Potassium ions and cyano group modified g-C3N4 for effective generation of H2O2 through two-electron oxygen reduction

Potassium ions (K+) doped graphitic carbon nitride (g-C3N4) was prepared by a thermal etching method using potassium hydroxide (KOH) as an ion source. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) results showed that the generation of the cyano group was detected while introducing K+. Under simulated sunlight irradiation, the sample with a K+ doping amount of 10% showed the highest hydrogen peroxide (H2O2) generation rate of 2,140.2 mu mol h-1 g-1. The apparent quantum yield (AQY) at 400 nm and the solar-to-chemical conversion (SCC) are 4.35% and 1.23%, respectively. K+ acted as a bridge between g-C3N4 layers, which enhanced charge transfer efficiency. Meanwhile, the cyano group enhanced the adsorption capacity of protons (H+) and promoted the yield of H2O2. The catalyst exhibited excellent photocatalytic stability based on four-cycle experiments. In addition, a mechanism study showed that superoxide radicals (<middle dot>O2-) were the most important active species in the reaction system. Photocatalytic production of H2O2 was achieved through consecutive single-electron steps. This study deepens the understanding of the oxygen reduction reaction process and opens up a new venue for improving H2O2 generation.