Alkaline earth metal substitution effects in sol-gel–derived mixed metal oxides and Mg 2-x M x /Al 1 (M = Ca, Sr, Ba)–layered double hydroxides

Layered double hydroxides (LDHs) are anionic clays with unique physical and chemical properties. In this study, an indirect sol-gel synthesis method was applied to prepare alkaline earth metal–substituted layered double hydroxides of Mg 2-x M x /Al 1 (M = Ca, Sr, Ba). In the sol-gel processing, metal nitrates Mg(NO 3 ) 2 ·6H 2 O, Al(NO 3 ) 3 ·9H 2 O, Ca(NO 3 ) 2 ·4H 2 O, Sr(NO 3 ) 2 and Ba(NO 3 ) 2 dissolved in deionized water were used as starting materials; and citric acid monohydrate and 1,2-ethanediol were used as complexing agents. The mixed metal oxides (MMOs) were obtained after thermal treatment of precursor gels at 650 °C and subsequently reconstructed in water to the LDHs. The synthesis products were characterized using X-ray powder diffraction (XRD) analysis and scanning electron microscopy (SEM). Nitrogen adsorption by the Brunauer, Emmet and Teller (BET) and the Barret method was used to determine the surface area and pore diameter of the synthesized alkaline earth metal–substituted MMO materials. It was demonstrated for the first time that the formation of Mg 2-x M x /Al 1 (M = Ca, Sr, Ba) LDH from the sol-gel–derived powders depends significantly on the nature and concentration on the alkaline earth metal.