Ligand–Metal Charge Transfer Induced via Adjustment of Textural Properties Controls the Performance of Single-Atom Catalysts during Photocatalytic Degradation

Because of their peculiar nitrogen-rich structure, carbon nitrides are convenient polydentate ligands for designing single-atom-dispersed photocatalysts. However, the relation of catalysts textural properties with their photophysical properties and as a result activity in photocatalytic applications is rarely elaborated. Herein we report the preparation and characterization of a series of single-atom heterogeneous catalysts featuring highly-dispersed Ag and Cu species on mesoporous graphitic C3N4. We show that adjustment of materials textural properties and thereby metal single atoms coordination mode enables ligand-to-metal (LMCT) or ligand-to-metal-to-ligand charge transfer (LMLCT), a property tha was long speculated in single-atom catalysis but never observed. We employ the developed materials in the degradation of organic pollutant under irradiation with visible light. Kinetic investigations under flow conditions show that single atoms of Ag and Cu decrease the amount of toxic organic fragmentation products, while leading to a higher selectivity towards full calcination. The results correlate with the selected mode of charge transfer in the designed photocatalysts and provide a new understanding of the surface state of single-atom catalysts. The concepts can be exploited further to rationally design and optimize other single-atom materials.