The covalent triazine framework CTF-1 as a member of the two-dimensional covalent organic frameworks (COFs) is a category of novel metal-free photocatalysts for water splitting. The large band gap severely restricts its energy conversion efficiency. By means of the first-principles calculations, we proposed the decoration of CTF-1 by anchoring halogen atoms onto benzene moieties for improving the solar-to-hydrogen (STH) efficiency. The electronic structures reveal that the halogen substitution successfully decreases the band gap of CTF-1. Meanwhile, the calculated free energy changes along the reaction pathway indicate that all these COFs can spontaneously drive overall water splitting under light irradiation in a specific acid-base environment. The time-dependent ab initio non-adiabatic molecular dynamics simulations suggest that the electron-hole recombination periods of these COFs fall in a few to tens of nanoseconds. Excitingly, CTF-1 modified by linking six iodine atoms onto the benzene ring in the para-position (CTF-1-6I) shows a quite low band gap of 2.81 eV, indicating that it is a visible-light driven COF for overall photocatalytic water splitting. Correspondingly, CTF-1-6I also exhibits an extraordinarily promising STH efficiency of 3.70%, which is an order magnitude higher than that of the pristine CTF-1.

作为二维共价有机骨架（COF）成员的共价三嗪骨架CTF-1是一类用于水分解的新型无金属光催化剂。大的带隙严重限制了其能量转换效率。通过第一性原理计算，我们提出了通过将卤素原子固定在苯部分上来修饰CTF-1的方法，以提高太阳能到氢（STH）的效率。电子结构表明，卤素取代成功地降低了CTF-1的带隙。同时，沿着反应路径计算的自由能变化表明，所有这些COF都可以在特定的酸碱环境下，在光照射下自发地驱动总水分解。时间相关的从头算非绝热分子动力学模拟表明，这些COF的电子-空穴复合周期下降了几纳秒至数十纳秒。令人兴奋的是，通过在对位（CTF-1-6I）上将六个碘原子连接到苯环上而修饰的CTF-1显示出2.81 eV的很低的带隙，表明它是可见光驱动的COF，可用于整体光催化水分解。相应地，CTF-1-6I的STH效率也极高，为3.70％，比原始CTF-1高一个数量级。