Cu nanostructures of various shapes and sizes as superior catalysts for nitro-aromatic reduction and co-catalyst for Cu/TiO2 photocatalysis

Cu nanostructures of various shapes and sizes have prepared to study their comparative optical, electrokinetic, catalysis for nitro-aromatic reduction and co-catalysis activity for photooxidation of acetic acid by Cu/TiO2 composites. As-prepared Cu nanospheres of three different sizes (3-20 nm), nanorods (length approximate to 600-700 nm and width approximate to 15-20 nm) and nanowires (lengthl approximate to 4-6 mu m and width approximate to 60-80 nm) displayed characteristic surface plasmon bands at 590-645 nm, 576 and 826 nm, and 559 and 905 nm, respectively. The zeta potential zeta=-35.9 mV for nanowires and -30.08 mV for nanorods is found to be higher than zeta=-12.28 mV for spherical nanoparticles. A significant enhancement in the reduction rate was observed with decreasing size (20-3 nm) and increasing surface to volume ratio (0.34-1.73 nm(-1)) of Cu nanospheres and lengthy Cu nanowires exhibit the highest catalytic activity (approximate to 96%) relative to nanorods (approximate to 80%) and nanospheres (approximate to 72%) for the reduction of nitrobenzene, m-nitrotoluene, m-chloronitrobenzene to their respective amines. The co-catalytic activity of Cu nanostructures imparted to TiO2 for the photocatalytic oxidation of acetic acid is highly decreased as: Cu nanowires/TiO2 (k=1.6x10(-2) min(-1)) > Cu nanorods/TiO2 (k=4.8x10(-3) min(-1)) > Cu nanospheres/TiO2 (k=3.8x10(-4) mm(-1)) > TiO2 (k=1.08x10(-5) min(-1)) because of the differences in photoexcited electron-hole pairs separation efficiency between Cu nanostructures of different shapes. (C) 2014 Elsevier B.V. All rights reserved.