The role of adsorption in photocatalytic degradation of ibuprofen under visible light irradiation by BiOBr microspheres

• The high activity of BiOBr is not due to photocatalysis but to surface adsorption.
• The photodegradation of ibuprofen by BiOBr is highly adsorptivity dependent.
• Anion exchange followed by the formation of Bi−O bond is the main adsorption force.

The adsorption behavior and mechanism of ibuprofen (IBP) on BiOBr microspheres were investigated for revealing the role of adsorption in BiOBr-based photocatalysis under visible light irradiation. Parameters such as initial concentration of IBP, catalyst dosage, solution pH value, cations and anions that affect the adsorption and photocatalytic efficiency of IBP were studied. We observed that approximately 80% of the IBP removal rate contributed from BiOBr adsorption in photocatalysis process. This suggests that the removal rate of IBP by BiOBr is highly adsorptivity dependent, with higher removal rate at higher adsorption capacity. We believe that the anion exchange between Br and dissociated IBP followed by formation of Bi–O bond on the surface of BiOBr microspheres is the main acting force during the IBP adsorption, which was further proved by XPS and FT-IR analysis. Furthermore, the TOC removal rate difference between adsorption and photocatalysis was only 11%, which indicated that most of the removal rate contribution was from adsorption. Therefore, the BiOBr adsorption property should be preferentially considered when discussing its photocatalytic mechanism. Our current work is expected to offer new insight into BiOBr-based photocatalysis.

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