THESIS
2019
xxiv, 158 pages : illustrations (some color) ; 30 cm
Abstract
Among different bismuth oxyhalides (BiOX; X=F, Cl, Br, I), the moderate bandgap of ~2.8 eV
of BiOBr makes it a suitable visible-light-driven photocatalyst. However, a comparison of its
different morphologies, e.g., plate-like and hierarchical structures, is not yet reported, leaving
behind fundamental questions as to which one is better for photocatalytic water treatment and
why? These questions were addressed in this study by conducting a vis-à-vis comparison of
photocatalytic performance of the two structures in degradation of pharmaceuticals and
personal care products (PPCPs) — an emerging class of ubiquitous water pollutants. The
photocatalytic degradation by the hierarchical structure was three times faster than its plate-like
counterpart. Contrary to the widespread notions...[
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Among different bismuth oxyhalides (BiOX; X=F, Cl, Br, I), the moderate bandgap of ~2.8 eV
of BiOBr makes it a suitable visible-light-driven photocatalyst. However, a comparison of its
different morphologies, e.g., plate-like and hierarchical structures, is not yet reported, leaving
behind fundamental questions as to which one is better for photocatalytic water treatment and
why? These questions were addressed in this study by conducting a vis-à-vis comparison of
photocatalytic performance of the two structures in degradation of pharmaceuticals and
personal care products (PPCPs) — an emerging class of ubiquitous water pollutants. The
photocatalytic degradation by the hierarchical structure was three times faster than its plate-like
counterpart. Contrary to the widespread notions in the literature that a hierarchical
photocatalyst performs better than its plate-like counterpart due to its better light harvestability
and/or adsorption capability, charge carrier separation was found to be the mechanistic feature predominantly affecting photocatalytic performance. Subsequently, material properties of the
two structures were comparatively examined using material characterization and
photoelectrochemical techniques. Compared to other material properties, crystal disorders
were found to have a profound effect on photocatalytic activity. Examination of
property-performance relationships, evaluated for a solid solution system, BiOBr
xI
1–x
(0 ≤ x ≤ 1), verified that charge carrier separation is a predominant mechanistic feature, and
crystal disorders constitute one of the most influential material properties governing
photocatalytic activity. Further, a magnetically separable BiOBr/Fe
3O
4@SiO
2 photocatalyst
was synthesized exhibiting not only fast PPCP degradation kinetics but also mineralization
capability. Conduction band electron-mediated reactions and direct-hole oxidation comprised
major degradation routes. The recycled BiOBr/Fe
3O
4@SiO
2 maintained about 80% of its
activity over five cycles. The typically co-present wastewater constituents, including NOM and
anions, inhibited photocatalytic performance to varying extents in real sewage. The results of
prototype photocatalytic experiments were comparable to those of batch experiments, and a
magnetic separation efficiency of ~99% was achievable in 5 min.
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