Enhancing Photocatalytic CO ₂ Reduction via Robust Polymer Fragment–Single‐Walled Carbon Nanotube Heterojunction Engineering

Abstract The construction of semiconductor heterojunctions presents a promising strategy for enhancing the efficiency of photocatalytic CO 2 reduction. However, the weak interfacial interactions between dissimilar materials often hinder effective charge separation, making the establishment of a robust and well‐connected interface, a significant challenge. In this study, a novel vacuum ultraviolet (VUV) irradiation‐driven fragmentation technique is introduced to synthesize graphitic carbon nitride fragments (CNF). These fragments are integrated in situ with single‐walled carbon nanotubes (SWNT), forming a SWNT/CNF heterojunction with optimized charge carrier dynamics and improves separation efficiency. Density functional theory (DFT) calculations demonstrate that CNF thermodynamically favors methane production by converting the *CO hydrogenation step from endothermic (pristine CN) to exothermic, thereby stabilizing the critical *CHO intermediate. The resulting SWNT/CNF heterostructure exhibits a higher specific surface area with abundant exposed active sites. The SWNT network acts as an efficient electron highway, establishing Ohmic contact that prolongs the lifetime of photogenerated carrier and suppresses recombination. Consequently, the SWNT/CNF photocatalyst achieves a methane production rate of 46.0 µmol h g −1 —representing 6.0‐fold and 2.5‐fold increases over pristine CN and CNF, respectively, along with an apparent quantum efficiency (AQE) of 0.96% for CH 4 and exceptional cyclic stability. This work provides a scalable strategy for engineering robust, high‐performance carbon nitride‐based heterojunctions, paving the way for more efficient and selective CO 2 photoreduction.