Surface-Specific Modification of Graphitic Carbon Nitride by Plasma for Enhanced Durability and Selectivity of Photocatalytic CO 2 Reduction with a Supramolecular Photocatalyst.

Photocatalytic CO reduction is in high demand for sustainable energy management. Hybrid photocatalysts combining semiconductors with supramolecular photocatalysts represent a powerful strategy for constructing visible-light-driven CO reduction systems with strong oxidation power. Here, we demonstrate the novel effects of plasma surface modification of graphitic carbon nitride (CN), which is an organic semiconductor, to achieve better affinity and electron transfer at the interface of a hybrid photocatalyst consisting of CN and a Ru(II)-Ru(II) binuclear complex (). This plasma treatment enabled the "surface-specific" introduction of oxygen functional groups via the formation of a carbon layer, which worked as active sites for adsorbing metal-complex molecules with methyl phosphonic-acid anchoring groups onto the plasma-modified surface of CN. Upon photocatalytic CO reduction with the hybrid under visible-light irradiation, the plasma-surface-modified CN with enhanced the durability of HCOOH production by three times compared to that achieved when using a nonmodified system. The high selectivity of HCOOH production against byproduct evolution (H and CO) was improved, and the turnover number of HCOOH production based on the used reached 50 000, which is the highest among the metal-complex/semiconductor hybrid systems reported thus far. The improved activity is mainly attributed to the promotion of electron transfer from CN to under light irradiation via the accumulation of electrons trapped in deep defect sites on the plasma-modified surface of CN.