Improved Superiority by Covalently Binding Dye to Graphene for Hydrogen Evolution from Water under Visible-Light Irradiation

A novel nanohybrid composed of bipyridine ruthenium complex ((2,2'-bipyridyl)-4-pyridyl-chlororuthenium(II), Ru(bpy)(2)(py)Cl), covalently functionalized graphene (Ru(bpy)(2)(py)Cl/G), has been synthesized successfully via coordination of Ru(bpy)(2)Cl-2 with pyridine covalently functionalized graphene (py/G), which was synthesized through 1,3-dipolar cycloaddition of azomethine ylides. Ru(bpy)(2)(py)Cl/G was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectra, Fourier transform infrared (FTIR), and ultraviolet-visible absorption (UV-vis). The fluorescence quenching efficiency of the nanohybrid excited at 290 and 535 nm was calculated to be 83% and 71%, respectively. The photocurrent density of the nanohybrid also significantly improved. The results revealed that fast photoinduced electron transfer from Ru(bpy)(2)(py)Cl moiety to graphene sheet occurred. Ru(bpy)(2)(py)Cl/G modified with platinum nanoparticles demonstrates remarkable enhanced photocatalytic activity for hydrogen evolution from water. Under 10 h UV-vis or visible light irradiation (>400 nm), the total amount of H-2 evolution was 39.3 and 7.6 mu mol mg(-1), respectively. In addition, Ru(bpy)(2)(py)Cl/G/Pt nanohybrid shows sufficient stability for photocatalytic H-2 evolution, and the hydrogen yield remains virtually unchanged in 50 h of irradiation. This study suggests that the carbon based nanohybrid composed of organic dye molecules covalently functionalized graphene is a promising candidate as a novel photocatalyst for photocatalytic hydrogen evolution.