Effect of Mo-Incorporation in the TiO₂ Lattice: A Mechanistic Basis for Photocatalytic Dye Degradation

Abstract

Photocatalytic activity of TiO 2 (anatase) is appreciably enhanced by substitutional doping of Mo in anatase lattice, in conjunction with the incorporation of nanostructured MoO 3 within the parent anatase lattice. The photocatalyst material was characterized in detail using X-ray diffraction, Raman spectroscopy, diffuse reflectance (DR-UV− Vis spectroscopy), X-ray photoelectron spectroscopy, and electron microscopy. Photocatalysis experiments were conducted using a model rhodamine-B (Rh−B) dye reaction using both UV and visible irradiation sources. The observed trends in the case of visible irradiative source can be summarized as follows: Mo-1 < Mo-2 < Mo-5 ≫ Mo-10. Attempts were made to isolate the structural factors that control photochemical behavior of these Mo−TiO 2 photocatalysts and to correlate photocatalytic activity with different structural aspects like oxidation state, band gap, surface species, etc. Mechanistic insights were acquired from ex situ 1 H NMR studies showing different intermediates and different probable routes for the Rh−B dye degradation with UV and visible radiations. The stable intermediates were formed by a direct oxidative fragmentation route, without any evidence of the initial deethylation route. The intermediates found were benzoic acid, different amines, diols, and certain acids (mostly formic and acetic acid). The adsorption of the Rh−B dye on the catalytic surface via the N-charge centers of the Rh−B was also observed.

Green synthesis of AgI nanoparticle-functionalized reduced graphene oxide aerogels with enhanced catalytic performance and facile recycling

“…The new peaks in the spectrum are associated with the intermediate products formed during degradation. The NMR results further confirmed that the de-ethylation and degradative changes of RhB occurs during the photo degradation processes 32,33 .…”

Rapid flame synthesis of internal Mo6+ doped TiO2 nanocrystals in situ decorated with highly dispersed MoO3 clusters for lithium ion storage

“…Moreover, the peak at 230.88 eV suggests that the presence of the Mo 5+ , which is consistent with the reported Mo 5+ and Mo 6+ states inherently in the MoO 3 itself. 34 After the calculation by XPS, the atomic ration of Mo/Ti is 17.4% (more than 10 %), indicating that the phase segregation of ultrafine MoO 3 crystals on the surface of TiO 2 , which is demonstrated by the XRD result and TEM observation.…”

Nanoscale TiO2 films and their application in remediation of organic pollutants

“…A c c e p t e d M a n u s c r i p t Edited June 15 6 27, [33][34][35][36][37][38][39][40][41] and non-metals (e.g., C, B, F, N, S, etc.) [28,30,[42][43][44][45][46][47], co-doping of metals/nonmetals with other metals/non-metals [48][49][50][51][52], coupling with carbonaceous nanoscale materials (fullerene (C 60 ), carbon nanotubes (CNTs) and graphene) [53][54][55][56][57][58][59] and metal oxides (WO 3 [60], [61], SnO 2 [62], MoO 3 [63], SiO 2 [64]), as well as capping (coating of one semiconductor or metal nanomaterial on the surface of another semiconductor or metal nanomaterial core) of TiO 2 [65,66].…”

“…A c c e p t e d M a n u s c r i p t Edited June 15 38 As briefly mentioned before, metal/non-metallic doping enhances the photocatalytic activity by either reducing the effective bandgap (introducing intraband states) or increasing the efficient separation of generated electrons-hole pairs. In general, metal doping is achieved by replacing Ti 4+ with other metallic ions, while O 2-anions is replaced with low atomic weight non-metals in non-metallic doping [6,175,176].…”