With careful rational optimization and substantial simplification
of the syntheses of the recently reported alloys BiO(Cl
x
Br1–x
), we fabricated,
via a very simple procedure and at room temperature, a unique visible-light-driven
photocatalyst with excellent activity. The alloy BiOCl0.875Br0.125 totally decomposed 15 mg/L aqueous Rhodamine B
solution within 120 s upon irradiation with visible light (λ
> 422 nm). The transparent substrate acetophenone was also swiftly
destroyed under the above conditions. The catalyst maintained partial
activity even after switching off the light source. Initial mechanistic
studies clearly suggest that the mode of action of these materials
is fundamentally different from previously reported photocatalytic
mechanisms. Evidently, the putative molecular mechanism does not engage
dye photosensitization or oxygen radicals.
In this study, a facile and effective method to modify
the photocatalytic
performance of a bismuth oxybromide (BiOBr) semiconductor through
the fabrication of a heterojunction with a hydrated bismuth oxide
(BHO) is reported. The new yBiOBr-(1 – y)BHO heterojunction, synthesized by a simple hydrothermal
method, exhibits a high photocatalytic activity under visible light
irradiation for the photodegradation of typical organic pollutants
in water, such as Rhodamine B (RhB) and acetophenone (AP). Both the
individual BiOBr and BHO components show very low photocatalytic efficiency.
Furthermore, the unique photocatalytic performance of the new hybrid
material was demonstrated through the uphill photocatalytic reaction
that involves the oxidation of potassium iodide (KI) to triiodide.
The remarkable photocatalytic activity of the coupled system is directly
related to the effectual charge carrier separation due to the formation
of the heterostructure. 0.9BiOBr-0.1BHO shows a higher photocatalytic
activity as compared with other members of the same family, 0.8BiOCl-0.2BHO
and 0.8BiOI-0.2BHO, which is directly ascribed to a synergistic effect
of the energy band-gap structure and flow of charge carriers through
the heterojunction, surface area, and light absorbance. In comparison with TiO2 (Degussa P25), the new composite material demonstrated 10.7 times
higher activity in removing aqueous RhB under visible light (λ
≥ 420 nm) irradiation. Study of the photocatalytic mechanism
proves that the degradation of RhB under visible light irradiation
over the as-prepared 0.9BiOBr-0.1BHO is mainly via a direct hole oxidation
mechanism and superoxide oxidation pathways. The resulting yBiOBr-(1 – y)BHO composites exhibit
high photocatalytic and thermal stabilities and are very promising
photocatalysts for degradation of organic pollutants in water and
for other applications.
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