precursor and crystallization agent, pH of suspension, crystallization temperature, pressure and period of the hydrothermal treatment.