Faculty of Materials Science and Engineering , Kunming University of Science and Technology , Kunming 650093 , P. R. China.
Inorg Chem. 2019 Nov 18;58(22):15344-15353. doi: 10.1021/acs.inorgchem.9b02328. Epub 2019 Nov 7.
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 BiOIO 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 BiOIO were analyzed and confirmed. The photocatalytic activity of BiOIO and BiOI were evaluated by the degradation of methyl orange. Methyl orange was almost completely photocatalytically decomposed by BiOIO 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 BiOIO are higher than those of BiOI. According to the results of density of theory calculations, the internal polarized electric field in BiOIO is ascribed to the spatial asymmetry of the IO group, which is estimated to ∼1.5 × 10 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 (•O) 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, BiOIO polar material can be used as one of the alternative materials for efficient photocatalytic reaction.
内建极化电场被发现是一种有效且可行的策略，可以分离光生载流子对。通过这种方法，可以显著提高光催化反应的效率。在此，通过一种简单的水热法合成了具有自发极化的层状化合物 BiOIO。以具有相似层状结构的另一种铋化合物 BiOI 作为对照，分析并证实了 BiOIO 的自发极化效应。通过降解甲基橙来评估 BiOIO 和 BiOI 的光催化活性。甲基橙在 40 和 90 min 内分别几乎完全被 BiOIO 和 BiOI 光催化分解。通过一系列光电化学表征研究了光生载流子的分离和转移行为。进一步证明了 BiOIO 的分离和传输效率高于 BiOI。根据密度泛函理论计算的结果，BiOIO 中的内建极化电场归因于 IO 基团的空间不对称性，其估计约为 1.5 × 10 V/m。在这个内建极化电场的作用下，光生电子和空穴会沿相反的方向转移，即光生电子和空穴分别聚集在 Bi/I 侧和 O 侧。此外，在降解过程中会产生超氧自由基（•O）和空穴（h），这是其具有高光催化活性的原因。最后，循环降解测试证明其光催化性能具有长期稳定性。因此，BiOIO 极性材料可以作为高效光催化反应的替代材料之一。
