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Journal of Microwave Power and Electromagnetic Energy, 47 (1), 2013, pp. 12-23.
A Publication of the International Microwave Power Institute
Microwave-assisted Melt Reaction Method
for the Intercalation of Carboxylic Acid
Anions into Layered Double Hydroxides
Roberto Rosa, Cristina Leonelli
Department of Engineering “Enzo Ferrari”, University of Modena and Reggio Emilia, via
Vignolese, 905/A, 41125, Modena, Italy
Carla Villa, Giulia Priarone
Department of Pharmacy, University of Genoa, viale Benedetto XV, 3, 16132, Genoa,
Italy
Received: November 27, 2012
Accepted: March 1, 2013
ABSTRACT
Carboxylic acid anions intercalated layered double hydroxides are currently gaining
increasing interest due to their potential applications in pharmaceutical field for controlled
drug release in novel tunable drug delivery systems.
In this work different aliphatic carboxylic acid anions were intercalated into the interlayers
of commercial as well as synthetically prepared layered double hydroxides, through a novel
microwave mediated melt reaction approach. The volumetric nature of microwave dielectric
heating was exploited in order to rapidly heat the intimate mixture of the lamellar inorganic
precursor and the appropriate organic acid, at the melting temperature of the particular monoor dicarboxylic acid used, reaching the intercalation in approximately two hours treatment.
KEYWORDS: Organo-layered double hydroxides; microwaves; melt reaction intercalation
method.
INTRODUCTION
Layered double hydroxides (LDHs) are anionic lamellar clays with great capacity for
anion intercalation. They are also widely known as hydrotalcite like compounds (HTlcs)
due to their structural similarities to hydrotalcite, a mineral with the chemical formula
Mg6Al2(OH)16CO3.4H2O resulting from the stacking of brucite (Mg(OH)2)-like layers containing
a positive residual charge deriving from the partial isomorphous substitution of Mg2+ cations
by Al3+ ones. This positive excess charge is counterbalanced by the CO32- anions, which are
present in the interlamellar regions together with the water molecules.
General chemical formula for LDHs is
with CO32-, SO42-,
Cl or NO3 as the most employed compensating anions.
LDHs are available as naturally occurring minerals as well as synthetic materials. In the
latter case they can be easily synthesized by both direct and indirect approaches. The most
common method applied to the preparation of hydrotalcite-like compounds is coprecipitation
which is a direct synthetic approach based on the reaction of a solution containing M2+ and M3+
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