Ab initiosimulation of the structural and electronic properties of aluminosilicate and aluminogermanate natotubes with imogolite-like structure

Abstract

A theoretical study of imogolite-like single wall nanotubes as a function of silicon and germanium content and their tubular radius is presented along with mapping of silicon-germanium content properties in models that contain from 9 gibbsite-like units ͑N u =9͒ to 13 gibbsite-like units ͑N u =13͒ with a silicon-germanium content ͓X =Si/͑Si+ Ge͔͒ of 0, 0.20, 0.40, 0.60, 0.80, and 1.00. The imogolite nanotubes were built setting periodic boundary conditions to density functional theory ͑DFT͒ geometry-optimized models along both radial and axial directions in order to obtain the stable structure. The DFT calculations were carried out on the ⌫ point and for various k points, using the GGA-PW91 functional, finding an optimal unit cell length of 8.72 and 8.62 Å using a double numeric ͑DN͒ and double numeric with polarization ͑DNP͒ basis set, respectively, along the axial direction. The structural properties were analyzed through the evolution of the x-ray diffraction pattern as a function of both N u and X. A linear correlation between the tube radius and the position of the first two peaks on the x-ray diffraction is found. The imogolite surface charge was mapped with the Hirshfeld charge showing the characteristic acid tendency experimentally reported. The reactivity of imogolite-like structures was studied employing the total density of states and the band gap evolution as a function of N u and X showing an increasing behavior with X. The local reactivity was analyzed by looking at the local density of states in models with X = 0.0 and 1.0 with N u = 10. Finally, the frequency analysis was carried out in the optimized structure on the ⌫ point finding a good agreement in the O-H vibrations with those reported in the literature.

Nanotubular Aluminosilicates: A Case Study for Science and Industry

“…Different theoretical studies estimated that the band gap of these aluminosilicates can vary between 3.67 to 10ev, depending on the calculation method used, which suggests that imogolite has insulating properties as semiconductor 7,53,57 . In a recent research Kuc and Heine (2009) raised the idea of a coaxial nanowire carbon nanotube (CNT) coated with an insulating sheath made of imogolite, which would broaden the scope of this nanomaterial to be used in nanoelectronic devices (see Figure 8) 54 .…”

“…Further research on these aluminogermanates indicates that this type of nanotube formation processes are faster and their packing is monoclinic and hexagonal as imogolite 30 . Its applications have focused on the possibility of developing biodevices able to detect biomolecules such as DNA, functioning as nanowires 53,57 .…”

“…From the perspective of nanotechnology, its structure, physical, and chemical properties and high flexibility to achieve surface modifications, position the imogolite as an excellent candidate for nanotechnology applications 6,22,[51][52][53][54][55] . One of the first modifications was proposed by Wada and Wada (1982), consisting of partial substitution of Si by Ge, forming aluminogermanates, which have a diameter of 3.3 nm, 50% wider than that determined for imogolite, while its length is 15 nm, 7 times shorter than that obtained for imogolite 10,30,38,56 .…”

Clay Mineral Nanotubes: Stability, Structure and Properties

“…Several theoretical studies (Tamura & Kawamura, 2002;Konduri et al, 2006;Alvarez-Ramirez, 2007;Guimaraes et al, 2007;Zhao et al, 2009;Demichelis et al, 2010;Lee et al, 2011) using different methodologies indicated that there is clearly a minimum in the strain energy curve of the imogolite. However, the minimum value is still a matter of controversy.…”

Synthesis and Characterization of Fe-Imogolite as an Oxidation Catalyst

“…Recently, imogolite has drawn a new attention as a new nano-material because of its unique nano-scale tubular structure similar to that of a single-walled carbon nanotube [3]. Studies on synthesis [4][5][6][7][8][9], mechanisms of formation [10], structural evolution [11,12], stability [13,14], electronic states [14,15] and application have been carried out. Proposed applications, such as a polymer composite [16,17], a fuel gas storage [18], an absorbent [19], an exchange material for heat pump system [20], a humidity-controlling material [6] and an antideweling material [6] have been discussed.…”