Highly Selective Production of Hydrogen Peroxide on Graphitic Carbon Nitride (g-C3N4) Photocatalyst Activated by Visible Light

Photocatalytic production of hydrogen peroxide (H2O2) on semiconductor catalysts with alcohol as a hydrogen source and molecular oxygen (O-2) as an oxygen source is a potential method for safe H2O2 synthesis because the reaction can be carried out without the use of explosive H-2/O-2 mixed gases. Early reported photocatalytic systems, however, produce H2O2 with significantly low selectivity (similar to 1%). We found that visible light irradiation (lambda > 420 nm) of graphitic carbon nitride (g-C3N4), a polymeric semiconductor, in an alcohol/water mixture with O-2 efficiently produces H2O2 with very high selectivity (similar to 90%). Raman spectroscopy and electron spin resonance analysis revealed that the high H2O2 selectivity is due to the efficient formation of 1,4-endoperoxide species on the g-C3N4 surface. This suppresses one-electron reduction of O-2 (superoxide radical formation), resulting in selective promotion of two-electron reduction of O-2 (H2O2 formation).