Formation of Single-Walled Aluminosilicate Nanotubes from Molecular Precursors and Curved Nanoscale Intermediates

Abstract

We report the identification and elucidation of the mechanistic role of molecular precursors and nanoscale (1-3 nm) intermediates with intrinsic curvature in the formation of single-walled aluminosilicate nanotubes. We characterize the structural and compositional evolution of molecular and nanoscale species over a length scale of 0.1-100 nm by electrospray ionization mass spectrometry, nuclear magnetic resonance spectroscopy ((27)Al liquid-state, (27)Al and (29)Si solid-state MAS), and dynamic light scattering. Together with structural optimization of key experimentally identified species by solvated density functional theory calculations, this study reveals the existence of intermediates with bonding environments, as well as intrinsic curvature, similar to the structure of the final nanotube product. We show that "proto-nanotube-like" intermediates with inherent curvature form in aqueous synthesis solutions immediately after initial hydrolysis of reactants, disappear from the solution upon heating to 95 °C due to condensation accompanied by an abrupt pH decrease, and finally form ordered single-walled aluminosilicate nanotubes. Detailed quantitative analysis of NMR and ESI-MS spectra from the relevant aluminosilicate, aluminate, and silicate solutions reveals the presence of a variety of monomeric and polymeric aluminate and aluminosilicate species (Al(1)Si(x)-Al(13)Si(x)), such as Keggin ions [AlO(4)Al(12)(OH)(24)(H(2)O)(12)](7+) and polynuclear species with a six-membered Al oxide ring unit. Our study also directly reveals the complexation of aluminate and aluminosilicate species with perchlorate species that most likely inhibit the formation of larger condensates or nontubular structures. Integration of all of our results leads to the construction of the first molecular-level mechanism of single-walled metal oxide nanotube formation, incorporating the role of monomeric and polymeric aluminosilicate species as well as larger nanoparticles.

Ostwald’s rule of stages governs structural transitions and morphology of dipeptide supramolecular polymers

“…The suppression of this mechanism in small volumes indicates that it is likely to be a nucleated process; moreover, the spatial development of the fibrillar phase leads to the depletion of the spherical phase, suggesting that the fibrils grow through monomer addition and that thermodynamic stability of the monomers in the fibrillar phase is greater than in the sphere phase; these observations suggest a thermodynamic driving force for the formation of the intermediate fibrillar phase. Interestingly, examples of transitions from amorphous aggregates into ordered tubular structures have been reported in the field of inorganic polymers 61,62 . While it has not been demonstrated that such systems follow the mechanism that we elucidate here for supramolecular polymer phase transitions, there are similarities in the overall process.…”

Synthesis and immobilization of silver nanoparticles on aluminosilicate nanotubes and their antibacterial properties

“…Single-walled aluminosilicate nanotubes (AlSiNTs) are excellent candidates for fabricating various functional nanohybrid materials due to their well-defined one-dimensional structure (Yucelen et al 2011;Thill et al 2012), vast range of tunable compositions (Avellan et al 2014), functionalizable surfaces (Kang et al 2011), attainability in pure form without a catalyst (Yucelen et al 2011), and ability to readily form hydrogels, transparent films, powders, and coatings (Jiravanichanun et al 2011;Kuroda et al 2012). As shown in Fig.…”

Nanotubular Aluminosilicates: A Case Study for Science and Industry

“…In addition to IR, XRD, TEM, SEM, and AFM, the formation and characterization of imogolite has been studied by techniques such as FTIR spectroscopy, X-ray absorption spectroscopy (XAS), nuclear magnetic resonance (NMR), electrospray ionization mass spectrometry (ESI-MS), and small-angle X-ray scattering (SAXS) 46,47 . However, the experimental conditions of the synthesis and the particular limitations of each characterization technique have hindered the elucidation of the growth mechanism for this aluminosilicate.…”

“…Research on structures analogous to imogolite, such as aluminogermanates ((OH) 3 Al 2 O 3 GeOH) have led to significant progress on a proposal for a general mechanism that explains the formation of imogolite 11,46,47 .…”

“…However, according to Yucelen et al, the precursors formed are of Keggin-ion type, and both precursors originate from the hydrolysis of the starting reagents 46,47 .…”