Nanohybrids of edible dyes intercalated in ZnAl layered double hydroxides
Introduction
Increasing attention has been paid to the layered double hydroxides (LDHs), anionic clays or hydrotalcite-like compounds [1], owing to their lamellar-type crystal structure and unique anion exchange capability [1], [2]. The LDHs are widely applied to the fields like catalysis, electrochemistry, separation technology, and drug delivery [3], [4], [5], [6].
The LDHs consist of positively charged metal hydroxide sheets with anions located between the layers to compensate the positive layer charges. The compositions are generally represented as , where M2+ and M3+ are divalent and trivalent cations, respectively, x is the ratio M3+/(M2++M3+), and is an anion with a charge of n (such as NO3−, CO32−, Cl− or SO42−). M2+and M3+ species represent Zn2+, Ni2+, Mg2+ or Cu2+, and Al3+, Cr3+, Fe3+, or Ga3+, respectively. Various kinds of organic and inorganic anions have been immobilized into such layers by the ion-exchange or coprecipitation method [1], [2].
Among various organic substances used as the interlayer guest species, a dye molecule is one of the interesting materials because its host–guest interaction may provide unique structural features and physicochemical properties [7]. Especially, edible dyes are widely used as color additives for foods, drugs, and cosmetics due to their high biocompatibility. To be useful, the edible dyes are often incorporated with polymers, which, unfortunately, did not exhibit high stability due to the incorporated processing parameters, such as heat, light, etc. [8], [9]. Thus, it would be one of the critical factors to enhance the thermal stability of the dyes.
In this study, we employed various anionic edible dyes, such as Allura® red AC (AR), sunset yellow FCF (SY), and brilliant blue FCF (BB), and intercalated them directly into our ZnAl–LDH nanoparticles by coprecipitation. It should be noted that the dyes used in this study, although they are synthetic, are certified as edible dyes meeting strict government specifications. The enhanced physicochemical properties of the dyes after intercalation are presented in detail.
Section snippets
Experimental section
A ZnAl–LDH containing edible dyes was prepared by a conventional coprecipitation method. The Zn/Al molar ratio was adjusted to 3. The edible dyes used in this study were AR (C18H14N2O8S22−: FD&C red no.40), SY (C16H10N2O7S22−: FD&C yellow no.6), and BB (C37H34N2O9S32−: FD&C blue no.1). A mixed aqueous solution containing Zn2+ (0.075 mol, from Zn(NO3)2·6H2O) ions, Al3+ (0.025 mol, from Al(NO3)3·9H2O) ones, and AR, SY, or BB (0.05 mol) was titrated dropwise with a NaOH (0.5 M) solution with vigorous
Results and discussion
The powder XRD patterns and the suggesting hybrid structures for the LDHs intercalated with Allura® red AC (AR–LDH), sunset yellow FCF (SY-LDH), and brilliant blue FCF (BB–LDH) are shown in Fig. 1. The observed basal d003 spacings were 24.0, 20.3, and 24.7 Å for AR–LDH, SY–LDH, and BB–LDH, respectively. Considering the thickness of 4.8 Å for the brucite layer, the gallery heights could also be estimated to be 19.2, 15.5, and 19.9 Å for AR–LDH, SY–LDH, and BB–LDH, respectively. Each value suggested
Conclusion
In the present study, we demonstrated that dye–LDH hybrids could be prepared by the direct coprecipitation method. The edible dyes, while intercalated into LDH layers, exhibited significant enhancement in color development and thermal stability compared to their salt forms. Such organic–inorganic-polymer hybrid systems can be very useful for various industrial applications due to their advanced and synergistic functions.
Acknowledgments
This work was financially supported by the SRC/ERC program of MOST/KOSEF through the Center for Intelligent Nano-Bio Materials (Grant: R11-2005-008-00000-0) at Ewha Womans University (Grant: R11-2005-008-01001-0).
References (10)
- et al.
Hydrotalcite-type anionic clays: preparation, properties and applications
Catal. Today
(1991) - et al.
Electrochemistry of hydrotalcite-supported bis(2-mercapto-2,2-diphenyl-ethanoate) dioxomolybdate complexes
J. Electroanal. Chem.
(1998) - et al.
Anion exchange of methyl orange into Zn–Al synthetic hydrotalcite and photophysical characterization of the intercalates obtained
Langmuir
(1999) - et al.
Layered double hydroxides exchanged with tungstate as biomimetic catalysts for mild oxidative bromination
Nature
(1999)
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