Abstract
In this study, the reconstruction peculiarities of sol–gel derived Mg2−xMx/Al1 (M = Ca, Sr, Ba) layered double hydroxides were investigated. The mixed metal oxides (MMO) were synthesized by two different routes. Firstly, the MMO were obtained directly by heating Mg(M)–Al–O precursor gels at 650 °C, 800 °C, and 950 °C. These MMO were reconstructed to the Mg2−xMx/Al1 (M = Ca, Sr, Ba) layered double hydroxides (LDHs) in water at 50 °C for 6 h (pH 10). Secondly, in this study, the MMO were also obtained by heating reconstructed LDHs at the same temperatures. The synthesized materials were characterized using X-ray powder diffraction (XRD) analysis and scanning electron microscopy (SEM). Nitrogen adsorption by the Brunauer, Emmett, and Teller (BET) and Barrett, Joyner, and Halenda (BJH) methods were used to determine the surface area and pore diameter of differently synthesized alkaline earth metal substituted MMO compounds. It was demonstrated for the first time that the microstructure of reconstructed MMO from sol–gel derived LDHs showed a “memory effect”.
Highlights
Layered double hydroxides ([M2+ 1−x M3+ x (OH)2 ]x+ (Ay− )x/y ·zH2 O, where M2+ and M3+ are divalent and trivalent metal cations, respectively, and Ay− is a intercalated anion, layered double hydroxides (LDHs)) are widely used in catalysis, in ion-exchange processes, as catalyst support precursors, adsorbents, anticorrosion inhibitors, anion exchangers, flame retardants, polymer stabilizers, and in pharmaceutical applications, optics, in separation science and photochemistry [1,2,3,4,5,6,7]
The synthesized Mg–Al–O precursor gels were converted to the mixed metal oxides (MMO) by heating the gels at 650 ◦ C
To study the reconstruction peculiarities of sol–gel derived Mg2−x Mx /Al1 (M = Ca, Sr, Ba) layered double hydroxides (LDHs), the precursor gels were firstly annealed at 650 ◦ C, 800 ◦ C, and 950 ◦ C for
Summary
Layered double hydroxides ([M2+ 1−x M3+ x (OH)2 ]x+ (Ay− )x/y ·zH2 O, where M2+ and M3+ are divalent and trivalent metal cations, respectively, and Ay− is a intercalated anion, LDHs) are widely used in catalysis, in ion-exchange processes, as catalyst support precursors, adsorbents, anticorrosion inhibitors, anion exchangers, flame retardants, polymer stabilizers, and in pharmaceutical applications, optics, in separation science and photochemistry [1,2,3,4,5,6,7]. The second synthetic technique widely used for the preparation of LDHs is anion exchange [11,12,13]. For the preparation of Mg3 Al1 LDHs, we developed the indirect sol–gel synthesis route [14,15,16,17]. In this synthetic approach, the synthesized Mg–Al–O precursor gels were converted to the mixed metal oxides (MMO) by heating the gels at 650 ◦ C. The proposed sol–gel synthesis route for LDHs showed some benefits over the co-precipitation and anion-exchange methods such as simplicity, high homogeneity, and good
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