One-pot synthesis of organophilic layered double hydroxides (LDHs) containing aliphatic carboxylates: extended "homogeneous precipitation" method.
One-pot synthesis of aliphatic carboxylate/LDH hybrids (org-LDHs) was accomplished via the so-called "homogeneous precipitation" method developed for preparing carbonate-type layered double hydroxides (CO(3)(2-) LDHs) with ammonia-releasing reagents such as hexamethylenetetramine (HMT) and urea. An aqueous solution of an aliphatic carboxylate (C2-C18) was added to a mixed aqueous solution of metal salts and HMT and then heated at 140-160 degrees C in a pressure vessel for 1day. Two kinds of LDHs were investigated: MgAl-LDH and NiAl-LDH. We found that only aliphatic carboxylates longer than decanoate (C10) and dodecanoate (C12) were incorporated successfully in the MgAl-LDH and NiAl-LDH interlayers without any CO(3)(2-) contamination, respectively. Shorter carboxylates were not incorporated, only yielding CO(3)(2-)LDHs. Isolation of the hydrophobic org-LDH phase from the aqueous medium containing carbonate ions was assumed to be the main reason for the lack of CO(3)(2-) contamination in the org-LDHs having longer-alkyl carboxylates. This method was also used successfully for preparing MgAl-LDHs containing dodecylbenzene sulfonate(DBS), a sulfonate-type anionic surfactant.