New Gallium-Substituted Hydrotaleites: [Mg1-xGax(OH)2](CO3)x/2 • mH2O

A series of Ga-containing hydrotalcite-like materials (GaHTs), [Mg(1-x)Ga(x)(OH)(2)](CO(3))(x/2) center dot mH(2)O where x = 0.072 similar to 0.35 (Mg/Ga = 12.9 similar to 1.8), was synthesized by a coprecipitation method. The resulting solids were characterized by means of X-ray diffraction, thermal gravimetric and infrared analyses. All GaHTs showed diffraction patterns typical of Mg-Al hydrotalcites. Small amounts of brucite, Mg(OH)(2), were detected only in the GaHT with Mg/Ga = 12.9. Attempts to obtain Ga-richer hydrotalcites, Mg/Ga < 1.8, resulted in solids with an invariably constant Mg/Ga = 1.8 ratio, which appears to be the maximum Ga content limit. Judging from the TGA pattern of a GaHT (Mg/Ga = 7.7), the layered structure is stable up to ca. 573 K, and at 873 K the resulting solid shows a MgO-like diffraction pattern, suggesting that Ga(3+) may be replacing some Mg(2+) ions in MgO. Once their layered structure collapses (i.e., at 873 K), GaHT can be easily converted back into the original layered material by treating in a carbonate-containing aqueous solution, i.e., they show the "memory effect" typical of Mg-Al hydrotalcites.