Effect
of Mo-Incorporation in the TiO<sub>2</sub> Lattice: A Mechanistic
Basis for Photocatalytic Dye Degradation
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Abstract
Photocatalytic activity of TiO<sub>2</sub> (anatase) is appreciably enhanced by substitutional doping
of Mo in anatase lattice, in conjunction with the incorporation of
nanostructured MoO<sub>3</sub> 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<sub>2</sub> 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 <sup>1</sup>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