One‐Step Realization of Crystallization and Cyano‐Group Generation for g‐C ₃ N ₄ Photocatalysts with Improved H ₂ Production

In contrast to conventional disordered g-C3N4, the ordered arrangement of s-triazine units and cyano-group is important for its improved photocatalytic H2 evolution activity. However, the usual synthetic methods include complex, multiple-step operations or containing the use of toxic materials. Herein, the ordered crystallization and cyano-group generation are simultaneously realized for the g-C3N4 photocatalyst (namely, cyano-group-modified crystalline g-C3N4) by a facile and green one-step Na2CO3-assisted synthesis approach. It is found that Na2CO3 first effectively promotes the denitrification of dicyandiamide (DCDA) and accelerates its polymerization to produce highly crystalline g-C3N4. When the temperature is over 500 °C, Na2CO3 facilitates the pyrolysis of partial s-triazine units to produce cyano-groups on the g-C3N4 surface, resulting in the final generation of cyano-group-modified crystalline g-C3N4. Consequently, the resulting cyano-group-modified crystalline g-C3N4 presents a highly increased hydrogen production activity, about twofold higher than that of the bulk g-C3N4. The increased hydrogen production activity is primarily because of the synergistic effect of the highly crystalline and cyano-group functional for the resulting cyano-group-modified crystalline g-C3N4. The current technology opens insights for the preparation of other crystalline photocatalysts.