Controlled Synthesis Of Pt And Pd Nanocrystals And Their Properties

Noble-metal nanocrystals such as platinum and palladium have been widely used in petrochemical industry, energy technology, healthcare, sensing and many other fields due to their unique properties. It is well known that the performance of a nanocrystal is mainly controlled by it’s size, shape, composition, and structure. Therefore, designing and tailoring the morphorgy of a nanocrystal to achieve shape controlled synthesis has become a hot topic during the last dacade.In this dissertation, we have developed several facial approaches to the synthesis of nanocrystals with various specific shapes including Pt nanobars, Pd nanosheets, and Pd nanorings. The growth mechanisms as well as their catalytic and localized surface plasmon resonance (LSPR) properties were carefully investigated. The main innovative results are listed as follows:(1) High-quality Pt nanobars faceted with six{100} have been synthesized by a facile hydrothermal approach with both OAm and formaldehyde as capping agents. The aspect-ratio of the Pt nanobars was simply tuned by varying the amount of formaldehyde fed in the synthesis. HRTEM analysis indicated that the shape of the bar was formed due to a particle coalescence mechanism. The Pt nanobars exhibited enhanced electrocatalytic activity and CO poison tolerance for methanol oxidation reaction (MOR) relative to the commercial Pt/C.(2) Pd hexagonal nanosheets with extremely thin thickness of ca.1.1 nm have been synthesized by a facial solution phase approach. The use of W(CO)6, CA, and CTAB was found to play key roles in facilitating the formation of such nanosheets. The edge length of Pd nanosheets can be simply tuned by varying the amount of CA fed in the synthesis, together with the subsequent seeded-growth process. The Pd nanosheets with average edge lengths form 6.4 to 59.2 nm show the tunable LSPR peaks form 820 to 1067 nm in the NIR region.(3) Ultrathin two-dimensional Pd nanorings with a hollow interior have been firstly synthesized by selective epitaxial growth of Pd atoms on the periphery of the as-preformed Pd nanosheets in combination with oxidative etching arising from Br-/O2 pairs. Interestingly, this approach can be extended to prepare Pd-based bimetallic ultrathin nanorings such as Pd-Pt. The Pd nanorings exhibited substantially enhanced activity towards the hydrogenation of p-nitrophenol, and were 2.2 and 33.4 times high as those of the Pd nanosheets and commercial Pd black, respectively. Significantly, the Pd nanorings were highly stable with 89.3% activity remained after 10 cycles compared to the Pd nanosheets and commercial Pd black.