Crystalline carbon nitride semiconductors prepared at different temperatures for photocatalytic hydrogen production

Carbon nitride (CN) polymer has been widely investigated as a photocatalyst for solar hydrogen production in recent years due to its unique properties. However, the pristine CN typically shows moderate photocatalytic performance. An important reason is its high-density defects in CN framework, and it could play the role as a recombination center of photogenerated electron-hole pair. Therefore, increasing the crystallinity can be one of efficient way to enhance its photocatalytic activity. Recently, we have report a new heptazine-based crystalline CN synthesized by ionothermal method, and the as-prepared sample has been exhibited high activity toward photocatalytic hydrogen production. Herein, we systematically investigated influences of the synthetic temperature on the properties and photocatalytic activity of the as-prepared crystalline CN polymer. Our results demonstrate that the crystalline CN synthesized by using 550 °C pre-heated precursor shows the highest activity in photocatalytic hydrogen production, and achieving an apparent quantum yield of 6.8%@420 nm with MeOH as sacrificial agent. When compared to the reference photocatalyst P25, the CCN550 shows remarkable photocatalytic hydrogen production under visible light irradiation, while P25 is virtually inactive. In addition, the amount of produced hydrogen gas by CCN550 is closed to P25 under full arc irradiation of Xe lamp, which highlights the potential solar energy utilization of such crystalline conjugated polymer in the future development.