Graphitic carbon nitride prepared from urea as a photocatalyst for visible-light carbon dioxide reduction with the aid of a mononuclear ruthenium(II) complex

Graphitic carbon nitride (g-C(3)N(4)) was synthesized by heating urea at different temperatures (773–923 K) in air, and was examined as a photocatalyst for CO(2) reduction. With increasing synthesis temperature, the conversion of urea into g-C(3)N(4) was facilitated, as confirmed by X-ray diffraction, FTIR spectroscopy and elemental analysis. The as-synthesized g-C(3)N(4) samples, further modified with Ag nanoparticles, were capable of reducing CO(2) into formate under visible light (λ > 400 nm) in the presence of triethanolamine as an electron donor, with the aid of a molecular Ru(II) cocatalyst (RuP). The CO(2) reduction activity was improved by increasing the synthesis temperature of g-C(3)N(4), with the maximum activity obtained at 873–923 K. This trend was also consistent with that observed in photocatalytic H(2) evolution using Pt-loaded g-C(3)N(4). The photocatalytic activities of RuP/g-C(3)N(4) for CO(2) reduction and H(2) evolution were thus shown to be strongly associated with the generation of the crystallized g-C(3)N(4) phase.