Poly-Phosphamide Catalyzed Visible-Light-Driven CH₄ and Dark-Phase-Mediated Cyclic Carbonate Productions Utilizing CO₂

A poly-phosphamide (POP) with a band gap of 2.8 eV is used for the photochemical conversion of CO₂ into CH₄ and chemical conversion of CO₂ and organo-epoxides into cyclic carbonates. The Tauc plot and Mott Schottky analyses indicate the conduction band potential at −1.49 V (vs NHE), much more negative than the multi-electron CO₂ reduction potential and the lifetime of the photo-excited electron is found 2.8 ns. On photoirradiation of 420 nm light, the POP in the presence of triethanolamine or ascorbic acid can selectively convert CO₂ into CH₄ (≈99%) with a yield of 4.6 mmol g⁻¹. On visible-light irradiation, the drop of charge-transfer resistance (R_ct) and an enhancement of cathodic current further confirm the photon-harvesting efficiency of the POP. In situ, FTIR study identifies the CO₂ adsorption to the POP and possible reaction intermediate, like *-CO, *-CH₂OH. POP also behaves as a catalyst for CO₂ conversion to cyclic carbonates under solvent-free conditions with more than 98% yield. After the light-phase and dark-phase reactions, POP can be successfully recycled at least five times without structural degradation. Herein, the POP acts as a bi-functional, and recyclable polymeric organic material to convert CO₂ to essential feedstocks under mild reaction conditions.