Highly crystalline graphitic carbon nitride (g-C₃N₄) possesses the high separation efficiency of photogenerated electron-hole pairs owing to the significantly decreased intralayer hydrogen bonds, which leads to drastic improvement of photocatalytic activity. However, the preparation of such g-C₃N₄ material remains a challenge by a simple and economic thermal-treatment in a furnace. Herein, we report a novel and effective strategy for high-yield synthesis of extremely active crystalline carbon nitride nanosheets (CCNNSs) by two-step calcination without the assistance of any additive or salt intercalation. As expected, the as-prepared CCNNSs exhibit a remarkably high hydrogen evolution rate of 9577.6 μmol h⁻¹ g⁻¹ under simulated solar light irradiation, which is 15.5 times than that of bulk g-C₃N₄, as well as higher than most of the reported crystalline g-C₃N₄. Moreover, a highly apparent quantum efficiency of 9.01% at 420 nm for hydrogen evolution can be achieved, which is also superior to the reported crystalline g-C₃N₄. Such two-step calcination approach not only provides an economical way to effectively regulate the crystallinity of bulk g-C₃N₄, but also achieves the preparation of CCNNSs with high yield. Our research opens up a new window to self-modification and fabrication of highly active metal-free photocatalysts for solar light-driven hydrogen production.

高度结晶的石墨碳氮化物（gC ₃ N ₄）由于层内氢键的显着减少而具有光生电子-空穴对的高分离效率，从而导致光催化活性的显着提高。然而，这种gC ₃ N ₄材料的制备仍然是在炉子中进行简单且经济的热处理所面临的挑战。本文中，我们报告了一种新颖有效的策略，可通过两步煅烧来高产率合成极活泼的结晶氮化碳纳米片（CCNNSs），而无需任何添加剂或盐的插入。如所预期的，所制备的CCNNS显示出9577.6μmolh ^-1的极高的氢气析出速率在模拟太阳光照射下的 g ^-1，是体相gC ₃ N _4的15.5倍，并且高于大多数报道的晶体gC ₃ N ₄。此外，可以实现在420 nm处有9.01％的高度表观量子效率产生氢，这也优于所报道的晶体gC ₃ N ₄。这种两步煅烧方法不仅提供了一种经济的方式来有效调节块状gC ₃ N ₄的结晶度，也可以实现高产量的CCNNS的制备。我们的研究为自行修饰和制造用于太阳光驱动制氢的高活性，不含金属的光催化剂开辟了新的窗口。