Manganese- and copper-doped titania nanocomposites for the photocatalytic reduction of carbon dioxide into methanol

In this work, the photocatalytic reduction of CO2 is comprehensively investigated with commercial and laboratory-made catalysts by doping their surface with an electron acceptor based on Mn and Cu metals. Manganese- and copper-doped titania has been prepared via the sol-gel route as to obtain different nanocomposites for the CO2 conversion to methanol. First, the XRD characterization demonstrated that both Mn and Cu were finely dispersed on the surface of the titanium oxide support preserving the crystalline structure. Second, the TEM morphological characterization pointed out representative titania grain sizes 15-25 nm as to avoid the surface recombination of electron-hole pairs and concomitantly enhancing the photoactivity. The structural analyses provided by BET and BJH techniques revealed a considerable shrinkage of the volume absorbed for both fresh and used titania specimens when increasing the Mn loading on the TiO2 substrate, and all the sol-gel derived titania photocatalysts exhibited a mesoporous structure for Mn- and Cu-dopped formulations. Afterwards, XPS spectra presented equivalent binding energies characteristic of pure Mn, Cu and Ti (2p(3/2), 2p(1/2)) by underlining the chemical composition and crystallographic structure of laboratory-made photocatalysts. Finally, several photocatalytic reductions of CO2 were performed with Mn- and Cu-doped titania catalysts by evaluating the methanol production. The Mn-0.22-Cu-0.78/TiO2 specimen was found to yield a maximum of 238.6 mu mol-MeOH/g(cat) with the highest energy (18.4%) and quantum (26.5%) efficiencies thereby acting as a potential candidate catalyst for the photocatalytic conversion of carbon dioxide. (C) 2012 Elsevier B.V. All rights reserved.