**2.4. TiO2-based heterostructure photocatalysts**

The heterojunctions provide a facile way to enable the effective separation of photoexcited electron–hole pairs, thus to enhance the photocatalytic performance. Table 1 lists recent prominent heterostructured photocatalysts as well as their photocatalytic application.


**Table 1.** Recent reports of diverse heterostructured photocatalysts.

According to different electronic energy levels and band gaps of photocatalysts, five kinds of semiconductor heterojunctions have been reported: straddling alignment (type I), staggered alignment (type II), Z-scheme system, homojunctions, and p–n heterojunctions [118, 119]. In those work, the dynamics of electron and hole were studied, including the band gap, the electron affinity, and the work function of different semiconductor heterojunctions.
