Assessment of the photocatalytic efficiency of Pd-M (M=Cu, Ag) nanoparticles supported on TiO₂

The effect of modifying TiO₂ with Pd, as well as of Cu and Ag co-catalysts on TiO₂, on the photocatalytic efficiency exhibited by these catalysts in the photocatalytic water splitting and nitrate reduction reaction was studied. Mono- (Pd, Cu, and Ag) and bimetallic (Pd-Cu and Pd-Ag) nanoparticles were prepared by a modified protocol of the alkaline polyol method [1]. The size, shape and specific morphologies of nanoparticles can be controlled from the preparation method [2, 3]. The physical and chemical properties of the Pd-M (M=Cu, Ag) catalysts supported on TiO₂ were investigated using different methods such as TEM, XRD, XPS, H₂-TPR, UV-Vis, CO chemisorption and fractal analysis. The photocatalytic activity of the prepared catalysts was tested by evaluating the generation of hydrogen from water under UV light (150 W high-pressure lamp with inner irradiation). The catalytic and photocatalytic removal of nitrates from aqueous solutions was examined using TiO₂-based materials containing bimetallic nanoparticles.

TEM and CO chemisorption measurements confirmed that the particle size is in the nanometric range. TEM images were examined in detail using the "box-counting method" to determine the fractal dimension [4]. The studied catalysts showed fractal behavior. H₂-TPR and XPS analyses provided information about the metal–support interaction and oxidation states of metallic components. Bimetallic Pd-Cu nanoparticles dispersed on TiO₂ with various molar ratios showed better activity for photocatalytic water splitting and nitrate reduction reaction compared to the Pd-Ag/TiO₂ sample. Depending on the surface atomic composition of the co-catalyst, an estimation of the optimal Pd-M (M=Cu, Ag) molar ratio was made to improve the photocatalytic performance in the H₂ generation reaction. A better understanding of the role of bimetallic nanoparticles is of the utmost importance for the design of efficient photocatalysts.