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. 2015 Nov 17;5(4):1971-1984.
doi: 10.3390/nano5041971.

Synthesis of Ordered Mesoporous CuO/CeO₂ Composite Frameworks as Anode Catalysts for Water Oxidation

Vassiliki Markoulaki Ι  1 , Ioannis T Papadas  2 , Ioannis Kornarakis  3 , Gerasimos S Armatas  4
Affiliations

Synthesis of Ordered Mesoporous CuO/CeO₂ Composite Frameworks as Anode Catalysts for Water Oxidation

Vassiliki Markoulaki Ι et al. Nanomaterials (Basel). .

Abstract

Cerium-rich metal oxide materials have recently emerged as promising candidates for the photocatalytic oxygen evolution reaction (OER). In this article, we report the synthesis of ordered mesoporous CuO/CeO₂ composite frameworks with different contents of copper(II) oxide and demonstrate their activity for photocatalytic O₂ production via UV-Vis light-driven oxidation of water. Mesoporous CuO/CeO₂ materials have been successfully prepared by a nanocasting route, using mesoporous silica as a rigid template. X-ray diffraction, electron transmission microscopy and N₂ porosimetry characterization of the as-prepared products reveal a mesoporous structure composed of parallel arranged nanorods, with a large surface area and a narrow pore size distribution. The molecular structure and optical properties of the composite materials were investigated with Raman and UV-Vis/NIR diffuse reflectance spectroscopy. Catalytic results indicated that incorporation of CuO clusters in the CeO₂ lattice improved the photochemical properties. As a result, the CuO/CeO₂ composite catalyst containing ~38 wt % CuO reaches a high O₂ evolution rate of ~19.6 µmol·h-1 (or 392 µmol·h-1·g-1) with an apparent quantum efficiency of 17.6% at λ = 365 ± 10 nm. This OER activity compares favorably with that obtained from the non-porous CuO/CeO₂ counterpart (~1.3 µmol·h-1) and pure mesoporous CeO₂ (~1 µmol·h-1).

Keywords: cerium oxide; mesoporous materials; nanocasting; nanostructured; water oxidation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Typical transmission electron microscopy (TEM) images; (b) High-resolution TEM image (the inset shows the corresponding FFT pattern indexed as the (110) zone axis of cubic CeO2) and (c) Selected-area electron diffraction (SAED) pattern of the mesoporous CuO(38)/CeO2 material. In (b), the white arrowheads indicate the bridge region between neighboring nanorods.
Figure 2
Figure 2
X-ray diffraction (XRD) patterns of mesoporous (a) mp-CeO2; (b) CuO(16)/CeO2; (c) CuO(26)/CeO2; (d) CuO(38)/CeO2 and (e) CuO(45)/CeO2 materials.
Figure 3
Figure 3
Nitrogen adsorption–desorption isotherms at 77 K and the corresponding nonlocal density functional theory (NLDFT) pore-size distribution plots calculated from the adsorption branch (inset) for mesoporous (a) mp-CeO2; (b) CuO(16)/CeO2; (c) CuO(26)/CeO2; (d) CuO(38)/CeO2 and (e) CuO(45)/CeO2 materials (STP: standard temperature and pressure). For clarity, the isotherms of (a), (b) and (c) are offset by 5, 40 and 20 cm3·g−1, respectively.
Figure 4
Figure 4
(a) Raman spectra and (b) ultraviolet-visible/near-IR (UV-Vis/NIR) diffuse reflectance spectra for mesoporous mp-CeO2 and CuO/CeO2 composite samples. Inset of (b) is the corresponding (αhv)2 versus energy curves, where α is the absorption coefficient, h is Planck’s constant and v is the light frequency.
Figure 5
Figure 5
(a) Oxygen evolution curves and (b) time courses of photocatalytic O2 evolution rates for mesoporous mp-CeO2 and CuO/CeO2 composite materials and bulk b-CuO(38)/CeO2 solid.
Scheme 1
Scheme 1
Photocatalytic O2 production mechanism on the CuO/CeO2 interface under UV-Vis light irradiation (VB: valence band, CB: conduction band, NHE: normal hydrogen electrode).
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