A critical assessment of the methods for intercalating anionic surfactants in layered double hydroxides

• Published in: Journal of materials science 2008-09, Vol.43 (18), p.6144-6158
• Main Authors: Moyo, Lumbidzani, Nhlapo, Nontete, Focke, Walter W.
• Format: Article
• Language: English
• Subjects: Anion exchanging; Aqueous solutions; Carboxylic acids; Characterization and Evaluation of Materials; Chemistry; Classical Mechanics; Crystallization; Crystallography and Scattering Methods; Decarbonation; Exact sciences and technology; General and physical chemistry; Heat treatment; Hexanoic acid; Hydroxides; Intercalation; Ion exchange; Materials Science; Organic acids; Other ion exchangers: preparations and properties; Polymer Sciences; Polyolefins; Precursors; Regeneration; Solid Mechanics; Surface physical chemistry; Surfactants
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-008-2935-0

Anionic surfactant intercalated layered double hydroxides (LDH) of high purity are easily prepared via direct coprecipitation and also by the ion exchange method provided that the precursor contains a monovalent anion, e.g., LDH–Cl or LDH–NO 3 . However, LDH–CO 3 is an attractive starting material as it is commercially available in bulk form owing to large-scale applications as a PVC stabilizer and acid scavenger in polyolefins. Thus, intercalation of dodecyl sulfate and dodecylbenzenesulfonate into a commercial (LDH) with approximate composition [Mg 0.654 Al 0.346 (OH) 2 ](CO 3 ) 0.173  · 0.5H 2 O] was explored. Direct ion exchange is difficult as the carbonate is held tenaciously. In the regeneration method it is removed by thermal treatment and the surfactant form obtained by reaction with the layered double hydroxide that forms in aqueous medium. Unfortunately the resulting products are impure, poorly crystallized and only partial intercalation is achieved. Better results were obtained using water-soluble organic acids, e.g., acetic, butyric, or hexanoic acid, to aid decarbonation of LDH–CO 3 . Intercalation proceeded at ambient temperatures with the precursor powder suspended in an aqueous dispersion of the anionic surfactant. The carboxylic acids are believed to assist intercalation by facilitating the elimination of the carbonate ions present in the anionic clay galleries.