Photocatalytic Activity of Bi 2 O 3 /BiOCl Heterojunctions Under UV and Visible Light Illumination for Degradation of Caffeine

Bismuth oxide (Bi 2 O 3 ) particles were synthesized by calcination and hydrothermal methods and then were treated in-situ with different amounts of hydrochloric acid (HCl) to construct a series of Bi 2 O 3 /BiOCl heterojunctions with different ratios. The physicochemical properties of the materials were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, UV–Vis diffuse reflectance spectroscopy, N 2 physisorption, Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Their photocatalytic activity was evaluated for the degradation of caffeine under UV radiation and visible light. All the heterojunctions possess an enhanced photocatalytic activity compared to pure Bi 2 O 3 and bismuth oxychloride (BiOCl) due to efficient charge separation and transfer across the interface. The heterojunctions obtained from the hydrothermal Bi 2 O 3 were more efficient than those from the calcined Bi 2 O 3 , mainly because of differences in their crystalline phases and band gap values. The hydrothermal Bi 2 O 3 has a β-Bi 2 O 3 phase and band gap of 2.4 eV, compared to the α-Bi 2 O 3 phase and 2.8 eV band gap of the calcined Bi 2 O 3 . The heterojunction with a Bi 2 O 3 /BiOCl ratio of 10/90 has the highest photocatalytic activity for caffeine degradation in UV and visible light experiments, achieving a caffeine degradation of 92% in 2 h with UV light and 25% in 5 h with visible light. This heterojunction shows excellent photostability and high efficiency for caffeine degradation in a three consecutive cycles photocatalytic experiment. The role of the different radical species involved in the photocatalytic process was evaluated, demonstrating that h + and · O 2 − are the major reactive species responsible for caffeine photodegradation. A possible mechanism for the photocatalytic activity of the heterojunctions was proposed. The Bi 2 O 3 /BiOCl heterojunctions reported in this study are promising for the degradation of organic pollutants in real wastewater effluents.