Two-Dimensional Titania: Structures and Properties Predicted by First Principle Calculation

Material innovations, especially in classic semiconductor materials such as titania, are expected and more and more accelerated by ab initio design for their wide applications. For better realization in laboratory, feasible stability of structures in ambient temperature and pressure should be prior to the structure–property relationship study. However, there is discrepancy between experiments and ab initio calculations about how the freestanding two-dimensional TiO2 exists. Herein, by the structural search method with the first principles evolution algorithm, the stable freestanding monolayers (MLs) were found to be composed by octahedral, hexahedral, or pentahedral Ti–O block (o-ML, h-ML, or p-ML) with nonplanar structure, where o-ML is right the lepidocrocite type found experimentally. Meanwhile, novel structure-dependent properties mainly due to quantum-confine effects were investigated and the abnormal optical absorption, better properties of insulation, and redox in photocatalysis were found for these titania sheets.