THE INTERCALATION OF PHENYLPHOSPHONIC ACID IN LAYERED DOUBLE HYDROXIDES

Magnesium-aluminum hydroxy nitrates ((NO3)-MgAl-LDHs) and zinc analogu es ((NO3)-ZnAl-LDHs) with MII/MIII ratios between 1/1 and 4/1 were syn thesized by the method of coprecipitation, Intercalation experiments w ith phenylphosphonic acid (PPA) revealed a correlation between the MII /MIII ratio of the LDH and the type of reaction it undergoes with PPA, For ratios smaller than or equal to 2/1, complete intercalation was a ccomplished (room temperature, pH = 6), resulting in an interlayer fre e spacing (IFS) of 1.14 nm. C,H analysis showed that the NO3- ions wer e replaced by the monovalent form of PPA. For the higher ratios, trans formation of the LDH structure in a layered metal phenylphosphonate to ok place. In the case of the (NO3)-MgAl-LDHs, this reaction was almost complete, and was accompanied by the removal of the Mg2+ ions, result ing in an almost pure Al phosphonate. For the (NO3)-ZnAl-LDHs, partial pillaring with PPA was still achieved, with approximate conservation of the Zn2+/Al3+ ratio. This pillaring reaction gave rise to a mixed Z n-Al phenylphosphonate, in combination with a well-pillared (PPA)-ZnAl -LDH phase. Pillaring of the LDHs did not result in the creation of mi croporosity, and this was due to the high charge density on the LDH la yers, leaving no free interlayer space after reaction. Direct linkage of the organophosphonate pillars to the LDH layers was accomplished by thermal treatment at temperatures below the dehydroxylation temperatu re. (C) 1998 Elsevier Science B.V. All rights reserved.