Photocatalytic Production of Hydrogen Over Tailored Cu-Embedded TiO₂

Copper nanoparticles embedded into TiO₂ showed promising photocatalytic hydrogen production using water/methanol solution. Preformed metal nanoparticles, surrounded by a porous TiO₂ matrix, were prepared by microemulsion method. XRD and HRTEM analysis indicated the presence of the anatase polymorph with minor traces of rutile and brookite. The performances of this nanostructured system were compared with those of a similar material prepared by conventional impregnation method. Using TiO₂ with identical structural and textural properties, a significantly lower CO chemisorption was measured for the impregnated sample with respect to the embedded one. Even though it is not possible to discriminate between the different ratio of the Cu containing species in the two samples, this is an indication that the embedded system presents highly accessible copper species and in a slightly larger quantity with respect to the corresponding impregnated sample. Consistently XRD and preliminary HRTEM investigations indicates presence of smaller Cu/CuO _x particles in the embedded catalyst. A CO adsorption capacity similar to that of the embedded system was obtained by impregnating with copper nitrate a TiO₂, obtained by sol–gel method. This last system present however a more significant contribution of the rutile phase. Notably, Cu embedded material showed significantly superior performances with respect to all the other samples. In this regard an optimal combination of low particle size, accessible active phase, ratio of Cu/CuO _x , presence of the more active anatase phase and excellent interfacial contact between Cu and surrounding TiO₂ particles was found critical. This latter aspect can lead to a better synergic electron/hole transfer which allow improved activity.