Synergistic Plasmonic and Molecular Engineering of Carbon Nitride: Breaking Photocatalytic Trade‐Offs for Efficient Noble‐Metal‐Free Solar CO ₂ Reduction

Abstract As a promising photocatalyst for CO 2 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.