2D MoO_3–xS_x/MoS₂van der Waals Assembly: A Tunable Heterojunction with Attractive Properties for Photocatalysis

Abstract

S1. Methodology and Computational Setup S1.1. Total energy calculations and electronic propertiesTotal energy calculations including geometry optimizations of all pristine and substituted single-and multi-layer structures were performed by the ab initio CRYSTAL17 code which works within periodic boundary conditions and adopts localized Gaussian-type function basis sets (BSs). The following BSs were used: Mo_SC_HAYWSC-311G(d31)_cora_1997 1 (for Mo atoms), S_86-311G*_lichanot_1993 2 (for S atoms) and O_8-411d11G_valenzano_2006 3 (for O atoms). For the exchange-correlation potential, the PBE functional 4 have been adopted and the van der Waals contributions were described by using the semi-empirical Grimme D3 approach 5 with optimized scaling factors 6 . The tolerances for the evaluation of Coulomb and exchange series are set to 8 ´ 8 ´ 8 ´ 8 ´16. 7 Since ordinary DFT within the PBE/GGA underestimate the band gap, all the electronic properties were computed via single-point calculations by using the range separated hybrid Heyd-Scuseria-Ernzerhof (HSE06) exchange correlation functional 8 on the PBE optimized geometries using CRYSTAL17. All calculations (including geometry optimizations and electronic properties) were performed with an energy threshold of 10 −10 Ha per unit-cell for the self-consistent field (SCF) process. The reciprocal space for the unitcell of pristine 2D MoS2 and MoO3 systems is sampled according to a sublattice with a 12´12 k-point mesh. The k-point mesh sampling is progressively reduced as the size of the monolayer and multilayer unit cells increases for the doped materials (see Tables S3 and S4). Three different energetic stability analysis were performed to analyze the stability of 2D MoO3-xSx and MoS2-xOx systems: (i) binding energy, (ii) reaction energy and (iii) thermodynamic phase diagram which were described in our previous work of the same systems in the bulk phase. 6

First-principles calculations of 0D/2D GQDs–MoS2 mixed van der Waals heterojunctions for photocatalysis: a transition from type I to type II

“…However, charge carriers can be separated efficiently due to the staggered alignment of type II heterostructures. 55 The electrons excited by photons transfer from C 32 H 14 to MoS 2 under the combined effect of the band offset and built-in electric field, 51 while the direction of hole flow is opposite. Achieving charge separation is only the basic requirement for photocatalysts.…”

Electronic structures of the MoS2/TiO2(anatase) heterojunction: influence of physical and chemical modifications at the 2D- or 1D-interfaces

“…For the physical interaction, one infinite 2D-MoS 2 nanosheet has been chosen which is known to exhibit larger bandgap than multilayers. 10 For the heterojunction, the MoS 2 nanosheet was optimized in parallel orientation with respect to the TiO 2 surfaces leading to a 2D-interface. For that, the unit cell of the two materials was multiplied in order to respect the commensurability of the respective lattice parameters (Fig.…”

“…8,9 Moreover, this 2D-MoS 2 material presents a nano-structure that could be easily tuned (doping elements, number of layers, size of the nanosheet…) in order to adapt its optoelectronic properties as a function of the requirements. 10 However, the limitation of the use of MoS 2 in photocatalysis may raise from its slightly too small bandgap (between 1.3 11 and 1.9 12 eV as a function of the number of layers). As an example, to realize efficiently the photoreduction of CO 2 in HCOOH at pH = 0 with H 2 O as the reducer, a bandgap higher than 2.1 eV would be necessary with properly tuned positions of the conduction and valence bands (CB/VB).…”

Development of defective molybdenum oxides for photocatalysis, thermal catalysis, and photothermal catalysis

“…86,87 After analyzing 2D MoO 3Àx S x /MoS 2 heterostructures using density flooding theory (DFT) calculations of the HSE06 functional, Bahers et al discovered a type II heterojunction in which the bandgap and charge transfer between the MoO 3 and MoS 2 layers are constantly driven by the S concentration in the MoO 3Àx S x single layer, providing an efficient direct Z-type system for photocatalytic water splitting. 88 Liu et al grew 0D CdS nanoparticles on two-dimensional plasmonic MoO 3Àx using a simple co-precipitation approach. The CdS/MoO 3Àx heterojunction enhances light absorption from 600 nm to 1400 nm by utilizing the LSPR effect of MoO 3Àx and speeds up the separation of photogenerated electrons and holes.…”