First principles evaluation on photocatalytic suitability of 2H structured and [0001] oriented WS2 nanosheets and nanotubes

Functional Materials and Nanotechnologies 2018

Zhukovskii, Y.F.^1 ; Piskunov, S.^1 ; Evarestov, R.A.^2

Institute of Solid State Physics, University of Latvia, 8 Kengaraga Street, Riga

LV-1083, Latvia^1

St. Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg

199034, Russia^2

关键词: Energy resolutions;    First principles;    First-principles calculation;    H2O molecules;    Multi-walled nanotubes;    Oxidation and reduction;    Photo-catalytic;    Thickness growth;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/503/1/012002/pdf
DOI  :  10.1088/1757-899X/503/1/012002

来源: IOP

【 摘 要 】

Pristine WS2 multilayer nanosheets (NSs), which thickness h NS varies from 1 to 12 monolayers (MLs), as well as single- and multi-walled nanotubes (SW and MW NTs) of different chirality, which diameter d NT exceeds 1.9 nm, display photocatalytic suitability to split H2O molecules. Obviously, such a phenomenon can occur since the band gap of these nanostructures corresponds to the energy range of visible light between the red and violet edges of spectrum (1.55 eV gap 2 NSs and NTs, the levels of the top of the valence band and the bottom of the conduction band must be properly aligned relatively to H2O oxidation and reduction potentials separated by 1.23 eV:VB 2/H2O 2 CB. The values of Δgap decrease with growth of h NS and increase with enlargement of dNT. 1 ML nanosheet can be considered as a limit of infinite SW NT thickness growth (d NT→∞), which band gap increases up to ∼2.65 eV. First principles calculations have been performed using the hybrid DFT-HF method (HSE06 Hamiltonian) adapted for 2H WS2 bulk. The highest solar energy conversion efficiency (15-18%) expected at Δgap = 2.0-2.2 eV (yellow-green range) has been found for 2 ML thick (stoichiometric) WS2 (0001) NS as well as WS2 NTs with diameters 2.7-3.2 nm (irrespectively on morphology and chirality indices n of nanotubes). Moreover, unlike discrete variation of hNS magnitudes, tuning of d NT values provides much higher energy resolution.