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

Graphitic carbon nitride (g-C3N4) 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-C3N4 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 H2PtCl6 (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-C3N4, which is considered to originate from the better access of Pt(cod)(2) to the g-C3N4 surface, as compared to that of H2PtCl6 in the preparation process. Unmodified g-C3N4 produces O-2 from an aqueous silver nitrate solution upon UV irradiation (lambda > 300 nm), although N-2, release due to self-decomposition of g-C3N4 by photogenerated holes takes place. Modification of g-C3N4 with RuO2, improves not only O-2 evolution activity but also stability against the self-decomposition, resulting in stable visible-light-driven O-2 evolution (lambda > 420 nm).