Oxygen Vacancy Formation on α-MoO₃ Slabs and Ribbons

Abstract

MoO3 is a versatile catalyst for oxidation reactions that consists of bilayers connected by van der Waals interaction. In principle a MoO3 nanocrystal can be exfoliated to create twodimensional ribbons. For this article, we study the difference between the chemistry of slabs having a variety of crystal faces and that of the edges of ribbons cut from a two-dimensional bilayer. As a descriptor of chemical reactivity we use the energy of oxygen-vacancy formation: the easier it is to form an oxygen vacancy, the better oxidant the face of a slab or the edge of a two-dimensional ribbon is. We find that the properties of ribbon edges are different from those of the corresponding slab surfaces. The surface energies of slabs are in the order (010)s < (100)s < (101)s < (001)s, whereas the edge energies of ribbons are in the order <100>r ~ <101>r < <001>r (the subscript s indicates a slab and r, a ribbon). Among the surfaces studied, we have found that (001)s and (101)s faces have the lowest oxygen-vacancy formation energies, and (010)s has the highest. In contrast, among the edges studied, <101>r has the lowest vacancy formation energies. Our calculations suggest that no benefit is obtained by creating <100>r or <001>r ribbon edges. However, a significant decrease of oxygen-vacancy formation energies is observed on formation of <101>r edge by exfoliating (101)s slabs. Also, among the structures studied, we found <101>r edges to be the most reactive and (010)s surfaces to be the least reactive.

Formation of intrinsic and silicon defects in MoO3 under varied oxygen partial pressure and temperature conditions: an ab initio DFT investigation

“…With Bader analysis, 86 the Bader charges on the oxygen atoms were found to be À0.68e, À0.99e and À1.10e, for the O1, O2 and O3 atoms respectively, with a Bader charge on the Mo of 2.77e. These results match within 8% the recent works of Agarwal et al 83 and Akande et al, 48 but have an up to 22% magnitude difference from older studies with no van der Waals treatment such as Coquet & Willock, 60 Sha et al, 53 and Lei & Chen, 52 indicating that van der Waals treatment has a noticeable effect on charge distributions in this material. Fig.…”

“…This work used the D3 treatment by Grimme, 62 while earlier studies used the D2, 47,80 the optB88-vdW 46,81,82 or in the case of early studies, 53,60,61 no treatment at all. The most common level of theory was GGA + U with a U parameter of 6.3 eV, however there were studies that used smaller U values, 83 no U parameter 53 or the HSE06 hybrid functional. 48 The band gap of the simulated structure of this work was found to be 1.5 eV, which is lower than the experimental values that range from 3 to 3.3 eV.…”

Fingerprint Acquisition Based on Photo‐Thermal Coloration of MoO3 Ceramic upon the Irradiation of Multiband Light outside the Bandgap

“…[ 33,34 ] It was reported that the formation of oxygen vacancies or Mo 5+ in the α‐MoO 3 host could cause the absorbance band in the longer wavelength region. [ 35–38 ] The electron paramagnetic resonance (EPR) spectra of M ceramic was measured to demonstrate the origin of the longer wavelength absorption. A distinct signal peak at g = 1.9948 of oxygen vacancies in M ceramic was found, [ 39–42 ] as displayed in Figure a.…”

Tweaking the Electronic and Optical Properties of α-MoO3 by Sulphur and Selenium Doping – a Density Functional Theory Study

“…For the DFT + U calculations of α-MoO 3 , a scattering range of U eff values from 1 to 8.6 eV have been used in the literature 21 . The value of U eff is usually empirically determined, and it is near impossible to find a universal U eff that is effective for all the different cases.…”

“…The recent work by Agarwal et al . explored the catalytic applications of the bulk MoO 3 and two-dimensional MoO 3 21 . Yang et al .…”