Ultrahigh dark and light-improved chloride removal performance of magnetite bismuth oxide thin flakes with low crystallinity

The high concentration of chloride (Cl-) ions in wastewater poses environmental risks. The bismuth oxide (Bi2O3)-based Cl- removal method has gained significant attention due to its high selectivity towards Cl- ions. However, it still faces challenges related to strong acid condition and excessive dosage. Herein, the mixed-ferrites (M-Fe3O4) nanoparticles with broadband absorption property were combined with Bi2O3 to form to the magnetite Bi2O3 (FBO) composites. Due to the space separation of M-Fe3O4 nanoparticles in the thin Bi2O3 flakes, FBO had a loose structure, and its sample after 100 oC treatment (FBO-100) possessed weak crystallinity and the largest specific surface area, which enabled it to possess the highest Cl- removal efficiency of 98.4% at pH = 1 in the dark. Under UV-Vis-NIR irradiation, the Cl- removal efficiencies of FBO-100 at pH = 2, 3, and 5 increased from 71.4%, 56.3%, and 54.5% to 84.6%, 65.5%, and 58.0%, respectively. During the light-irradiated Cl- removal process, the heterostructures of Bi2O3/M-Fe3O4, Bi2O3/BiOCl/M-Fe3O4, and BiOCl/M-Fe3O4 were successively built, and the oxidative photocorrosion of Bi2O3 caused by holes played the predominant role in improving the Cl- removal efficiency, compared with the •OH, Cl•, and O2•− radicals. FBO-100 had stable cyclic Cl- removal performance and high safety, which is expected to be of a good application prospect for Cl- removal.