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

• Published in: Applied catalysis. B, Environmental Environmental, 2013-03, Vol.132-133, p.408-415
• Main Authors: RICHARDSON, P. L, PERDIGOTO, Marisa L. N, WANG, W, LOPES, Rodrigo J. G
• Format: Article
• Language: English
• Subjects: Catalysis; Chemistry; Copper; Doping; Exact sciences and technology; Formic acid; Gallium; General and physical chemistry; Nanocomposites; Photocatalysis; Photocatalysts; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Titanium dioxide
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2012.11.045

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 CuxaGa1-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, beta -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 BrunaueraEmmettaTeller and BarrettaJoyneraHalenda 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 by means of XPS reproduced the binding energies relative of Ti, Cu and Ga (2p3/2, 2p1/2), and the K-edge XANES characterization confirmed the effective doping and modulation of the electronic properties of the laboratory-made photocatalysts. Several experimental runs have been carried out with Cu0.78aGa0.22/TiO2 exhibiting the highest formic acid yields (394 mu 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 electronahole pairs, thereby enhancing the photo-activity of CuxaGa1-x/TiO2 nanocomposites.