Fast Scalable Synthetic Methodology to Prepare Nanoflower-Shaped Bi/BiOCl_xBr_1−x Heterojunction for Efficient Immobilized Photocatalytic Reactors under Visible Light Irradiation

The metal/photocatalyst heterojunction has demonstrated an excellent capability for pollutant degradation under visible light irradiation. In this study, for the first time, highly stable colloidal dispersions of Bi/BiOCl_xBr_1−x heterojunction with an exposed (001) facet are successfully prepared from inorganic simple salts using low-frequency ultrasound irradiation (LFUI) at ambient conditions without further post-treatment. The colloidal dispersion series of Bi/BiOCl_xBr_1−x heterojunction (x = 0, 0.2, 0.5, 0.8 and 1) is simply obtained by adding stoichiometric aqueous solutions of NaCl and NaBr, into an acidic aqueous solution of Bi(NO)₃.5H₂O in a typical ultrasonication bath at room temperature within ≈5 min. Bi/BiOCl_xBr_1−x heterojunction films are also fabricated using a simple drop-casting technique and tested as immobilized photocatalytic reactors. Compared to its counterparts, the Bi/BiOCl_0.8Br_0.2 film possesses a 3D flower-like morphology with a highly exposed (001) facet showing the highest electron-hole generation and separation efficiencies. In addition, the Bi/BiOCl_0.8Br_0.2 film demonstrates the highest photocatalytic degradation rate of the rhodamine RhB aqueous solutions (≈5 ppm), achieving ≈99% in 60 min under the visible light component of the solar spectrum. This study demonstrates the potential of LFUI as a rapid scalable synthetic strategy for cost-effective and energy-efficient practical production of highly active immobilized photocatalytic reactors.