Photo-reduced Cu/CuO nanoclusters on TiO2 nanotube arrays as highly efficient and reusable catalyst

Abstract

Non-noble metal nanoparticles are becoming more and more important in catalysis recently. Cu/CuO nanoclusters on highly ordered TiO₂ nanotube arrays are successfully developed by a surfactant-free photoreduction method. This non-noble metal Cu/CuO-TiO₂ catalyst exhibits excellent catalytic activity and stability for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with the presence of sodium borohydride (NaBH₄). The rate constant of this low-cost Cu/CuO based catalyst is even higher than that of the noble metal nanoparticles decorated on the same TiO₂ substrate. The conversion efficiency remains almost unchanged after 7 cycles of recycling. The recycle process of this Cu/CuO-TiO₂ catalyst supported by Ti foil is very simple and convenient compared with that of the common powder catalysts. This catalyst also exhibited great catalytic activity to other organic dyes, such as methylene blue (MB), rhodamine B (RhB) and methyl orange (MO). This highly efficient, low-cost and easily reusable Cu/CuO-TiO₂ catalyst is expected to be of great potential in catalysis in the future.

Figure 1. Fabrication and reusability schematic of Cu/CuO-TiO₂ catalyst for the 4-NP reduction with NaBH₄.

Figure 2. SEM images of the fabricated catalysts.

(a) C-0.02; (b) C-0.1; (c) C-0.5 and (d) their corresponding XRD patterns compared with TiO₂ nanotube arrays. Insets show the high magnification images of the catalysts.

Figure 3

(a) TEM image of Cu/CuO nanoparticle obtained from C-0.1; (b) High resolution TEM image of the marked region.

Figure 4. XPS spectra of catalyst C-0.1.

(a) XPS survey spectrum; (b) Cu 2p spectrum; (c) O 1 s spectrum and (d) Ti 2p spectrum.

Figure 5

Time-dependent UV-vis absorption spectra for the reduction of 4-NP with (a) C-0.02; (b) C-0.1; (c) C-0.5; and (d) the corresponding plots of ln (C_t/C₀) versus reaction time.

Figure 6. Time-dependent UV-vis absorption spectra for the reduction of 4-NP with different catalysts.

(a) Au-TiO₂; (b) Ag-TiO₂; (c) Pd-TiO₂. (d) The corresponding plots of ln (C_t/C₀) of different catalysts versus reaction time.

Figure 7. Reusability of the C-0.1 catalyst for the reduction of 4-NP.

(a) Plots of C_t/C₀ versus reaction time for 7 reaction cycles and (b) the corresponding conversions of 4-NP.

Figure 8

Time-dependent UV-vis absorption spectra for the degradation of (a) MB; (b) RhB and (c) MO with catalyst C-0.1. The corresponding plots of ln (C_t/C₀) versus reaction time for (d) MB; (e) RhB and (f) MO.