Guanidinium-Enhanced Production of Hydrogen on Nafion-Coated Dye/Tio2 under Visible Light

Guanidinium cations (abbreviated as G) enhanced the visible light-induced hydrogen production by three times in the dye(Ru(bpy)(3)(2+))-sensitized system using TiO2 nanoparticles coated with nafion polymer. The enhanced photoactivity in the presence of G adsorbed on the nafion coating was related to the retardation of the charge recombination between the electrons injected into the TiO2 conduction band (CB) and oxidized dye molecules, which was confirmed by time-resolved diffuse reflectance spectroscopic measurements. It is proposed that G cations located near the TiO2 surface repel the oxidized dyes to retard the recombination with CB electrons. In addition, the dye luminescence in nafion was enhanced in the presence of G, which was ascribed to the retardation of self-quenching of the excited dyes. The dual roles of G in the nafion layer increase the photoelectron density in TiO2 CB and subsequently enhance the production of hydrogen.