Microwave synthesis of iodine-doped bismuth oxychloride microspheres for the visible light photocatalytic removal of toxic hydroxyl-contained intermediates of parabens: catalyst synthesis, characterization, and mechanism insight.

The iodine-doped bismuth oxychloride (I-doped BiOCl) microspheres are synthesized as the visible light photocatalysts for the photocatalytic removal of three toxic hydroxyl-contained intermediates of parabens. With the aid of the unique heating mode of microwave method, the I-doped BiOCl photocatalysts with tunable iodine contents and dispersed energy bands, instead of a mixture of BiOI and BiOCl or solid solution, are synthesized under the controllable conditions. Due to the stretched architectures, high specific surface area, and effective separation of photogenerated carriers, they exhibit high activity to the photocatalytic degradation of methyl 2,4-dihydroxybenzoate (MDB), methyl 3,4-dihydroxybenzoate (MDHB), and ethyl 2,4-dihydroxybenzoate (EDB). As a typical result, it is indicated that though MDB as the most difficult intermediate of parabens to be degraded, a 91.2% removal ratio can still be achieved over the I-doped BiOCl with an energy band of 2.79 eV within 60 min. In addition, it is also confirmed that these photocatalysts remain stable throughout the photocatalytic reaction and can be reused, and more importantly, the photogenerated h+ and •O2- are the key reactive species, while •OH plays a negligible role in the photocatalytic reaction. Resorcinol was identified as the main photodegraded intermediate. These results demonstrate that this photocatalytic system not only exhibit a high efficiency but also avoid the consequent secondary pollutions due to the no formation of complex hydroxyl derivatives.