Bi₂MoO₆ microspheres for the degradation of orange II by heterogeneous activation of persulfate under visible light

The 3D microspheres of Bi₂MoO₆ samples were synthesized hydrothermally using different Bi:Mo molar ratios and evaluated for the removal of orange II under visible light by activating with K₂S₂O₈. The Bi-Mo-2 sample (Bi:Mo molar ratio of 2:1, i.e., stoichiometric composition of Bi₂MoO₆) showed the strongest catalytic activity by removing 99.43% orange II within 120 min among the several different Bi-Mo materials. The surface of the microspheres was composed of irregular nanosheets with exposed reactive sites, which are beneficial for degrading orange II. Moreover, the Bi₂MoO₆ catalyst demonstrated good cycling stability and could be reused for at least five runs with only a 6.99% decrease in degradation. The proposed mechanism of photocatalytic activity could be explained by the generation of superoxide radical O₂ ^[rad]− along with SO₄ ^[rad]− and OH^[rad] radicals, which were found to be responsible for the orange II degradation. Our research led to an efficient and stable photochemical catalyst for orange II dye degradation in wastewater.