Efficient Photocatalytic Hydrogen Evolution and CO₂ Reduction: Enhanced Light Absorption, Charge Separation, and...

Although graphitic carbon nitride (g-C₃N₄) has been identified as a promising photocatalyst, pristine g-C₃N₄ has a limited light absorption, insolubility, small specific surface area, and rapid electron-hole pair recombination. In this study, hydroxyl-grafted oxygen-linked tri-s-triazine-based polymer (HGONTP) is achieved through the polycondensation of hydrothermally pretreated dicyandiamide (DCDA). The content of C-O-C linkers and terminal OH groups in HGONTP can be regulated by the cyclization and hydrolysis degrees of DCDA through the replacement of the pendant NH₂ groups with OH groups. The HGONTP photocatalyst exhibits an outstanding light absorption from UV to near-IR, possessing a narrow band gap of 2.18 eV, a hydrophilic surface, a large specific surface area of 96.1 m² g^-1, and reduced charge recombination. As a result, HGONTP exhibits a hydrogen evolution rate 27.7-fold higher than that for pristine g-C₃N₄ (6.54 vs 0.236 mmol g^-1 h^-1). The apparent quantum yield reaches 12.6% at 420 nm and 4.1% at 500 nm. In addition, the photocatalytic conversion efficiency of CO₂ to CO reaches as high as 3.3 μmol g^-1 h^-1 without cocatalysts and sacrificial agents. The selectivity of CO₂ to CO achieves 88.4%. The proposed strategy paves a new avenue to design high-performance polymeric photocatalysts used in water.