Infrared Response in a Polymeric Carbon Nitride Via an Upconversion Mechanism

Abstract

We propose an upconversion process in polymeric carbon nitride (C³N⁴). This phenomenon in our O-doped porous nanosheet carbon nitride (MCN1-4) results in hydrogen generation from water splitting under infrared light irradiation by two (multi)-photon excitation (λ≥800 nm, 22.84 μmol h^-1g^-1). In addition to exhibiting upconversion, MCN1-4 has a σ*_C-O orbital localized on the triazine matrix ring resulting from O doping, a porous ultra-thin nanosheet morphology, and an elemental distribution gradient from the inside to the surface of the material. Synergy induces extension of the lifetime of photoexcited electrons, which increases the photocatalytic activity under both infrared and visible light. Under visible light (λ≥420 nm) irradiation, MCN1-4 exhibits a solar-to-hydrogen energy conversion efficiency of 0.44% and an apparent quantum efficiency of 23.02% at 420 nm.

Keywords: photocatalysis, polymeric carbon nitride, upconversion, infrared response, two(multi)-photon absorption