Synthesis and topotactic exchange reactions of new layered double hydroxides intercalated with ammonium/sulfate

Layered double hydroxides with the composition M2+/Al3+ (M2+ 1/4 Zn, Mn, Mg or Co) and M2+:Al3+ molar ratios of 2:1, intercalated with NH4+/SO42- were investigated. After optimizations steps varying the pH of precipitation and observing the X-ray diffraction patterns and Fourier-transform infrared spectra, the phases were synthesized by co-precipitation at increasing pH and characterized by several instrumental techniques. The basal distance of all optimized compounds was close to 11 angstrom, but after the ripening process at 90 degrees C, ammonium was only maintained in the materials containing Zn and Co, presenting the chemical composition (NH4) [M62+Al3(OH)(18)(SO4)(2)] while the materials containing Mn and Mg presented the chemical composition close to M42+Al2(OH)(12)(SO4)(1.)0. Investigations to exchange topotactically NH4+ with Na+ and Na+ with NH4+ in Zn2+/Al3+ samples indicated that these reactions are partially reversible, with a partial reduction of the intercalated sulfate anions content.