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.
Highlights
As the costs of energy production increase, due to both limitation of resources and the impact of an oil-fuelled economy on the climate, the interest in materials and technologies capable of converting sunlight into commercially viable forms of energy such as electrical current or chemical fuels has been steadily growing [1,2,3]
For sunlight and artificial visible light to be used, the energy gap between occupied and empty electronic states of the PC need to match the visible light spectrum (1.6–3.1 eV) and ideally the sun radiance peak (1.6–2.1 eV) [14]. (ii) The nature of the electronic excitation or its decay needs to lead to effective separation of the excited electron (e*) and hole (h), preventing their recombination. (iii) The separated e* and h must diffuse efficiently and independently to the surface of the PC. (iv) For photocatalytic applications, the photogenerated excited e* and h need to be transferred to reactants with high efficiency
The well-known limitations of standard local and semilocal exchange-correlation functionals in accurate simulation of band gap (BG), electronic localization and polaronic distortions in metal-oxide materials [117,118,119] further increase the range of challenges and accuracy compromises to be faced for realistic modelling of Imo-NTs at standard density functional theory (DFT)-level. Such compromises can be ameliorated by realization of the remarkable progress made in linear-scaling implementations of DFT (LS-DFT), which have made it possible to simulate systems up to several thousand atoms at DFT-level on academically available hardware [120], and have been recently benchmarked on Imo NTs [114]. Following this initial computational benchmark, here we present an exploration using LS-DFT of the relationships between the composition of Imo NTs and their electronic and optical properties as well as their potential as model systems for the development of novel photocatalytic strategies based on inorganic nanotubes
Summary
As the costs of energy production increase, due to both limitation of resources and the impact of an oil-fuelled economy on the climate, the interest in materials and technologies capable of converting sunlight into commercially viable forms of energy such as electrical current or chemical fuels has been steadily growing [1,2,3] Crucial to this energy conversion is the availability of photocatalysts (PCs). PCs are substances capable of generating, upon light absorption, highly reactive excited electron–hole (e*-h) pairs that may eventually transfer excited state energy or, following their separation, enter an electric circuit or be transferred to reactants. Ideally, (vi) the ratio of absorbed photons to e* (h) transferred and generated product (quantum yield) should be as high as possible [1,2,3,4,5,6,7,8,9,10,11,12,13], and (vii) the selectivity of a given PC towards a specific reactant or product in a multi-component medium should be controllable and tuneable [15]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
