Synthesis of Nanocrystalline Mg-Al Hydrotalcites in the Presence of Starch-the Effect on Structure and Composition.

Alicja Michalik,Joanna Kryściak-Czerwenka,Bogna D Napruszewska,Dorota Duraczyńska,Ewa M Serwicka,Anna Walczyk

doi:10.3390/ma13030602

Alicja Michalik, Joanna Kryściak-Czerwenka + Show 4 more

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https://doi.org/10.3390/ma13030602

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Abstract

The study describes the synthesis of Mg-Al hydrotalcite (Ht) with the use of starch as a structure controlling biotemplate. Syntheses were carried out at room temperature, by co-precipitation at pH = 10. The investigated synthesis parameters included the nature of the precipitating agent (NaOH/Na2CO3 or NH3aq/(NH4)2CO3), the nature of starch (potato, corn and cassava), the method of starch addition to reagents, the method of drying and the effect of washing. The materials were examined with X-ray diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy and infrared spectroscopy. The data show that synthesis of Ht materials in the presence of starch, with use of the ammonia-based precipitant, enabled preparation of nanocrystalline Ht with very fine (<50 nm) particle size. All investigated starches had a similar effect on the crystallinity and the grain size of Ht precipitates. Ht with the smallest nanocrystals was obtained when starch was present in all solutions used for synthesis, and the final product subjected to freeze drying. Washing with water was found to enhance recrystallization and exchange of nitrates for carbonates. Infrared spectra showed that an interaction exists between the biopolymer template and the Ht particles, resulting in a higher degree of order within the Ht-adhering starch component.

Highlights

Synthetic hydrotalcite-like materials (Ht), related to the naturally occurring mineral of chemical composition [(Mg0.75 Al0.25 )(OH)2 ](CO3 )0.125 ·0.5H2 O, are referred to as layered double hydroxides (LDHs), or anionic clays [1]
Results of the present study show that the synthesis of Ht materials in the presence of starch biotemplate, with use of the ammonia-based precipitant, enables preparation of nanocrystalline precipitates with very fine (< 50 nm) particle size, comparable with those obtained by means of the inverse micellar route, but at much lower cost and with significantly less effort
Under the adopted experimental conditions all investigated types of starch had a similar effect on the crystallinity and the grain size of the Ht precipitates

Summary

Introduction

Synthetic hydrotalcite-like materials (Ht), related to the naturally occurring mineral of chemical composition [(Mg0.75 Al0.25 )(OH)2 ](CO3 )0.125 ·0.5H2 O, are referred to as layered double hydroxides (LDHs), or anionic clays [1]. The Ht materials are described by the general formula [M2+ 1−x M3+ x (OH)2 ]x+ (An− x/n )·mH2 O, where M2+ and M3+ are the elements forming the hydroxide layer, An- is the interlayer anion compensating the layer charge, and H2 O refers to the interlayer water. Ht with controllable particle size, morphology, crystallinity and texture. Ht have the advantage of being prepared in laboratory, the conventional methods of their synthesis, e.g., co-precipitation at a constant pH, yield generally precipitates composed of aggregated particles, and offer only limited control over textural properties. Among advanced synthetic procedures developed with aim to prepare Ht materials with carefully designed nanostructure, the most

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