Formic acid and hydrogen generation from the photocatalytic reduction of CO2 on visible light activated N-TiO2/CeO2/CuO composites
Luz I. Ibarra-Rodríguez, Juan C. Pantoja-Espinoza, E. Luévano-Hipólito, Luis F. Garay-Rodríguez, Alejandro López-Ortíz, Leticia M. Torres‐Martínez, V. Collins-Martı́nez
Abstract
• N-TiO 2 powders were obtained by Pechini´s method and impregnated with CeO 2 /CuO. • UV–Vis shows a redshift relate to improving light absorption of ternary composites. • Composites surface exhibited Ti mixed-valence relate to the presence of O vacancy. • N-TiO 2 /CuO presents the highest formic acid due to the ability of CO 2 adsorption. • N-TiO 2 /CeO 2 /CuO shows the highest H 2 production due to high Ti 3+ sites presence. Ternary of titania-based composites were prepared in two steps. First, pure and nitrogen-doped titanium dioxide powders were obtained using Pechini´s method. Then, these powders were impregnated with 3% wt. of cerium and copper oxide particles. The X-ray diffraction characterization shows the presence of rutile and anatase phases. The morphological characterizations exhibited some CuO agglomeration that resulted in a limited dispersion. Nitrogen-doped composite materials present better surface area due to the synergy effect of the urea precursor employed in their synthesis. UV–Vis analysis shows a redshift displacement for double and triple composites related to enhancing light absorption. XPS characterization made it possible to identify a mixed-valence state of Ti associated with the presence of oxygen vacancies, which presumable are responsible for the increase of adsorption of interest molecules. N-TiO 2 /CuO presents the highest formic acid production (33 µmol g −1 min -1 ) attributed to a better capacity to adsorb CO 2 molecules and the formation of a Z-scheme where charges are spatially separated. The addition of CeO 2 co-catalyst decreases formic acid performance due to its inherent ability to adsorb CO 3 −2 and OH ions that could hinder available active sites. On the other hand, in the case of hydrogen production, N-TiO 2 /CeO 2 /CuO material exhibited the highest production due to its highest Ti 3+ /Ti 4+ valence state ratio, which presumably increases available active sites for molecular water adsorption and consequently for transformation into H 2 .