Synergistic Plasmonic and Molecular Engineering of Carbon Nitride: Breaking Photocatalytic Trade-Offs for Efficient Noble-Metal-Free Solar CO₂ Reduction

As a promising photocatalyst for CO₂ conversion, graphitic carbon nitride (CN) suffers from limited visible-light absorption and rapid charge recombination. Here, a noble-metal-free plasmonic system, comprising titanium nitride (TiN) nanoparticle-decorated between CN nanolayers, functionalized with 2,2′-bipyridine-4,4′-dicarboxylic groups (dcbpy) is introduced. The CN-dcbpy-TiN hybrid exhibits activated dcbpy-induced substates, plasmonic features, and thus broadband light absorption, accompanied by elevated energy levels at the TiN-CN plasmonic Ohmic interface. Through steady-state and time-resolved photoluminescence, as well as transient absorption spectroscopy, it is shown that the dual-functionalization of dcbpy terminals and plasmonic TiN efficiently suppresses the exciton recombination and promotes internal electron transfer to the dcbpy-associated shallow-trapping sites. Moreover, plasmonic TiN enables ultrafast electron transfer (<400 fs) and generates long-lived active electrons via energetic high-lying electrons and a nanoheating effect. The optimized CN-dcbpy-TiN15 demonstrates a notable CO production rate of 1180 µmol g⁻¹ h⁻¹ under visible-light irradiation (λ > 420 nm) and an apparent quantum yield of 2.53% at 420 nm. This work develops a novel mechanism of “noble-metal-free plasmon-induced defect-state electron enhancement” that successfully addresses the trade-off between light absorption and thermodynamics/kinetics, offering new insights to resolve the trilemma of traditional photocatalysts—simultaneously achieving broad-spectrum responsiveness, high carrier energy, and long-lived charge separation.