Synergistic Semimetal-Bridge and Single-Atom-Site Engineering in Heterojunction Photocatalysts for Photothermally Promoted CO2 Methanation and Benzylamine Oxidation

Abstract Photocatalytic coupling of CO2 methanation with benzylamine (BnNH2) oxidation offers a compelling route toward the co-production of value-added fuels and fine chemicals, yet practical performance remains fundamentally constrained by insufficient electron and hole supply at redox sites and sluggish proton release and consumption across the paired half-reactions. Here, we demonstrate that these bottlenecks can be simultaneously unlocked via synergistic marriage of semimetal-bridge engineering and single-atom-site engineering within an inorganic–organic S-scheme heterojunction. In this architecture, semimetallic Bi, sandwiched between the hollow ZnS core and the porous porphyrin-conjugated polymer (PCP) shell, concurrently functions as a near-infrared (NIR) absorption antenna, electron transfer highway, and energetic-carrier generator; meanwhile, single-atom Co anchored within the PCP in an N4-coordinated configuration reinforces CO2 adsorption and activation while substantially lowering the rate-determining barrier to methanation. The Bi interlayer further amplifies the heterojunction’s photothermal response, boosting the population of active electrons and holes for CO2 reduction and BnNH2 oxidation while reducing their respective barriers toward CH4 and N-benzylidenebenzylamine (BBA) formation. Consequently, the resulting ZnS/Bi@CoPCP delivers CH4 and BBA production rates of 1.4 and 6.6 mmol gcat–1 h–1, with selectivities of 98.7% and 100%, respectively. This work establishes a promising strategy for concurrently ameliorating charge kinetics and surface reactivity in bifunctional heterojunction photocatalysts.