Dual Pyridinic Nitrogen Atoms as Key Nodes in Triazine-Based Conjugated Porous Polymers toward Photocatalytic Hydrogen Evolution

The conversion of solar energy into chemical fuels using photocatalysts has attracted a lot of attention. Herein, two conjugated porous polymers (CPPs) are synthesized using the Suzuki–Miyaura coupling reaction, linking 2,4,6-triphenyl-s-triazine (PTA) with either 1,10-phenanthroline [photoluminescence spectrum (PL)] or phenanthrene (PR), yielding polymers designated as PTA–PL and PTA–PR, respectively. Incorporating pyridinic nitrogen atoms in PL is compared with PR to assess its influence on the photocatalytic hydrogen evolution (PHE) reaction. PTA–PL demonstrated a hydrogen evolution rate of 363.65 μmol h–1 under full arc illumination and 115.61 μmol h–1 under visible light, without requiring a cocatalyst. Experimental and theoretical analyses suggest that the enhanced PHE activity of PTA–PL over PTA–PR is attributed to more effective photoinduced electron–hole separation and a reduced recombination rate. Nitrogen doping at the atomic level significantly enhanced activity in CPPs, by providing additional active centers, which are competitive with the best cocatalyst-free photocatalysts reported to date. The in situ-formed Pd nanoparticles on PTA–PL are smaller than those of PTA–PR because of the interaction between Pd and dual pyridinic N atoms of PTA–PL, which can accelerate the separation and migration of charge carriers induced by light irradiation.