Kinetic and Surface Study of Single-Walled Aluminosilicate Nanotubes and Their Precursors

Nicolás Arancibia-Miranda,Mauricio Escudey,Mauricio Molina,María García-González

doi:10.3390/nano3010126

Nicolás Arancibia-Miranda, Mauricio Escudey + Show 2 more

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https://doi.org/10.3390/nano3010126

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Abstract

The structural and surface changes undergone by the different precursors that are produced during the synthesis of imogolite are reported. The surface changes that occur during the synthesis of imogolite were determined by electrophoretic migration (EM) measurements, which enabled the identification of the time at which the critical precursor of the nanoparticles was generated. A critical parameter for understanding the evolution of these precursors is the isoelectric point (IEP), of which variation revealed that the precursors modify the number of active ≡Al-OH and ≡Si-OH sites during the formation of imogolite. We also found that the IEP is displaced to a higher pH level as a consequence of the surface differentiation that occurs during the synthesis. At the same time, we established that the pH of the reaction (pHrx) decreases with the evolution and condensation of the precursors during aging. Integration of all of the obtained results related to the structural and surface properties allows an overall understanding of the different processes that occur and the products that are formed during the synthesis of imogolite.

Highlights

Two low-range-ordered aluminosilicates can be found in volcanic ash-derived soils, one of which consists of single-walled aluminosilicate nanotubes or metal-oxide nanotubes, and is known as imogolite [1]
After 72 h of aging, bands appeared at 990 and 939 cm−1, which belong to the Si-O stretching vibrations that are specific to tubular structures; these bands remained almost invariable throughout the aging time (Figure 1a) [5,30,31,32]
Micrographs taken at different stages of preparation showed the structures formed during the aging process, which evolve from amorphous structures to imogolite nanotubes

Summary

Introduction

Two low-range-ordered aluminosilicates can be found in volcanic ash-derived soils, one of which consists of single-walled aluminosilicate nanotubes or metal-oxide nanotubes, and is known as imogolite [1]. The simplicity of its synthesis and its high chemical flexibility [4,5], which results from the surface groups that constitute and functionalize the imogolite in a natural way (silanols, ≡Si-OH, on the inner surface and aluminols, ≡Al-OH, on the outer surface), have rendered this material an excellent substrate for various nanotechnological applications [6,7,8]. The research conducted to elucidate the mechanism of formation of imogolite has revealed that the subnanometric precursors are formed in the coprecipitation stage and are the key to inducing a self-assembly process during aging [11,12,13,14]. Studies on the mechanism of formation of imogolite, proposed in the literature, agree that the curved structure is due to a series of substitutions of the surface –OH groups of the

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