Electron-Withdrawing Pyridine-Functionalized g-C3N4-Coordinated Cobalt Phthalocyanine for Enhanced Photocatalytic CO2 Reduction

To enhance the charge separation efficiency of g-C3N4 and facilitate electron transfer between photosensitizer and molecular catalyst, polarization and coordination strategies are taken by grafting pyridine rings onto the edge of g-C3N4 framework. Herein, electron-withdrawing pyridine edge-functionalized g-C3N4 (g-C3N4-Px) was synthesized via a facile one-step thermal polymerization of urea and 4-aminopyridine, and employed as visible-light photosensitizer hybridized with cobalt phthalocyanine (CoPc) for efficient photoreduction of CO2. Both experimental and theoretical results confirm that electron-withdrawing pyridine grafting facilitates in-plane charge separation and directs electron migration toward the edge of g-C3N4, narrows its band gap for enhanced visible-light absorption, and provides dynamic coordination sites that significantly boost interfacial electron transfer from g-C3N4-Px to CoPc. A significant enhancement in CO yield was achieved with the optimized CoPc/g-C3N4-P1.5 hybrid, reaching 14.95 mmol g⁻¹ after 6 hours of visible-light irradiation—a 6.1-fold improvement over the unmodified CoPc/g-C3N4 (2.47 mmol g-1). This work paves a facile approach for developing highly efficient hybrid photocatalysts for CO2 reduction and improving the charge separation and visible light absorption in organic semiconductors.