Selective charge transfer to dioxygen on KPF6-modified carbon nitride for photocatalytic synthesis of H2O2 under visible light

Abstract

Photochemical production of H2O2 through O-2 reduction has been proposed as an alternative method of solar energy storage. A carbon nitride (CN) photocatalyst was selected for this purpose. The incorporation of KPF6 into the CN structure greatly enhanced the apparent quantum yield (AQY) of H2O2 production in the UV and visible light region. The AQY of KPF6-modified CN was measured to be 35.9% and 24.3% under monochromatic irradiation at 370 and 420 nm, respectively, which are 8.3 and 26.1 times higher than for bare CN. The KPF6-enhanced activity is ascribed to several factors including (i) enhanced absorption of UV and visible light, (ii) higher charge carrier density, (iii) retarded radiative recombination of charge pairs, (iv) highly selective two-electron transfer to O-2, and (v) hindered photodecomposition of in-situ generated H2O2. The markedly high selectivity of KPF6-modified CN toward the two-electron reduction of O-2 (leading to H2O2) was demonstrated in comparision with other photoreductive conversions such as the reduction of polyoxometalate (POM -> POM-), hexavalent chromium (Cr-VI -> Cr-III), CCl4 (dechlorination), and protons (H-2 production). This study developed a simple method of efficient production of H2O2 using visible light, which could be utilized for a variety of applications that employ H2O2 as a solar fuel or a green oxidant.