Hydroxyl vacancies in single-walled aluminosilicate and aluminogermanate nanotubes

Abstract

We report the first theoretical study of hydroxyl vacancies in aluminosilicate and aluminogermanate single-walled metal-oxide nanotubes. The defects are modeled on both sides of the tube walls and lead to occupied and empty states in the band gap which are highly localized both in energy and in real space. We find different magnetization states depending on both the chemical composition and the specific side with respect to the tube cavity. The defect-induced perturbations to the pristine electronic structure are related to the electrostatic polarization across the tube walls and the ensuing change in Brønsted acid-base reactivity. Finally, the capacity to counterbalance local charge accumulations, a characteristic feature of these systems, is discussed in view of their potential application as insulating coatings for one-dimensional conducting nanodevices.

Large-scale density functional theory simulation of inorganic nanotubes: a case study on Imogolite nanotubes

“…Although density functional theory (DFT) modelling and derived tight-binding approximations (TB-DFT) have assisted research in the growth mechanisms of AlSi NTs, 29,30 been used to elucidate the properties of periodic defect-free AlSi and AlGe NTs models [48][49][50][51][52][53] and to investigate possible phosphorous-and arsenic-based functionalisation, 54 the recent experimental progress in the field of Imogolite-like open-ended nanotubes (Imo-NTs) has yet to be matched by the material modelling community. With the exception of three DFT contributions focused on point defects and Fe-doping in AlSi and AlGe NTs, 50,51,55 the structural and electronic characterisation of defects, dopant and termination effects in Imo-NTs and their role in tuning the NT electronic and spectroscopic properties as well as its chemical reactivity is to date unexplored.…”

Chemically Selective Alternatives to Photoferroelectrics for Polarization‐Enhanced Photocatalysis: The Untapped Potential of Hybrid Inorganic Nanotubes

“…The permanent polarization of the NT‐wall and a real‐space separation of the valence (VBE) and conduction band (CBE) edges of pristine AlSi and AlGe Imo‐NTs,11 suggest enhanced e–h separation, and selective reduction and oxidation of different reactants on different sides of the NT‐cavity, leading to integration of photocatalytic “Z‐schemes”12 across the NT‐wall. Crucially, and motivating this work, the changes to the Imo‐NTs' curvature, wall‐polarization, VBE–CBE separation, band‐alignment, and optical properties due to organic functionalization are to date unknown.…”

“…Pristine AlSi and AlGe Imo‐NTs present an intriguing real‐space separation of the VBE and CBE,11 which may be beneficial for e–h separation via optical charge‐transfer excitations across the NT‐walls. We find this separation to be qualitatively unaffected by methylation, the diameter of the NTs, and adopted XC‐functional (Figure 2b and Figure S8, Supporting Information).…”

“…Experimental and DFT results11 indicate that, due to accumulation of negative (positive) charge on the inner (outer) tube surface, the AlSi and AlGe walls are permanently polarized. The extent to which the wall‐polarization is jointly affected by the functionalization and curvature of the NT has not been previously considered for Imo‐NTs or, to the best of our knowledge, any other NT.…”

“…Thus, the walls of the larger NTs are less polarized than the smaller ones. The positive value of μ σ indicates that, as for the pristine AlSi and AlGe systems,11 the AlSi N ‐Me NTs present accumulation of negative (positive) inside (outside) the NT‐cavity. The decrease of μ σ with N is coupled with a depletion of negative charge on the inner methyl group as N increases (Table S5, Supporting Information).…”