Intercalation of Macrocyclic Crown Ether into Well-Crystallized LDH: Formation of Staging Structure and Secondary Host−Guest Reaction

Abstract

A carboxyethyl substituted azacrown ether derivative (CSAE) was intercalated as a second host into a parent host of well-crystallized crystal of Mg-Al layered double hydroxide (MgAl-LDH) by a CSAE/NO 3 ion-exchange reaction. The influence of intercalation temperature on the structures and compositions of CSAE-LDH nanocomposites was investigated. The composites obtained at the temperatures below 70 °C had almost the same CASE contents and layered structures with a basal spacing of about 1.6 nm, corresponding to the vertical orientation of CSAE plane to the LDH layer. The chemical analysis showed that a considerable amount of CO 3 2-(with CO 3 2-/CSAE molar ratio of 1.4) was incorporated in the interlayer of LDH. The CSAE content decreased while CO 3 2content increased with an increase of the intercalation temperature in the region above 70 °C. At 100 °C, a second staging phase of 2.33 nm appeared, attributed to the ordered stacking of the 1.6 nm phase and a 0.77 nm phase produced by the CO 3 2-/CSAE exchange. At higher temperatures, a new phase with a basal spacing of 1.18 nm appeared, which corresponds to the tilt/twisted orientation of CSAE anions in the interlayer. The other second staging phase of 2.08 nm appeared obviously at 150 °C, due to the regular stacking of the 1.18 and 0.77 nm phases. The adsorptive properties for transition metal ions were studied using the 70 and 150 °C reacted composites. The 70 °C reacted one showed higher adsorptivity toward transition metal ions; the adsorptive capacity increased in the sequence of Cu 2þ > Ni 2þ > Co 2þ > Zn 2þ , and distribution coefficient for Cu 2þ was markedly higher than those for the other ions. However, the 150 °C reacted one showed little adsorptivity toward these ions. The adsorption for transition metal ions was accompanied by the intercalation of nearly equivalent amount of nitrate ions. This shows that the interlayer CSAE ions in the 1.6 nm phase act as a second host, but those in the 1.18 nm phase do not.

Nanosheets of Oxides and Hydroxides: Ultimate 2D Charge‐Bearing Functional Crystallites

“…The encapsulation of drug molecules in LDHs can improve the solubility and biocompatibility of the drugs and protect labile drug molecules from the effects of pH, heat, light, or radiation 70. LDH nanosheets would be more efficient for adsorption or release and hybridization of organic anions or drug molecules than their parent compounds 72. Organic polymer hybrid LDH nanosheets formed through in situ polymerization could create nanocomposite materials with improved mechanical and thermal properties 73.…”

Water–n-BuOH solvothermal synthesis of ZnAl–LDHs with different morphologies and its calcined product in efficient dyes removal

“…Layered double hydroxides (LDHs), which are consist of positively-charged metal hydroxide layers and counter-anions in the interlayer, are anion-exchanging lamellar materials [26][27][28][29][30].…”

A new, low-cost adsorbent: Preparation, characterization, and adsorption behavior of Pb(II) and Cu(II)

“…Structurally [38], LDHs have the characteristics of anion exchange, which make them adsorb mainly inorganic pollutants such as phosphate [39], borate [40], fluoride [41], and other organic anions [42,43] as well as metal ions in the form of anionic Cr (VI) [44]. The LDH-based composites materials which were prepared by intercalating certain chemical compounds such as crown ether [45], EDTA [46], nitrilotriacetate [47], chromotropic acid [48], aurintricarboxylic acid [49], and polysulfides [50] can adsorb metal ions. However, from the industry side, the dream of these LDH-based adsorbents really used in industry for adsorbing metal ions, is quite hard to realize, because the used guest anions are very expensive.…”