Solar Energy, Vol.205, 292-301, 2020
Superior co-catalytic activity of Pd(core)@Au(shell) nanocatalyst imparted to TiO2 for the selective hydrogenation under solar radiations
The bimetallic core-shell nanostructures of galvanic metals have gained considerable scientific interest in improving the TiO2 photocatalysis under solar radiations over the monometallic analogues. In the present research work, Pd@Au core-shell supported TiO2 nanostructures were synthesized via galvanic replacement reaction and were examined for their catalytic/photocatalytic hydrogenation. Three different types of bimetallic Pd@Au nanostructure were synthesized by varying Pd:Au weight ratio i.e. (1:1), (1:2) and (1:3). DLS measurements revealed that with increasing Au weight ratio, the hydrodynamic size increases from 126 to 157 nm. The optical studies showed a considerable blue shift in the absorption band of Au nanoparticles from 529 to 518 nm in the case of Pd@Au (1:1). The co-existence of absorption characteristic of Pd and Au suggests the successful synthesis of bimetallic nanostructure. STEM and EDS mapping further confirmed the formation of Pd@Au nanostructure with inner Pd core and outer Au shell. Bimetallic Pd@Au nanocatalyst displayed superior activity and selectivity towards hydrogenation of cinnamaldehyde in comparison to monometallic analogues. However, when Pd@Au nanostructures were impregnated on the surface of TiO2, a significant improvement in the hydrogenation reaction was observed under solar radiations relative to catalytic conditions. The photocatalytic performance of Pd@Au-TiO2 was found to be varied as a function of shell thickness and the optimized APT-2 (Pd-1@Au-2-TiO2) photocatalyst exhibited higher rate constant (2.3 x 10(-1) h(-1)) for cinnamaldehyde hydrogenation. Hence, the plasmonic Pd@Au-TiO2 hetero-junction could be a promising greener photocatalyst for selective hydrogenation of unsaturated carbonyls for large scale industrial applications.