Size- and shape-controlled platinum and palladium nanoparticles for catalytic and biomedical applications

The aim of this doctoral project has been centered on the development of innovative green synthetic methods able to govern the key physico-chemical properties of noble metal nanoparticles (NPs). To fully uncover the potential of metallic NPs, it is necessary to finely control the shape of nanomaterials while keeping the ultra-small characteristics, in order to achieve superior efficiency (per mass unit), selectivity and enhanced activity in catalytic processes. Size and shape of the nanomaterial together with the capping agents govern the surface properties and all the processes happening at the surface, such as catalysis. Different shapes offer great versatility to tune the nanocrystal (NCs) catalytic properties, which are dictated by surface facets. Green synthetic procedures have been developed to obtain pure, monodisperse, citrate-capped Pt and Pd NPs with accurate control on their size and the shape, without the use of polymers, surfactants and organic solvents. For Pd NPs, different geometrical shapes were achieved, such as icosahedrons, cubes, rods and wires while maintaining the thickness of 7 nm and length ranging from 38 to 470 nm (in the case of rods and wires) and the size (in the case of cubes and icosahedron) below 10 nm. These engineered nanomaterials exhibited good biocompatibility along with interesting enzymatic and catalytic properties, due to the absence of sticky molecules, high quality of the surface and the removal of toxic reagents. Moreover, a green synthetic procedure has been developed to obtain ultra-small Pt NCs by combining a strong and a weak reducing agent in aqueous environment in a single reaction vessel in only 10 minutes. NCs with size as low as 2.8 nm and high percentage of {111} surface domains have been achieved. These NCs have been physico-chemically and electrochemically characterized, disclosing significant perspectives for their use as innovative electrocatalysts or nanozymes in portable diagnostics.