THERMAL INTERCALATION OF LAYERED DOUBLE HYDROXIDES - CAPRIC ACID INTOAN MG-AL LDH

Molten decanoic acid, capric acid, reacted with the layered double hyd roxide (LDH) of initial composition Mg6Al3.4(OH)(18.82)(CO3)(1.51)(NO3 )(0.36). 4.5 H2O, at a temperature of 150 degrees C using a heating ra te of 1 degrees C min(-1). Powder X-ray diffraction (PXRD) showed that the reaction products were microcrystalline. The polyphasic nature of the reaction products was thought to derive from the presence, in all cases, of some residual unreacted LDH host plus mono- and bi-layers o f caprate anion guests in the LDH. Typically, dominant phases were non -intercalated LDH (at initial capric acid:LDH ratios of up to 2:1); st acks of horizontal caprate anions (4:1); full, intercalated monolayers (6:1) and full bilayers (8:1). Al-27 Solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR) studies indicated that the exclu sively octahedral nature of the aluminium sites of the host LDH were n ot altered by thermal reaction with capric acid. Two-dimensional (2D) Al-27 MAS NMR suggested that the thermal reaction products contained t wo octahedral aluminium environments. C-13 MAS NMR confined the presen ce of the monoanion of capric acid, CH3(CH2)(8)COO-. The suggested mec hanism for intercalation involves the removal of the LDH interlayer ca rbonate in a similar manner to that observed in the corresponding LDH- sebacic acid thermal reactions. The products of the thermal reaction w ere compared with material prepared via a modified coprecipitation rea ction. PXRD suggested that the products of this coprecipitation reacti on and the 8:1 thermal reaction product contained bilayers having simi lar calculated slant angles. 2D Al-27 MAS NMR suggested that the copre cipitated reaction differed from the thermal reaction products in that it contained a tetrahedral aluminium site in addition to the two octa hedral sites also exhibited by the thermal reactions. There was no dir ect evidence of kinking of the acid or anion carbon chains in the ther mal or coprecipitation reaction products owing to possible interaction with the alcohol during washing of the products.