Eco-Friendly Photochemical Production of H2O2 through O2 Reduction over Carbon Nitride Frameworks Incorporated with Multiple Heteroelements

We report that in situ incorporation of both potassium and phosphate species into a polymeric carbon nitride (CN) framework highly enhanced the photoproduction of hydrogen peroxide (H2O2) without the use of any noble-metal cocatalysts. The incorporation of earth-abundant heteroelements (K, P, and O) (i) introduced the negative surface charge over the entire pH range through surface functionalization by phosphate species, (ii) increased the lifetime of the transient species to a picosecond time scale via the formation of charge separation states, (iii) facilitated the interfacial electron transfer to dioxygen, and (iv) inhibited the decomposition of in situ generated H2O2. As a result, the modified CN showed apparent quantum yields (Φ, for H2O2 production) that are enhanced by about 25 and 17 times (Φ420 = 8.0%; Φ320 = 26.2%) from those of bare CN (Φ420 = 0.32%; Φ320 = 1.55%) under monochromatic irradiation of 420 and 320 nm, respectively. This study clearly demonstrated a simple way to design multiple heteroelement-incorporated CN compounds that consist of earth-abundant elements only (C, N, K, P, O) for the development of practical and economical solar conversion photocatalytic materials.