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 (CO32- 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 °C in a pressure vessel for 1 day. 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 CO32- contamination, respectively. Shorter carboxylates were not incorporated, only yielding CO32-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 CO32- 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.

Graphical abstractOne-pot and one-step synthesis of organophilic LDHs containing long-chain alkyl carboxylates was accomplished via the “homogeneous precipitation” method using hexamethylenetetramine (HMT).Figure optionsDownload full-size imageDownload as PowerPoint slide