Spontaneous Polarization Effect and Photocatalytic Activity of Layered Compound of BiOIO₃

Internal polarized electric field is found to be an effective and available strategy to separate photogenerated electron-hole pairs. By this method, the efficiency of photocatalytic reactions can be obviously enhanced. Here, the layered compound of BiOIO₃ with spontaneous polarization was synthesized by a simple hydrothermal method. Taking another bismuth compound BiOI as a counterpart, which has a similar layered structure, the spontaneous polarization effects of BiOIO₃ were analyzed and confirmed. The photocatalytic activity of BiOIO₃ and BiOI were evaluated by the degradation of methyl orange. Methyl orange was almost completely photocatalytically decomposed by BiOIO₃ and BiOI in 40 and 90 min, respectively. The separation and transfer behaviors of photogenerated electron-hole pairs were investigated by a series of photoelectrochemical characterizations. It is further proved the separation and transmission efficiency of BiOIO₃ are higher than those of BiOI. According to the results of density of theory calculations, the internal polarized electric field in BiOIO₃ is ascribed to the spatial asymmetry of the IO₃ group, which is estimated to ∼1.5 × 10¹⁰ V/m. Under the action of this internal polarized electric field, the photogenerated electrons and holes would transfer along opposite directions, i.e., photogenerated electrons and holes respectively gather at the Bi/I side and O side. Additionally, superoxide radicals (•O₂^-) and holes (h⁺) are produced during the degradation process, which are responsible for the high visible-light photocatalytic activity. Finally, the cyclic degradation test proves that its photocatalytic performance has long-term stability. Therefore, BiOIO₃ polar material can be used as one of the alternative materials for efficient photocatalytic reaction.