Ionothermally synthesized S-scheme isotype heterojunction of carbon nitride with significantly enhanced photocatalytic performance for hydrogen evolution and carbon dioxide reduction

Graphitic phase carbon nitride (CN) is a safe and green photocatalyst, but the activity of the pristine CN photocatalyst is still unsatisfactory due to the significant recombination of photogenerated charges, so it is still challenging to realize the practical application of CN for photocatalysis. Herein, we report that a mechanical mixture consisting of pre-thermally polymerized melamine (Me) and 3-amino-1,2,4-triazole (AT) can be transformed into a crystalline isotype heterojunction material (ISCNMT) by ionothermal synthesis. A series of characterizations and photocatalytic tests demonstrate that the polymerizability, porosity and photoelectric conversion efficiency of the constructed ISCNMT have been improved. The photogenerated charge pairs of the ISCNMT can migrate in S-scheme, indicating that ISCNMT retains the strongest reduction capacity and greatly improving the separation efficiency of photogenerated charge pairs. As a result, the ISCNMT exhibits outstanding performance. Its catalytic efficiency for visible light-triggered hydrogen evolution from water can reach 9.64 mmol·g−1·h−1 with an apparent quantum efficiency (AQE) of 26.23%, which is 21 or 45 times higher than that of the carbon nitride material directly polymerized by Me or AT (CNM or CNT). In addition, the ISCNMT has a catalytic efficiency of 15.64 μmol·g−1·h−1 for photocatalysis CO2 reduction under water vapor. This work provides a facile pathway for designing S-scheme isotype heterojunction CN-based photocatalysts for the efficient conversion of solar energy.