(206d) Continuous Green Millifluidic Synthesis of Five-Fold Palladium Nanorods Using L-Ascorbic Acid and Their Catalytic Application

Pd nanorods (PdNRs) have recently come into attention for their wide array of applications. Sustainable synthesis of five-fold PdNRs have been challenging in the past due to the need to control their aspect ratios very precisely. Millifluidic continuous flow reactors have been explored as mean of maximizing PdNR synthesis by utilizing the ability to precisely control mixing and heat transfer in such reactors. A further development of this idea is to use compartmentalized flow of reaction solution to exploit benefits of improved mixing and heat transfer present in liquid compartments. In an aqueous synthesis of colloidal metal nanostructure such as PdNRs, the final shape taken by a nanocrystal is dictated by the twin structures of seeds and the rates of growth of different crystallographic facets. This study explores the use of L-ascorbic acid as a sustainable reducing agent for sodium tetrachloropalladate (Na₂PdCl₄) precursor in a segmented flow millifluidic reactor with assistant of potassium bromide (KBr) and polyvinylpyrrolidone (PVP) as capping agent and stabilizing agent, respectively. The experiment employs plug flow of reaction solution resulting from vaporization of aqueous solvent at boiling temperature within millifluidic tubing. The effects of various reaction parameters such as reagent concentrations are studied, and these findings are utilized to improve the yield of synthesized PdNRs. The morphologies obtained for the Pd nanocrystals can be icosahedron, octahedron, truncated octahedron, decahedron, rectangular bar, hexagonal and triangular plates, and cube that strongly depends on the synthesis condition and kinetic parameters. The correlation between five-fold PdNR synthesis and the rate of Pd precursor reduction is examined in the kinetic study, and the variation in the reduction rate with reaction progress is investigated to systematically control the shape of Pd nanocrystals. Characterization techniques such as Transmission Electron Microscopy (TEM) and Ultraviolet-Visible (UV-Vis) spectroscopy are used to study the reaction mechanism and kinetics of PdNR synthesis. Palladium nanocrystal is a great catalyst for several reactions, where its activity is strongly dependent on the size, morphology, and different facets expressed on its surface. The ability to precisely control and synthesize Pd nanocrystals with many different shapes including PdNRs provides an outstanding platform to tune their properties for catalytic application and their performance.