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

• Cu nanospheres of three different sizes, nanorods and nanowires have prepared.
• Optoelectronic properties of various shapes and sizes of CuNPs have been studied.
• Cu nanowires exhibited highest co-catalytic effect to TiO2 photoactivity.
• Highest reduction rate in short time interval was observed with Cu nanowires.
• Electron-withdrawing or releasing group influences nitroaromatic reduction rate.

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 ≈ 600–700 nm and width ≈ 15–20 nm) and nanowires (length ≈ 4–6 μm and width ≈ 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 ζ = −35.9 mV for nanowires and −30.08 mV for nanorods is found to be higher than ζ = −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 (≈96%) relative to nanorods (≈80%) and nanospheres (≈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 = 1.6 × 10−2 min−1) > Cu nanorods/TiO2 (k = 4.8 × 10−3 min−1) > Cu nanospheres/TiO2 (k = 3.8 × 10−4 min−1) > TiO2 (k = 1.08 × 10−5 min−1) because of the differences in photoexcited electron–hole pairs separation efficiency between Cu nanostructures of different shapes.

The lengthy Cu nanowires (CuNW) and CuNW/TiO2 exhibit superior catalytic effect and co-catalytic efficiency for m-chloronitrobenzene reduction and photooxidation of acetic acid as compared to nanorods (NR) and spherical (NS) shaped Cu nanoparticles, respectively.Figure optionsDownload high-quality image (209 K)Download as PowerPoint slide