Halogen-doped ultrathin Bi₂WO₆ for promoted separation of photogenerated carriers and efficient photocatalysis

Although photocatalysis is a viable and sustainable technique to remove refractory pollutants from wastewater, it is plagued by the low separation efficiency of photo-generated carriers. Herein, in situ surfactants (CTAC, CTAB, and DTAI) assisted synthesis of halogen-doped ultra-thin Bi₂WO₆ (BWO) nanosheets with oxygen vacancies, which efficiently degraded RhB and TC under visible light. Surfactant as a halogen source can also prevent the formation of BWO layered structures, thus making the sample thinner and thus reducing the transmission distance of photogenerated electrons. The degradation rates of rhodamine B (RhB) and tetracycline (TC) by BWO-Cl-90 and BWO-Br-90 upon visible light illumination are 5.8 times / 5.5 times and 2.5 times / 2.8 times by those of pure BWO, respectively. The free radical trapping experiments and ESR reveal that singlet oxygen (¹O₂) and photogenerated holes (h⁺) are the main active free radicals in the degradation of organic pollutants by BWO-Cl-90, while the superoxide radical (·O₂^-) and photogenerated holes (h⁺) play the main roles for BWO-Br-90. The photocatalytic mechanism is proposed. In addition, the EIS, photocurrent and photoluminescence (PL) experiments show that halogen doping improves the separation ability of photogenerated carriers. This study reveals a practical method to modify Bi₂WO₆-based materials for effective wastewater treatment and purification. © 2024 Published by Elsevier B.V.