The potential of imogolite nanotubes as (co-)photocatalysts: a linear-scaling density functional theory study

Abstract

We report a linear-scaling density functional theory (DFT) study of the structure, wall-polarization absolute band-alignment and optical absorption of several, recently synthesized, open-ended imogolite (Imo) nanotubes (NTs), namely single-walled (SW) aluminosilicate (AlSi), SW aluminogermanate (AlGe), SW methylated aluminosilicate (AlSi-Me), and double-walled (DW) AlGe NTs. Simulations with three different semi-local and dispersion-corrected DFT-functionals reveal that the NT wall-polarization can be increased by nearly a factor of four going from SW-AlSi-Me to DW-AlGe. Absolute vacuum alignment of the NT electronic bands and comparison with those of rutile and anatase TiO2 suggest that the NTs may exhibit marked propensity to both photo-reduction and hole-scavenging. Characterization of the NTs' band-separation and optical properties reveal the occurrence of (near-)UV inside-outside charge-transfer excitations, which may be effective for electron-hole separation and enhanced photocatalytic activity. Finally, the effects of the NTs' wall-polarization on the absolute alignment of electron and hole acceptor states of interacting water (H2O) molecules are quantified and discussed.

Solid wetting-layers in inorganic nano-reactors: the water in imogolite nanotube case

“…S13 in the ESI, † such an increase of the Ge-INT's wall dipole density markedly affects the electrostatics inside the cavity with a $1.3 eV shi of the vacuum electrostatic plateau inside the nanotube's cavity. Given the increased m s for the pHyd Ge-INT with respect to the dry Ge-INT, and the calculated sensitivity of the electron acceptor/donor states of nano-conned species to the cavity electrostatics, 65,66 these results suggest that the pHyd Ge-INTs may be substantially more effective as redox co-catalysts than the pristine dehydrated Ge-INT.…”

Metal Chalcogenides Based Heterojunctions and Novel Nanostructures for Photocatalytic Hydrogen Evolution

“…More importantly, INTs present a real-space separation of the valence band and the conduction band edges, which may be beneficial for electron-hole (e − /h + ) separation via optical charge-transfer excitations across the nanotube walls [95]. The forward-looking improvement of e − /h + separation can therefore be effective in sustaining photocatalytic reactivity directly by the nanotube itself [96][97][98]. Although the computed VB and CB edges and the corresponding energy drive toward photoreduction (or photooxydation) appear to depend weakly on the nanotube diameter and the curvature, the separation of charges in methyl-modified INTs seems to be related to the nature of isomorphic substitution with respect to the inner cavity (Figure 15a,b) [73].…”

Enzyme‐Like Catalytic Activity of Porphyrin‐Functionalized Ceria Nanotubes for Water Oxidation

“…In this work, CeO 2 nanotubes (NTs) implanted with porphyrin species were fabricated as model hybrid catalysts for a proof‐of‐concept study on the enzyme‐like oxidation. CeO 2 NTs that have a large surface area, and are intrinsically polarized, offering a different environment to reactant species adsorbed inside and outside the tube . Porphyrin species are well‐known photosensitizers (PSs) employed in photo‐generation of mechanism‐dependent ROS for especially photodynamic therapy (PDT) .…”

“…CeO 2 NTs that have a large surface area, and are intrinsically polarized, offering a different environment to reactant species adsorbed inside and outside the tube. [12] Porphyrin species are well-known photosensitizers (PSs) employed in photo-generation of mechanismdependent ROS for especially photodynamic therapy (PDT). [13] In recent years, porphyrin's role in catalytic water splitting has been examined, indicating that in addition to being an antenna, porphyrins can catalyze oxidation of water to form H 2 O 2 through a two-electron process, [14] or to generate O 2 by twoelectron oxidation.…”