Electron-withdrawing pyridine-functionalized g-C3N4-coordinated cobalt phthalocyanine for enhanced photocatalytic CO2 reduction

Abstract

To enhance the charge separation efficiency of g-C₃N₄ and facilitate electron transfer between photosensitizer and molecular catalyst, polarization and coordination strategies are used by grafting pyridine rings onto the edge of the g-C₃N₄ framework. Herein, electron-withdrawing pyridine edge-functionalized g-C₃N₄ (g-C₃N₄-P_x) was synthesized via 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-P_x to CoPc. A significant increase in the CO yield was achieved with the optimized CoPc/g-C₃N₄-P_1.5 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 provides a facile approach for developing highly efficient hybrid photocatalysts for CO₂ reduction and improving the charge separation and visible-light absorption in organic semiconductors.

Keywords: CO₂ photoreduction; Cobalt phthalocyanine/g-C₃N₄ hybrid photocatalysts; Polarization engineering; Directional electron transfer; Coordination interaction; Electron-withdrawing effect.