Noble Metal-Free Photocatalysts Consisting of Graphitic Carbon Nitride, Nickel Complex, and Nickel Oxide Nanoparticles for Efficient Hydrogen Generation

A facile and simple synthetic route is developed to prepare earth-abundant and noble metal-free hybrid photocatalysts, which are composed of graphitic carbon nitride (CN), nickel complex, and NiOx nanoparticles. Bimolecular nucleophilic substitution reaction was employed to attach a nickel complex onto a graphitic CN framework through covalent bonds to support its high loading and dispersion. NiOx nanoparticles were further incorporated into the catalysts to serve as a hole-transporting medium to improve the separation of photogenerated carriers for higher photocatalytic activity. Both yNiL/CN and yNiL/NiOx/CN exhibit superb H-2 evolution activity. The optimum H-2 evolution rate of the binary photocatalysts yNiL/CN reaches 303.3 mu mol.h(-1).g(-1), whereas that of the ternary photocatalysts yNiL/NiOx/CN reaches 524.1 mu mol.h(-l).g(-1), and the apparent quantum efficiency reaches 1.46% at 450 nm. This finding reveals that coordination of a nickel complex is significant in promoting photocatalytic performance, and the incorporation of NiOx nanoparticles as a hole-transporting medium is beneficial for separation of the photogenerated charge carriers. The novel hybrid system offers a new horizon for designing transition-metal complex-modified graphitic CN as noble metal-free and highly active photocatalysts for efficient visible light-driven hydrogen generation.