Photothermal Methane-to-Ethanol Conversion over Cu Single-Atom–Cu₉S₅ Coupled Crystalline Carbon Nitride

We report the rational design and synthesis of a novel trifunctional catalyst comprising atomically dispersed copper single-atom (Cu-SAC) sites and Cu9S5 nanoparticles co-loaded onto a highly crystalline carbon nitride (CCN) support for the photothermal conversion of methane to ethanol. The distinct active sites operate in synergy: the Cu-SAC sites, coordinated to the nitrogen-rich CCN framework, serve as highly efficient centers for the initial activation of methane’s C-H bond to form methyl radicals, while the plasmonic Cu9S5 nanoparticles act as dedicated sites for the subsequent C-C coupling and partial oxidation steps, driven by a combination of photochemical and photothermal effects. Under mild conditions (200°C, full-spectrum light), the optimized Cu-SAC–Cu9S5/CCN catalyst achieves an exceptional ethanol production rate of 385 μmol g−1 h−1 with a selectivity of 85% at a methane conversion of 5.2%. Mechanistic studies reveal that a Z-scheme heterojunction between CCN and Cu9S5 facilitates efficient charge separation, while the spatial decoupling of C-H activation and C-C coupling functions is crucial for suppressing the formation of CO2. This work presents a powerful catalyst design strategy that integrates atomically precise active sites with plasmonic co-catalysts for tackling challenging chemical transformations.