Heterogeneous photo-enhanced conversion of carbon dioxide to formic acid with copper- and gallium-doped titania nanocomposites

Authors: P.L. Richardson, Marisa L.N. Perdigoto, W. Wang, Rodrigo J.G. Lopes

Abstract:
Copper- and gallium-doped titania photocatalysts prepared by means of sol–gel technique were comparatively evaluated with commercial TiO₂ (P25) for the photo-reduction of carbon dioxide to formic acid. The laboratory-made Cu_x–Ga_1−x/TiO₂ nanocomposites have been thoroughly characterized in crystallographic, structural, morphological, and elemental composition analyses. XRD revealed photocatalysts owning the specific crystalline phases of anatase, β-Ga₂O3 and Cu₂O, which allowed inferring on the doping phenomena of both transition and post-transition metals. The quasi-homogeneous deposition of a Ga and Cu layer has been identified from the TEM morphological characterization and the Brunauer–Emmett–Teller and Barrett–Joyner–Halenda techniques unveiled quantitative differences in textural properties among the mesoporous Ga- and Cu-doped titania photocatalysts by underlining a decrease of surface area when augmenting the gallium dose. The laboratory-made photocatalysts presented bandgaps higher than 3 eV and the DRS spectra underlined the optical absorption edge of the nanocomposites with a considerable shift to the visible light region. The elemental composition quantified bymeans ofXPS reproduced the binding energies relative of Ti,Cuand Ga (2p_3/2, 2p_1/2), and theK-edge XANES characterization confirmed the effective doping and modulation ofthe electronic properties ofthe laboratory-made photocatalysts. Several experimental runs have been carried out with Cu_0.78–Ga_0.22/TiO₂ exhibiting the highest formic acid yields (394 mol/gcat) as well as superior quantum efficiency (49%) and selectivity (0.84). Accordingly, the photo-reduction of CO2 was considerably promoted by doping Ga and Cu into the titania substrate, which ultimately avoided the surface recombination of electron–hole pairs, thereby enhancing the photo-activity of Cu_x–Ga_1−x/TiO₂ nanocomposites. 

Keywords:
Photo-reduction
Carbon dioxide
Copper
Gallium
Titania
Formic acid

Published in: Applied Catalysis B: Environmental (Volumes 132–133, Pages 1-552, 27 March 2013)

Publisher: Elsevier  

ISSN Information: 0926-3373

Heterogeneous photo-enhanced conversion of carbon dioxide to formic acid with copper- and gallium-doped titania nanocomposites

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