Photocatalytic Activities of Graphitic Carbon Nitride Powder for Water Reduction and Oxidation under Visible Light

Graphitic carbon nitride (g-C 3 N 4 ) with a band gap of 2.7 eV is studied as a nonmetallic photocatalyst for H 2 or O 2 evolution from water under ultraviolet (UV) and visible light. The g-C 3 N 4 catalyst exhibits activities for water reduction into H 2 or water oxidation into O 2 in the presence of a proper sacrificial electron donor or acceptor, respectively, even without the need for precious metal cocatalysts. When bis(1,5-cyclooctadiene)platinum complex [Pt(cod) 2 ] (a nonionic complex) is used as a precursor of Pt cocatalyst instead of H 2 PtCl 6 (an ionic complex), enhanced H 2 evolution activity is acquired. This difference in activity is primarily due to the better dispersion of Pt nanoparticles on g-C 3 N 4, which is considered to originate from the better access of Pt(cod) 2 to the g-C 3 N 4 surface, as compared to that of H 2 PtCl 6 in the preparation process. Unmodified g-C 3 N 4 produces O 2 from an aqueous silver nitrate solution upon UV irradiation (λ > 300 nm), although N 2 release due to self-decomposition of g-C 3 N 4 by photogenerated holes takes place. Modification of g-C 3 N 4 with RuO 2 improves not only O 2 evolution activity but also stability against the self-decomposition, resulting in stable visible-light-driven O 2 evolution (λ > 420 nm).